Cookers plugs and direct connection

[Tom York]

Morning,

I'll preface this with the fact I have already told them I am not as yet competent to do it and they should get a trained sparky in.

Trainee electrician at early stages. Friend asked me to change their cooker. Old one is on its own circuit and also has a fused (not sure on size) double pole switch in the kitchen leading to cooker outlet then direct attached. All looks pretty standard and compliant.

New one has a 13.5amp plug as it came from the manufacturer so assuming for the purposes of this that it's draw is below that.

As I see it I would have had two options.

1 replace the outlet with a socket for the manufacturer's plug and away we go. Seems neat and doesn't risk the manufacturer's warranty and is as intended so all good. It then has two fuses protecting it and an RCD on its own circuit the size of the MCB is I think less important as the other fuses are present, and double is better than nowt as I see it. Have I missed anything in my thinking? Except checking the fuse size in the currently installed fused switch.

2. Cut the plug off and wire it into the outlet after checking cable size etc. Thinking on this is the fuse in the switch as long as it is the same size fuse as in the plug provides the manufacturer's level of fuse protection and as the cooker is on its own circuit covered by an RCD and the MCB in the CU it's all good.

I have read a fair few forums and people offer widely varying advice. Not so worried about voiding warranties in this case as I won't be doing it anyway but I want to learn on the electrical side of this what is best practice and why. Also if my thinking is floored I would rather be told here than set someone's house on fire.

Cheers

Tom

 

[telectrix]

change the cooket outlet for a single socket. plug new cooker in. (obviously perform safe isolation befoer sticking fingers in.).

 

[Dartlec]

By Cooker do you mean Oven? Or free-standing cooker with gas hob?

Many ovens (even some hobs these days) come with a plug on. Often the Manufacturers Instructions will state that it can be removed if being installed by a 'qualified installer' or whatever wording they decide to use.

Doing so shouldn't affect the warranty, although if there was an issue where it had been incorrectly terminated they would of course not cover that...

You are more or less right in your two options.

With option 1), it's not ideal to have two 13A fuses in line, as it's then harder to tell which one has blown. The nice solution here would be to replace the Fused switch with a 20A DP switch for isolation and leave the fuse in the plug. The only issue then is that if the fuse does blow, you have to remove the oven to get at it. (Assuming the plug isn't separately accessible below or above the oven.

However, in practise, with an RCD/MCB in place, the chances of the plug/FCU fuse(s) blowing first are probably slim, so it's not a huge issue IMO.

The one issue with some ovens these days is that many come from Europe, where they are designed for a 15A circuit. These will either come with a cable, or no cable at all - but shouldn't be connected to a Fused Spur with a 13A fuse in as they will run at just over the fuse rating, probably not blowing it, but over time causing heat damage to the various parts.

In those cases, you usually have to ensure that the cabling is suitably installed and protected upstream (Radial circuit with 16A or 20A MCB usually) and then put a DP isolation switch in (no fuse).

 

[Taylortwocities]

change the cooket outlet for a single socket. plug new cooker in. (obviously perform safe isolation befoer sticking fingers in.).

What he said ^^^^^^

A couple of points (apologies for pedantry)

Old one is on its own circuit and also has a fused (not sure on size) double pole switch in the kitchen leading to cooker outlet then direct attached.

Cooker isolation switches have no fuse. The fuse/MCB protecting the circuit is in the fuseboard/consumer unit.

New one has a 13.5amp plug

13.5? is that typo?

 

[Tom York]

What he said ^^^^^^

A couple of points (apologies for pedantry)

Cooker isolation switches have no fuse. The fuse/MCB protecting the circuit is in the fuseboard/consumer unit.

13.5? is that typo?

Thanks very much for taking the time to reply and the pedantry. The 13.5 was a typo yes. The switch with a fuse is a lack of knowledge on my part. Thanks for pointing it out. The fuse holder on the switch must be something else.

So difficult to get a grasp of what I don't know....except for everything ?

 

[Dartlec]

Thanks very much for taking the time to reply and the pedantry. The 13.5 was a typo yes. The switch with a fuse is a lack of knowledge on my part. Thanks for pointing it out. The fuse holder on the switch must be something else.

So difficult to get a grasp of what I don't know....except for everything ?

It might still be a Fused Spur - Someone may have put it in because they didn't know better, or it's possible that it's on a Ring Final Circuit and someone wanted the fuse there (though an oven should really be on it's own circuit)

But doing things 'correctly' it would usually be a Double Pole Isolation switch as mentioned...

 

[Tom York]

By Cooker do you mean Oven? Or free-standing cooker with gas hob?

Many ovens (even some hobs these days) come with a plug on. Often the Manufacturers Instructions will state that it can be removed if being installed by a 'qualified installer' or whatever wording they decide to use.

Doing so shouldn't affect the warranty, although if there was an issue where it had been incorrectly terminated they would of course not cover that...

You are more or less right in your two options.

With option 1), it's not ideal to have two 13A fuses in line, as it's then harder to tell which one has blown. The nice solution here would be to replace the Fused switch with a 20A DP switch for isolation and leave the fuse in the plug. The only issue then is that if the fuse does blow, you have to remove the oven to get at it. (Assuming the plug isn't separately accessible below or above the oven.

However, in practise, with an RCD/MCB in place, the chances of the plug/FCU fuse(s) blowing first are probably slim, so it's not a huge issue IMO.

The one issue with some ovens these days is that many come from Europe, where they are designed for a 15A circuit. These will either come with a cable, or no cable at all - but shouldn't be connected to a Fused Spur with a 13A fuse in as they will run at just over the fuse rating, probably not blowing it, but over time causing heat damage to the various parts.

In those cases, you usually have to ensure that the cabling is suitably installed and protected upstream (Radial circuit with 16A or 20A MCB usually) and then put a DP isolation switch in (no fuse).

Thanks for taking the time to reply. I looked over the cu and it looks like 6mm cable and 32 breaker on a radial circuit. Which from reading sounded reasonable but I don't know anything about the old one and as I'm not doing the work I've not looked into it further.

 

[Tom York]

It might still be a Fused Spur - Someone may have put it in because they didn't know better, or it's possible that it's on a Ring Final Circuit and someone wanted the fuse there (though an oven should really be on it's own circuit)

But doing things 'correctly' it would usually be a Double Pole Isolation switch as mentioned...

Ah ok. That makes sense. As I'm as certain as I can be that the cooker is on its own circuit I'm puzzled by the fuse on the switch unless it's for the attached socket. Either way I'll add it to my ever growing list of things to learn. Thanks for your time and knowledge

 

[goasis]

Thank goodness no one's mentioned solid brass links....?

 

[Dave OCD]

The night is young...... ?

 

[DPG]

Say his name 3 times, I dare you ?