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Default Hiring an RCD tester

I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six months
without tripping. On average I'm getting a trip around once every two
months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.
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Default Hiring an RCD tester

Caecilius expressed precisely :
Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.


It would suggest the possibilities of hiring is doubtful, but DIY would
be not really that difficult....

A suitable pot in series with a resistor to limit the maximum current
between the L and E. Then just tweak the pot to the point where it just
trips. Measure the overall resistance, you can check your mains voltage
and from that work out the trip current. All you are missing is the
time, but that might not be so important to your needs.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


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Default Hiring an RCD tester

On 15/12/2012 14:59, Caecilius wrote:
I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six months
without tripping. On average I'm getting a trip around once every two
months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.


A RCD tester won't do much more than your improvised equipment will do
in terms of things you are interested in (i.e. trip thresholds, rather
than response times).

The price of swapping the RCD will be lower than any other option...

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.


You could always grab one from ebay, use and re-sell.


--
Cheers,

John.

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Default Hiring an RCD tester

On Sat, 15 Dec 2012 15:28:20 +0000, John Rumm
wrote:
The price of swapping the RCD will be lower than any other option...


I'll be changing the RCD anyway. As you say, it's a cheap option. I
just wanted to see what difference it had made. In the past, I've made
changes and thought the problem cured when months went by without a
trip, only for the RCD to trip six months later.

You could always grab one from ebay, use and re-sell.


Yes, that's a possibility.
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Default Hiring an RCD tester

In article ,
John Rumm writes:
On 15/12/2012 14:59, Caecilius wrote:
I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six months
without tripping. On average I'm getting a trip around once every two
months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.


A RCD tester won't do much more than your improvised equipment will do
in terms of things you are interested in (i.e. trip thresholds, rather
than response times).


I still use the one I made 20 years ago, with a 5mA, 10mA, 15ma, 30mA
switch. If I was making it today, I would also include a couple of
diodes and switches to do the pulsed DC test.

I've never found an RCD which failed by taking too long to trip.
Only those that are too sensitive, or don't trip at all.

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


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Default Hiring an RCD tester

On 15/12/2012 16:35, Caecilius wrote:
On Sat, 15 Dec 2012 16:00:17 +0000 (UTC),
(Andrew Gabriel) wrote:

I've never found an RCD which failed by taking too long to trip.
Only those that are too sensitive, or don't trip at all.


That's interesting. Perhaps the leakage plug method is not too crude
after all.

My current 30ma RCD always trips at 16ma (15K resistor) and sometimes
trips at 11ma (22K resistor), so it looks like it trips somewhere
between these two values. I realise it should be somewhere between
15ma and 30ma, but I'd like to see something closer to 30 than 15.


I wouldn't mind betting that the leakage that's causing your trips is
coming from a single source. It may or may not be over 30ma, and it may
be highly intermittent, but finding that slightly duff appliance would
be a better bet than replacing the RCD for stopping the trips. A new RCD
may well be very nearly as sensitive as the one you have already.

If it was my system, I'd be trying to measure the actual leakage current
so I could go around plugging things in one-by-one, hoping to see a
significant increase at some point.

Since you don't seem to mind fiddling about a bit, you could temporarily
connect a multimeter to the current sensing coil and then characterise
the reading you get against your leakage plugs.

On the other hand, you could just replace your kettle. It always turns
out to be that in the end ;o)

Cheers,

Colin.
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Default Hiring an RCD tester

On Dec 15, 2:59*pm, Caecilius wrote:
I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six months
without tripping. On average I'm getting a trip around once every two
months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.


The way to find out if the RCD is faulty is to swop two over.
You can then see if the fault lies with the circuit or the breaker.

You are unlikely to discove ranything on an intermittent fault with
instrumentation.


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Default Hiring an RCD tester

On 15/12/2012 15:59, Caecilius wrote:
On Sat, 15 Dec 2012 15:28:20 +0000, John Rumm
wrote:
The price of swapping the RCD will be lower than any other option...


I'll be changing the RCD anyway. As you say, it's a cheap option. I
just wanted to see what difference it had made. In the past, I've made
changes and thought the problem cured when months went by without a
trip, only for the RCD to trip six months later.


