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Default Do circuit breakers die of old age?

I'm having intermittent problems with either the main breaker or the
ring main breaker tripping out.

Main breaker is a Wylex 80/2 30m/a trip - the ring breaker is a 30A.
A local spark has been around to carry out an hours worth of testing to
ensure nothing silly had been done by the previous owners and other
than saying that the ring breaker is normally 32A and that it's not
such a good idea to have a RCD type main breaker all is as it should
be.

I work from home most days and have approximately 6 workstations in my
home office, occasionally they are all on concurrently along with a
number of associated small power supplies feeding printers etc - most
of the time all is well however this morning turning on a single
workstation tripped the ring breaker. Reset ring breaker then tried the
workstation again and it tripped the main breaker, reset main breaker
and tried another workstation and all was well - then turned on the
first workstation again and again all was well.

Sparky suggested having a dedicated ring installed just for my office
so I could within reason have as many workstations on as I needed -
but if the main breaker trips now with a very light load it will still
trip even if I did have a separate ring.

I've unplugged everything else that is connected to the ring such as
TVs fridges etc and yet I can still - but only occasionally get the
ring breaker or main breaker to trip when just turning on a signal
workstation.

The ring breaker has been changed for another 30A and it still tripped
either itself or the main - the ring breaker has also been upped to a
40A and it still exhibits the same intermittent trip issue when
different workstations are powered up.

The only component not changed is the main breaker; do they have a life
span of x years? - the board takes type 2 breakers which I have been
told are like rocking horse droppings to find these days (seams to be
plenty on ebay) - I'm tempted to get the whole board updated.

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Default Do circuit breakers die of old age?

wrote:

The only component not changed is the main breaker; do they have a life
span of x years?


RCDs do sometimes fail, but more often than not they lose sensitivity,
not gain it. MCBs usually tend to last for ever, unless abused.

- the board takes type 2 breakers which I have been
told are like rocking horse droppings to find these days (seams to be
plenty on ebay)


What type (maker), and what tripping characteristic - Type 1, 2, 3, B, C
or D? The MCB trips you're getting are puzzling. One of the following
must apply:

- you have a faulty piece of equipment with an intermittent short, etc.,
or a similar fault in the fixed wiring;

- the total load on the ring is near the limit (~7 kVA) so that the
switch-on surge of one more item causes a trip. It would take an awful
lot of PC equipment to get anywhere near that;

- the MCB is over-sensitive (not something I've ever experienced).

BTW changing the MCB to 40 A could be dangerous unless anyone's done
some design calculations to show that it's OK. It makes the whole
circuit non-standard and unlikely to comply with the wiring regs if the
circuit's wired in 2.5 mm^2 twin & earth, as is usual.

- I'm tempted to get the whole board updated.

That sounds like a good idea in this case. The whole-house RCD approach
is now a strongly deprecated practice, and is always going be
problematic in your case, where any trip (for whatever reason) will be a
major nuisance.

Upgrade to a modern split-load board with a separate non-RCD protected
socket circuit for your office. The sockets will need to be labelled as
not suitable for portable equipment outdoors, and Section 607
high-integrity earthing should be applied. All other sockets in the
house should be on the RCD protected side. (This assumes TN earthing.
If it's a TT-earthed installation a 2-RCD set-up will be needed, or a
supply upgrade to PME if available.)

--
Andy
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Default Do circuit breakers die of old age?


wrote in message
oups.com...
I'm having intermittent problems with either the main breaker or the
ring main breaker tripping out.

snip

The ring breaker has been changed for another 30A and it still tripped
either itself or the main - the ring breaker has also been upped to a
40A and it still exhibits the same intermittent trip issue when
different workstations are powered up.

The only component not changed is the main breaker; do they have a life
span of x years? - the board takes type 2 breakers which I have been
told are like rocking horse droppings to find these days (seams to be
plenty on ebay) - I'm tempted to get the whole board updated.


Lets get this right. You have an RCB which is the "main" incoming switch
for your consumer unit and an MCB for the ring circuit.

That on occasions either the MCB or the RCD will trip if you turn on a
workstation.

First of all when you say "turn on" a work station, is power already going
to the PS and you're hitting the (soft) start button, or are you turning on
the switch on the PS itself? Secondly does the MCB trip with just one or 2
workstations connected? Are all the workstations the same?

