Totally stumped. Night Storage Heater tripping out MCB, but ok on daytime circuit.

[Steve Poulton]

Please help. I have a basic understanding of electirics, but 5 Electricians are stumped and I don't know where to go next. My mother in law heats her house by 4 Night Storage Heaters, all of which are wired to a Economy 7 supply/fuse board, with no RCD just MCB. The largest of the Night Storage Heaters began to fail and trip the MCD. To cut a long story short, she ended up having a new one fitted. Unfortunately this new one also now trips the MCB. The electricians have tried swapping the various supplies to the various heaters around in the E7 fuse board and the same heater is tripping the different MCB. It would be an obvious thing to consider that there is a fault on the circuit between the board and the night storage heater. However, they have now wired it into the day time board and it is not tripping. Has anyone got any ideas as we need to get it wired back into the E7 circuit??

 

[KEV 1 N]

what a good idea Stanley

Maybe these were two of the five electricians?

 

[telectrix]

Indeed....I spent 8 hours over 3 visits last week to trace what turned out to be an intermittent lighting fault.

is an intermittent lighting fault one that occurs only when switched on but fine if left off. ?

 

[ipf]

the replacing of the heater was a bit cart before the horse

it should not take 5 visits to be in the same/worse situation than you started with

As regards the heater, maybe.....but how do you know it's state, or whether previous tests were or were not carried out.
Five visits seems excessive but how do we know what they involved or how long they took?

 

[elsparko]

no a temporary temporary....it'll prove a point. Just chuck a bit of T/E round for a night or two and disconnect the circuit cable feeding the offending heater

is an intermittent lighting fault one that occurs only when switched on but fine if left off. ?

a farmer i know supplied one of his sheds with steel fence wire, over about a kilometer nailed directly to the top of fence posts

basically a 230v electric fence, cant remember what sort of animal was unfortunate enough to land on said fence but it blew the main fuse

 

[KEV 1 N]

a farmer i know supplied one of his sheds with steel fence wire, over about a kilometer nailed directly to the top of fence posts

basically a 230v electric fence, cant remember what sort of animal was unfortunate enough to land on said fence but it blew the main fuse

Would have been fine if the fence posts were taller!

 

[elsparko]

Would have been fine if the fence posts were taller!

i think it was a deer but may have been a cow, this is war story that was swapped so never seen it first hand

 

[KEV 1 N]

i think it was a deer but may have been a cow, this is war story that was swapped so never seen it first hand

I can believe it, it’s the sort of thing a farmer would do as opposed to spending money!

 

[elsparko]

I can believe it, it’s the sort of thing a farmer would do as opposed to spending money!

why should he shell out for insulated copper when he has an almost infinite supply of steel fence wire?

bloody farmers...

 

[KEV 1 N]

why should he shell out for insulated copper when he has an almost infinite supply of steel fence wire?

bloody farmers...

Haha! There’s a bloke at our place keeps horses (or used to when there was money in them!) He fitted some lights in a farmers barn......his payment?
Three bails of hay!

 

[buzzlightyear]

this post is now getting like one that flew over the cuckoos nest.

 

[KEV 1 N]

this post is now getting like one that flew over the cuckoos nest.

A classic!

 

[SparkyChick]

Could it not be (as @Murdoch has also hinted) that it's simply a case of the MCBs in the E7 board are getting a little past it?

7 hours a day running near the limit for extended periods of time is going to have some effect on the bi-metal strip.

If they've been thorough and the heater checks out, the cabling etc. checks out and it doesn't trip on an MCB in the 24 hour board, really that leaves only one thing... the MCB in the E7 board. Change the one feeding the heater that causes the trips for a new one and see if that solves it.

 

[buzzlightyear]

If they've been thorough and the heater checks out, the cabling etc. checks out and it doesn't trip on an MCB in the 24 hour board, really that leaves only one thing... the MCB in the E7 board. Change the one feeding the heater that causes the trips for a new one and see if that solves it.

how can 5 sparks not work out were the fault lies .not very good is it .

 

[Bob Geldoff1234]

If i was trying to fault find this i would do the following.
1.Clamp meter the live cable feeding the heater to find out the current it is pulling.
2.Change the 20 amp switch.
3.Change the flex feeding the heater.
4.Depending on the current try fitting a 20 amp breaker instead.

The other difference between day time running and night is the temperature drop during the night.It might have something to do with it?Maybe not.

From what i can read from this,then my guess is that the day time running(when its not tripping) is not run for long enough for the fault to develop.ie. 3 hours into the night the breaker trips.Day time half an hour running everything seems ok.
Like others have said failing all the above,run a temporary wire to the heater to see if this helps and if so then rewire it.

 

[marconi]

Reading the symptoms and what has been tried out I reckon the problem is the MCB for the large NSH (3.4kW) is of inadequate rating for the load current 14A at 240V. The E7 board does not take into account derating of this MCB for grouping and ambient temperature. In service it has too low a rating for its load current and its situation alongside 3 other MCBs through which steady currents of circa 10-14A are flowing for prolonged periods. It is not surprising they are getting warm, and that the one that trips first is the one through the highest current is flowing for the large NSH.

Switching the large NSH to the 24/7 board I guess powers it from an MCB which is situated alongside only lightly loaded MCBs - it can more readily dissipate the Ohmic heat and thus has a higher in-service rating.

The answer if possible is to swap the MCBs for 20A ones - a study will have to be done on the E7 cabling and its installation method to ensure this is safe to do.

see this piece on Hager MCBs for more information: