Installed electric oven, and circuit now trips.

[gsf600y]

Ok, firstly, I really don't know a lot about electrics, so excuse me if I get any/all terminology wrong here.

Basically, we've got a 25 year old house. The consumer unit (or fuse box as I call it) is pretty old, and has about 7 fuses/jumpers/what ever the correct term is. 3 are 30amp (plugs on left side of house, plugs on right side of house, and the hob/oven).

On one of the 30amp ones, we run an electric hob - the cable comes out the wall, goes into a square white "junction box" thing, cable out other side and into the hob. (this is all under the kitchen units).
All is fine and dandy at this point, everything working ok.

Now, in addition to the cable running to the hob, an additional cable went to a plug socket. The intention was to plug the oven into the plug socket.

So, I installed the oven yesterday. Of course, the oven doesn't have a plug on the end, so I figured instead of running a cable from junction box to the plug socket, i'd wire the oven into the junction box and remove the plug cable/box.

Which I did. And it all turned on fine. And the oven worked fine for an hours worth of cooking. Then later on (about 1 hour later), whilst we were NOT using the oven, or the hob, the 30 amp breaker that the oven/hob are on tripped out.

I popped the breaker back in again, and the oven & hob display lit up ok.

I'm also wondering if the consumer unit needs replacing?
We tend to suffer for what seem like totally random tripping on the 30 amp breakers. You'd think it was the load, but then it will happily run with the same load for months without tripping, then goes through a spell of tripping a lot.

Anyway, I'm just after some general advice here on if the wiring I've described is ok or sounds dodgy?

 

[gsf600y]

Best diagram I could come up with:

 

[Chri5]

Overload, quite why it popped afterward's rather than during is a quiz ?

Please confirm the wattage of the 2 items, the hob and the oven. (google will help).

Then add them together, say 5000w for a hob and 4500w oven (fictive figures for example only).

That's 9500w divided by 230v equals amp load 42 amps odd , my example is an overload of a 32a fuse, cable and (often) switch gear.


It does sound as if your place could be due a periodic inspection report. For £200 odd your get a full report with basic testing of condition of the electrical system, recommendations etc.

Let us know what sort of watt / kw load the hob and oven is.

 

[rebuke]

What is your oven rated at - assuming it's something like 3kW, you shouldn't have wired it straight in to the junction box, as the flex it will have attached won't be rated to 30A (therefore if a fault occurs the flex could melt and catch fire before the breaker trips). You should either have wired a plug onto the end of the flex, or put in an FCU (Fused connection unit), which would provide protection for the flex.

In your CU, are they breakers or fuses - you initially state they're fuses, but then talk about them tripping out - a fuse doesn't trip, it just blows and needs replacing...

Assuming all the connections made are correct and tight etc, then the only way you're likely to find the fault is using specialist test equipment (e.g. an insulation resistance tester). I would strongly suggest you get a qualified electrician in to take a look. Also, note that electrical work in a kitchen is notifiable under Part P, so you should have notified your LABC before wiring in your oven...

 

[gsf600y]

I'll double check the wattage when I get home, but originally I did calculate before that the 30amp would cope ok. I've a feeling the oven in 2400w, but I'll double check.

One thing I forgot to say, was that where the cable comes out of the wall, it comes from a switched FCU above the worktop. When that is switched off, the oven and hob will turn off.

From what you said rebuke, the CU has breakers, as once they are tripped I push the button back in and don't have to replace anything.

Just reading up on the LABC stuff now - I honestly had no idea that wiring an oven in needed this. I suppose it's to protect against people like me burning their house/street down......

 

[rebuke]

I strongly suspect it's a cooker switch, not an FCU - if it was an FCU then your hob would almost certainly have blown the fuse in it, as the maximum fuse you can put in an FCU is 13A...

When you wired in the oven, was the cable already attached to the oven, or did it just come with terminals on the back (in which case what size cable did you use)?

 

[gsf600y]

Oh, yes, you're right. Its is this exact switch:
http://www.screwfix.com/prods/28394...olex-45A-DP-Sw-13A-Skt-Blk-Ins-SC-Angled-Edge

The oven came with the cable attached to it. Thickness of the three cables inside the main cable was around 2mm...maybe 3mm. Defintely not as thick as the flat grey cable coming out of the wall, and running up to hob.

If I need to put an FCU in place, is 13amp enough for an oven?
Or should I just put the plug socket back on again, and stick a plug with 13amp fuse on the oven cable?

Either way, sound like wiring the oven cable into the junction box is not a good idea?

 

[rebuke]

Normal way to do it would be either a 13A FCU, or a standard socket and plug with 13A fuse. Ideally the fuse should be accessible (for replacement if it blows etc), e.g. in my kitchen the FCU is underneath the shelf the oven sits on, and there's a cover that can just pop off to get at it, without having to remove the oven...

 

[gsf600y]

ok, I'm going to put that plug socket back on, and put a plug (with 13amp fuse) on the oven cable. Stupidly I binned the plug socket thinking I wouldn't need it again.....trip to B&Q on the way home.....

All the cables are very easily accessed via removing the plinth under the kitchen units.

 

[ban-all-sheds]

The oven came with the cable attached to it.

But no plug??

If I need to put an FCU in place, is 13amp enough for an oven?

If it's less than 3kW.

Or should I just put the plug socket back on again, and stick a plug with 13amp fuse on the oven cable?

If it's less than 3kW.

What did you do with the cable supplying the socket when you removed that?

What size cable is it? (Note - cable sizes are specified as the cross-sectional area in mm² of the main conductors - see here as a guide if you can't measure yours.

Can you plug the oven into the socket on the control unit?

Either way, sound like wiring the oven cable into the junction box is not a good idea?

No, it's not.

 

[gsf600y]

But no plug??

Nope, no plug, just bare wires at the end (whirlpool oven by Ikea).

What did you do with the cable supplying the socket when you removed that?
What size cable is it?

I chucked it in the bin, along with the socket, thinking I wouldn't need it. Doh.
It was the same size as the thick grey flat cables supplying all the sockets around the kitchen. Chunky stuff. I might upload some photos when I get home.


Thanks to all for help and advice btw REALLY appreciated.