A pal has a light fitting comprising 15 20 watt 12 volt lamps. Fed from a
pretty massive toroidal transformer in the base. After having had a new
consumer unit fitted, it tripped the MCB. Every time. It's on a 6 amp
lighting circuit.

The sparks who installed the new CU doesn't want to know - he was sort of
supplied by the people who fitted a new bathroom with some form of
whirlpool bath - and they insisted it had to be upgraded. I've a feeling
they also installed/split the lighting load into two - it's a small house
and originally only had one circuit. My pal is a bit vague about such
things.;-) The fitting has been replaced by a single bulb pendant which
works ok. Other clue was the wall switch sparked when this fitting was
switched on.

My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

There's plenty of room in the base for two or more electronic
transformers - but altering the wiring inside the fitting to split the
load might not be so easy.

--
*When cheese gets its picture taken, what does it say? *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
A pal has a light fitting comprising 15 20 watt 12 volt lamps. Fed from a
pretty massive toroidal transformer in the base. After having had a new
consumer unit fitted, it tripped the MCB. Every time. It's on a 6 amp
lighting circuit.

The sparks who installed the new CU doesn't want to know - he was sort of
supplied by the people who fitted a new bathroom with some form of
whirlpool bath - and they insisted it had to be upgraded. I've a feeling
they also installed/split the lighting load into two - it's a small house
and originally only had one circuit. My pal is a bit vague about such
things.;-) The fitting has been replaced by a single bulb pendant which
works ok. Other clue was the wall switch sparked when this fitting was
switched on.

My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

Massive.
Toroids are very efficient magnetically. So a few turns of thick wire is
all they are using..

Leakage inductance if they are under load is not huge So there is ****
all to stop massive inrush currents.

Things that may help a-

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.

Oddly, long thin leads to the LV bulbs. These have resistance which
limits the cold resistance to a minimum value. I found this by accident
here - I have three lights fed from a remote transformer: They take a
second to come up to brightness.

The last two solutions will limit the peak cold load on the thing, and
reduce inrush current massively. Its not unusal to see partial core
saturation when driving massive loads..for a brief instance. That screws
even the leakage inductance.


There may be a slow start switch using either a zero crossing switch or
a dimmer type triac..again, I know its theoretically possible, but don't
know more than that.

Essentially you have to find some way of limiting peak current, or
coping with it. I prefer the former.


There's plenty of room in the base for two or more electronic
transformers - but altering the wiring inside the fitting to split the
load might not be so easy.

I'm not sure those will be better. Toroids are very tough good things.
Once the fact that they ARE sodding efficient has beentaken out of the
equation..

On 21 May, 15:35, The Natural Philosopher
wrote:
Dave Plowman (News) wrote:
A pal has a light fitting comprising 15 20 watt 12 volt lamps. Fed from a
pretty massive toroidal transformer in the base. After having had a new
consumer unit fitted, it tripped the MCB. Every time. It's on a 6 amp
lighting circuit. *

The sparks who installed the new CU doesn't want to know - he was sort of
supplied by the people who fitted a new bathroom with some form of
whirlpool bath - and they insisted it had to be upgraded. I've a feeling
they also installed/split the lighting load into two - it's a small house
and originally only had one circuit. My pal is a bit vague about such
things.;-) The fitting has been replaced by a single bulb pendant which
works ok. Other clue was the wall switch sparked when this fitting was
switched on.

*My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? *I could obviously just fit a type C MCB *- but am curious
about the sparking light switch too.

Massive.
Toroids are very efficient magnetically. So a few turns of thick wire is
all they are using..

Leakage inductance if they are under load is not huge So there is ****
all to stop massive inrush currents.

Things that may help a-

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.

Oddly, long thin leads to the LV bulbs. These have resistance which
limits the cold resistance to a minimum value. I found this by accident
here - I have three lights fed from a remote transformer: They take a
second to come up to brightness.

The last two solutions will limit the peak cold load on the thing, and
reduce inrush current massively. Its not unusal to see partial core
saturation when driving massive loads..for a brief instance. That screws
even the leakage inductance.

There may be a slow start switch using either a zero crossing switch or
a dimmer type triac..again, I know its theoretically possible, but don't
know more than that.

Essentially you have to find some way of limiting peak current, or
coping with it. I prefer the former.



*There's plenty of room in the base for two or more electronic
transformers - but altering the wiring inside the fitting to split the
load might not be so easy.

I'm not sure those will be better. Toroids are very tough good things.
Once the fact that they ARE sodding efficient has beentaken out of the
equation..

A useful and interesting reply.

I was under the impression that one of the significant advantages of
the electronic transformers was that they were slow start. I've got a
4 light track with an electronic transformer and subjectively that
comes on noticeably slower than the mains driven GU10 bulbed one I had
there previously and blew bulbs regularly. The fact that the 12v
system hasn't blown any bulbs I put down to the transformer being slow-
start.

Rob

Dave Plowman (News) wrote:

Anyone have an idea what the peak current demand would be this sort of
arrangement?

Humongous. Particularly if the source impedance of the supply is low and
the tranny is connected on a short cable from the consumer unit.

I could obviously just fit a type C MCB

Yes. this would be my first port of call. You may find that a C type
still trips out, in which case you should consider ditching the toroidal
for electronic transformer(s).

In article ,
"Dave Plowman (News)" writes:
A pal has a light fitting comprising 15 20 watt 12 volt lamps. Fed from a
pretty massive toroidal transformer in the base. After having had a new
consumer unit fitted, it tripped the MCB. Every time. It's on a 6 amp
lighting circuit.

The sparks who installed the new CU doesn't want to know - he was sort of
supplied by the people who fitted a new bathroom with some form of
whirlpool bath - and they insisted it had to be upgraded. I've a feeling
they also installed/split the lighting load into two - it's a small house
and originally only had one circuit. My pal is a bit vague about such
things.;-) The fitting has been replaced by a single bulb pendant which
works ok. Other clue was the wall switch sparked when this fitting was
switched on.

