Oven connected into ring - EGBR says this is ok?

[HappyHippyDad]

I have just been asked by a customer if he can just plug his new cooker into a socket. I have said 'No' it needs to be on a dedicated circuit..

I then thought I'd do a bit of research as its only a 2.5kW oven and wanted to see it in black and white in the regs.

I didn't ecpect the Electricians Guide to the Building Regulations (Page 55 - 4.4) to say

"For lightly loaded circuits ovens of rating 13A or less may be connected into a ring final circuit"

Not sure if his kitchen is on its own ring, but if it is I guess its ok to plug in the oven?

Just doesn't seem right, especially after seeing all of Jason's entrys about having to be 2kW or less?

ps... I'll make this my last post for a bit, getting a bit carried away and a bit addicted to this electrics lark ...:rolleyes4:

 

[DieselShunter]

Sorry just realised you took the flex of hob This might affect the warranty.

It might. But it won't affect your statutory rights, which are nearly always more effective than a warranty. Warranties, especially 12 month ones, are usually there to browbeat you into foregoing your rights under the SoG act.

 

[Geoffsd]

As stated the hob should be protected By a 23 amp fuse

That is presumably a misprint. Do you think, perhaps it should be 13?

Cooking appliance manufacturers state either:
It must be protected by a certain fuse - because that is needed to protect the (cheapest) flex they have fitted.
Or, without flex, it requires a certain amperage of supply - because that is required for it to work.

So I would say that if there is a fault with the Hob the internal wiring and terminal block of the hob can safely run at up to 23 amps

It will obviously be designed for its maximum load, whatever that is.

whereas the only over load protection for the hob is 32 amps

The hob cannot overload.

So yes the circuit will take the load but will the Hob ??

Neither it nor the cable will have to. Overload cannot happen.

Do you think the cabling inside cookers protected by a 30A BS3036 is all capable of carrying 42A, i.e. 6mm?

 

[Guitarist]

Yes G, it really did say that, I'm not one to exagerate. You are one of the more experienced forum users and I would genuinely appreciate to hear what you would have done?

6mm cable fed from a 32A MCB to 45A cooker switch which splits (with 6mm) to a socket for oven (approx 2.5KW) and hob 5KW (which had 2.5mm flex attached).


Yes :winkiss:

Well, for a start, I would contact the manufacturer directly and ask them where I can obtain this mythical 23A fuse. Sounds like they have simply decided that 5kw is about 23A, so that should do, without allowing for any diversity.

 

[SPARTYKUS]

I cant believe you are replying to this when Han Solo is at this very moment fleeing the imperial fleet!!!

Autopilot

 

[Flanders]

1. That is presumably a misprint. Do you think, perhaps it should be 13?

2. Cooking appliance manufacturers state either:
It must be protected by a certain fuse - because that is needed to protect the (cheapest) flex they have fitted.
Or, without flex, it requires a certain amperage of supply - because that is required for it to work.

It will obviously be designed for its maximum load, whatever that is.

3 The hob cannot overload.

4 Neither it nor the cable will have to. Overload cannot happen.

5 Do you think the cabling inside cookers protected by a 30A BS3036 is all capable of carrying 42A, i.e.
6mm?

1 .How can it be 13 amps when the unit is ratted a 5KW (about 22 amps at 230or 21 amps at 240) Apply a bit of diversity and a 20 amp MCB will be fine

2. So your saying the fuse is to protect the Flex not the appliance from overload ?

3. Why cant the Hob Over load??

4. So there was no need to change the cable to 6mm If the Hob can't overload ?

Here an example for you
There was 32 amp fork lift truck charger plug into a 32 amp socket protected by a 32 amp MCB , all ok
But then the folk truck charger was replaced by someone with a 16 amp ratted unit,using the same flex and 32 amp socket and was still and protected by the same 32amp MCB.

There was a fault on the fork lift charger coursing it to catch fire.
The customer asked why it did not trip the MCB first .
I told them it was because the MCB was overrated for the charger unit. Are you telling me that this was not the case ?


