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??

 

[Deleted member 26818]

Sounds like a fault with one of the elements in one of the heaters.

 

[ChristianG]

I'd go to the pub!

 

[telectrix]

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.

 

[i=p/u]

check the resistance of both elements see if there is a difference, be careful and test before touch

 

[Engineer54]

I'd go with Spin's assessment, ...one or maybe two of those heaters has an element fault on it!!

 

[Rockingit]

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...........

 

[Marvo]

Insects somewhere they shouldn't be?

 

[Deleted member 26818]

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.

 

[Silly Sausage]

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

 

[chiplard]

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.

 

[mickys86]

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!

 

[Guest 004]

why dont you do an IR test on the heaters?

 

[mickys86]

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?

 

[hasel5]

What are your insulation readings on all circuits as suspect somewhere you have a N-E fault