Possible faulty RCD?

[rubble2]

Hi,

We have a split load consumer unit installed less than 5 years ago, about a week ago we had an instance where the RCD that controls the D/S power and U/S lights tripped (this was about 11-30 at night so not a lot of appliances operating). I reset the RCD and it tripped again within 10 seconds, tried a couple more times with no improvement.

The only thing running at the time was the dishwasher (less than a month old) so I left that switched off and the RCD remained on, about 20 minutes later I tried the Dishwasher and everything ran ok - no tripping.

All was well until last evening when the same series of events happened again, this time the dishwasher wasn't running but the same RCD tripped out 4 or 5 times in succession until finally resetting and has been OK since.

Does this point to a faulty RCD? with it being so intermittent I was thinking it couldn't be a wiring problem (nothing has changed recently).

Is there any easy (DIY) method of isolating what the cause is likely to be?

Thanks

 

[DaftPunk]

It's a wiring fault.

 

[AndyPRK]

you could try completely unplugging the dishwasher and see if you still get RCD trips.

 

[rjm2k]

any outdoor sockets/lights on those circuits? could be water getting in one, if there are DP isolators for them I'd try switching them off for a while.

 

[ericmark]

I have had RCD's fitted to all power since 1992 and every now and again we get a spite of tripping and without doing anything it stops again. I would assume some one on the same phase has a fault in their house sending spikes down the mains which trip my RCD.
Sometimes both will trip together which clearly points to something on the supply rather than in my house. Also found when resetting one it will trip the other one.

There are now better quality RCD's around they are not all the same. The X-Pole by Moeller even has a warning light to show when about to trip and trips at 90 - 100% rather than normal 50 - 100% rated leakage.

Untitled

• ericmark
• 6 Dec 2008
• 34

The RCD shown would never be fitted in a house far too expensive around £300 each but it will after tripping auto test the circuit and if clear auto reset.

I have debated which way to go many times getting the X-Pole would likely reduce tripping but also using RCBO's rather than just two RCD's also reduces tripping and as long as not on a TT supply likely RCBO is best route.

Yes it could be something in the house. So no harm in taking normal precautions to reduce tripping. Any Class I item (Has an earth wire) can have a neutral - earth fault which will only trip the RCD when there is a load on the circuit. So unplugging class I items will remove this problem. The toaster is favourite little bit of damp bread in toaster can cause RCD to trip when some high powered item like dish washer, kettle, washing machine, tumble dryer is used.

 

[Gutterball]

random rcd trips are sometimes down to leakage currents from computers and other equipment with electronic components. This can slowly build up over time until it reaches the trip threshold of the rcd.

do you use the same program on your dishwasher? i had a fault on a clients washing machine once that it only tripped on one setting, the rest all were ok.

 

[mfarrow]

The RCD shown would never be fitted in a house far too expensive around £300 each but it will after tripping auto test the circuit and if clear auto reset.

It would not be possible to use the auto-reset feature one in a domestic environment (530.3.5).

 

[EFLImpudence]

It would not be possible to use the auto-reset feature one in a domestic environment (530.3.5).

WHAT!

I've just ordered ten.

 

[ericmark]

The RCD shown would never be fitted in a house far too expensive around £300 each but it will after tripping auto test the circuit and if clear auto reset.

It would not be possible to use the auto-reset feature one in a domestic environment (530.3.5).

Not in my copy must be an amendment 1 change what does it say?

 

[GaryGarden]

The RCD shown would never be fitted in a house far too expensive around £300 each but it will after tripping auto test the circuit and if clear auto reset.

It would not be possible to use the auto-reset feature one in a domestic environment (530.3.5).

Not in my copy must be an amendment 1 change what does it say?

It is an amendment.
Only to be installed in an installation intended to be under supervision of skilled or instructed persons.

 

[rubble2]

Thanks for all the replies.

We do have an outside socket connected to the kitchen ring main so I will start with that at the weekend

 

[mfarrow]

Not in my copy must be an amendment 1 change what does it say?

