RCD Nuisance Trips Conundrum
 

We have a newly installed RCD that trips in a very puzzling way. Let me
explain.

We have two separate consumer units. One has a split load RCD and supplies
the back of the house - it has never tripped. The other is an older "fuse
wire" consumer unit with 16 circuits supplying the front of the house. It is
protected by an RCD on its incoming feed and it is this RCD that trips
several times per day.

There is no single cause that trips it - sometimes it is a light, sometimes
the computer, etc. What is really puzzling is that the TV can trip it. The
TV is in the back of the house fed from the other consumer unit and
therefore is not even supplied through the troublesome RCD.

The RCD has been checked with an RCD tester and it passed OK.

Any ideas? Our electricians are baffled.

Thanks

"Hzatph" wrote in message
...
We have a newly installed RCD that trips in a very puzzling way. Let me
explain.

We have two separate consumer units. One has a split load RCD and supplies
the back of the house - it has never tripped. The other is an older "fuse
wire" consumer unit with 16 circuits supplying the front of the house. It
is protected by an RCD on its incoming feed and it is this RCD that trips
several times per day.

There is no single cause that trips it - sometimes it is a light,
sometimes the computer, etc. What is really puzzling is that the TV can
trip it. The TV is in the back of the house fed from the other consumer
unit and therefore is not even supplied through the troublesome RCD.

The RCD has been checked with an RCD tester and it passed OK.

Any ideas? Our electricians are baffled.

Thanks


Check that the RCD is not too sensitive,
check the insualtion been the tv ariel cable and N as well as E. Check there
is no N / E reversal

Hzatph wrote:

We have two separate consumer units. One has a split load RCD and supplies
the back of the house - it has never tripped. The other is an older "fuse
wire" consumer unit with 16 circuits supplying the front of the house. It is
protected by an RCD on its incoming feed and it is this RCD that trips
several times per day.

16 circuits is quite alot to have on one RCD. It would be interesting to
carry out RCD test while on load to see how much extra leakage is
required to trip it.

There is no single cause that trips it - sometimes it is a light, sometimes
the computer, etc. What is really puzzling is that the TV can trip it. The
TV is in the back of the house fed from the other consumer unit and
therefore is not even supplied through the troublesome RCD.

The RCD has been checked with an RCD tester and it passed OK.

That does not mean that it is not pre sensitied by cumulative leakage
from all the circuits it is feeding to the point where it right at the
point of tripping with little provocation. You could try to isoate if
there is a circuit that is doing the bulk of the leaking by
disconnecting each in turn for a day and seeing if that reduces the trip
rate.

You did not mention what sort of supply you had, or the trip current of
the RCDs. Also what sort of circuits are fed from the re-wireable
consumer unit?



--
Cheers,

John.

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

In article ,
Hzatph wrote:
We have a newly installed RCD that trips in a very puzzling way. Let me
explain.

We have two separate consumer units. One has a split load RCD and
supplies the back of the house - it has never tripped. The other is an
older "fuse wire" consumer unit with 16 circuits supplying the front of
the house. It is protected by an RCD on its incoming feed and it is
this RCD that trips several times per day.

There is no single cause that trips it - sometimes it is a light,
sometimes the computer, etc. What is really puzzling is that the TV can
trip it. The TV is in the back of the house fed from the other consumer
unit and therefore is not even supplied through the troublesome RCD.

Is there any equipment which could cause the earth from one CU at some
point to to be shared with the earth for the other somewhere else? I
realise both CUs will share an earthing point.

Perhaps an aerial lead from a DA? Hi-Fi equipment interconnection?

--
*Nothing is foolproof to a sufficiently talented fool.

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

To answer some of the questions.

Both RCDs are 30mA.

The 16 circuits have:

4 ring mains
2 power spurs (cooker, immersion heater)
The rest are lighting circuits as far as I know.

The only connection we can think between the consumer units is the aerial on
the TV - we have TVs on both parts of the house. We tried disconnecting this
but we still got a trip. The aerial has a masthead amplifier powered by a
transformer on a normal socket fed by the main fused consumer unit.

As Dave says both consumer units connect to an earth which I think is
connected to the neutral in the incoming supply. There is a cable from there
to ground on the Manweb side of our supply about 30m from the house.

Hope that helps.

Thanks for all the suggestions.

Hzatph wrote:

The 16 circuits have:

4 ring mains
2 power spurs (cooker, immersion heater)

^^^^^^^^^^^^^^^^
Prone to high leakage!

Try turning off / pulling the fuse for this and see if it helps.

If that does not find it then you are going to need to start testing the
wiring for each circuit with a megger.

--
Cheers,

John.

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

In article , John
Rumm writes
Hzatph wrote:

The 16 circuits have:

4 ring mains
2 power spurs (cooker, immersion heater)

^^^^^^^^^^^^^^^^
Prone to high leakage!

Try turning off / pulling the fuse for this and see if it helps.

If that does not find it then you are going to need to start testing the
wiring for each circuit with a megger.


Also look for Nutral/Earth shorts or leakage, these are often overlooked
and don't usually show up until some current is flowing through the
system.....
--
Tony Sayer

I would suspect that, but both these items are switched off. We have kept a
log of things that trip the RCD and it is a long list - there is no regular
pattern.
"John Rumm" wrote in message
...
Hzatph wrote:

The 16 circuits have:

4 ring mains
2 power spurs (cooker, immersion heater)

^^^^^^^^^^^^^^^^
Prone to high leakage!

Try turning off / pulling the fuse for this and see if it helps.