That can happen even if the RCD works perfectly... It could be for
example that it is borderline "sensitized" - i.e. the normal leakage
through it is close to tripping point. Hence it only takes an unexpected
mains transient to create a brief moment of extra imbalance that pushes
it over the edge.


--
Cheers,

John.

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Default Hiring an RCD tester

On Sat, 15 Dec 2012 18:29:14 +0000, Colin Stamp
wrote:

I wouldn't mind betting that the leakage that's causing your trips is
coming from a single source. It may or may not be over 30ma, and it may
be highly intermittent, but finding that slightly duff appliance would
be a better bet than replacing the RCD for stopping the trips. A new RCD
may well be very nearly as sensitive as the one you have already.


It's possible, but after a few years of trying to find the problem (it
only trips very occasionally) I'm willing to risk GBP 30 or so on a
new RCD just to eliminate that.

One thing that tends to implicate the RCD is that the house is only
around ten years old, and my next door neighbour also has problems
with the RCD tripping. I expect the builders used the cheapest things
they could get hold of.

If it was my system, I'd be trying to measure the actual leakage current
so I could go around plugging things in one-by-one, hoping to see a
significant increase at some point.


I've done that. I've meggered (can you use that as a verb?) all the
equipment between L+N (shorted together) and E. No problems found. But
this only measures the insulation resistance, so...

I broke the erath wire out of an extension lead, cut it and then ran
all the equipment through that, using a multimeter on AC mA to measure
earth leakage current. No problems found - nothing above around 100 uA
IIRC.

I wonder about things like the fridge, which is on a thermostat and
maybe has a defrost heater that comes on occasionally. That's
difficult to measure.

I guess I could megger the fixed wiring, but it seems like clutching
at straws.

Since you don't seem to mind fiddling about a bit, you could temporarily
connect a multimeter to the current sensing coil and then characterise
the reading you get against your leakage plugs.


That's possible. Once I've got the new RCD in, I might play about with
the old one to see if I can convert it into an earth leakage
measurement device.

On the other hand, you could just replace your kettle. It always turns
out to be that in the end ;o)


Not as easy as that I'm afraid. I've checked the kettle earth leakage.

While this has been going on, I've had a few genuine earth leakage
problems which have been found and fixed. One was the iron, and the
other the oven element. But the underlying nusience trips remain.

Cheers,

Colin.

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On Sat, 15 Dec 2012 19:08:18 +0000, John Rumm
wrote:

Have you tested for neutral to earth shorts on each of the circuits?


No, I've not done any fixed wiring tests yet.
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On 15/12/2012 19:06, Caecilius wrote:
On Sat, 15 Dec 2012 18:29:14 +0000, Colin Stamp
wrote:

I wouldn't mind betting that the leakage that's causing your trips is
coming from a single source. It may or may not be over 30ma, and it may
be highly intermittent, but finding that slightly duff appliance would
be a better bet than replacing the RCD for stopping the trips. A new RCD
may well be very nearly as sensitive as the one you have already.


It's possible, but after a few years of trying to find the problem (it
only trips very occasionally) I'm willing to risk GBP 30 or so on a
new RCD just to eliminate that.


It might be interesting to see what happens, assuming you can get a
significantly less sensitive RCD but, even if the trips stop, I reckon
something somewhere will still be occasionally leaking abnormally.
Still, as you say, it'll give you a spare RCD to play with.


One thing that tends to implicate the RCD is that the house is only
around ten years old, and my next door neighbour also has problems
with the RCD tripping. I expect the builders used the cheapest things
they could get hold of.

If it was my system, I'd be trying to measure the actual leakage current
so I could go around plugging things in one-by-one, hoping to see a
significant increase at some point.


I've done that. I've meggered (can you use that as a verb?) all the
equipment between L+N (shorted together) and E. No problems found. But
this only measures the insulation resistance, so...

I broke the erath wire out of an extension lead, cut it and then ran
all the equipment through that, using a multimeter on AC mA to measure
earth leakage current. No problems found - nothing above around 100 uA
IIRC.


