Wiring in a 13A induction hob

[Eagles83]

I managed to pickup a cheap Lamona 1802 induction hob. I didn’t realise at the time it was a 13A hob with a built in plug.

I currently have a single fan oven and ceramic hob which is hard wired into a connector plate.

Without causing risk of a fire am I able to cut the plug off and hardwire that into the existing connector plate?
Thanks

 

[bsr]

Yes

 

[briwire]

Not sure if you have done it yet but cutting off the plug removes the protection of its built in fuse. What size fuse/breaker is protecting the connector plate? Could be as high as 32 amp. If higher than 13 amp, it will be a fire hazard so you need to tap into the plate and connect to a 13A spur, then connect the hob into that, maintaining the 13A overcurrent protection.

 

[Eagles83]

Not sure if you have done it yet but cutting off the plug removes the protection of its built in fuse. What size fuse/breaker is protecting the connector plate? Could be as high as 32 amp. If higher than 13 amp, it will be a fire hazard so you need to tap into the plate and connect to a 13A spur, then connect the hob into that, maintaining the 13A overcurrent protection.

Ah crap! Yeah I have already wired it in to the connection plate. The cooker switch has a socket built into it. I guess I should drill a hole into the worktop and rewire the plug then connect.

The breaker I think is 45a

 

[foxhole]

Just install socket spur next to it for your hob.

 

[RandomGrinch]

***EDIT***
See post #11

Not sure if you have done it yet but cutting off the plug removes the protection of its built in fuse. What size fuse/breaker is protecting the connector plate? Could be as high as 32 amp. If higher than 13 amp, it will be a fire hazard so you need to tap into the plate and connect to a 13A spur, then connect the hob into that, maintaining the 13A overcurrent protection.

Although this seems common sense, I'm afraid it's not the case!
You would have a lot of fun trying to argue this on the electrician's forum
Put simply, any fuse/MCB in the system is there to protect the cable leading to the appliance from over-current.
The fuse or MCB, isn't there to protect the appliance itself.
It's perfectly acceptable to connect a 13A appliance directly into a cooker outlet plate fed from a 32A MCB.

 

[Eagles83]

Okay the breaker is 32a. Can I just ask why it needs to have its own fuse when the old 6600w ceramic hob I removed was hardwired into the circuit?

 

[RandomGrinch]

***EDIT***
See post #11

I hope this makes sense!

Okay the breaker is 32a. Can I just ask why it needs to have its own fuse when the old 6600w ceramic hob I removed was hardwired into the circuit?

It doesn't in a dedicated cooker circuit when it's hard-wired.

The fuse is required when it is plugged into a socket circuit, because (very simplisticly) plugs have space for fuses; there are usually other appliances plugged into a ring main taking power; sockets and plugs are tested to sustain a certain current for a set period of time; and the mechanism for a plug and socket to make an electrical connection can have far more resistance than an undisturbed screw terminal.
These are all factors that you would want to limit the current for, with a fuse.

As an example, I could buy a 3.5kW oven, that has a maximum current draw of 15A. This is only just over the 13A of your hob, but I don't think anyone would question that it couldn't be hard-wired to a 32A cooker circuit.

And as for fire risk - a normal failure mode for an appliance, may be a short circuit. As V=IR, any electrical short could, for a brief moment, create a massive over-current; this would be enough to blow most fuses, be they 3A or 32A!

In the worst case, if there were some sort of fault that could cause a near short, for a sustained period (extremely unlikely), then yes, a 13A fuse would break sooner. However, there would still be little fire risk, as that over current would still be within the capabilities of the (possibly) 6mm² cable used on the cooker circuit.

 

[Eagles83]

I hope this makes sense!



It doesn't in a dedicated cooker circuit when it's hard-wired.