If that does not find it then you are going to need to start testing the
wiring for each circuit with a megger.

I would suspect that, but both these items are switched off. We have kept a
log of things that trip the RCD and it is a long list - there is no regular
pattern.

On Sat, 20 Aug 2005 21:45:49 +0000 (UTC), "Hzatph"
wrote:

I would suspect that, but both these items are switched off. We have kept a
log of things that trip the RCD and it is a long list - there is no regular
pattern.

Hi,

I wonder if the neutrals on the the two consumer units are connected
somewhere, maybe on a lighting circuit.

Does the TV trip the RCD on switch on? If so it's probably the large
current draw from the degauss circuit.

A good way to track down the fault would be isolate each L-N circuit
in turn by disconnecting the neutral as well as just pulling the fuse.

Be very careful though, no responsibility accepted if you fry
yourself! :^)

cheers,
Pete.

Hzatph wrote:

We have a newly installed RCD that trips in a very puzzling way. Let me
explain.

We have two separate consumer units. One has a split load RCD and supplies
the back of the house - it has never tripped. The other is an older "fuse
wire" consumer unit with 16 circuits supplying the front of the house. It is
protected by an RCD on its incoming feed and it is this RCD that trips
several times per day.

There is no single cause that trips it - sometimes it is a light, sometimes
the computer, etc. What is really puzzling is that the TV can trip it. The
TV is in the back of the house fed from the other consumer unit and
therefore is not even supplied through the troublesome RCD.

The RCD has been checked with an RCD tester and it passed OK.

Any ideas? Our electricians are baffled.

Thanks


Neutral earth leakage somewhere.

"Pete C" wrote in message
...
On Sat, 20 Aug 2005 21:45:49 +0000 (UTC), "Hzatph"
wrote:

I would suspect that, but both these items are switched off. We have kept
a
log of things that trip the RCD and it is a long list - there is no
regular
pattern.

Hi,

I wonder if the neutrals on the the two consumer units are connected
somewhere, maybe on a lighting circuit.

Does the TV trip the RCD on switch on? If so it's probably the large
current draw from the degauss circuit.

A good way to track down the fault would be isolate each L-N circuit
in turn by disconnecting the neutral as well as just pulling the fuse.

Be very careful though, no responsibility accepted if you fry
yourself! :^)

cheers,
Pete.

Pete - you are correct in your statement that it is switching the TV on. I
wonder about a neutral connection and also about the degauss type effect.
Thank you. We are going to change the 30mA RCD for a 100mA one and replace
the fused consumer unit with a modern one with 30mA RCDs on the ring mains
and power spurs.This should ease the problem we hope, and it if continues to
happen then we will have a better idea of where the fault lies.

In article , Hzatph
writes

"Pete C" wrote in message
.. .
On Sat, 20 Aug 2005 21:45:49 +0000 (UTC), "Hzatph"
wrote:

I would suspect that, but both these items are switched off. We have kept
a
log of things that trip the RCD and it is a long list - there is no
regular
pattern.

Hi,

I wonder if the neutrals on the the two consumer units are connected
somewhere, maybe on a lighting circuit.

Does the TV trip the RCD on switch on? If so it's probably the large
current draw from the degauss circuit.

That shouldn't make any difference.

A good way to track down the fault would be isolate each L-N circuit
in turn by disconnecting the neutral as well as just pulling the fuse.

Yes you can do that..

Be very careful though, no responsibility accepted if you fry
yourself! :^)

cheers,
Pete.

Pete - you are correct in your statement that it is switching the TV on. I
wonder about a neutral connection and also about the degauss type effect.
Thank you. We are going to change the 30mA RCD for a 100mA one and replace
the fused consumer unit with a modern one with 30mA RCDs on the ring mains
and power spurs.This should ease the problem we hope, and it if continues to
happen then we will have a better idea of where the fault lies.



You really shouldn't have to do that. You have either a fault in an
appliance somewhere, or you have some leakage somewhere either live to
earth or neutral to earth.

We have 6 properties and some commercial premises where a single 30 ma
RCD protects the lot in each case, and around one trip every year or two
is about the norm for the lot!, and thats usually a cooker element or
immersion heater giving up the ghost, and one of the "premises" which is
on a remote hilltop, the odd lightning strike!......
--
Tony Sayer

On Tue, 23 Aug 2005 21:23:02 +0000 (UTC), "Hzatph"
wrote:


Pete - you are correct in your statement that it is switching the TV on. I
wonder about a neutral connection and also about the degauss type effect.
Thank you. We are going to change the 30mA RCD for a 100mA one and replace
the fused consumer unit with a modern one with 30mA RCDs on the ring mains
and power spurs.This should ease the problem we hope, and it if continues to
happen then we will have a better idea of where the fault lies.

Hi,

I'd expect there is a neutral-earth short somewhere as others have
said. When you switch the TV on the current surge probably puts a
small voltage on the local neutral which causes more fault current to
flow through the short to earth and trip the RCD, even if it's in the
other CU as the neutrals are commoned.

I'd get another better electrician to look at it, describe the
symptoms to them and see if they mention the above. It should be
possible to find the fault by disconnecting each neutral in turn and
checking for a short between it and earth. While doing so any
connected equipment should be plugged in and any isolators switched on
initially in case the fault lies there.

Changing the CUs is just treating the symptom of the problem instead
of the cause, a good electricial might find the fault within an hour
or less. If your current guy can't diagnose or find a N-E fault then
getting him to change the CU might lead to other problems...

cheers,
Pete.