I don't think you've got everything covered with those tests. The Megger
doesn't allow the appliances to be powered, so many potential leaks
won't have a chance to occur during the test. Also, leakage current
doesn't always come back through the earth wire of the leaking
appliance. The beauty of using an RCD to measure the leakage is that
you'll end-up getting a proper RCD's-eye view of the imbalance between
live and neutral currents with the appliance running.

Having said all that, I'd put money on the fault being highly
intermittent and difficult create whilst you're watching for it. (


I wonder about things like the fridge, which is on a thermostat and
maybe has a defrost heater that comes on occasionally. That's
difficult to measure.

I guess I could megger the fixed wiring, but it seems like clutching
at straws.

Since you don't seem to mind fiddling about a bit, you could temporarily
connect a multimeter to the current sensing coil and then characterise
the reading you get against your leakage plugs.


That's possible. Once I've got the new RCD in, I might play about with
the old one to see if I can convert it into an earth leakage
measurement device.

On the other hand, you could just replace your kettle. It always turns
out to be that in the end ;o)


Not as easy as that I'm afraid. I've checked the kettle earth leakage.


They can be tricky buggers. One gave me the runaround for over a year,
tripping the RCD in the middle of the night once every few months and
then playing all innocent the following day. It turned out the tiny
water leak into the handle only became a problem if it was left nearly
full for many hours.


While this has been going on, I've had a few genuine earth leakage
problems which have been found and fixed. One was the iron, and the
other the oven element. But the underlying nusience trips remain.


I feel for you. These problems can be soooo frustrating. If you get
*really* desperate, perhaps you could arrange an independently RCDd
supply that could be used to power strong suspects long-term whilst
waiting for the next trip.

Cheers,

Colin.



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In article ,
Caecilius wrote:
Have you ruled out an additional 5-15mA leakage elsewhere, adding
to your test leakage?


Sort of. I turned off the MCBs for all the RCD-protected circuits
except for a small ring in the converted loft room, then unplugged
everything else from that ring and tested from there.


Unless they are double pole MCBs it won't help if the problem is in the
wiring. The RCD will trip with a neutral to earth fault.

--
*The early bird gets the worm, but the second mouse gets the cheese *

Dave Plowman London SW
To e-mail, change noise into sound.
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On 15/12/2012 18:54, harry wrote:
On Dec 15, 2:59 pm, Caecilius wrote:
I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six months
without tripping. On average I'm getting a trip around once every two
months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.


The way to find out if the RCD is faulty is to swop two over.
You can then see if the fault lies with the circuit or the breaker.

You are unlikely to discove ranything on an intermittent fault with
instrumentation.


Depends how D-I-Y you want to get...

I faced a similar problem, and built a D-I-Y leakage meter.

I took an old 2-pole RCD ( Merlin Gerin, as it happened ), and carefully
opened it.

I removed all the mechanical switching parts, leaving only the current
transformer with it's 2 heavy windings passing L and N, and the sense
coil which I wired to a pair of external jacks.

A 10k resistor was placed as a load across the sense coil, to provide a
voltage output rather than a current output. This is important,
otherwise the open-cct output voltage from a current transformer can
posentially get hazardously high.

I then performed a calibration with a 12vAC supply, some test resistors,
and a pair of flukes set up to measure mV out versus mA leakage. I
calibrated in 1mA steps from 1 to 10mA, then in 5mA steps up to 50mA.
The calibration was outstandingly linear, and I printed up a table of mV
to mA. I got 45mV / mA.


Now, by wiring this in-circuit with the troublesome circuit ( both L and
N, obviously ) I was able to make actual measurements and isolated
several faults.

Finally, you may wish to consider replacing the single RCD with multiple
RCBOs, if your CU can take them.


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Default Hiring an RCD tester

Caecilius expressed precisely :

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.


Surely a new RCD would be cheaper.

As harry said, you can adjust the current trip threshold with just resistors. If you then set trip current with capacitors instead, you'd be closer to real world conditions and can see if it filters out such transients effectively, as it should.

The only thing that doesn't test is whether it trips within prescribed time limits, but that has not too much to do with your problem.