My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

There's plenty of room in the base for two or more electronic
transformers - but altering the wiring inside the fitting to split the
load might not be so easy.

Inrush is inherent with toriodal transformers for two reasons;
they have no air gap, and they are made with different type of
steel core. Transformers made with EI stampings always have an
airgap where the E and I stampings meet, however small. The core
material for mains frequency toroids has to be something which
can be coiled up, and the type of steel used retains magnetism
from the moment the transformer was last switched off, which
interferes with the next switch-on.

No air gap means the transformer has virtually no tolerance to
DC current. When you switch on, for the first 100th of a second,
before the AC mains gets to reverse polarity, the transformer is
effectively presented with DC, and current is limited mainly by
the resistance of the primary windings. It actually takes a few
mains polarity reversals before the transformer is behaving as
though it has an AC supply, so a typical toroidal transformer
might draw something in the 20-50A region for the first half
cycle, which decays over the following few half-cycles.

Secondly, the stored magnetism in the core left from when the
transformer was last switched off means that the core is quite
likely to saturate at switch-on until the AC field counteracts
it (and I suspect this is what makes the no air-gap problem take
a few AC cycles to clear). This varies each switch-on, depending
on the polarity and strength of the field left at switch-off
verses the polarity of the supply at the instant of switch-on.

This element of the inrush is nothing to do with any load on
the secondary -- the toriod doesn't even generate any
significant secondary output until the primary inrush is
decaying down, and the primary inrush will happen even if there's
no load. However, a load such as LV filament lamps, when they
start getting power from the secondary, will generate a load
surge too, which may be the straw which breaks the camel's back
after the toriodal primary inrush surge. The toroidal inrush
surge and its decay as the transformer starts working properly
actually results in the secondary voltage ramping up quite
slowly (compared with an EI transformer), and that probably
goes some way to limit the filament inrush.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Rob G wrote:

I was under the impression that one of the significant advantages of
the electronic transformers was that they were slow start. I've got a

Many of them are...

4 light track with an electronic transformer and subjectively that
comes on noticeably slower than the mains driven GU10 bulbed one I had

Even without the slow start xformer they will still seem a little slower
than the mains equivalent since the filament is thicker and has more
thermal mass.

there previously and blew bulbs regularly. The fact that the 12v
system hasn't blown any bulbs I put down to the transformer being slow-
start.


It certainly helps. however 12V lamps are far less fragile than the
mains halogens, and tend to last much better regardless of how you power
them. They give a better light quality as well.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The Natural Philosopher wrote:

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.

I had to help diagnose a trip problem with moderate sized RF power amp
once (10kW)

It would occasionally trip its at least one of its 40A MCBs (one on each
phase). This had your more conventional EI style transformer (although
it was used as a step-up transformer and was fairly large - probably
about 3' tall) to generate the 10kV required to run the main valve. In
order to power it up, it had to do a "stepped start". using a pair of
contactors under software control. The first would apply mains, but with
an inline dropper resistor to limit inrush. This however would get hot
rather quickly, so a second contactor would short it out 500ms later.
Even so we still got the occasional trip. We did various measurements
with a clamp meter hooked up to a storage scope, and found some quite
substantial inrush currents could occur even with the stepped starting.
Much depending on where in the mains cycle the waveform was when the on
switch was thrown. IIRC they had to go up a circuit breaker rating, and
a letter to guarantee you would never get s switch on trip.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Andrew Gabriel wrote:
In article ,
"Dave Plowman (News)" writes:
A pal has a light fitting comprising 15 20 watt 12 volt lamps. Fed from a
pretty massive toroidal transformer in the base. After having had a new
consumer unit fitted, it tripped the MCB. Every time. It's on a 6 amp
lighting circuit.

The sparks who installed the new CU doesn't want to know - he was sort of
supplied by the people who fitted a new bathroom with some form of
whirlpool bath - and they insisted it had to be upgraded. I've a feeling
they also installed/split the lighting load into two - it's a small house
and originally only had one circuit. My pal is a bit vague about such
things.;-) The fitting has been replaced by a single bulb pendant which
works ok. Other clue was the wall switch sparked when this fitting was
switched on.

My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

There's plenty of room in the base for two or more electronic
transformers - but altering the wiring inside the fitting to split the
load might not be so easy.

Inrush is inherent with toriodal transformers for two reasons;
they have no air gap, and they are made with different type of
steel core. Transformers made with EI stampings always have an
airgap where the E and I stampings meet, however small. The core
material for mains frequency toroids has to be something which
can be coiled up, and the type of steel used retains magnetism
from the moment the transformer was last switched off, which
interferes with the next switch-on.

No air gap means the transformer has virtually no tolerance to
DC current. When you switch on, for the first 100th of a second,
before the AC mains gets to reverse polarity, the transformer is
effectively presented with DC, and current is limited mainly by
the resistance of the primary windings. It actually takes a few
mains polarity reversals before the transformer is behaving as
though it has an AC supply, so a typical toroidal transformer
might draw something in the 20-50A region for the first half
cycle, which decays over the following few half-cycles.

Secondly, the stored magnetism in the core left from when the
transformer was last switched off means that the core is quite
likely to saturate at switch-on until the AC field counteracts
it (and I suspect this is what makes the no air-gap problem take
a few AC cycles to clear). This varies each switch-on, depending
on the polarity and strength of the field left at switch-off
verses the polarity of the supply at the instant of switch-on.

This element of the inrush is nothing to do with any load on
the secondary -- the toriod doesn't even generate any
significant secondary output until the primary inrush is
decaying down, and the primary inrush will happen even if there's
no load. However, a load such as LV filament lamps, when they
start getting power from the secondary, will generate a load
surge too, which may be the straw which breaks the camel's back
after the toriodal primary inrush surge. The toroidal inrush
surge and its decay as the transformer starts working properly
actually results in the secondary voltage ramping up quite
slowly (compared with an EI transformer), and that probably
goes some way to limit the filament inrush.


Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse. Other possibles a
- move the fitting onto a 32A circuit (and provide thermal protection
if lacking)
- fit a 3 position switch to power it. The halfway position supplies
the toroidal via a filament lamp to limit initial surge
- run it from an isolating transformer, the resistances of which will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc


NT

In article ,
Andrew Gabriel wrote:
Inrush is inherent with toriodal transformers for two reasons;
they have no air gap, and they are made with different type of
steel core. Transformers made with EI stampings always have an
airgap where the E and I stampings meet, however small. The core
material for mains frequency toroids has to be something which
can be coiled up, and the type of steel used retains magnetism
from the moment the transformer was last switched off, which
interferes with the next switch-on.

[snip]

Nice info Andrew - but doesn't help with the problem. ;-)

--
*I got a sweater for Christmas. I really wanted a screamer or a moaner*

Dave Plowman London SW
To e-mail, change noise into sound.

In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

Other possibles a
- move the fitting onto a 32A circuit (and provide thermal protection
if lacking)

It's a hall light.


- fit a 3 position switch to power it. The halfway position supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

- run it from an isolating transformer, the resistances of which will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

--
*When you've seen one shopping centre you've seen a mall*

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
"Dave Plowman (News)" writes:
In article ,
Andrew Gabriel wrote:
Inrush is inherent with toriodal transformers for two reasons;
they have no air gap, and they are made with different type of
steel core. Transformers made with EI stampings always have an
airgap where the E and I stampings meet, however small. The core
material for mains frequency toroids has to be something which
can be coiled up, and the type of steel used retains magnetism
from the moment the transformer was last switched off, which
interferes with the next switch-on.

[snip]

Nice info Andrew - but doesn't help with the problem. ;-)

Change to an electronic transformer.
Better regulation, dimmable, etc.

I have a 100W toroid to which I fitted a NTC thermistor,
but this isn't the sort of modification I would suggest
someone does unless they are fully familiar with designing
safe mains appliances. e.g. a thermister in series with a
toroidal transformer could in theory burn out and sustain
an arc for long enough to ignite nearby materials with the
transformer acting as a ballast and preventing any fuse
blowing, and you need to design a solution which removes
the fire risk from that failure mode.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
Andrew Gabriel wrote:
Nice info Andrew - but doesn't help with the problem. ;-)

Change to an electronic transformer.
Better regulation, dimmable, etc.

Just looking at TLC, the largest they do is 150 watts. And with 15 20 watt
lights that doesn't compute for two of them. And as I said it might be
difficult to rewire it to split the load.

--
*I finally got my head together, now my body is falling apart.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

yes, but your 6A circuit will become 5A.


Other possibles a
- move the fitting onto a 32A circuit (and provide thermal protection
if lacking)

It's a hall light.

and...

- fit a 3 position switch to power it. The halfway position supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

I assume youve heard of relays

- run it from an isolating transformer, the resistances of which will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

Hardly difficult. 15x20w = 300w = 1.25A at mains, so it would require
a 12v 15w transformer. If thats too challenging you may as well give
up.


NT

Dave Plowman (News) wrote:
In article ,
Andrew Gabriel wrote:
Inrush is inherent with toriodal transformers for two reasons;
they have no air gap, and they are made with different type of
steel core. Transformers made with EI stampings always have an
airgap where the E and I stampings meet, however small. The core
material for mains frequency toroids has to be something which
can be coiled up, and the type of steel used retains magnetism
from the moment the transformer was last switched off, which
interferes with the next switch-on.

[snip]

Nice info Andrew - but doesn't help with the problem. ;-)

And the connection between cause and effect is plain wrong.

Andrew Gabriel wrote:
In article ,
"Dave Plowman (News)" writes:
In article ,
Andrew Gabriel wrote:
Inrush is inherent with toriodal transformers for two reasons;
they have no air gap, and they are made with different type of
steel core. Transformers made with EI stampings always have an
airgap where the E and I stampings meet, however small. The core
material for mains frequency toroids has to be something which
can be coiled up, and the type of steel used retains magnetism
from the moment the transformer was last switched off, which
interferes with the next switch-on.
[snip]

Nice info Andrew - but doesn't help with the problem. ;-)

Change to an electronic transformer.
Better regulation, dimmable, etc.

I have a 100W toroid to which I fitted a NTC thermistor,
but this isn't the sort of modification I would suggest
someone does unless they are fully familiar with designing
safe mains appliances. e.g. a thermister in series with a
toroidal transformer could in theory burn out and sustain
an arc for long enough to ignite nearby materials with the
transformer acting as a ballast and preventing any fuse
blowing, and you need to design a solution which removes
the fire risk from that failure mode.

I cant quite get my head riound it, but I am sure there is something
comprising a big triac, and a diode capacitor and a few components that
acts as a 'startup dimmer'

Also a zero crossing switch is possible, but again memory fails me...

"Dave Plowman (News)" wrote in message
...
A pal has a light fitting comprising 15 20 watt 12 volt lamps. Fed from a
pretty massive toroidal transformer in the base. After having had a new
consumer unit fitted, it tripped the MCB. Every time. It's on a 6 amp
lighting circuit.

The sparks who installed the new CU doesn't want to know - he was sort of
supplied by the people who fitted a new bathroom with some form of
whirlpool bath - and they insisted it had to be upgraded. I've a feeling
they also installed/split the lighting load into two - it's a small house
and originally only had one circuit. My pal is a bit vague about such
things.;-) The fitting has been replaced by a single bulb pendant which
works ok. Other clue was the wall switch sparked when this fitting was
switched on.

My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

There's plenty of room in the base for two or more electronic
transformers - but altering the wiring inside the fitting to split the
load might not be so easy.

I've added this link to a soft start circuit for toroidal PSUs on power
amps - so should do what is needed technically. However, it may be over
complicated for what you want, and especially in terms of getting new
circuitry into the enclosure of the lamp.

http://sound.westhost.com/project39.htm

Charles F

In article
,
wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

yes, but your 6A circuit will become 5A.

Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.


Other possibles a
- move the fitting onto a 32A circuit (and provide thermal protection
if lacking)

It's a hall light.

and...

Are you suggesting re-wiring the entire lighting circuit in 4mm and using
a 32 amp MCB? Can't you see this is slightly impractible? For a start the
fitting wouldn't take cable of that size - and in any case it wouldn't
conform to regs as the only protection on a radial is the MCB, etc.

- fit a 3 position switch to power it. The halfway position supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

I assume youve heard of relays

Well as I said it's not my house. And I've no idea if there's room for a
bodge like that.

- run it from an isolating transformer, the resistances of which will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

Hardly difficult. 15x20w = 300w = 1.25A at mains, so it would require
a 12v 15w transformer. If thats too challenging you may as well give
up.

You've lost me there. Where does 12v and 15 watts come in? The fitting
takes 300 watts.



--
*Laugh alone and the world thinks you're an idiot.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Charles Fearnley wrote:
I've added this link to a soft start circuit for toroidal PSUs on power
amps - so should do what is needed technically. However, it may be over
complicated for what you want, and especially in terms of getting new
circuitry into the enclosure of the lamp.

http://sound.westhost.com/project39.htm

Thanks for that - very interesting. I'm wondering in this app whether the
relay connected directly across the supply would provide a long enough
delay to prevent the MCB tripping? After all, they don't operate
immediately. I do have some 10 amp 240v coil relays lying around and there
would be room for one plus resistors inside the 'base'. Making up the
timer section would be too costly, time wise.

--
*Everybody lies, but it doesn't matter since nobody listens*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article
,
wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

yes, but your 6A circuit will become 5A.

Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

Fuses are still fully compliant, but they are out of fashion. MCBs are
more about convenience than safety.


Other possibles a
- move the fitting onto a 32A circuit (and provide thermal protection
if lacking)

It's a hall light.

and...

Are you suggesting re-wiring the entire lighting circuit in 4mm and using
a 32 amp MCB?

no

Can't you see this is slightly impractible? For a start the
fitting wouldn't take cable of that size - and in any case it wouldn't
conform to regs as the only protection on a radial is the MCB, etc.

Lots of plug-in transformers have no fuse. The mains plug fuse
protects as far as the transformer itself, and the thermal cutout
protects from there on. The same principle can be applied here.
Whether a higher current feed is available nearby in this case only
you can tell us.


- fit a 3 position switch to power it. The halfway position supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

I assume youve heard of relays

Well as I said it's not my house. And I've no idea if there's room for a
bodge like that.

Its effective, safe, reliable, cost effective, and the finished item
looks fine. Where's the problem?


- run it from an isolating transformer, the resistances of which will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

Hardly difficult. 15x20w = 300w = 1.25A at mains, so it would require
a 12v 15w transformer. If thats too challenging you may as well give
up.

You've lost me there. Where does 12v and 15 watts come in? The fitting
takes 300 watts.

OK, first we increase the mains voltage by 12v. This is done with a
12v transformer. Then we add a dropper to bring it back to 240, ie a
capacitor, choke or less likely a resistance. The point of this is a
lot of series limiting reactance has been introduced, and the switch
on surge is thus much reduced.

300w is 1.25A roughly, so you'd need a 12v 1.25A transformer.

I suspect another option would be simpler though: ignore the built in
toroidal and run it off an external EI transformer rated 12v 300w.


NT

"Dave Plowman (News)" wrote in message
...
In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

Other possibles a
- move the fitting onto a 32A circuit (and provide thermal protection
if lacking)

It's a hall light.


- fit a 3 position switch to power it. The halfway position supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

- run it from an isolating transformer, the resistances of which will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

Have you thought of wiring a soft start dimmer in the supply?
Just leave it on max and hide it somewhere.
Make sure it can handle inductive loads though.

Dave Plowman (News) wrote:
In article ,
Charles Fearnley wrote:
I've added this link to a soft start circuit for toroidal PSUs on power
amps - so should do what is needed technically. However, it may be over
complicated for what you want, and especially in terms of getting new
circuitry into the enclosure of the lamp.

http://sound.westhost.com/project39.htm

Thanks for that - very interesting. I'm wondering in this app whether the
relay connected directly across the supply would provide a long enough
delay to prevent the MCB tripping? After all, they don't operate
immediately. I do have some 10 amp 240v coil relays lying around and there
would be room for one plus resistors inside the 'base'. Making up the
timer section would be too costly, time wise.


There may be an easier way..

Use a relay in series with a diode and a resistor, and with a fat
electrolytic across the coil.

In fact, I suspect something like a triac would work in that mode, too.

But I still like the thermistor the best.

Less components, and possible to use a really big fat one!

The CL-80 from here looks about right

http://www.farnell.com/datasheets/85914.pdf

peak current would be limited to about 5A, and at 2A resistance has
dropped from a cold value of 47ohms to less than an ohm.
The only issue is that these things will get very hot, and may be
running at mains potential, so you need something like an earthed mesh
box to pop it into.

I think I would be tempted to put it in the actual backing box of the
switch itself.

One end into the switched live terminal, and the other crimped to the
switche live wire. Then glue some insulation to any nearby part of the
backing box in case it touches that.

Or, if it was not appropiate to use the backing box, use another backing
box with a 4 terminal block in it, and mount that where it can get hot
in peace!

"John Rumm" wrote in message
o.uk...
The Natural Philosopher wrote:

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.

I had to help diagnose a trip problem with moderate sized RF power amp
once (10kW)

It would occasionally trip its at least one of its 40A MCBs (one on each
phase). This had your more conventional EI style transformer (although it
was used as a step-up transformer and was fairly large - probably about 3'
tall) to generate the 10kV required to run the main valve. In order to
power it up, it had to do a "stepped start". using a pair of contactors
under software control. The first would apply mains, but with an inline
dropper resistor to limit inrush. This however would get hot rather
quickly, so a second contactor would short it out 500ms later. Even so we
still got the occasional trip. We did various measurements with a clamp
meter hooked up to a storage scope, and found some quite substantial
inrush currents could occur even with the stepped starting. Much depending
on where in the mains cycle the waveform was when the on switch was
thrown. IIRC they had to go up a circuit breaker rating, and a letter to
guarantee you would never get s switch on trip.

--
Cheers,

John.


I love your idea of moderate sized transmitters John ;-)

I remember reading in "Radio Communication" decades ago
about a fellow Amateur whos transmitters' mains fuse
would blow every night, but only if he was transmitting
at the time. The thing he noticed was it blew with a strange
regularity, each night a short time later than the previous
night. He could draw a graph of his observations.
I'll stop there and ask if you can see where I am going
with this...

--
Graham.

%Profound_observation%

"Dave Plowman (News)" wrote in message
...
In article ,
Charles Fearnley wrote:
I've added this link to a soft start circuit for toroidal PSUs on power
amps - so should do what is needed technically. However, it may be over
complicated for what you want, and especially in terms of getting new
circuitry into the enclosure of the lamp.

http://sound.westhost.com/project39.htm

Thanks for that - very interesting. I'm wondering in this app whether the
relay connected directly across the supply would provide a long enough
delay to prevent the MCB tripping? After all, they don't operate
immediately. I do have some 10 amp 240v coil relays lying around and there
would be room for one plus resistors inside the 'base'. Making up the
timer section would be too costly, time wise.

I have something similar made up to delay the switch-off of a heating pump,
with an older boiler that doesn't sensibly control it - but I had enough
space for small transformer. I wonder if you could use a high voltage DC
relay, with directly rectified mains, a resistor and C - to just slow the
relay closure down enough. Would all be rather nasty high voltage stuff
though....

Charles F

Charles Fearnley wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
Charles Fearnley wrote:
I've added this link to a soft start circuit for toroidal PSUs on power
amps - so should do what is needed technically. However, it may be over
complicated for what you want, and especially in terms of getting new
circuitry into the enclosure of the lamp.

http://sound.westhost.com/project39.htm

Thanks for that - very interesting. I'm wondering in this app whether the
relay connected directly across the supply would provide a long enough
delay to prevent the MCB tripping? After all, they don't operate
immediately. I do have some 10 amp 240v coil relays lying around and there
would be room for one plus resistors inside the 'base'. Making up the
timer section would be too costly, time wise.

I have something similar made up to delay the switch-off of a heating pump,
with an older boiler that doesn't sensibly control it - but I had enough
space for small transformer. I wonder if you could use a high voltage DC
relay, with directly rectified mains, a resistor and C - to just slow the
relay closure down enough. Would all be rather nasty high voltage stuff
though....

Charles F

I'd vote for the simple relay timer over the electronics too. A
ordinary mains coil relay is fine on dc, just pick the series resistor
(on the relay coil) to act as a suitable dropper for it, then add the
C to give delay.


NT

Graham. wrote:
"John Rumm" wrote in message
o.uk...
The Natural Philosopher wrote:

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.

I had to help diagnose a trip problem with moderate sized RF power amp
once (10kW)

It would occasionally trip its at least one of its 40A MCBs (one on each
phase). This had your more conventional EI style transformer (although it
was used as a step-up transformer and was fairly large - probably about 3'
tall) to generate the 10kV required to run the main valve. In order to
power it up, it had to do a "stepped start". using a pair of contactors
under software control. The first would apply mains, but with an inline
dropper resistor to limit inrush. This however would get hot rather
quickly, so a second contactor would short it out 500ms later. Even so we
still got the occasional trip. We did various measurements with a clamp
meter hooked up to a storage scope, and found some quite substantial
inrush currents could occur even with the stepped starting. Much depending
on where in the mains cycle the waveform was when the on switch was
thrown. IIRC they had to go up a circuit breaker rating, and a letter to
guarantee you would never get s switch on trip.

--
Cheers,

John.


I love your idea of moderate sized transmitters John ;-)

Well you had to put this into context - the smaller power amps were 1
and 2kW models in 19" rack cases (that included things like antenna
tuning units and matching units etc), and the large ones were things
similar to the Voice of America 1MW HF transmitter that was sat 15 yards
away from the one I was working on. That was quite a beast - the auto
pre amp that drove it has a 250kW output and the coax feeder on the
output was approx 1' in diameter!

For reference it looked like:

http://www.internode.co.uk/temp/243.jpg

and with the covers off:

http://www.internode.co.uk/temp/241.jpg

(the pictured one is an old model prior to the control system upgrade I
was working on. The basic amp was a 40 odd year old design. The lump
glued to the top was a state of the art DSP based digital "drive" (posh
HF transceiver)

I remember reading in "Radio Communication" decades ago
about a fellow Amateur whos transmitters' mains fuse
would blow every night, but only if he was transmitting
at the time. The thing he noticed was it blew with a strange
regularity, each night a short time later than the previous
night. He could draw a graph of his observations.
I'll stop there and ask if you can see where I am going
with this...

Sounds like he had something that kicked in on a time switch, which
combined with the Tx load was enough to blow the fuse. Each blow of the
fuse resulting in the clock stopping, and hence subsequent switchings on
of said load would be slightly later each time.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Dave Plowman (News) wrote:

yes, but your 6A circuit will become 5A.

Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

http://www.tlc-direct.co.uk/Products/WYNSC30.html

HRC fuses are fine and can have advantages from time to time.
Re-wireable are allowed, but there is no sane reason for fitting one.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
John Rumm wrote:
Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

http://www.tlc-direct.co.uk/Products/WYNSC30.html

HRC fuses are fine and can have advantages from time to time.
Re-wireable are allowed, but there is no sane reason for fitting one.

I only really looked for Hager - that's the CU fitted.

--
*Starfishes have no brains *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

http://www.tlc-direct.co.uk/Products/WYNSC30.html

HRC fuses are fine and can have advantages from time to time.
Re-wireable are allowed, but there is no sane reason for fitting one.

