Economy 7 RCCB Trips from 24hr Circuits Your Thoughts

[Pip]

Hi Guys,

Called out yesterday morning client has 2 x Wylex Boards with MCB's each has a 63Amp, 100Ma RCCB as the main switch on a TT System.

Board 'A' is the main 24hr feed for the house, Sockets., Lights etc 8 circuits
Board 'B' is the economy 7 night storage heaters. feeding 7 circuits. Midnight to 7am

A Smart meter has been installed recently, where the neutral is split to feed both boards and of course the 2 live feeds. No issue there I think?

Problem they have had for at least 12 months they tell me, happens more in the winter months, is intermittent tripping on the Board 'B' RCCB when it is not energised.

Most recently one afternoon when they put the kettle on and then a small table light, the lamp blew, which they do, only it tripped the Board 'B' RCCB

OK Live - Neutral imbalance due to the lamp blowing but why Board 'B' and not 'A'

Both Boards are 20+ years old and have a cupboard built around them so getting access to the circuits is difficult without destroying the cupboard.
All I have done is RCD tested x1= 17.3 x5 = 5.0 (I know not a requirement but meter does it) Ramp test at 85Ms. BOTH Boards tripping at the same time during these tests. Should They?
PFC 0.48Ka & 0.47 Ohms at a kitchen socket very close to the boards.

So before I remove the cupboard and make a mess to start IR all the circuits etc. does the panel think its a weak RCCB on Board 'B'?

Board 'B' still live somehow?

I don't have a Earth Leakage Clamp Meter, but reading some posts on here I'm tempted, but I don't a discussion of the pros and cons here, but would it help in this case? if yes why?

Anyway over to you my learned friends.

Thanks

 

[davesparks]

Have you had a look through the forum at all of the other threads discussing RCDs tripping when circuits which aren't connected to them are used?

 

[Pip]

Hi DaveSparks,

Yes, some, but finding ones that don't go off topic and relate to this scenario I've yet to find, I'll have to hone my search skills.

Thanks

 

[davesparks]

I'll give you a hint, they will all contain the advice that IR testing needs to be carried out and that this is the classic symptom of an N-E fault.

 

[Pip]

Hint Taken, Yes my thoughts N-E Fault, looks like the cupboard is coming out, may get the client to keep a diary first, and do a little more nosing around the property to see if there is something obvious plugged in that shouldn't be.

Thanks for your hints and help

 

[davesparks]

If your thoughts are N-E fault why haven't you tested for this?
Why do you want to waste time looking for something plugged in, unless they have sockets connected to the off peak board that is?
You do actually understand how a N-E fault causes the symptoms you have don't you?

 

[Pip]

Hi,

Have not tested as can not get access to the board as I mentioned it has a cupboard built around it so removing the front cover is not possible.

As you say IR test and I'll nosey around for any DIY picture hanging etc.. And I don't know what they have plugged in anywhere yet but as you say I doubt anything on the off peak

Thanks

 

[Parker27]

Looking around for DIY picture hanging, loose floorboards is not the answer, you are jumping around a logical fault finding procedure.
You need to get the C/U front cover off to carry out testing, the testing you have carried out so far are incomplete - insist that your able to remove the cupboard, even if you destroy it.
Ask the customer what is more important to them a safely working electrical installation or the visual appearance of a cupboard.

 

[davesparks]

Try this for logic:
You have a N-E fault of some impedance on an off peak circuit. The tripping is worse in winter than in summer.
The off peak circuits supply heaters and an immersion heater.

If you really can't get to the CU without wrecking the house then maybe a quick test of the storage heaters and immersion heater might pay off.

 

[Richard Burns]

If you switch off the main switch for board B then you should have separated neutral and earth for those off peak circuits so you can now do IR testing for the whole board from the heaters themselves and start narrowing down your options.
Splitting down the neutrals for the individual cables will be difficult but at least you can eliminate the heaters if the results come out well.
Presumably your results will be OK on all items and you can then start searching for the cross connection to board A.