Or you can just replace the RCD.


NT
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On Sun, 16 Dec 2012 09:42:54 +0000, Ron Lowe wrote:

I faced a similar problem, and built a D-I-Y leakage meter.


That's very interesting. Once I've replaced my RCD, I may use the old
one to build a similar device. Thanks for the information.

Finally, you may wish to consider replacing the single RCD with multiple
RCBOs, if your CU can take them.


Not enough room in my CU unfortunately. But I 've seriously considered
changing the CU for one with RCBOs on all RCD-protected circuits. If
I'm still having the problem after swapping the RCD and checking the
fixed wiring for N/E problems, I'll probably do that.


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On Sat, 15 Dec 2012 19:06:34 +0000, Caecilius
wrote:


I guess I could megger the fixed wiring, but it seems like clutching
at straws.


Not quite, neutral to earth faults in fixed wiring are not that
uncommon and quite often go unnoticed for years. One of the most
common causes is a nail through a cable which shorts neutral to earth.
Some years ago I helped a friend with such a fault. It was discovered
when plugging in a drum type extension lead (with nothing attached to
it). Plugging it in to some sockets would cause the RCD to trip.
Plugging in to others (on the same ring or an alternative) wouldn't.
The extension lead was perfectly OK when tested. An alternative
extension lead did the same thing - but on different sockets!

Both leads were fine if his wife was putting clothes into the airing
cupboard (noticed only by chance rather than skilled detective work).
It turned out that the upstairs ring had a floorboard nail neatly
through it on the landing near the airing cupboard. When standing
near it it moved just enough to break the E-N link.

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On 16/12/2012 13:19, Caecilius wrote:
On Sun, 16 Dec 2012 09:42:54 +0000, Ron Lowe wrote:

I faced a similar problem, and built a D-I-Y leakage meter.


That's very interesting. Once I've replaced my RCD, I may use the old
one to build a similar device. Thanks for the information.

Finally, you may wish to consider replacing the single RCD with multiple
RCBOs, if your CU can take them.


Not enough room in my CU unfortunately. But I 've seriously considered
changing the CU for one with RCBOs on all RCD-protected circuits. If
I'm still having the problem after swapping the RCD and checking the
fixed wiring for N/E problems, I'll probably do that.



Out of interest, how many circuits are being protected by the single RCD?


--
Cheers,

John.

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On 16/12/2012 09:42, Ron Lowe wrote:
On 15/12/2012 18:54, harry wrote:
On Dec 15, 2:59 pm, Caecilius wrote:
I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six months
without tripping. On average I'm getting a trip around once every two
months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops direct
me to a PAT tester which isn't what I'm looking for. I don't want to
buy one for a single project.


The way to find out if the RCD is faulty is to swop two over.
You can then see if the fault lies with the circuit or the breaker.

You are unlikely to discove ranything on an intermittent fault with
instrumentation.


Depends how D-I-Y you want to get...

I faced a similar problem, and built a D-I-Y leakage meter.

I took an old 2-pole RCD ( Merlin Gerin, as it happened ), and carefully
opened it.

I removed all the mechanical switching parts, leaving only the current
transformer with it's 2 heavy windings passing L and N, and the sense
coil which I wired to a pair of external jacks.

A 10k resistor was placed as a load across the sense coil, to provide a
voltage output rather than a current output. This is important,
otherwise the open-cct output voltage from a current transformer can
posentially get hazardously high.

I then performed a calibration with a 12vAC supply, some test resistors,
and a pair of flukes set up to measure mV out versus mA leakage. I
calibrated in 1mA steps from 1 to 10mA, then in 5mA steps up to 50mA.
The calibration was outstandingly linear, and I printed up a table of mV
to mA. I got 45mV / mA.


Now, by wiring this in-circuit with the troublesome circuit ( both L and
N, obviously ) I was able to make actual measurements and isolated
several faults.


You can buy high sensitivity clamp meters designed to assist with this
kind of test - looping it round L & N it measures the imbalance.