I only really looked for Hager - that's the CU fitted.

Oddly Hager was always my first choice for HRC carriers - however when I
looked this time I could not see them.

I have one here feeding my garage/workshop. The existing cable was a bit
smaller than I would have liked (but a relatively major pain to
upgrade), so to get best usage on it, I put a 32A HRC at the head and
use a 32A MCB on the power circuit for the workshop - which should
hopefully discriminate on a fault.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article , John
Rumm scribeth thus
Graham. wrote:
"John Rumm" wrote in message
o.uk...
The Natural Philosopher wrote:

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.

I had to help diagnose a trip problem with moderate sized RF power amp
once (10kW)

It would occasionally trip its at least one of its 40A MCBs (one on each
phase). This had your more conventional EI style transformer (although it
was used as a step-up transformer and was fairly large - probably about 3'
tall) to generate the 10kV required to run the main valve. In order to
power it up, it had to do a "stepped start". using a pair of contactors
under software control. The first would apply mains, but with an inline
dropper resistor to limit inrush. This however would get hot rather
quickly, so a second contactor would short it out 500ms later. Even so we
still got the occasional trip. We did various measurements with a clamp
meter hooked up to a storage scope, and found some quite substantial
inrush currents could occur even with the stepped starting. Much depending
on where in the mains cycle the waveform was when the on switch was
thrown. IIRC they had to go up a circuit breaker rating, and a letter to
guarantee you would never get s switch on trip.

--
Cheers,

John.


I love your idea of moderate sized transmitters John ;-)


Dunno we used to work on 40 kW TV ones some years ago;!..

Well you had to put this into context - the smaller power amps were 1
and 2kW models in 19" rack cases (that included things like antenna
tuning units and matching units etc), and the large ones were things
similar to the Voice of America 1MW HF transmitter that was sat 15 yards
away from the one I was working on. That was quite a beast - the auto
pre amp that drove it has a 250kW output and the coax feeder on the
output was approx 1' in diameter!

For reference it looked like:

http://www.internode.co.uk/temp/243.jpg

and with the covers off:

http://www.internode.co.uk/temp/241.jpg

(the pictured one is an old model prior to the control system upgrade I
was working on. The basic amp was a 40 odd year old design. The lump
glued to the top was a state of the art DSP based digital "drive" (posh
HF transceiver)

Who was that for?..

I remember reading in "Radio Communication" decades ago
about a fellow Amateur whos transmitters' mains fuse
would blow every night, but only if he was transmitting
at the time. The thing he noticed was it blew with a strange
regularity, each night a short time later than the previous
night. He could draw a graph of his observations.
I'll stop there and ask if you can see where I am going
with this...

Sounds like he had something that kicked in on a time switch, which
combined with the Tx load was enough to blow the fuse. Each blow of the
fuse resulting in the clock stopping, and hence subsequent switchings on
of said load would be slightly later each time.


Humm dunno that they should be allowed so much "input power"
--
Tony Sayer

I remember reading in "Radio Communication" decades ago
about a fellow Amateur whos transmitters' mains fuse
would blow every night, but only if he was transmitting
at the time. The thing he noticed was it blew with a strange
regularity, each night a short time later than the previous
night. He could draw a graph of his observations.
I'll stop there and ask if you can see where I am going
with this...

Sounds like he had something that kicked in on a time switch, which
combined with the Tx load was enough to blow the fuse. Each blow of the
fuse resulting in the clock stopping, and hence subsequent switchings on
of said load would be slightly later each time.

No.
It's a long time since I read the article but AFAICR it was something
the electricity board or CEGB were putting on the supply to command
street lighting (solar timing). They did it by somehow superimposing
DC on the mains for a short time. Does that sound feasible? I'm sure
it was something like, that and it took a lot of determined investigation
to get an admission of what was going on.
Apparently the fuse blew because the tranny was operating near saturation
and the dc component was the last straw. He noticed increse in vibration
from the transformer just before it blew its fuse.

I take Tony's point that he may have been pushing things too.

--
Graham.

%Profound_observation%

wrote in message
...
Dave Plowman (News) wrote:
In article
,
wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

yes, but your 6A circuit will become 5A.

Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

Fuses are still fully compliant, but they are out of fashion. MCBs are
more about convenience than safety.


Other possibles a
- move the fitting onto a 32A circuit (and provide thermal
protection
if lacking)

It's a hall light.

and...

Are you suggesting re-wiring the entire lighting circuit in 4mm and using
a 32 amp MCB?

no

Can't you see this is slightly impractible? For a start the
fitting wouldn't take cable of that size - and in any case it wouldn't
conform to regs as the only protection on a radial is the MCB, etc.

Lots of plug-in transformers have no fuse. The mains plug fuse
protects as far as the transformer itself, and the thermal cutout
protects from there on. The same principle can be applied here.
Whether a higher current feed is available nearby in this case only
you can tell us.


- fit a 3 position switch to power it. The halfway position
supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

I assume youve heard of relays

Well as I said it's not my house. And I've no idea if there's room for a
bodge like that.

Its effective, safe, reliable, cost effective, and the finished item
looks fine. Where's the problem?


- run it from an isolating transformer, the resistances of which
will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

Hardly difficult. 15x20w = 300w = 1.25A at mains, so it would require
a 12v 15w transformer. If thats too challenging you may as well give
up.

You've lost me there. Where does 12v and 15 watts come in? The fitting
takes 300 watts.

OK, first we increase the mains voltage by 12v. This is done with a
12v transformer. Then we add a dropper to bring it back to 240, ie a
capacitor, choke or less likely a resistance. The point of this is a
lot of series limiting reactance has been introduced, and the switch
on surge is thus much reduced.

I think I follow, but it seems a bit bizarre.
You are adding 12v to the mains by using a transformer.
Primary connected to the mains conventionally, and
secondary in series, and in phase with the feed to torroid
via a reactive dropper?
The configuration will certainly add 12v to the mains but I would hardly
call your transformer a step-up transformer.
I am wondering what make of transformer is speced to have its secondary
floating at mains potential in a domestic installation?

