Fault driving me mad!!

[Rockingit]

Evening gents & gentesses, PLEASE if anyone has any ideas on the following it will save me either from madness or an extreme night of drunkeness down the pub... :hanged:

Perfectly ordinary two up/down, MK sentry split board, slightly dodgy rewire done a while back by another that I've already done a load of fixing on and a full (100%) periodic and thought had resolved all issues.

They have four dimplex panel convector heaters wired as two pairs, each pair off a B16 on same side of board. RCD on that side of the board intermittently trips when heaters on. Inspect heaters, test, no fault found. Replace RCD, no change. Chase my tail for a day, eventually find additional fault on an immersion circuit the same side of the board, resolve, problem seems to go away. Fast wind four months later to the cold autumn returning and I've just returned from a call-back, same fault.

I've checked and re-checked all the installation wiring - no insulation faults, no crossed neutrals, no naughty earths, no nothing (anymore). Have long-leaded from every joint to every joint on those two circuits. IR checked the fsu's, all 100% ok even at 1kV.
Have had my power analyser running on it all day, nothing unusual and heaters not particularly earth leaky (digital controllers, probably). Certainly would pass the normal PAT criteria.
RCD time & ramp tests all perfectly normal, and certainly well above the leak level of the heaters.
Ring dimplex helpline to see if they have a preference for 'S' types or something, discover chocolate fireguard at the other end.
One of them shows itself as being erratic on current draw as the thermostat is approaching close, and customer advises it was a 2nd hand buy, So I figure has to be that, remove, RCD stays set.
Pack up...... and RCD goes again. So scratching my head I do the only other thing I can think of and swap one of the circuits across to the other side of the board so it's on the other RCD.
Set the controls to stun, watch the numbers on the clamp meter go very high once I've turned on virtually everything on every circuit including the cooker and power-shower and leave for 20 mins to see what happens. Drink tea, cross fingers, all holds fine.

Pack up....... and......you guessed it.......

Putting RCBO's in aside, anyone got any ideas at all??

 

[Rockingit]

Many thanks one and all - thought I'd just wrap this up with my findings of today:

The wiring is fine, totally. Not an ideal install, not as a 'seasoned pro' would have gone about it, but in the electrical sense it's all there, safe and all working.
Heaters are also fine.

So the problem is????? The entire place is just too leaky, basically. Too much domestic IT, routers, tv's etc etc. Split board with two RCD's that ramp test to around 21-22mA each - meter the main tails (without the rads on) ands it's already showing more than 50mA spikes to earth (meter resolution is faster than response time of the RCD's, remember). So add in four heaters each individually leaking around 5mA and max spiking at 15+ (most likely from the digital controllers) and hey presto - we get the big click of doom.

Solution? Well.... short of a whole rewire using almost commercial methods, there's not a great deal really. The customer is fairly bright so I've explained it all to them, shown them the meters working etc and they know it's an imperfect situation. What I plan to do in order to try to minimise the nuisance tripping is to put the two heater circuits (being the most individually leaky) onto individual 100mA RCBO's and declare them as dedicated circuits (which they are, anyway) and record it as a deviation on the certificate.

 

[Deleted member 26818]

Do the heater circuits require 30mA RCD protection?
Are the cables concealed in walls at a depth less than 50mm, are there any socket-outlets intended for general use by ordinary persons on the circuits?
When you use the term deviation, I assume you actually mean departure.
If so can you guarantee that the departure offers the same degree of safety as would be achieved by compliance with the Regulations?

 

[Marvo]

Can't you install a second RCCD and split the loads with standing leakage between the two. This should bring it back to within the 30mA threshold.

 

[malcolmsanford]

I would go with what Marvo suggested and fit a 2nd CU perhaps 3 or 4 RCBO's in it and start putting the most 'leaky" circuits onto them.

It will of course depend on if you have the room to fit it next to the existing, extending cables, etc etc, but surely it would bring you into line of the regs especially 314.1 and 531.2.4

 

[ackbarthestar]

I've had something similar. We chased a suspect fault around for two days and would you believe, it was the dish washer running through a particular cycle knocked out the RCD. (the one item of equipment not being used when we were there).
I think this problem would have much easier to sort out if each circuit was on DP RCBOs.

 

[Rockingit]

Can't you install a second RCCD and split the loads with standing leakage between the two. This should bring it back to within the 30mA threshold.

It's a split board already, and shoe-horned into a tight space so fitting another CU won't work.

@Spin - reason for still wanting to have them on RCD is simply that the heaters themselves are vulnerable to things like drinks spills, toddlers pulling on the inlet cables etc. So yes, whilst I could probably justify having them only on MCB's, I'd rather have them with some leakage protection, even if it's higher than usual. And yes, I did of course mean departure!

All of this, and reading Ackbar's thoughts, begs the question of what do we do as installers and designers to slow this process down in the future. Are we really going to start installing high integrity circuits in domestic houses, splitting circuits down to 1-1 configurations on RCBO's etc? So much technology in peoples houses now, no chance of that slowing down, so what do we to future proof? I've just done a tender / design on a massive 'grand designs' kind of build, and it's almost pretty much one rccb, one cable, one outlet. Big expense.

 

[Marvo]

I never thought of RCBO's, we don't see them much where I am. I would say these are the way of the future, a single RCCD is putting all your eggs in one basket when it comes to an earth leakage fault (or overall accumulation in your case). It's the equivalent of running multiple socket circuits on a 60A MCB and expecting it to effectively protect them. If RCBO's are economically viable and they fit into a single space in the CU then they have to be the best option.

 

[spark 68]

Hi,

Split board with two RCD's that ramp test to around 21-22mA each

to minimise the nuisance tripping is to put the two heater circuits (being the most individually leaky) onto individual 100mA RCBO's and declare them as dedicated circuits

It's a split board already, and shoe-horned into a tight space so fitting another CU won't work.

I may be missing something here, but if it is a split load board already, protected by two 30mA RCD's, one for each side, then how is it possible to fit 100mA RCBO's ?, as this will not solve your problem, as the 30mA RCD's will still trip before the 100mA RCBO's, as there is no discrimination whatsoever here, the only way would be to put a mini CU fed with tails from the incoming side, as others have already suggested.

What Iam saying here, is you will have 30mA RCD's feeding 100mA RCBO's.

 

[Silly Sausage]

68, I assume he's going to fit the 100mA RCBOs into the high integrity section of his CU, ie the bit fed straight off the main isolator

 

[Rockingit]

I may be missing something here, but if it is a split load board already, protected by two 30mA RCD's, one for each side, then how is it possible to fit 100mA RCBO's ?, as this will not solve your problem, as the 30mA RCD's will still trip before the 100mA RCBO's, as there is no discrimination whatsoever here, the only way would be to put a mini CU fed with tails from the incoming side, as others have already suggested.

What Iam saying here, is you will have 30mA RCD's feeding 100mA RCBO's.

You are!! The board gets reconfigured as a three-way, so 2 x 30mA RCD's feeding whatever, and then two separate RCBO's on the same DIN rail but fed directly. Simples.

 

[Rockingit]

68, I assume he's going to fit the 100mA RCBOs into the high integrity section of his CU, ie the bit fed straight off the main isolator

 

[malcolmsanford]

Then surely if your just going to have 2 X heaters on an RCBO on an high integrity side 30mA RCBO's will be enough? surely the 2 heater alone can not produce 20+ mA Protective conductor current and i'm sure you said in a previous post that they only produced about 5mA a piece, this way you would not have to worry about not having additional protection problems

 

[Silly Sausage]

M, I think R's fed up with problem.
100mA should stop any nuisance tripping, they're knackered 2nd hand ones.
:smiley2::smiley2::smiley2:

 

[spark 68]

68, I assume he's going to fit the 100mA RCBOs into the high integrity section of his CU, ie the bit fed straight off the main isolator ​

You are!! The board gets reconfigured as a three-way, so 2 x 30mA RCD's feeding whatever, and then two separate RCBO's on the same DIN rail but fed directly. Simples

Ahh!,
I had a look through the previous posts, and did not see anywhere it mentioned three way boards, and thought at first you were going to add a mini CU, but if you are going the Three way with RCBO route, then I would do as others have said, and put the heaters on their own 30mA RCBO's, or two per RCBO, then it will still comply with buried cables etc..etc., and the leakage will still be within bounds.

I think you may be correct though, the way things are going RE: amount of home IT and electronic gadgetry in houses now, we maybe going the RCBO route more often than in the past.


Thanks for clearing that up.


All the best Spark 68

Cross posted with Malcom

 

[Deleted member 26818]

Rockingit, if there is no requirement for 30MA RCD protection on these circuits, then providing 100mA RCD protection will not be a departure.
However if there is a requirement for 30mA RCD protection, perhaps due to cables being concealed in walls, providing 100mA RCD protection would be a departure, onlly not an acceptable one, because it would not offer the same degree of safety as would be achieved with providing 30mA RCD protection.