(although I have not tried it, you may be able to get a similar effect
with a "normal" clamp meter, clamped round test leads with multiple
turns in them to magnify the current sensed. I use a similar arrangement
to measure loadings on IT kit for UPS sizing, with and extension lead
with ten turn coils made up and broken out)


--
Cheers,

John.

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|-----------------------------------------------------------------|
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On Sun, 16 Dec 2012 15:48:20 +0000, John Rumm
wrote:
Out of interest, how many circuits are being protected by the single RCD?


There's a total of five circuits, all on B32 MCBs. They are three
rings for sockets, one unused radial for the cooker (changed from elec
to gas hob, so not needed now), and one radial for a shower steam
unit.

The things not on the RCD are the lights (thank goodness), smoke
detectors, and a radial for the immersion heater.
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On Sunday, December 16, 2012 1:19:22 PM UTC, Caecilius wrote:
On Sun, 16 Dec 2012 09:42:54 +0000, Ron Lowe wrote:


I faced a similar problem, and built a D-I-Y leakage meter.


That's very interesting. Once I've replaced my RCD, I may use the old
one to build a similar device. Thanks for the information.


http://wiki.diyfaq.org.uk/index.php?title=Megger


NT


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On 16/12/2012 16:38, Caecilius wrote:
On Sun, 16 Dec 2012 15:48:20 +0000, John Rumm
wrote:
Out of interest, how many circuits are being protected by the single RCD?


There's a total of five circuits, all on B32 MCBs. They are three
rings for sockets, one unused radial for the cooker (changed from elec
to gas hob, so not needed now), and one radial for a shower steam
unit.


Having all the house sockets on one RCD can often be enough to get close
to the trip limits. Especially if you have a house full of electronic
gadgets.

Shifting stuff like kitchen circuits off to a separate RCBO can
sometimes make all the difference to nuisance trip problems.


--
Cheers,

John.

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On Sun, 16 Dec 2012 08:51:49 -0800 (PST), wrote:

On Sunday, December 16, 2012 1:19:22 PM UTC, Caecilius wrote:
On Sun, 16 Dec 2012 09:42:54 +0000, Ron Lowe wrote:


I faced a similar problem, and built a D-I-Y leakage meter.


That's very interesting. Once I've replaced my RCD, I may use the old
one to build a similar device. Thanks for the information.


http://wiki.diyfaq.org.uk/index.php?title=Megger

I've already got a megger (albeit a fairly cheap one). It's good for
checking insulation resistance, but it doesn't allow me to measure the
earth leakage under operating conditions like the device Ron describes
would.
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On 15/12/2012 14:59, Caecilius wrote:
I've been experiencing occasional nuisance RCD tripping for a few
years now. It's very occasional - sometimes going for up to six
months without tripping. On average I'm getting a trip around once
every two months.

I've done some equipment testing with a megger and basic RCD
sensitivity testing with some home-made leakage plugs (plugs with
resistors between live and earth to give a known leakage current).
Based on this, I think my RCD is over sensitive.

My plan is to replace the RCD, which is fairly cheap and simple. But
I'd like to test the old one and the new one with something better
than leakage plugs to see if there's any change in sensitivity.

Does anyone know if it's possible to hire RCD testers for short
periods at a reasonable rate? When I've looked, most hire shops
direct me to a PAT tester which isn't what I'm looking for. I don't
want to buy one for a single project.


You can buy affordable clamp meters where if you can pass just the live
and neutral through the clamp together you can measure residual current
directly. Depending on supplementary bonding you can also get an
indication by measuring the current flowing in the protective conductor.
You might then be able to find the offending circuit.

As others have suggested, each appliance does have an allowable leakage
and combined it may be close to the RCD limit.

Moving some circuits on the non-RCD portion whilst using RCBOs on the
most likely offending circuits like the kitchen circuit may solve the
problem.

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On Sun, 16 Dec 2012 17:37:19 -0000, "ARW"
wrote:


What is the make and model no of the RCD? I might have a spare and I if I
have it's all your's for P&P (or just post a picture of it).


The RCD is a Tenby unit, in a tenby C series CU. Installed around year
2000 I think.

http://i1021.photobucket.com/albums/...U/P1000068.jpg
http://i1021.photobucket.com/albums/...U/P1000072.jpg

I really want to replace it with a different model though, because I
suspect it's the cheapest the builders could find.