--
Graham.

%Profound_observation%

tony sayer wrote:
In article , John
Rumm scribeth thus
Graham. wrote:
"John Rumm" wrote in message
o.uk...
The Natural Philosopher wrote:

Uprated MCB to a 'slo blo' type. I have no personal experience. I hope
others here do.

A thermistor in series, that starts high resistance, gets hot and goes
low. We used to use these occasionally on big power amps. For exactly
this reason.
I had to help diagnose a trip problem with moderate sized RF power amp
once (10kW)

It would occasionally trip its at least one of its 40A MCBs (one on each
phase). This had your more conventional EI style transformer (although it
was used as a step-up transformer and was fairly large - probably about 3'
tall) to generate the 10kV required to run the main valve. In order to
power it up, it had to do a "stepped start". using a pair of contactors
under software control. The first would apply mains, but with an inline
dropper resistor to limit inrush. This however would get hot rather
quickly, so a second contactor would short it out 500ms later. Even so we
still got the occasional trip. We did various measurements with a clamp
meter hooked up to a storage scope, and found some quite substantial
inrush currents could occur even with the stepped starting. Much depending
on where in the mains cycle the waveform was when the on switch was
thrown. IIRC they had to go up a circuit breaker rating, and a letter to
guarantee you would never get s switch on trip.

--
Cheers,

John.

I love your idea of moderate sized transmitters John ;-)

Dunno we used to work on 40 kW TV ones some years ago;!..

Well you had to put this into context - the smaller power amps were 1
and 2kW models in 19" rack cases (that included things like antenna
tuning units and matching units etc), and the large ones were things
similar to the Voice of America 1MW HF transmitter that was sat 15 yards
away from the one I was working on. That was quite a beast - the auto
pre amp that drove it has a 250kW output and the coax feeder on the
output was approx 1' in diameter!

For reference it looked like:

http://www.internode.co.uk/temp/243.jpg

and with the covers off:

http://www.internode.co.uk/temp/241.jpg

(the pictured one is an old model prior to the control system upgrade I
was working on. The basic amp was a 40 odd year old design. The lump
glued to the top was a state of the art DSP based digital "drive" (posh
HF transceiver)

Who was that for?..

The one in the picture - no idea - it was probably a lab model. The Navy
use quite a number of them though (often the smaller 1 and 2kW jobbies
on ship and those sort of things in shore stations)

They can be used anywhere you want a tunable narrowband transmitter[1]
basically. Marconi sold them all over the place for a variety of
applications. They were even used for some early trials in RADAR
applications for the JORN system:

http://en.wikipedia.org/wiki/Jindale..._Radar_Network

(the actual JORN amp was 20kW and solid state - and used in banks of 28!)

[1] no use for frequency agile apps though - they take several seconds
to tune.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
o.uk...
Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

http://www.tlc-direct.co.uk/Products/WYNSC30.html

HRC fuses are fine and can have advantages from time to time.
Re-wireable are allowed, but there is no sane reason for fitting one.

I only really looked for Hager - that's the CU fitted.

Oddly Hager was always my first choice for HRC carriers - however when I
looked this time I could not see them.

I have one here feeding my garage/workshop. The existing cable was a bit
smaller than I would have liked (but a relatively major pain to upgrade),
so to get best usage on it, I put a 32A HRC at the head and use a 32A MCB
on the power circuit for the workshop - which should hopefully
discriminate on a fault.

--
Cheers,

John.

They still show on Hagers web site

http://www.hager.com.sg/menu/product...r/800-2343.htm

Adam

Graham. wrote:
wrote in message
...
Dave Plowman (News) wrote:
In article
,
wrote:
Dave Plowman (News) wrote:
In article
,
wrote:
Toroidals are famous for bad surges at start. Simplest solution, if
posible, is to replace the MCB with a fuse.

Would that conform to 17th edition regs - the CU does.

yes, but your 6A circuit will become 5A.

Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

Fuses are still fully compliant, but they are out of fashion. MCBs are
more about convenience than safety.


Other possibles a
- move the fitting onto a 32A circuit (and provide thermal
protection
if lacking)

It's a hall light.

and...

Are you suggesting re-wiring the entire lighting circuit in 4mm and using
a 32 amp MCB?

no

Can't you see this is slightly impractible? For a start the
fitting wouldn't take cable of that size - and in any case it wouldn't
conform to regs as the only protection on a radial is the MCB, etc.

Lots of plug-in transformers have no fuse. The mains plug fuse
protects as far as the transformer itself, and the thermal cutout
protects from there on. The same principle can be applied here.
Whether a higher current feed is available nearby in this case only
you can tell us.


- fit a 3 position switch to power it. The halfway position
supplies
the toroidal via a filament lamp to limit initial surge

Two way switched too.

I assume youve heard of relays

Well as I said it's not my house. And I've no idea if there's room for a
bodge like that.

Its effective, safe, reliable, cost effective, and the finished item
looks fine. Where's the problem?


- run it from an isolating transformer, the resistances of which
will
limit i.
- run it via a 10v step up transformer and dropper or choke.
etc etc

Thanks for the most impractical suggestions this far. ;-)

Hardly difficult. 15x20w = 300w = 1.25A at mains, so it would require
a 12v 15w transformer. If thats too challenging you may as well give
up.

You've lost me there. Where does 12v and 15 watts come in? The fitting
takes 300 watts.

OK, first we increase the mains voltage by 12v. This is done with a
12v transformer. Then we add a dropper to bring it back to 240, ie a
capacitor, choke or less likely a resistance. The point of this is a
lot of series limiting reactance has been introduced, and the switch
on surge is thus much reduced.