5. never though about that You may have a point

 

[Geoffsd]

1 .How can it be 13 amps when the unit is ratted a 5KW (about 22 amps at 230or 21 amps at 240) Apply a bit of diversity and a 20 amp MCB will be fine

We don't know. Perhaps the loads add up to 5kW but only 3kW can be switched on at once.

2 So your saying the fuse is to protect the Flex not the appliance from overload ?

Yes, definitely.

3 Why cant the Hob Over load??

It is a fixed load. It can't suddenly start drawing more current.

4 So there was no need to change the cable to 6mm If the Hob can't overload ?

No. 433.3.1.2(ii)

Here an example for you

Therewas 32 amp fork lift truck charger plug into a 32 amp socketprotected by a 32 amp MCB , all ok
But then the folk truck charger was replaced by someone with a 16 amp rated unit, using the same flex and 32 amp socket and was still and protected by the same 32amp MCB.

There was a fault on the fork lift charger coursing it to catch fire.
The customer asked why it did not trip the MCB first .
I told them it was because the MCB was overrated for the charger unit. Are you telling me that this was not the case ?

It may be different if someone has fitted the wrong plug to the charger and the charger is supposed to be protected by the MCB.

5 never though about that You may have a point

 

[Flanders]

So can there not be a fault with an appliance that courses an over load for example leakage to earth or neutral (not a dead short) I thought the fuse in the plug top were there to protect it ?

And Did you mean Reg 433.3.1(ii)

 

[Sparky Ninja]

It would cause an overcurrent called fault current.
An overload current will only occur in an electrically sound circuit.

 

[Flanders]

It would cause an overcurrent called fault current.
An overload current will only occur in an electrically sound circuit.

So the fuse is there to protect from Fault current, if there was a fault current coursed by the Hob would the 32 amp MCB trip out before any damaged is coursed to the Hob

 

[Geoffsd]

So can there not be a fault with an appliance that courses an over load for example leakage to earth or neutral (not a dead short) I thought the fuse in the plug top were there to protect it ?

That is not an overload but a fault current which will operate the 32A MCB in 0.1s. or less.

As long as the cpc can cope with fault current then all is well.
Hence the link to 434 in 433.3.1(ii) and my reference above to knowledge and test equipment.

A current leakage enough to overload a, say, 2.5mm conductor but not operate the 32A MCB would have to be very specific indeed - around a constant 6, 7 or 8Ω.
This isn't really possible, is it?, and we do not have to cater for it.
Such a fault would melt the internal wiring or element wire first anyway.

And Did you mean Reg 433.3.1(ii)

Yes.

 

[Geoffsd]

So the fuse is there to protect from Fault current, if there was a fault current coursed by the Hob would the 32 amp MCB trip out before any damaged is coursed to the Hob

Well, not really because such a fault can only be caused by a damaged part or

poking your screw driver around.

 

[Sparky Ninja]

So the fuse is there to protect from Fault current, if there was a fault current coursed by the Hob would the 32 amp MCB trip out before any damaged is coursed to the Hob

The fuse is there simply to protect the cable to the appliance from the over-current likely to occur in a fault.
The appliance is designed with a cable that will accommodate the full demand, and an overload cannot occur as it is a purely resistive load.
The fuse will operate in the case of a fault current flowing, but depending on the characteristics of the final circuit the circuits protective device may operate first.

 

[Flanders]

Fair comment Thanks For putting me straight

 

[HappyHippyDad]

A current leakage enough to overload a, say, 2.5mm conductor but not operate the 32A MCB would have to be very specific indeed - around a constant 6, 7 or 8Ω.
This isn't really possible, is it?, and we do not have to cater for it.

So are you saying it would have been ok to leave the 2.5mm flex on the hob which was protected just by the 32A MCB?

 

[Guitarist]

Whilst complying with regs, remember the prime directive of the current regs is to follow manufacturers instructions where they demand something specific. As I said, I would personally be getting in touch with the manufacturer to confirm that fuse rating. If they are adamant that a 32 amp OCPD is too high, then your only option is to fuse down. I realise that millions of hobs are wired into the main cooker outlet, but if hippy wants to cover his backside (and knowing him, sleep at night) then he will need to find a way of getting a 20A MCB supplying this circuit.