One thing I would appreciate is advice on good quality RCDs. I see
screwfix have BG (British General), Wylex, Volex, and MK for between
GBP 20 and 35. I'd probably go for MK, as it's a brand I know, but a
view from someone in the trade would be useful. I don't really care
about a few pounds if it's likely to improve the situation.

I'm assuming that any 80A 30ma RCD will fit in my CU. They all look
pretty similar to me from the images on the screwfix website. If
there's some compatability issues that I should be aware of, please
let me know.

I'll even test it and give you the test results.

I am a little too busy to read all the thread ATM but is this a whole house
RCD?


It's a split load CU with lighting and immersion without RCD
protection, and all the power circuits protected by a single RCD.


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On Sun, 16 Dec 2012 21:52:38 +0000, Fredxx wrote:

You can buy affordable clamp meters where if you can pass just the live
and neutral through the clamp together you can measure residual current
directly. Depending on supplementary bonding you can also get an
indication by measuring the current flowing in the protective conductor.
You might then be able to find the offending circuit.


That's interesting. I thought that sensitive clamp meters were fairly
expensive. I'll have a look around. Another toy for the collection if
nothing else :-)

As others have suggested, each appliance does have an allowable leakage
and combined it may be close to the RCD limit.


Yes, I suspect this is part of the problem, together with a fairly
sensitive RCD.

Moving some circuits on the non-RCD portion whilst using RCBOs on the
most likely offending circuits like the kitchen circuit may solve the
problem.


Yes, RCBO is doubtless the way to go, and they look quite affordable
now. But I don't think my CU is big enough for them, as they look much
taller than a normal MCB, and my CU is about ten years old.

Here's some photos of my CU:

http://i1021.photobucket.com/albums/...U/P1000068.jpg
http://i1021.photobucket.com/albums/...U/P1000072.jpg

Nicely located less than an inch from the ceiling, and right behind
the garage door rail.

If an RCBO will fit in that, then I'd probably take that route. I
guess I could put a couple of circuits on RCBOs and move the RCD over
so it protects less circuits. If I could do that for the cost of a
couple of RCBOs plus a busbar then I'd be a happy bunny.
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On Monday, December 17, 2012 5:40:28 PM UTC, Caecilius wrote:
On Sun, 16 Dec 2012 17:37:19 -0000, "ARW"
wrote:



I really want to replace it with a different model though, because I
suspect it's the cheapest the builders could find.
One thing I would appreciate is advice on good quality RCDs. I see
screwfix have BG (British General), Wylex, Volex, and MK for between
GBP 20 and 35. I'd probably go for MK, as it's a brand I know, but a
view from someone in the trade would be useful. I don't really care
about a few pounds if it's likely to improve the situation.


All brands need to meet the same electrical spec.


NT
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On 17/12/2012 17:40, Caecilius wrote:
On Sun, 16 Dec 2012 17:37:19 -0000, "ARW"
wrote:


What is the make and model no of the RCD? I might have a spare and I if I
have it's all your's for P&P (or just post a picture of it).


The RCD is a Tenby unit, in a tenby C series CU. Installed around year
2000 I think.

http://i1021.photobucket.com/albums/...U/P1000068.jpg
http://i1021.photobucket.com/albums/...U/P1000072.jpg

I really want to replace it with a different model though, because I
suspect it's the cheapest the builders could find.

One thing I would appreciate is advice on good quality RCDs. I see
screwfix have BG (British General), Wylex, Volex, and MK for between
GBP 20 and 35. I'd probably go for MK, as it's a brand I know, but a
view from someone in the trade would be useful. I don't really care
about a few pounds if it's likely to improve the situation.


To be fair I have not noticed much difference between them. I have a
mixture of MK, Hager, and possibly some Contactum ones here - they all
do what they are supposed to.

I'm assuming that any 80A 30ma RCD will fit in my CU. They all look
pretty similar to me from the images on the screwfix website. If
there's some compatability issues that I should be aware of, please
let me know.


