oven installation, "All Pole Connection Unit???"

savemoney · 14 Feb 2004

New Kitchen, new electric oven, gas hob. At the momement I have no cable to the kitchen for the use of oven as my old one was all gas. The new oven is a single fan assisted rated 2.5kw. The installation instructions says to connect it by means of an "all-pole disconnect switch with a minimum contact gap of 3mm". Can someone please tell me what this "all-pole disconnect switch" is as I was automatically just going to run a cooker circuit from the consumer unit via a double pole cooker unit. Am I right in thinking that I can run the new oven off the existing ring main circuit as the oven is only 2.5kw?
Thanks!!!

BR · 14 Feb 2004

An "all pole disconnect switch" is a switch which will as the name suggests, isolate all (three in your case) poles. This term is normally used in industrial installations where apparatus has to be totally disconnected. In practise a double pole switch is quite sufficient.

Although you could in theory feed the cooker circuit via a spur from the ring main, I would advise that if at all possible, fit a new (non RCD protected) MCB (it is impractical to RCD protect the cooker) and feed the double pole switch from this.

Perhaps somebody could advise me, the earth is considered a 'pole' in industrial wiring. Is this the case in domestic installations?

securespark · 15 Feb 2004

BR No!!!!!!

The regs specifically state something like (this is from memory)

No switching device shall be inserted in a protective conductor.
(Except for two exclusions, neither of which apply here).

I think it is regulation 543-03-04

This is because you don't want to isolate the appliance from the cpc (earth wire).

If the appliance is 2.5kw then a 13A fused switched connection unit will suffice (They have a 3mm contact gap) This can be wire from the ring.

However, if you're at the stage where you can easily install cables etc, then it might make sense to install a radial circuit for a cooker. That way you future-proof the installation.

savemoney · 15 Feb 2004

Thanks for the help so far. I am at the stage where I can put a radial circuit in or it looks like on closer inspection of the wiring already botched in my house that I might aswell put a new ring circuit in anyway so I could incorporate a fused connection unit into the new circuit either option is open to me at the momement. If I decide to go with the radial will 2.5mm T&E cable be ok or should I use a larger cable to cover possible future installations? If so what size cable?
Thanks.

breezer · 15 Feb 2004

fot your current oven you could inatall 2.5 with a socket on the end and plug in your oven, this also covers the "3 pole dissconect rule"

For future changes you could run in a 6mm twin and earth and not connect it at either end (bit of trouble tring to put a 13a socket on the end, but if you change your cooker it will be there waiting (but obvioulsy it will then need to be connected to a cooker point etc)

securespark · 15 Feb 2004

breezer does a plug & socket satisfy the 3mm disconnection gap rule?

breezer · 15 Feb 2004

only if you pull the plug out

securespark · 15 Feb 2004

"all-pole disconnect switch with a minimum contact gap of 3mm"

That's what the cooker instructions say.

ban-all-sheds · 16 Feb 2004

securespark said:
"all-pole disconnect switch with a minimum contact gap of 3mm"

That's what the cooker instructions say.

So what?

It's a 2.5kW appliance, surely it should be installed in the same way as any other 2.5kW appliance, irrespective of what the instructions say concerning means of isolation? A plug socket is fine, according to the regs.

I've no idea what the contact gap is of your typical 20A DP switch, but presumably it meets whatever the regulations say it should be to safely disconnect the load.

The cooker instructions can say what they like - it's a 10A load; just wire it safely using the isolation method of your choice.

securespark · 16 Feb 2004

I recommend following manufacturers advice because at the end of the day, they have your b***s in a noose - if anything goes wrong (even unrelated stuff) and you have not followed their installation instructions, they can turn round and say stuff off, we're not honouring our warranty.

I know that things like this should not make a difference, but refer you to my case involving a BA pcb that went faulty. "What fuse did you put in the FCU?" asked the tech help line. "3A" I replied. "Ah, it should have been 2A. Can't help you, I'm afraid"

Even though their board went faulty and it was nothing to do with the fact I had used a 3A fuse, they refused the honour the warranty because I had "installed it incorrectly" - their own words.

That's the reason I say follow the instructions!

savemoney · 18 Feb 2004

O.K. one last question for now if I could.
I have found a 3 pole disconnection switch rated at 10A is this ok for the oven? Or can someone give me a formula for working it out.
Thanks!!

ban-all-sheds · 18 Feb 2004

savemoney said:
O.K. one last question for now if I could.
I have found a 3 pole disconnection switch rated at 10A is this ok for the oven? Or can someone give me a formula for working it out.
Thanks!!

Given my recent diatribe in the Other Place about watts, VA, phase angle and power factor, it would be a tad ironic for me to say that Watts = Volts x Amps, but.....

W=V*A. Therefore A = W/V.

Don't know what supply voltage your oven maker assumes, so use the worst case of an assumption of 230V and our reality of 240V, that means that your 2.5kW oven will draw

(2500/230) * (24/23) = 11.3A, so a bit tight for your 10A switch.

Which you don't need anyway - it's 3-pole, and you only have 2 poles to switch - as securespark said, you must not isolate the appliance earth.

How do you plan to wire the oven in? Why not use a plug and socket, as that will give you at least a 3mm gap when unplugged. Or look at the technical data for cooker control units to see what the contact gap of the main switch is?

savemoney · 18 Feb 2004

I was quite happy about running a new circuit from the cu for the oven and using a 2 pole swicth but then securepak got me a thinkin' about if anything went wrong then this would give the menufacturers an excuse not to honour the warrenty but. The 3 pin plug sounds fine except I don't like the thought of how it will look....sorry, new kitchen and all that...so I just wanted it nice and neat and tucked away and I must admit that I don't like the idea about disconnecting the earth???Hhmm. Anyway thanks for the info about working voltage and amps etc. I think I will probably run a new circuit in and take my chances that the oen will be ok. If anyone has any more to advise please feel free.......Just wondering does anyone know if you can get a 3 pole disconnect switch rated more than 10A???

il78 · 18 Feb 2004

Install the socket outlet low level under worktop / in a base unit, this keeping your kitchen pretty.

Scoby_Beasley · 18 Feb 2004

securespark said:
breezer does a plug & socket satisfy the 3mm disconnection gap rule?

breezer said:
only if you pull the plug out

By 3mm !!!!

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oven installation, "All Pole Connection Unit???"

breezer

breezer

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