Induction hob circuit

[Bob556]

Hi guys
I've just bought a house in Spain. It was partly renovated, including electrics. Some of the work done is decidedly a bit sketchy but the electrics seem mostly OK (I do need help with one problem that I'll post separately).

We've decided to have an induction hob fitted because I don't get on with radiant ring electric hobs and gas is not practical.

There is a dedicated oven circuit fitted with 20A breaker. Now, I don't know what the previous owner intended for the hob except the extractor fan wiring is located near the oven wiring.

The hob takes 7.4kW so there's no way it can run off the same circuit as the oven (correct me if I'm wrong).

I've called in a couple of electricians. The first said he could do the job - kind of "dig up the tiles, put cables in new conduit and connect to the junction box there, then replace tiles etc". His price seemed a bit high 1500 euro for lifting/replacing 7 (narrow tiles, we have spare) and making good.

For the 2nd electrician, I took the cover off the junction box and as expected there was only wires for sockets 2.5mm2. He nodded, made a few noises etc. Then I asked if the hob would need a new circuit. He agreed. Eventually he said 6mm2 cable and 30A mcb. Then he said he wouldn't be able to get new 6mm2cable through the plastic conduit so he would use 3x2.5mm2 for each conductor instead. I thought that if he couldn't get 3x6mm2 through the conduit he won't get 9x2.5mm2 through it, but then I thought the thinner cable will be more flexible so maybe it will go through easier.

But then I realised he wasn't talking about getting 9 wires back to the consumer unit, he was simply taking them to the junction box and connecting to the existing wiring.

So, there may be some things lost in translation but is his initial specification of 3x6mm2 + 30A mcb OK? I think the mcb is a bit low (judging from my experience in the UK) and it should be C35.

He also claimed that a isolator switch eg 45A dp wasn't needed, anyone know this for sure?

Now, I'm assuming that even if the wires in the junction box could take the load, this hob NEEDS a completely independent circuit through to the consumer unit? His idea of piggybacking on the socket wires seems bonkers even if there is a dozen wires in there.

One more thing, I understand the house is TT earthing. I can't find anything near to the meter box that could house an earthing rod. Could it be under the pavement tiles?

 

[Bob556]

24 hours later, 60 views and not one comment... Maybe you all got confused. Lol
So let's break it down.
1) does a 7.4kW induction hob need a dedicated circuit, or can multiple socket wires be used in parallel

2) if a dedicated circuit is needed, what are the requirements - 6mm2/10mm2 + 30A/35A/40A

3)in place of 6/10mm2, can 3/4 2.5mm2 be run in parallel instead?

4) in UK, a double pole isolator is need close to the appliance. Anyone know if this applies in Spain?

5) should I be able to find the earth rod? Is its location usually visible and is it marked by anything? Plate on wall etc?

 

[pete01]

You can have upto 15kw of cooking appliances on a 6mm 32 amp circuit.....some say 20kw.

 

[Ragnar_AT]

It will probably work on even a 2.5 mm2/20 A circuit unless you try to put on four pots of cold water at the same time. You definitely want a dedicated circuit though and if you‘re already opening up walls I‘d go for 6 mm2.

 

[Murdochcat]

I suspect the lack of comments reflects the void on the forum when it comes to Spanish electrical regulations knowledge

 

[Rodders53]

Most 7.4kW total induction hobs have two input circuits (5-wire cable) each circa 3.7kW or 16A to suit continental use: possibly isolated via a "3-phase" 4-pole switch? That'll depend on the local regs... ask someone there who knows?

Additionally most can be electronically limited to draw a lower load: My Bosch has 13A, 16A, 20A and unlimited (possibly has others but that's from memory)

:rtfm: or provide make and model so we can find it to confirm.

In UK we connect both with links to make a single phase 32A unit.

EDIT My youngest son has a 4 burner 13A plug in induction hob and cooks family meals with no problems... but has had practice wrt that. You can't put 4 pans on to boil from cold and expect it to be fast. (Even my 32A 4-burner won't allow both burners on one side to run at max / boost power.)

 

[Ragnar_AT]

As far as I know the two single-phase circuit option is only used in the Netherlands but that’s more of an education assumption than factual knowledge.

 

[Bob556]

Ignore

 

[Bob556]

I suspect the lack of comments reflects the void on the forum when it comes to Spanish electrical regulations knowledge

It is true that Spain is a weird place. Over-regulated with permits (aka planning permission) strictly speaking needed for the most trivial of home improvementd (eg fitting a new front door, esp if its a different style) but with the rules being widely flouted.

ask someone there who knows?
The problem at the, moment is that everyone in this area is either on holiday or working short hours. In addition, the culture is very much to ignore invitations to quote for work at this time of work (I'm told it's only at this time), meaning it's difficult to get anyone to even look at a job. Maybe that's why the 2 who did come out were a bit shifty.

The manual gives the total power as 7335W. The cable is 3 core, pic attached.

 

[Bob556]

It will probably work on even a 2.5 mm2/20 A circuit unless you try to put on four pots of cold water at the same time. You definitely want a dedicated circuit though and if you‘re already opening up walls I‘d go for 6 mm2.

Yeah, it might be possible to run it from a socket, but not practical.

In terms of "opening walls", in Spain, everything runs in conduit (in walls/floor) with wires joined at junction boxes (see example pic). Theoretically, if there's enough space in the conduit in the junction box nearest the hob, a cable could be pulled through. The problem is, that junction doesn't seem to go direct to the consumer unit and if you can imagine JBs in every room, with wires going through perhaps multiple JBs, pulling a cable through won't be physically easy, even if you can trace a route to the consumer unit. Maybe someone experienced could work it out but I'm struggling.


In terms of "opening walls", in Spain, everything runs in conduit (in walls/floor) with wires joined at junction boxes (see example pic). Theoretically, if there's enough space in the conduit in the junction box nearest the hob, a cable could be pulled through. The problem is, that junction doesn't seem to go direct to the consumer unit and if you can imagine JBs in every room, with wires going through perhaps multiple JBs, pulling a cable through won't be physically easy, even if you can trace a route to the consumer unit.

The pic is of the JB nearest the hob and it all looks like 2.5mm cable.