Induction hob wiring

[Octopus]

Sorry for the juvenile drawing. It's something like this:
View attachment 47023

If its like that you need to rip it out and have it done properly

 

[nyb]

The hob should be OK to be connected in with the 32A supply for the oven using the first diagram with the L1 and L2 teminals linked and the N1 and N2 terminals linked.
To have to independently isolated supplies to one appliance could be confusing and dangerous because if someone was working on a faulty part, isolated a single switch and found the faulty part was off, they could then start opening up the equipment not realising there was still a live supply present, though they would have to be missing out on a lot of standard safety practice.
The house ring looks like there are a lot of potentially overloaded cables there and this should be addressed by rearranging the wiring to form a single ring.

Yeah I agree about isolation confusion. I hope to get an *good* electrician to come and sort out this mess for me (I have had bad experiences thus far with the folk I've hired and hence where I find myself now).
Until then I'm worried about general safety on use (cables melting ). I agree with your assessment of the overloaded spur off the ring - that's why I've turned off the isolation switch from the 2 plates of the hob connected to that circuit and am just using the two hobs connected to the cooker circuit for now.
I'd be worried piping all 6400W from the hob to the cooker because currently it's spurred off the cooker switch on what looks (to me) like 2.5mm (but I'm not sure exactly what cable was used here for the spur). I'm not sure that can handle the 6400W (28A?) if someone turns on all the plates at once? Would this be an issue?
Also the cooker circuit is currently on a 32A breaker (I have no idea if the wiring was 6mm or 10mm) so if I use the oven + 2 hob plates presumably this should trip the thing? I did a small test now by turning on the oven fully (trying to load the full 4800W) and then turning on the two hob plates connected to that circuit to full but nothing tripped (3200W). I'm not sure if this is a worrying sign or not?!? (surely I had loaded 35A on that radial circuit?)

 

[nyb]

The hob should be OK to be connected in with the 32A supply for the oven using the first diagram with the L1 and L2 teminals linked and the N1 and N2 terminals linked.
To have to independently isolated supplies to one appliance could be confusing and dangerous because if someone was working on a faulty part, isolated a single switch and found the faulty part was off, they could then start opening up the equipment not realising there was still a live supply present, though they would have to be missing out on a lot of standard safety practice.
The house ring looks like there are a lot of potentially overloaded cables there and this should be addressed by rearranging the wiring to form a single ring.

Yeah I agree about isolation confusion. I hope to get an *good* electrician to come and sort out this mess for me (I have had bad experiences thus far with the folk I've hired and hence where I find myself now).
Until then I'm worried about general safety on use (cables melting ). I agree with your assessment of the overloaded spur off the ring - that's why I've turned off the isolation switch from the 2 plates of the hob connected to that circuit and am just using the two hobs connected to the cooker circuit for now.
I'd be worried piping all 6400W from the hob to the cooker because currently it's spurred off the cooker switch on what looks (to me) like 2.5mm (but I'm not sure exactly what cable was used here for the spur). I'm not sure that can handle the 6400W (28A?) if someone turns on all the plates at once? Would this be an issue?
Also the cooker circuit is currently on a 32A breaker (I have no idea if the wiring was 6mm or 10mm) so if I use the oven + 2 hob plates presumably this should trip the thing? I did a small test now by turning on the oven fully (trying to load the full 4800W) and then turning on the two hob plates connected to that circuit to full but nothing tripped (3200W). I'm not sure if this is a worrying sign or not?!? (surely I had loaded 35A on that radial circuit?)

 

[Richard Burns]

On a practical basis the cables will not burn out rapidly, however they could well get too hot to have a reasonable lifetime and this could also make any poor connections worse.
The existing oven I might often expect to have a 45A switch for isolation but a 20A one is possible.
A 20A switch would not be suitable for both oven and hob, however if the cable to the switch is the standard 6mm² then Oven and hob could be connected to the circuit because they would not all use full power at all times and so would not cause the cable to overload or the breaker to trip.

 

[nyb]

Any idea why the 32A cooker circuit breaker didn't trip?

 

[Richard Burns]

In accordance with the standards on domestic circuit breakers a circuit breaker must be able to carry 1.13 times its rated current (36.16A) for at least one hour.
The thermostats on the heating elements will cut in and lower the power draw well before that point.

 

[nyb]

That's interesting to know. Have learned a lot from you today. Thanks!
Now that my house doesn't seem to be in imminent danger of going up in flames, I guess it's off to search for a good electrician to clean this all up. I wish I knew how to find someone I could trust (without going for a large company that charges too much for me to afford).

 

[Wilko]

Hi - if you ask, someone from here may be nearby and willing to help.

 

[Richard Burns]

Or you could look in the electricians directory on the forum. No guarantee of quality but at least they may have used the forum to learn things!

 

[Midwest]

Please DO NOT connect a single load to 2 circuits - a VERY bad idea, and extremely dangerous

I've already said that

 

[Risteard]

In accordance with the standards on domestic circuit breakers a circuit breaker must be able to carry 1.13 times its rated current (36.16A) for at least one hour.
The thermostats on the heating elements will cut in and lower the power draw well before that point.

I thought 1.13 times the rating was indefinite, with 1.45 times the rating operating within conventional time (1 hour).

 

[Richard Burns]

I thought 1.13 times the rating was indefinite, with 1.45 times the rating operating within conventional time (1 hour).

Yes, at 1.13 times it must not operate within one hour, at 1.45 times it must operate within one hour. I do not know of a time requirement for tripping at 1.13 times only for not tripping. Though I could be wrong.