530.3.5 An auto-reclosing device for protection, isolation, switching or control may be installed only in an
installation intended to be under the supervision of skilled or instructed persons and intended to be inspected and
tested by competent persons.
An auto-reclosing device shall not be used to meet the requirements of Regulations 411.3.3, 415.1, 522.6.102 or
522.6.103 unless the device is of a type that automatically verifies the insulation resistance in the part of the
installation it controls is satisfactory before the device recloses.
An auto-reclosing device shall be of a type that satisfies all the following requirements:
(i) The automatic reclose function of the device cannot be engaged after the device is manually switched to the
off (or open) position
(ii) There is a time delay before the first automatic reclosure
(iii) The number of consecutive automatic reclosures is limited (to 3, for example).
A warning notice shall be clearly displayed on or near the device, indicating that no work should be carried out on
the part of the installation controlled by the device unless the automatic reclose function of the device is disengaged,
the device is manually switched off, and that part of the installation is securely isolated from the supply.

BS 7671 does not define what an auto-reclosing device is. What perhaps needs clarification is the inclusion of devices for "switching or control". There are many items that one could argue fall into this category, for example timers, time-clocks, PIRs, and dawn/dusk sensors.

 

[JohnW2]

BS 7671 does not define what an auto-reclosing device is. What perhaps needs clarification is the inclusion of devices for "switching or control". There are many items that one could argue fall into this category, for example timers, time-clocks, PIRs, and dawn/dusk sensors.

Good point. One can but assume that, even though they don't say or define it, the IET intended the same interpretation as most of us probably make - i.e. that this regulation is meant to refer specifically to devices which "auto-reclose" after having opened in response to some fault/overload situation. It would seem unlikely that they intended, and unworkable even if they did, that the reg should to apply to the other sorts of 'auto-closing' devices you list.

I have to say that I am pretty uncomfortable with the concept of "auto-reclosing" devices (as 'we' understand the meaning) since, at the very least, one is reliant on the devices working correctly to avoid potential disasters. There might possibly be some commercial/industrial situations in which that risk is outweighed by the risk resulting from not rapidly restoring power following a 'nuisance' trip, but I certainly can't see such a device ever being appropriate in a domestic setting.

Kind Regards, John

 

[mfarrow]

One can but assume that, even though they don't say or define it, the IET intended the same interpretation as most of us probably make - i.e. that this regulation is meant to refer specifically to devices which "auto-reclose" after having opened in response to some fault/overload situation. It would seem unlikely that they intended, and unworkable even if they did, that the reg should to apply to the other sorts of 'auto-closing' devices you list.

Whilst that is logical, when you break it down the IET have specifically listed

... auto-reclose devices for:
- Protection (those being the only devices I understand can have opened in response to some fault/overload situation)
- Isolation, Switching, or Control (which would NOT have necessarily opened in response to some fault/overload situation, and would include everything I've listed)

... as all being allowed only in "installation intended to be under the supervision of skilled or instructed persons and intended to be inspected and tested by competent persons"

I have to say that I am pretty uncomfortable with the concept of "auto-reclosing" devices (as 'we' understand the meaning)

Agreed.

 

[JohnW2]

One can but assume that, even though they don't say or define it, the IET intended the same interpretation as most of us probably make - i.e. that this regulation is meant to refer specifically to devices which "auto-reclose" after having opened in response to some fault/overload situation. It would seem unlikely that they intended, and unworkable even if they did, that the reg should to apply to the other sorts of 'auto-closing' devices you list.

Whilst that is logical, when you break it down the IET have specifically listed
... auto-reclose devices for:
- Protection (those being the only devices I understand can have opened in response to some fault/overload situation)
- Isolation, Switching, or Control (which would NOT have necessarily opened in response to some fault/overload situation, and would include everything I've listed)
... as all being allowed only in "installation intended to be under the supervision of skilled or instructed persons and intended to be inspected and tested by competent persons"

Yes, I agree with all that - so I probably wasn't clear. As you say, it would appear that the wording they have used does include all of those 'isolation, switching or control devices'. What I was suggesting is that this is probably not really what they intended (instead actually "intending" only 'protection' devices, per what you and I would expect) but wrote it completely wrong!

I suppose 'a court of law' would probably have to take the written words literally, and therefore outlaw time switches, PIRs, dawn/dusk switches (maybe even thermostats?!) etc. etc. in normal domestic locations!

Kind Regards, John