Odd immersion problem

[ARW]

For those that are interested in the sort of odd/weird jobs I come across.

GP surgery this morning. No hot water and the business manager said it packed in last week whilst she was off (and questioned how the hell she managed to get an electrician out in less that 10 minutes from phoning up).

Firstly the 20A DP switch was off and the stat on the immersion was on the lowest setting - so someone has been messing but no-one knows who.

So I did the obvious and you could hear the water beginning to boil/kettle.

Now the temperature only went up 5 deg in 20 minutes however there is a circulating pump so there could be a lot of water to heat.

The clamp meter said the current was 2A on a 3kW immersion.

I would have expected a blowing MCB or f*ck all.

It has to be a faulty element but I have never seen one fail like this.

[paul]

That is gassing hydrogen & oxygen from splitting water, not boiling.

I had this, assume outer of element corroded and inner parted, tripped RCD. Tested with a transformer and meter, stopped when I heard bubbling before any chance to boil.

Paul.

[Fredxx]

AC will heat water without electrolysis. I've seen Fear Eastern kettles use just two electrodes. Obviously no RCD in sight.

These also appear to bubble in the same way an heater element would.

I guess in Adam's case, the heating is very localised, just the area around the blown sheath.

[Fredxx]

Is the circuit protected by RCD?

Does it still heat if you disconnect the neutral?

Do you measure 2A in both the live and neutral sides?

If the answers are No, Yes and No then paul probably has the answer.

[Jeff Layman]

I was puzzled on how you could get 2A, but checking on the construction of immersion heaters it seems they can have several independent elements. I would guess that yours should have had six (500W/2A each), and all but one had blown.

[newshound]

Never seen anything like that. IIRC there used to be some with two lengths so you could just heat the top of the tank. Three phase ones have three elements. I suppose one with cartridge heaters might have several.

[Andrew]

Shouldn't your employer have told them to make an appointment and you would be there in about 6 weeks time ? :-)

[ARW]

NO RCD

Did not try it

No

But it sounds plausible.

Cheers to you both

[Animal]

Splitting open is a standard way they die. FWIW it's not really hazardous, despite electricity going through the water.

PS stinger kettles are fine on an RCD. Fine until you stick a spoon in anyway. Or soup, it gets a weird taste, from the metals I presume.

[Brian Gaff (Sofa]

They can get corroded and hence be higher resistance than they should be. Last time I had to get one changed the guy showed me the old one, all pitted bent and had tiny holes in the outside and the bit where it went into the top had a kind of crazed look. Brian