I've had an RCDs trip when I've switched on at the PS which I assumed was
due to suppression within the PS causing asymmetric current spikes on live
and neutral. Hitting the soft start button on the front has never caused me
any problems. Also, if needed, switching on at the wall helped because on
mains socket outlets only the live is switched.

For the MCB to trip it must be sensing some large current. The only thing I
can think of is that some old power supplies had awful power factors, making
the sensed current higher.


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Default Do circuit breakers die of old age?



What type (maker), and what tripping characteristic - Type 1, 2, 3, B, C
or D? The MCB trips you're getting are puzzling. One of the following
must apply:

- you have a faulty piece of equipment with an intermittent short, etc.,
or a similar fault in the fixed wiring;


The breakers are all Type 2 - i'm not aware what this signifies but it
did cross my mind that they might be simillar to standard fuses
insomuchas they can be slow blow, quick blow etc - at any one time i
might have 10 workstations plugged in but not powered up - however i
assume power is still going to their power supplies - i would imagine
there to be a bit of a "peak inrush" (i forget the exact term) - demand
if all of them had powered applied at the same time (this is what
happens when i try to reset the trips) - maybe i need a slow blow type
breaker?

BTW changing the MCB to 40 A could be dangerous unless anyone's done
some design calculations to show that it's OK. It makes the whole
circuit non-standard and unlikely to comply with the wiring regs if the
circuit's wired in 2.5 mm^2 twin & earth, as is usual.


40A breaker was swopped just as a test, it's back to the 30A now.


Upgrade to a modern split-load board with a separate non-RCD protected
socket circuit for your office. The sockets will need to be labelled as
not suitable for portable equipment outdoors, and Section 607
high-integrity earthing should be applied. All other sockets in the
house should be on the RCD protected side. (This assumes TN earthing.
If it's a TT-earthed installation a 2-RCD set-up will be needed, or a
supply upgrade to PME if available.)


Do all new installations/upgrades include RCD main breakers ?

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Lets get this right. You have an RCB which is the "main" incoming switch
for your consumer unit and an MCB for the ring circuit.


Correct

That on occasions either the MCB or the RCD will trip if you turn on a
workstation.


Correct

First of all when you say "turn on" a work station, is power already going
to the PS and you're hitting the (soft) start button, or are you turning on
the switch on the PS itself? Secondly does the MCB trip with just one or 2
workstations connected? Are all the workstations the same?


I have a number of workstations, any of them has been known to trip
either breaker - they are less prone to trip if they are turned on via
the wall socket and then via the soft start.

All have 350 - 450W internal PSUs.



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Default Do circuit breakers die of old age?

wrote:

The breakers are all Type 2 - i'm not aware what this signifies but it
did cross my mind that they might be simillar to standard fuses
insomuchas they can be slow blow, quick blow etc


Yes, that's the idea. MCBs have two distinct tripping mechanisms -
magnetic for "instant" tripping at high current, and thermal for smaller
overloads. The "Type" determines where the transition between the two
lies. Type 2 (now obsolete) will trip instantly at somewhere between 4
and 7 times the nominal current, so a minimum of 120 A for a 30 A unit.

The current Type B will go at between 3 and 5 times then nominal
current, are more sensitive to inrush surges. For your office a Type C
might be appropriate (5 to 10 times).

might have 10 workstations plugged in but not powered up - however i
assume power is still going to their power supplies - i would imagine
there to be a bit of a "peak inrush" (i forget the exact term) - demand
if all of them had powered applied at the same time (this is what
happens when i try to reset the trips) - maybe i need a slow blow type
breaker?


Yes, see above. Even then, switching that lot on in one go might
continue to be a problem. Big CRT monitors - any of those? - add to the
inrush current, due to the degaussing coils. Staggered switching is the
name of the game here. You can buy multi-way IEC distribution blocks
with built-in staggered turn-on - they're used in the broadcast industry
for switching banks of TV monitors.

Do all new installations/upgrades include RCD main breakers ?


No, a split-load board has a main switch, then a bank of MCBs for the
circuits that don't need RCD protection, then an RCD that only protects
selected circuits. The selected circuits should be only those which
feed socket outlets for general use (in particular those likely to be
used for portable appliances outdoors) and, if you want to pre-empt the
new 17th edition regulations coming in in 2008, everything in a bathroom.

--
Andy
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Default Do circuit breakers die of old age?

