Induction hob wiring

[nyb]

Hi all

I just had an electrician around to install a 6400W induction hob. Honestly I'm a little worried as to the job done. Also I noticed some weird wiring done (for the previous owners of the house I guess) that looked very suspect to me.

Basically this is the issue. The kitchen has one ring (strangely shared with some of the bedroom sockets!) for the sockets (32A breaker) and another separate circuit (I have no idea if ring or radial - I assume radial?) for the oven and hob.

The oven is connected to this through what looks to me like a 20A switch (the oven is rated at 4400W). The hob seems spurred off this on (what I at least hope is not less than) 2.5mm.

The new 6400W induction hob's wiring diagrams give two options. a 1L/1N and 2L/2N wiring options. The electrician opted for the 2nd option and wired the first part to the hob circuit off this existing spur (which had a 13A switch, now replaced with a 20A one) and the second hob circuit to another 20A which is spurred off an existing spur to the kitchen ring main.

So I have a few concerns:

Firstly, the 2nd hob circuit (connected to the spur of the ring main) can draw presumably 3200W (half the hob rated power) which is around 14A. The spur that it's connected to I noticed has another spur off it to a socket with an extension cable connected to a washer and to a dryer and a further extension cable off the original spurred socket itself to 2 dishwashers!

This seems crazy to me as to me the sums just don't add up. The spur to the main looks like 2.5mm so that would manage max 27A presumably?
If the hob can draw 14A and each appliance a few kW each (I have no idea exactly what they're rated for but they heat their own water),that seems like danger territory if they all run at once (which is possible in my house).
Even the extension leads (that have two appliances on each) don't seem safe on their own (can they handle two appliances).

For now to mitigate, I turned off the 20A switch from the part of the induction to the ring (leaving only the 20A switch on to the cooker circuit). This works ok even though we can only use 2 out of the 4 plates on the hob.

I al also worried about the separate cooker circuit. Can it take the leftover 3200W from the hob + the 4400W from the oven ok?

Thanks,
D

 

[Midwest]

Somewhat confused by your post. Diversity can be applied to cooking appliances, so I have roughly 13A for your oven and just over 15A for your hob. So they could be supplied by a 32A supply, is that what you are saying?

Not unusual to have a ring divided between one side of a house grd & 1st floor, and the other side.

Edit: an appliance (certainly domestic) should have just one supply & isolating. Some hobs allow for a 3 phase connection, perhaps that what the 1 L, 2L is? Also sometimes copper links (provided by the manufacturer) have to be inserted .

 

[nyb]

For reference, here's the manufacturers hob wiring diagram:



The electrician did the last one, connecting L1/N1 to the cooker circuit and L2/N2 to that spur off the ring.

 

[nyb]

Btw that diagram I posted above has an error (L1 and L2 seem to be reversed in the diagram). The manual has the fixed version; the electrician did as per the diagram in the manual and not as per the above upon realizing that it was wrong (and in effect connecting the cooker and ring circuits together!)

 

[nyb]

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

 

[Midwest]

What make & model is the hob? Never connected a hob from two separate sources. Is this in a domestic property?

 

[nyb]

Yes domestic property. I think the thoughts connecting it this way were to spread the load over two circuits. Is it a problem to do this? This is the hob: https://smile.amazon.co.uk/gp/product/B075WQY64H/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

 

[Octopus]

Yes domestic property. I think the thoughts connecting it this way were to spread the load over two circuits. Is it a problem to do this? This is the hob: https://smile.amazon.co.uk/gp/product/B075WQY64H/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

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

 

[Midwest]

Quick google search doesn't reveal any installation manuals, but I'd go for (one supply) connection to Live & Neutral (& earth) to the terminals shown on the left hand diagram #3.

 

[nyb]

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

I agree that's why I was worried and now I probably need to get another electrician in (not sure what he can do except install a separate circuit for the hob).
In this instance, I do think that it's not, in fact, a single load. I think it's 2 loads (1 circuit for each 3200W hob pair). Fact is when I turn off one 20A switch, the 2 plates on that side do not work at all.

 

[Wilko]

As per @Murdoch #8. If I've understood correctly you've now got one appliance on 2 circuits. While large cookers may sometimes use 3 phase, all phases are switched simultaneously for safety.

 

[nyb]

I understand what you're saying but I'm not sure it's the case here. Yes L1/N1 is one circuit and L2/n2 is another (switched separately through 20a switches). But I don't think there's continuity between the two hob-pairs (L1/N1 + L2/N2) on the induction hob. I think they're entirely separate loads. That's why we did it this way.
I suppose I could simply test for continuity? If the two hob-pairs aren't connected to eachother at all, what's the issue of having them on separate circuits?

 

[Wilko]

Hi - single point of isolation.

 

[Risteard]

I'm afraid the setup described isn't at all clear to me. I took it that it wasn't two circuits but that the other appliance connection is looped through the oven, but even that wasn't clear to me.

I think quite a bit of clarification will be needed.

 

[Richard Burns]

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.