In broad terms, yes - although there is some variation - things like the
distance front to back that the live terminal exits the enclosure which
can make lining up the busbar with other devices difficult if they don't
match well, or a very slight difference in the height they "ride" the
din rail - making the protruding sections not line up etc.

(there is also the point that a mix and match set won't have type
approval - so you may be taking pot luck on device cooling
characteristics etc)

We had a stab a while ago at doing a grid of interchangeability - its
not up to date but may give you something to go on. Bottom of this page:

http://wiki.diyfaq.org.uk/index.php?title=Consumer_unit



--
Cheers,

John.

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In article , Peter Parry
scribeth thus
On Sat, 15 Dec 2012 19:06:34 +0000, Caecilius
wrote:


I guess I could megger the fixed wiring, but it seems like clutching
at straws.


Not quite, neutral to earth faults in fixed wiring are not that
uncommon and quite often go unnoticed for years. One of the most
common causes is a nail through a cable which shorts neutral to earth.
Some years ago I helped a friend with such a fault. It was discovered
when plugging in a drum type extension lead (with nothing attached to
it).


So just the extension lead with Nothing at all plugged into that to load
the circuit?..

Plugging it in to some sockets would cause the RCD to trip.
Plugging in to others (on the same ring or an alternative) wouldn't.
The extension lead was perfectly OK when tested. An alternative
extension lead did the same thing - but on different sockets!


That wasn't a proper ring main was it?..


Both leads were fine if his wife was putting clothes into the airing
cupboard (noticed only by chance rather than skilled detective work).
It turned out that the upstairs ring had a floorboard nail neatly
through it on the landing near the airing cupboard. When standing
near it it moved just enough to break the E-N link.


So if that was on a ring main how come some sockets made it trip and
others didn't?..

Think of what's going on here!...

--
Tony Sayer

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Caecilius wrote:
On Sun, 16 Dec 2012 17:37:19 -0000, "ARW"
wrote:


What is the make and model no of the RCD? I might have a spare and
I if I have it's all your's for P&P (or just post a picture of it).


The RCD is a Tenby unit, in a tenby C series CU. Installed around year
2000 I think.

http://i1021.photobucket.com/albums/...U/P1000068.jpg
http://i1021.photobucket.com/albums/...U/P1000072.jpg

I really want to replace it with a different model though, because I
suspect it's the cheapest the builders could find.

One thing I would appreciate is advice on good quality RCDs. I see
screwfix have BG (British General), Wylex, Volex, and MK for between
GBP 20 and 35. I'd probably go for MK, as it's a brand I know, but a
view from someone in the trade would be useful. I don't really care
about a few pounds if it's likely to improve the situation.

I'm assuming that any 80A 30ma RCD will fit in my CU. They all look
pretty similar to me from the images on the screwfix website. If
there's some compatability issues that I should be aware of, please
let me know.

I'll even test it and give you the test results.

I am a little too busy to read all the thread ATM but is this a
whole house RCD?


It's a split load CU with lighting and immersion without RCD
protection, and all the power circuits protected by a single RCD.


I can probably find something to fit and replace your RCD. However I really
do not think that this is the answer. Your solution is to divide and
conquer - could you lose the RCD and install RCBOs on the RCD side? I
suspect that the CU will not accomodate them.

In another post it was mentioned that you could get an all RCBO CU from
Denmans for £100 (Mr Roberts was not specific on how many RCBOs he got but I
suspect that it is 8). Your best solution is to do what Mr Roberts did and
install a full RCBO CU. All RCBO installations are the new Peter Kaye Garlic
Bread.

The offer still stands if you want me to send you a RCD (if I can find one)

Cheers
--
Adam




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On Saturday, December 15, 2012 2:59:54 PM UTC, Caecilius wrote:
I've been experiencing occasional
nuisance RCD tripping for a few years now.


I presume there is no rubber cable in use - and this is a 1980+ installation? I presume you have checked any outdoor sockets & lights for water penetration, isolated any external shed circuit?

Hiring an RCD tester is going to be £80, perhaps £80+VAT, with delivery & collection. So replacing with RCBO is indeed the better solution and may pin the fault down to one circuit, well worth doing.

