UK Kettle Element Keeps Blowing

[Moedot7]

Hi,

I'm the landlord of a rented property.
I recently had the fuse box (dcu) changed from the old "wire type" to the newer mcb/rcd type.

It has been 5 months since it was replaced by a qualified electrician.

My tenant has informed me that he has replaced 4 kettles since then.

1. All kettles were of different make and models
2. There was no issue with the fuse in the plug
2a. Fuse was changed to check this
3. Happens in the morning when boiling the kettle
4. Only the mcb trips
5. The heating element of the kettle gets damaged
6. Kettle was only 3 weeks old
7. No limescale issues
8. Nothing else in the house is affected

I have spoken to a few electricians, they have no idea what the problem could be. I trust the tenant, he wouldn't make something like this up.

Can someone please help me with this issue.
If you need more details surrounding this issues please ask.

Thank you.

 

[marconi]

Re Buzzlightyear's #7 - reversed polarity:

I've been mulling over Buzzlightyear's interesting hypothesis . It would have a possible association with the recent swap of consumer unit; before it all was well and afterwards it was not in the lives of kettles. And there is a further consequence of reversed polarity - the wire element will spend most of its life at mains potential which in turn means the insulation around it and encased by the metal casing is permanently subject to mains voltage electric field. This electric field is the same magnitude (240V rms, 350V peak) all along its length. For the brief periods the element is on to heat water, the electric field will be tapered from 240/350V at the line end to 0V at the neutral (and now switch) end. With correct polarity there is no electric field for the vast majority of the day and when used it is only a tapered electric field.

With reversed polarity there would be then a change in the electrical stress on the element and in particular its insulation. Maybe then the insulation is breaking down because of the unusual prolonged mains electric field? eg partial discharge - at a place or places along the wire element? Over time this earth fault current combined with the LN current is high enough to trip the mcb (but which mechanism thermal or magnetic?). Depending on the overcurrent it is not unknown for mcbs to trip before a 13A fuse ruptures.

Partial discharge - Wikipedia - https://en.wikipedia.org/wiki/Partial_discharge

Why most often first thing in the morning? Because at this time the element has spent the longest time energised for partial discharge (or something else) to begin to form a tracking path to earth for a low leakage current to begin with which eventually breaks down under the influence of heat for a significant flow of current. The rcd does not trip (it is stated #1) perhaps because the tracking only causes a small earth leakage current to begin with - though I would have expected both the mcb and rcd to trip when the element's insulation eventually failed catastrophically - so I admit my theory does not fit well if the rcd stays closed.

The long and the short of it then is I would check the polarity of the supply at the socket the kettle normally uses and while at it in the CU too.


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For the Landlord - does the mcb trip when the kettle is first turned on or during the heat cycle?

 

[Zerax]

Overload of the circuit is my guess and the plug fuses blowing and an assumption the kettles are dead

Very true... we need to see copies of the autopsy reports on those kettles ! And if they've already been buried... exhumation orders to follow... I wonder what the 'boys back at the lab' would uncover ? (aka Lucien & Marconi)

 

[Lucien Nunes]

Any kettle sold in the EU should operate correctly with arbitrary polarity, since some countries use non-polarised plugs. Sheathed heating elements are not unlike MI cable, just with a nichrome spiral in place of copper conductors. Although the ultimate breakdown voltage of MI is sometimes lower than a polymer-insulated cable, it is unlikely to be affected by continuous connection to the line.

 

[electric al]

Very true... we need to see copies of the autopsy reports on those kettles ! And if they've already been buried... exhumation orders to follow... I wonder what the 'boys back at the lab' would uncover ? (aka Lucien & Marconi)

I concur zap - forensic reports and toxicology tests undertook by our very own lab boffins could be an entirely different kettle of fish
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Zerax even

 

[freddo]

But if the circuit is overloaded why would the appliance fuses blow?

The fuses aren't blowing according to post #1

 

[DPG]

The fuses aren't blowing according to post #1

True but post 28 suggested that an overload of a circuit could cause appliance fuses to blow.

 

[static zap]

Re Buzzlightyear's #7 - reversed polarity:
I've been mulling over Buzzlightyear's interesting hypothesis .

I'm still pondering another angle.
(that would require a 3kW isolation transformer and MFT to investigate)
Paper would be-Entitled
"Poor IR situations in re-boiled over filled modern auto off Kettles & and possible metallic sputtering of contacts onto plastic in a confined streamy enviroment. "
-- I do enjoy a good think --

( previously tasked with "re-animating" a few from the grave-by Mr Frugal)

 

[electric al]

I'm still pondering another angle.
(that would require a 3kW isolation transformer and MFT to investigate)
Paper would be-Entitled
"Poor IR situations in re-boiled over filled modern auto off Kettles & and possible metallic sputtering of contacts onto plastic in a confined streamy enviroment. "
-- I do enjoy a good think --

( previously tasked with "re-animating" a few from the grave-by Mr Frugal)

I think all your paper requires zap is a couple of algebraic equations in order for it rock the scientific establishment. I'm certain our resident boffins could come up with something that would prove something even if it's only that equations make my head ache

 

[radiohead]

I cant help thinking there's too much thinking going on here.

 

[pirate]

Just for information,here in Spain, if the power fails, it's almost always the kettle.
That's because of the cal, because the water isn't that good. So whenever the power goes down, we unplug the kettle, and everything works again.
Just saying...

 

[marconi]

Moedot7: If the tenancy is in London or not too far away, would you like Wilko and me to visit the tenant and take a look? If so, the availability of the previous kettles would be very useful to us. Sometime during the day would suit us - not evenings.