The fuse is required when it is plugged into a socket circuit, because (very simplisticly) plugs have space for fuses; there are usually other appliances plugged into a ring main taking power; sockets and plugs are tested to sustain a certain current for a set period of time; and the mechanism for a plug and socket to make an electrical connection can have far more resistance than an undisturbed screw terminal.
These are all factors that you would want to limit the current for, with a fuse.

As an example, I could buy a 3.5kW oven, that has a maximum current draw of 15A. This is only just over the 13A of your hob, but I don't think anyone would question that it couldn't be hard-wired to a 32A cooker circuit.

And as for fire risk - a normal failure mode for an appliance, may be a short circuit. As V=IR, any electrical short could, for a brief moment, create a massive over-current; this would be enough to blow most fuses, be they 3A or 32A!

In the worst case, if there were some sort of fault that could cause a near short, for a sustained period (extremely unlikely), then yes, a 13A fuse would break sooner. However, there would still be little fire risk, as that over current would still be within the capabilities of the (possibly) 6mm² cable used on the cooker circuit.

Yes that does, what you are saying makes perfect common sense to me.

Thank you! I really didn’t want to faff around with adding a 13a spur to the circuit if it wasn’t necessary. It’s been connected for the last couple of weeks and so far so good. That includes having the oven on for well over an hour and x3 hobs on high for a Sunday roast!

 

[briwire]

Some of the postings above are totally wrong. Trust me, fit a 13a fused spur from the plate and connect the hob into that. As it is now, you have an appliance that is rated at less than 13a protected by a 45a overcurrent device. The fuse or breaker is supposed to be the weakest link, as it is now, in the event of an overcurrent fault, the appliance wiring is likely to overheat before the fuse blows.

 

[RandomGrinch]

Some of the postings above are totally wrong. Trust me, fit a 13a fused spur from the plate and connect the hob into that. As it is now, you have an appliance that is rated at less than 13a protected by a 45a overcurrent device. The fuse or breaker is supposed to be the weakest link, as it is now, in the event of an overcurrent fault, the appliance wiring is likely to overheat before the fuse blows.

You are more than welcome to that opinion!
After many years of PAT'ing, I was of the same opinion, however reading many of the posts on the electrician's forum convinced me otherwise!
If the OP is in any doubt, please post the question on the electrician's forum, where their experience is infinitely greater than mine!

***EDIT***

I have just been re-reading some of the discussions on the electronics forum and others such as the IET.

One of the arguments suggesting that appliances connected to the cooker circuit, did not need to be fused at 13A, was based on the assumption that most appliances have their own built in fused protection.
Taking for example, an item in France may be powered from a 20A circuit, but have no fuse protection in the plug.
However, investigating the PCB, for the hob, suggests that it has a UK specific power PCB, that shorts out the additional fuse protection:

Filter and Smps Card | Lamona Spare Parts | Genuine Parts for Lamona Appliances

Lamona Spares meta description

www.lamonaspares.co.uk

So, although the case still stands that the most likely failure modes for the hob would still be protected against (a dead short will trip a 32A MCB before any damage to the cable can occur); there is a chance (albeit small) of damage occuring to the 1.5mm² connection cable from a (extremely unlikely) sustained high current fault of over 16A.

So, the absolute safest way to connect the hob may be by installing an FCU, or by changing the connection cable to a larger cable size.
Another alternative would be to change the MCB to 16A, but this would be costly and you already have an oven on the circuit.

I apologise if I have mislead, but it seems that the decision to connect a 3kW appliance to a cooker circuit may have to be made on an appliance, to appliance basis - this nuance may have been missed in previous discussions.
Although the risk of harm is still very small.

 

[Eagles83]

Thanks everyone, this seems a bit less clear cut than originally thought. The hob was only fitted as a stop gap until we get our kitchen replaced. I really don’t want to start messing with wiring if I can help it.

Is there any plug and play induction hob solutions I can use in my existing setup without any potential fire risk? I can see that you can get 16a or 32a induction hobs. As they require to be hardwired does this make them plug and play?

The other option would be to refit the old manky ceramic hob I took out which I would rather not do!