Buying an RCD tester can work - if you get an end of line electrical factor clone like Newey & Eyre or Alto Electrical "Own Brand" which whilst new can be a fraction of the Megger branded RCDT320 etc.
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On Tue, 18 Dec 2012 19:12:04 -0000, "ARW"
wrote:

In another post it was mentioned that you could get an all RCBO CU from
Denmans for £100 (Mr Roberts was not specific on how many RCBOs he got but I
suspect that it is 8). Your best solution is to do what Mr Roberts did and
install a full RCBO CU. All RCBO installations are the new Peter Kaye Garlic
Bread.


Yes, I think I probably need to bite the bullet and replace the CU
with one that can take RCBOs.

That's a bit beyone my DIY skills though, so I'll need to get someone
in to do it. Do you have any idea of the labour charge for a CU
replacement like this? I'm in medway towns, kent if it makes any
difference.

The offer still stands if you want me to send you a RCD (if I can find one)


Thanks for the offer, but I think I'll go down the RCBO route as you
suggested.
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Caecilius wrote:
On Tue, 18 Dec 2012 19:12:04 -0000, "ARW"
wrote:

In another post it was mentioned that you could get an all RCBO CU
from Denmans for £100 (Mr Roberts was not specific on how many
RCBOs he got but I suspect that it is 8). Your best solution is to
do what Mr Roberts did and install a full RCBO CU. All RCBO
installations are the new Peter Kaye Garlic Bread.


Yes, I think I probably need to bite the bullet and replace the CU
with one that can take RCBOs.

That's a bit beyone my DIY skills though, so I'll need to get someone
in to do it. Do you have any idea of the labour charge for a CU
replacement like this? I'm in medway towns, kent if it makes any
difference.

The offer still stands if you want me to send you a RCD (if I can
find one)


Thanks for the offer, but I think I'll go down the RCBO route as you
suggested.


Get a couple of quotes and I'll beat them if you like.

I was going to be down your way between Xmas and New Year but I ended up
with a rewire in Edinburgh instead. Depending on your timescale I could do
it in January when I finish off a job in Lambeth (hopefully finish - she
keeps changing her mind). And in Feb/March I should be starting a first fix
of 6 apartments in Deptford so I could do it then (they were supposed to
start in August). It will have to be a Saturday or Sunday depending on when
I leave London.

You have to be aware that installing RCDs onto circuits that currently have
no RCD could cause problems. However your installation is of the age where
that is unlikely to be a problem.

Of course I would actually use the job as an excuse to meet up with TMH
again for a massive breakfast in a cafe.

--
Adam


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On 17/12/2012 17:54, Caecilius wrote:
On Sun, 16 Dec 2012 21:52:38 +0000, Fredxx wrote:

You can buy affordable clamp meters where if you can pass just the live
and neutral through the clamp together you can measure residual current
directly. Depending on supplementary bonding you can also get an
indication by measuring the current flowing in the protective conductor.
You might then be able to find the offending circuit.


That's interesting. I thought that sensitive clamp meters were fairly
expensive.


They are, but... I bought a Fluke 360 a couple of years ago and
wouldn't be without it now.

And to answer your original question:
(e.g.) http://adastrahire.co.uk/search?q=rcd+tester

Or ring round your local electrical wholesalers, many of them do test
equipment hire. What you really need is a leakage data logger though...

--
Andy
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On 17/12/2012 17:54, Caecilius wrote:
On Sun, 16 Dec 2012 21:52:38 +0000, Fredxx wrote:

You can buy affordable clamp meters where if you can pass just the live
and neutral through the clamp together you can measure residual current
directly. Depending on supplementary bonding you can also get an
indication by measuring the current flowing in the protective conductor.
You might then be able to find the offending circuit.


That's interesting. I thought that sensitive clamp meters were fairly
expensive. I'll have a look around. Another toy for the collection if
nothing else :-)


I came across this one by accident the other day. It's got a 2A range,
so 1mA resolution.

http://uk.farnell.com/tenma/72-7222/...ure/dp/1283639

Cheers,

Colin.



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