On 9 Nov 2006 01:30:03 -0800 someone who may be
wrote this:-

I work from home most days and have approximately 6 workstations in my
home office, occasionally they are all on concurrently along with a
number of associated small power supplies feeding printers etc - most
of the time all is well however this morning turning on a single
workstation tripped the ring breaker. Reset ring breaker then tried the
workstation again and it tripped the main breaker, reset main breaker
and tried another workstation and all was well - then turned on the
first workstation again and again all was well.


Do remember that these "breakers" are operating for different
reasons. The main one is operating because it detects a lack of
balance between the current flowing in the live and neutral
conductors that is above the set value. The ring one is operating
because it detects a current flowing on the live conductor for a
time that is above the time/current characteristics.

The ring breaker has been changed for another 30A and it still tripped
either itself or the main - the ring breaker has also been upped to a
40A


Did you, or anyone else, calculate whether the wiring is suitable
for this first?

Intermittent faults are always the worst to diagnose. It needs
proper recording equipment to find out what is going on. Guessing
what is happening may work, but it may not.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54
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Default Do circuit breakers die of old age?

What is the trip current for the RCD? If 30mA then the RCD problem is
easy to explain.

Computer power supplies tend to be of the switch-mode type rather than
linear. Anyway the point is that switch-mode power supplies generally
have a relatively high earth leakage current (typically 3-5mA). This
means that it isn't at all surprising that you can trip the RCD
occasionally as you must have 2 or 3 power supplies per workstation if
you include printers, fax, monitors etc.

To fix this you need not to have an RCD seeing the combined leakage
current, i.e. get rid of the RCD incomer. Alternatively you may be able
to swap it for an RCD with a higher trip current to avoid nuisance
trips (100mA).

Bear in mind that this will then mean none of your circuits is
protected by a 30mA RCD and so additional RCD protection is required
for any circuits where equipment may be used outside. This can be fixed
by using RCBOs for other socket circuits.

As to why the MCB trips, no obvious reason, should only be overcurrent.
I'd either test all the power supplies or at least try to identify
whether a particular psu is causing the problem by switching them one
one at a time (with all the others disconnected). Testing is better.

Fash

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The ring breaker has been changed for another 30A and it still tripped
either itself or the main - the ring breaker has also been upped to a
40A


Did you, or anyone else, calculate whether the wiring is suitable
for this first?


What calculation would that be ? - I've simply exchanged a suspect 32A
breaker for a known good 40A one as part of a process of ellimination -
the same issues were found so i changed it back.

I have 4 TFTs - no CRTs - a small laser printer and couple of
hub/routers + a max of 8 workstations.

I normally use the soft start buttons to power up - therefore all of
the internal PSUs are being fed from the ring but taking no real load -
very often i have all workstations running without issue and can turn
on/off via soft start without tripping yet at times even if i just have
a couple connected to the ring it blows.

Looks like a non RCD ring + indivdual on/off for each workstation is
the way to go ?

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To fix this you need not to have an RCD seeing the combined leakage
current, i.e. get rid of the RCD incomer. Alternatively you may be able
to swap it for an RCD with a higher trip current to avoid nuisance
trips (100mA).


I did half come to this conclusion a few weeks ago but have managed to
soldier on since - are 100ma RCDs commonly used/easy to obtain? - all i
have found are 30ma versions.



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Default Do circuit breakers die of old age?


"Fash" wrote in message
ups.com...

David Hansen wrote:
On 9 Nov 2006 10:38:46 -0800 someone who may be
wrote this:-

Did you, or anyone else, calculate whether the wiring is suitable
for this first?

What calculation would that be ?


The rather obvious cable sizing calculations. Had the wiring caught
fire during this "process of elimination", which presumably lasted
for some time, you might have been in a difficult position.

I have 4 TFTs - no CRTs - a small laser printer and couple of
hub/routers + a max of 8 workstations.


Sounds like you need the specialist advice of an electrical
designer.

Looks like a non RCD ring + indivdual on/off for each workstation is
the way to go ?


Possibly.

The leakage current isn't affected by whether there is load or not from
the power supply. And yes it is fairly easy to get hold of 100mA RCDs.
Try
http://www.tlc-direct.co.uk/Main_Ind...cds/index.html
just don't expect screwfix to stock them. However screwfix do stock
plenty of 1 module RCBOs which you could then use to protect your
socket circuits that don't feed your office.

Still worries me that the mcb was tripping.


It would concern me too.
There is no reason why a PC power supply should trip a 30A breaker.
I would like to know what these workstations are so I can avoid them.

As for a solution either..

fix the PSUs in the workstations

or

use one or more UPS to power the workstations.


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