Storage Heater Trips Rcd On A 2 Mcb Cu

[robin1412]

Hi,

For a long time I have had an RCD tripping problem with my 2 Storage Heaters (SH) each connected to an MCB on a CU with 2 MCB's and one RCD.

Rightly or wrongly, I have now come to the conclusion that the much older 1.7kw Tricity SH is the problem. I think that when the Tricity gets fully charged it then does something that trips the RCD (not its own MCB or the other SH's MCB but the RCD).

This means the other SH a 3.4KW Sunhouse (3 years old) which is also on the same CU is cut off from the supply. My solution has been to never increase the manual dial on the Tricity past 5 (the range being 1-7).

My reason for the full charge claim is that when the Economy 7 (7hours 30 mins) kicks in if the Tricity is above dial position 5 about exactly 7 hours later the RCD is tripped. Keep it to 1-5 and keep the other SH on any dial and this won't happen.

Can you tell me why?

 

[DJ1]

Just out interest is the storage heater on a North facing wall? I've had a similar issue a few years ago, tripping RCD after the a period off time. this was due to moisture in the element, however it wasn't after 7 hours on though.

Try removing one element at a time and running the storage heater each time, its possible the element insulation is breaking down over the heat period and leaking current to earth.

Sounds like the insulation is breaking down when an element is getting very hot.

 

[robin1412]

Thanks for the reply. No not a north facing wall, in fact an internal wall. You are right about the 7 hour delay before tripping. There have been occasions when I have got up in the morning and the place is freezing which means RCD was tripped much earlier in the night. Any way keeping the Tricity to 5 and under kind of deals with the problem but I am renting out my place in a few weeks and not sure if all tenants would pay attention to this kind of instruction.

So if the element insulation is breaking down over the heat period and leaking current, what should one do about it?

Thanks

 

[Steve3948]

Change the element or elements, I would replace all as changing just one will under sods law mean the other will go soon after.

It could also be a fault to the wiring inside the unit when the unit gets very hot, so check that first for burnt cables.

 

[DJ1]

Agreed, look for the obvious signs of over heating wiring and switch gear etc.

If nothing visual, carefully lift off the bricks , top one first, disconnect one element at time, each night run the storage heater as usual switch the dial to the highest setting.

if the RCD has not tripped over night, it's likey you have found the fault.

However the metal outside of the element shouldn't really find a fault path to earth, unless your bricks have some moisture in them, tough I doubt that.

I would still remove the front bricks and inspect the element terminals for over heating signs.

 

[binky]

Does sound like an element starting to breakdown. I had the same problem with a cooker grill element some years ago, you could get it to work if you didn't turn the grill on full straight away. This lasted a few months before it started tripping RCd at lower and lower settings. Eventually I gave in at bought a replacement element. Question is do you really need RCD for that circuit anyway??? I prefer to arrange heating, cookers and freezers on non-RCD protected circuits for reasons of reliability. That way only 'proper fault' will trip MCB, not the minor breakdowns in insulation that RCDs detect.

 

[robin1412]

Thank you all for your ideas and suggestions.

I did open the front and looked for obvious signs, vacuumed everything, tightened the two very loose elements, checked the cabling which seemed solid. But after all that the thing poped again. I guess 40 years of work was just about enough for that storage heater so I am now the proud owner of a brand new bankrupt stock storage heater, no problems any more )

Regards