Powering a cooker hood

[cludo]

Hi,

Apologies first of all if this is an obvious answer to some...

I have an oven extractor fan whose power cable has 2 wires (no earth). Can I attach a plug to it and then plug it into the socket on the cooker power switch or would this kind of installation mean it was not earthed?

I\\\'ve cheked the instructions that came with it and the 2 lines of how to wire it does not cover this.

Cheers.

 

[ban-all-sheds]

I have an oven extractor fan whose power cable has 2 wires (no earth).

I take it you mean a cooker hood?

Can I attach a plug to it and then plug it into the socket on the cooker power switch or would this kind of installation mean it was not earthed?

It won't be earthed, but it's not supposed to be, that's why it only has 2 wires...

3A fuse in the plug, and it'll be fine.

 

[cludo]

Hi ban all sheds,

Yes, sorry I meant a cooker hood.

That certainly makes my life easier, thanks for the response!

 

[ban-all-sheds]

I have an oven extractor fan whose power cable has 2 wires (no earth).

I take it you mean a cooker hood?

Yeah - you did, didn't you.

Exactly as per the title of this thread, "Powering a cooker hood".

Sorry...

 

[Steve]

Can I attach a plug to it and then plug it into the socket on the cooker power switch

wouldnt that look a wee bit tatty? Plus, theres the safety issue of having its flex dangling around over the cooker?? And why has nobody else picked up on this???

 

[oldfart]

I agree with crafty, if you havent decorated yet, you could always chop in a switched fused spur unit next to your cooker point, taking the power off that, using a 3amp fuse in it. chase a cable from the spur upto a fixed connection unit near your hood or inside if its big enough. No dangly cables and you can isolate it using the swithed spur if you need to.

 

[breezer]

you could always chop in a switched fused spur unit next to your cooker point, taking the power off that

er, how does NO sound
you can not spur off an electric cooker point
(you would need to use same size cable (6mm) to do it, so its an almost physical imposibility

 

[oldfart]

Hi breezer,

excuse my ignorance I thought it was ok to tap off cooker point with 2.5 cable. If it is,nt I apoligse for the duff advice(please disregard)!.

Breezer, I,ve recently done this, the cooker point has a socket outlet as well, I,ve taken power using 2.5 to a spur which is directly adjacent to it.
Sounds like I may have dropped a clanger, what are the implications?

Its all part of a two storey extension, the room above has,nt been floored
yet so I have the option of changing what i,ve done.

cheers

 

[ban-all-sheds]

It is considered safe to run a spur in 2.5mm² from a ring with a 32A breaker.

It is not considered safe to run a spur in 2.5mm² from a cooker circuit with a 32A breaker.

Discuss.

 

[oldfart]

thanx ban,

interesting point, like u say circiuts on the same size breaker, I assumed rightly or wrongly, I was ok.
being protected either end by breaker & rcd at cu and 3amp fuse in switched spur, perhaps breezers thinking about the amount of power the 6mm is carrying and then transferring to the 2.5 and a possible heat increase?

I obvoiusly want to do the job right and safely just unsure to what extremes I take it.

 

[plugwash]

it is specifically allowed to run a 2.5mm spur off a 32A ring

it is not specifcially allowed to run one off a 32A cooker cuircuit but i don't think its specificially prohibited either and i can't see it being any less safe.

running such a spur off a higher rated cooker cuircuit is more dodgy though.

 

[Nick M.]

It is considered safe to run a spur in 2.5mm² from a ring with a 32A breaker.

It is not considered safe to run a spur in 2.5mm² from a cooker circuit with a 32A breaker.

Discuss.

Interesting point & something that I had an argument with someone recently about this.

This is my take on this,

Firstly can I use the words bad practice instead of unsafe as I don't think its unsafe, it has the same loading whether its run off a ring or a radial, the cable can't tell what its connected to.

Secondly "what does the spur feed", if its a cooker hood with a load of say 250W & the cooker is rated at 6kw, theres nothing wrong with that, I would argue till I am blue in the face that you haven't exceeded the design current of the circuit & I have done this recently in a kitchen & had a row with a LABC inspector who had done a three day course (part P) & read somewhere that this couldn't be done, he couldn't show me why though.
If the spur is feeding a tumble dryer for arguments sake, then I would say that is bad design & unworkable, not unsafe as the protective device should operate & protect the cables from overheating as it should do.

Just my tuppence worth

Nick

 

[ban-all-sheds]

You've hit 2 nails firmly on the head there.

1) Good/Bad practice and the instant LABC expert. This is really a distillation of the environment, encouraged by the OSG, of what I term "electrical installations for the hard of thinking". The reliance on the use of standard circuits means that people don't bother to do proper design, or think about what design principles underpin those standard circuits, they just follow "the rules" and don't consider other options or other designs.

2) What the "spur" feeds. You're right about the cooker hood load, but your tumble drier comment is interesting - I'll bet there's at least 1 person in the country with a T/D plugged into the integral socket on a CCU not knowing that the design current for that socket is only 5A. We're back to the "rules", and how you either have to unthinkingly follow them or work things out properly. A spur in 2.5mm² is considered safe because the rules say only 1 socket, so when you follow the rules you can't overload the cable.


When I said "discuss", it wasn't a rhetorical, or sarcastic remark. A cooker circuit is of course a radial, so a circuit coming off of it is not a spur, it is a leg of the radial, and there are no rules explicitly limiting the number of sockets on it - you're into the realm of designing the circuit properly. There is no simple "only 1 socket" rule that "prevents" more from being added, which is why you do have to be very careful, and which is why I agree that you should not attach a 2.5mm² leg to a 32A 6mm² radial, except via an FCU to provide proper protection of the cable. A spur on a ring is a special exemption to the Ib <= In <= Iz rule, and it does not apply to other circuits.

 

[mapj1]

Ah, but an 13A FCU from a cooker box, in 2.5mm cable is OK, because the cable is protected against overload at the load end, by the FCU fuse, and against short circuit (nail gun?) by the 32A breaker at the other end.
Not prohibited at all, and quite common for running a 3kw oven under a higher rated hob.
repeat after me " we should think rather than just blindly use standard circuits"

 

[ban-all-sheds]

Indeed, the 2.5mm² is protected as you say, just as it is when spurring off a ring. I don't do that, either (or at least, have so far managed not to) - I put FCUs directly onto the ring.