I think I follow, but it seems a bit bizarre.
You are adding 12v to the mains by using a transformer.
Primary connected to the mains conventionally, and
secondary in series, and in phase with the feed to torroid
via a reactive dropper?

yup

The configuration will certainly add 12v to the mains but I would hardly
call your transformer a step-up transformer.

not sure it makes much difference what you call it

I am wondering what make of transformer is speced to have its secondary
floating at mains potential in a domestic installation?

Its rare that they dont have sufficient insulation for that. Microwave
tranformers dont, and probably some very old bobbinless ones.


NT

On Thu, 21 May 2009 15:07:06 +0100, "Dave Plowman (News)"
wrote:

My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

Ah, had a similar problem. I fitted a dimmer specified for use with
transformers, and the problem went away...


Thomas Prufer

In article ,
Thomas Prufer wrote:
My guess is the inrush current is simply too great for a standard MCB. I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

Ah, had a similar problem. I fitted a dimmer specified for use with
transformers, and the problem went away...

Snag is it's on a landing and two way switched - and each of the two way
switches are 2 gang.

--
*If only you'd use your powers for good instead of evil.

Dave Plowman London SW
To e-mail, change noise into sound.

ARWadsworth coughed up some electrons that declared:


"John Rumm" wrote in message
o.uk...
Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

http://www.tlc-direct.co.uk/Products/WYNSC30.html

HRC fuses are fine and can have advantages from time to time.
Re-wireable are allowed, but there is no sane reason for fitting one.

I only really looked for Hager - that's the CU fitted.

Oddly Hager was always my first choice for HRC carriers - however when I
looked this time I could not see them.

I have one here feeding my garage/workshop. The existing cable was a bit
smaller than I would have liked (but a relatively major pain to upgrade),
so to get best usage on it, I put a 32A HRC at the head and use a 32A MCB
on the power circuit for the workshop - which should hopefully
discriminate on a fault.

--
Cheers,

John.

They still show on Hagers web site


http://www.hager.com.sg/menu/product...r/800-2343.htm

Adam

Might be special order time down at TLC, who do have an account with Hager
directly (almost obviously) and can, if asked nicely, actually get
*anything* from Hager's catalogue (I got them to get me some double pole
RCBOs - try B&Q for that!)

Personally, I would try a type C breaker first - they're easy enough to get
for Hager boards (I have a Hager, specifically because the massive choice
of MCBs and RCBOs is excellent).

Cheers

Tim

Dave Plowman (News) coughed up some electrons that declared:

In article ,
Thomas Prufer wrote:
My guess is the inrush current is simply too great for a standard MCB.
I
have the fitting to check out - but no bulbs with it as yet, as he
couldn't find them.

Anyone have an idea what the peak current demand would be this sort of
arrangement? I could obviously just fit a type C MCB - but am curious
about the sparking light switch too.

Ah, had a similar problem. I fitted a dimmer specified for use with
transformers, and the problem went away...

Snag is it's on a landing and two way switched - and each of the two way
switches are 2 gang.


GET touch dimmers are OK with transformers (and CFLs)[1] that are designed
to be dimmed - and have both soft start and remote control (n-way
switching). Wiring wise, you need to present supply live and one remote
control wire at all secondary points back to where the actual switch is. Is
that an option?

Homebase sell the GET dimmers I'm talking about for less than most places if
you wanted to try one.

Cheers

Tim

[1] Well, strictly, GET do another range of knob dimmers called "LV" - but
the bloke at GET told me that the touch dimmers produce roughly the same
dimming pattern on the mains in terms of how they chop the sine wave up as
any other dimmer, so whilst they would not guarantee the touch dimmer with
dimmable CFLs, in actual fact they seem fine when I tested them.

In article ,
Tim S wrote:
Ah, had a similar problem. I fitted a dimmer specified for use with
transformers, and the problem went away...

Snag is it's on a landing and two way switched - and each of the two
way switches are 2 gang.


GET touch dimmers are OK with transformers (and CFLs)[1] that are
designed to be dimmed - and have both soft start and remote control
(n-way switching). Wiring wise, you need to present supply live and one
remote control wire at all secondary points back to where the actual
switch is. Is that an option?

If it were my place I'd examine all the options - but the owners only want
the fitting to work as it did before the CU was changed. And would, I
think, had a deal of resistance to having to have a dimmer where they
don't actually want one.

Homebase sell the GET dimmers I'm talking about for less than most
places if you wanted to try one.

I'll try a C type MCB first - and if that doesn't work replace it with a
fuse.

--
*A 'jiffy' is an actual unit of time for 1/100th of a second.

Dave Plowman London SW
To e-mail, change noise into sound.

Tim S wrote:
ARWadsworth coughed up some electrons that declared:


"John Rumm" wrote in message
o.uk...
Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
Right. I thought MCBs were mandatory these days. A quick glance at TLC
doesn't show them available for modern CUs.

http://www.tlc-direct.co.uk/Products/WYNSC30.html

HRC fuses are fine and can have advantages from time to time.
Re-wireable are allowed, but there is no sane reason for fitting one.

I only really looked for Hager - that's the CU fitted.

Oddly Hager was always my first choice for HRC carriers - however when I
looked this time I could not see them.

I have one here feeding my garage/workshop. The existing cable was a bit
smaller than I would have liked (but a relatively major pain to upgrade),
so to get best usage on it, I put a 32A HRC at the head and use a 32A MCB
on the power circuit for the workshop - which should hopefully
discriminate on a fault.

--
Cheers,

John.

They still show on Hagers web site


http://www.hager.com.sg/menu/product...r/800-2343.htm

Adam

Might be special order time down at TLC, who do have an account with Hager
directly (almost obviously) and can, if asked nicely, actually get
*anything* from Hager's catalogue (I got them to get me some double pole
RCBOs - try B&Q for that!)

Personally, I would try a type C breaker first - they're easy enough to get
for Hager boards (I have a Hager, specifically because the massive choice
of MCBs and RCBOs is excellent).

Cheers

Tim

At 10x rated current a type C can trip in as little as 0.0015 seconds.
I doubt it would do. A wire fuse is closer to a D type, which is
orders of magnitude slower at 10x rated current.


NT