Water heater tripping trip

Hi All,

A friend has a smallholding with a small woden bungalow and has asked me to fix a problem with his water heater / electrics. Firstly, a little background (a little hazy as i've got most of it second hand)....

He used to have some kind of immersion heater which fed all the water in the bungalow inc a shower and he also had a full size cooker. The bungalow is fed from approx 100 metres of (I think 3 core) cable buried in the ground which is fed from a meter cupboard up the track.

All was "well" until a few years ago when someone (the supply company??) fitted an RCD (100ma I think, time delayed maybe (it's a soft of S shaped switch which you turn clockwisw to set) in the meter cupboard.

At that point, he had to have the imersion heater and the cooker removed (no more hot shower) as they kept tripping the RCD. The immersion was replaced with some sort of under sink stored water heater, and the cooker with a kind of "son of baby Belling (2 solid rings and a very small oven)

All has been sort of well-ish for a few years, but he has suffered from nuicance trips on a regular basis, usually either when he's tucked up in bed, or else off site (and has to talk someone through where to find the meter cupboard, how to reset the trip).

Back to our story, the water heater is now tripping the RCD. I cecked with him whether this behaviour started when he tried to get it going at the start of the season and he said yes. I am inclined to think that the element in the water heater has absorbed some moisture, and if this could be "driven off" all would be well. It has been suggested here before that in a domestic 16th edition type setting, you could temporarily connect the heater up to a non RcD supply to do just that. but how to proceed in this particular setting?

One thought is to take a butchish generator up there and run the heater on that for a while (how long might be long enough?) I suppose the other option might be to try and isolate it's earth connection and exposed metalwork from and then run it from the existing supply?

How would I check that the earth leakage is in fact minimal before trying any of the above?

Anyone any other ideas?

TIA

Chris

Reply to
Chris Holmes
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On Monday 10 June 2013 09:09 Chris Holmes wrote in uk.d-i-y:

That would be a likely explanation.

I doubt it. Such practices are used to dry out MICC cable that has been stored too long - but you hav to ask with a water heater element: "if moisture got into a sealed element, is there a pinhole leak?" and the answer is probably.

Wouldn't it be simpler and safer to relace the heater - or try to get the element replaced?

Reply to
Tim Watts

From your description it sounds like the whole installation is a complete mess. For a start, Emersion heaters that absorb moisture are dead heaters, probably distorted out of shape and let water in. Can one not just try a new element? Secondly you do not say what sort of cable this long run is, but if its been down there as long as you suspect it might in itself be a source of slight leakage by now and need replacing. I did not get the logic for the original replacement of the old equipment, unless they threatened to raise his charges or something. Very odd, and I must make a mental note not to go round his way for meals without insulated boots and one hand in my pocket!

Brian

Reply to
Brian Gaff

Puzzles me as well, the DNO doesn't care what happens after the main cut out, the company you pay electricity for doesn't care after the meter.

I suspect some half educated spark has shoved the breaker in to "protect" the submain but could only get a 40A rated one so had to reduce the load by removing the immersion and cooker. Note that unless this breaker is an RCBO of some sort it doesn't provide any extra *overload* protection to the submain above that provided by the DNOs cut out.

Reply to
Dave Liquorice

I had a similar problem with a tripping circuit and it turned out to be the immersion element, had it replaced, all fine. Coincidentally had the same thing with the washing machine, it would trip seemingly randomly and the engineer (it was covered by insurance) traced it to the element which was only required on some washes and not others, hence the intermittency.

Reply to
Mentalguy2k8

I did say in the OP that it's an RCD.

From memory (from last year), the installation consists of

Supplier provided earth ) Meter (with built in service Fuse)

60A MCB in it's own enclosure

80A/100ma RCD

XX Metres of 3 core (4mm? 6mm?) black PVC sheathed cable (might be more like 50 metres rather than 100)

Old (Wylex?) CU of the type which can take plug in MCBs

MCBs to various circuits.

It may be that the Supply Co recommended he get the RCD fitted, all I know was it wasn't his idea. I am pretty sure the tripping that led to the cooker and immersion tanks demise was Overcurrent in the milliamp range rather than them blowing MCBs.

A lot of installations out here in the sticks used to have identical ELCBs fitted, and this made me wonder if the supply co had had a spate of persuading people to have them fitted? And maybe something similar went on here. I did also read up in an electrical forum a while back that 100ma time delayed RCDs were often fitted/recommended in situations such as these for fire/property protection rather than PPE.

With regard to the OP, I think I will go for replacing the heater, or if possible the element.

Reply to
Chris Holmes

You could replace things at random till it stops, it might even work. I'd begin by getting clear on what the set up actually is, and testing each bit of it for earth leakage. Unless you do those, you don't have much clue whats going on.

NT

Reply to
meow2222

No chance.

The element is f***ed. End of. Replace it

Reply to
ARW

An update in case anyone is interested (or should come Googling after).

I spent the morning at the "farm" on Saturday and having had a closer look at the meter cupboard discovered that this is in fact a TT installation. I am informed that the 100ma RCD is mandatory in this case.

The owner said the problem had been with running the water heater at the same time as other stuff, and that he had tried running it on it's own and it hadn't tripped the RCD. I tried various bits of kit in isolation and in combination, and at one point I had the water heater, plus a burco type water heater, plus a kettle, plus the oven and 2 rings of the Baby belling all going at once without the sum of any leakage tripping the RCD. I also tried putting each of them in turn onto a 30ma plug in RCD and none of them had a high enough leackage current to trip it.

A friendly electrician is going to come and do some measurements and make some recommendations. I think if we can persuade the owner make the investment, these will probably include a time delayed RCD at the meter cupboard, and at least two 30ma RCDs at the bungalow end.

Ciao

Chris

Reply to
Chris Holmes

On Monday 17 June 2013 09:25 Chris Holmes wrote in uk.d-i-y:

Thanks - always useful to have "answers" to tie the threads off :)

Seems reasonable. No way should an installation be tripping a 100mA RCD as a matter of course.

Reply to
Tim Watts

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