Electric/MCB tripping at random times...

[Schmidt]

Hello,

I've got a Hager B16 MCB tripping, sometimes randomly, which supplies my electric oven in the kitchen.

I find it (obviously) only tends to happen if the fused spur to the oven is turned on and certainly happens if the oven is on - however, if I reset the MCB, sometimes it will be fine again for a long while / sometimes it trips within seconds.

I'm not an Electrician (I'm a Gas Engineer) but I am competent with my fluke multimeter. Is there anything I can test/check or am I best to get in touch with an Electrician?

I'm going to isolate and remove the oven, take the back off it and test the supply cable etc.

But I'm not familiar with Consumer Units, do MCB's tend to 'expire'?
I don't want to waste time/money having someone spend time investigating it if there's things I can eliminate myself.

(I've just answered my own question there, haven't I? - if you don't know what you're doing, get someone who does?)

Cheers

 

[JohnW2]

I find it (obviously) only tends to happen if the fused spur to the oven is turned on ....

When you say that it "only tends to happen" with the fused spur switched on, do you actually mean that it only ever happens when that FCU is switched on?

Do I take it that this circuit supplies nothing other than the oven?

Was there a time when this didn't happen, or has it been happening since the oven was installed?

What is the 'maximum power' rating of the oven? If it's over about 3.7kW, the current draw could exceed 16A at switch-on from cold, but it ought to take a fair bit more than that to trip the MCB.

Is the circuit RCD protected and, if so, has the RCD ever tripped?

MCBs do sometimes 'expire', and that could well be the problem. However, if it's always happened, it could be that the 16A one is not high enough rated, or there could be an intermittent L-N fault.

Kind Regards, John

 

[sparkwright]

My gut reaction is an element in the oven is failing, though there are of course other possibilities.

 

[Schmidt]

When you say that it "only tends to happen" with the fused spur switched on, do you actually mean that it only ever happens when that FCU is switched on?
The fused spur is one of those 'double' ones with a standard socket on one side and a big switch for the oven. The MCB only trips when the fused spur is ON - even if the oven is not in use, however, less likely when the oven is not on.

Do I take it that this circuit supplies nothing other than the oven?
Correct. Apart from the plug socket on the fused spur.

Was there a time when this didn't happen, or has it been happening since the oven was installed?
The oven is probably 6 years old now and this started happening over Christmas.

What is the 'maximum power' rating of the oven? If it's over about 3.7kW, the current draw could exceed 16A at switch-on from cold, but it ought to take a fair bit more than that to trip the MCB.
Off the top of my head I honestly don't know - I'll dig out the instructions/check the data label when I remove it this weekend.

Is the circuit RCD protected and, if so, has the RCD ever tripped?
The circuit IS protected with an RCD but this has never tripped, there's a 'flash' at the MCB and it pops off.

MCBs do sometimes 'expire', and that could well be the problem. However, if it's always happened, it could be that the 16A one is not high enough rated, or there could be an intermittent L-N fault.

Kind Regards, John

Thanks for the reply, John, I really appreciate your time.

 

[JohnW2]

Thanks for the reply, John, I really appreciate your time.

You're welcome. Given the additional information you've now provided, I'm inclined to agree with sparkwright that a failing oven element is probably the most likely cause, the only other reasonably possible one being a failing MCB (although there are other 'less likely' possibilities!).

The "fused spur" you describe is probably actually a 'cooker control unit' (without a fuse), but that does not really alter anything.

Kind Regards, John

 

[John D v2.0]

for the record, the fact that it sometimes trips within seconds but not always suggests it's an overload rather than a short, as the overload protection relies on something heating up (so it would already be hot when you reset it)

but I agree with the above posters there's a fault with your oven and it's using too much power.

 

[jj4091]

What make & model is your oven?

 

[Schmidt]

What make & model is your oven?

It's from IKEA so I couldn't say. I'm off work today, so I'm removing it and checking some basics.

 

[Schmidt]

Ok, so a little update for y'all...

I removed the Oven today and checked across L - N, N - E & L - E on the flex to the oven. All were 0L on my Multi-meter, so I'm fairly confident there's no short circuit (at least until it's in use and the element heats up?).

Whilst I had the oven out, I noticed there was a metal backbox which was rusted, some condensation on the wall above it (possibly this bloody cavity wall insulation we have?) and the wiring, which came in from the top was poor, to say the least. The feed was too long, the sheathing was nipped in places and the live out to the oven was loose and possibly shorting - causing my MCB to trip?

A quick trip to Screwfix and I purchased a plastic backbox, a cooker outlet point and started again.

I've come in from the bottom of the new backbox, neatened the wiring up and made sure all my connections were tight. The outlet point has a slight angle to the front where the flex to the oven now comes out of and everything seems better!

For added anti-condensation, I placed some insulation tape over the joint at the top of the backbox/cooker outlet (I know, I'm a nerd!)

So, I'm currently 20 minutes in to baking a nice Saturday afternoon lunch and I believe I may have sorted it.

Thanks again for your advice everyone, I do really appreciate it.

 

[flameport]

some condensation on the wall above it (possibly this bloody cavity wall insulation we have?)

Condensation is caused by too much moisture in the air.
Not cavity wall insulation, or any other kind of insulation.

 

[John D v2.0]

Condensation is caused by too much moisture in the air.
Not cavity wall insulation, or any other kind of insulation.

Not quite as simple as that, condensation is caused by too much moisture in the air which would be increased if most of the wall insulation was improved but not a thermal bridge. Then the moisture only has one place to condense out, meaning it hangs around longer causing mould which is the visible sign of long term condensation.
So cavity wall insulation can change the balance of the house such that mould occurs afterwards, but of course reducing the moisture in the air and improving air circulation would solve the problem