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Rockingit

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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??
 
disconnect 2 heaters and leave for a couple of days. if no trip, then you've eliminated the 2 still connected. reconnect 1 of the dissed ones and repeat. narrow it down to the faulty 1.
 
Sounds like a fault with one of the elements in one of the heaters.

Well, agreed, but I've tried all the various combinations of in/out of circuit and separation. As for elements, the one I suspect as different I've disconnected out of the circuit and put a plug on the end deliberately so that the customer can try running it off a socket and see if that takes the relevant RCD out. The other three test clean and clear, and when On show no leakage and little mains distortion. They don't even surge when they fire up. Admittedly I haven't taken them off the walls and had them apart but I doubt I'd find anything useful. And the fault is intermittent, so you'd think that if it was a faulty element it would be a bit more regular, surely?

I'm convinced it's an installation based fault somewhere, but damned if I can find it!

Off to the pub...........
 
These black iron heating elements absorbe moisture from the atmosphere.
If they're left switched off for any length of time, they will have earth leakage.
Often you will find that by keep switching them on, you can get them to dry out enough to stay on by themselves.
Overtime, the problem becomes worse untill eventually the elements fail.
This is why I don't like putting these and cookers on RCDs.
 
With the amount of time your spending on trying to solve this problem might it just be better and cheaper to condemn all 4 heaters, you said they were 2nd hand, and fit new ones?
Inform the customer that they are on their way out and best to renew?
Are they like these...
Panel Convector Heaters
 
If the customer is willing then knock each circuit off one by one for a couple of days. Just to give each circuit a day or 2 to go through a 'normal' daily operation.

You will at least then determine which pair of heaters ( or other fault/circuit ) is causing the problem.

This might be a case of you can't see the wood for the trees!

Good luck with it.
 
Could it be that on the dodgy re-wire there was a supply taken outside that possible was forgotten about? I once had a fault where an electrician hadn't given a cable enough protection and the cable got damaged. When it rained the cable got wet causing the earth to Short against the live  took a day to find that fault!
 
I read this at half 4 this morning so forgive me if I have missed something. What's to say it's definitely the heaters?? I remember reading it's on a split board and not rcbo's?
 
What are your insulation readings on all circuits as suspect somewhere you have a N-E fault
 
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.
 
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?
 
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.
 
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
 
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.
 

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