Range Cooker - 3 Phase or Single Preferred?

[phykell]

Hi,

My property has a 3-phase CU and my new range cooker appears to offer the option of being wired as single or 3-phase (connection diagram attached). The electricians have installed two cables aiming to share the load for a single phase appliance (they didn't know the cooker would be capable of being wired for 3-phase). My (Schneider) CU uses RCBOs for each circuit so I'm guessing it's going to be expensive for a 3P RCBO...

1. Are there any advantages to having it wired as 3-phase? I thought it might be the case that I use everything all at once on full power (however unlikely)

2. What happens if one phase fails? I'm in a rural area so when there's the odd power cut, it usually affects just one phase.

Thanks

 

[Taylortwocities]

Would you care to reveal the power ratings for this monster please?

 

[phykell]

Would you care to reveal the power ratings for this monster please?

Maximum total electrical load at 230 V (approximate total including hob, oven lights, oven fan, etc.): 16.24 kW.

The hob appears to be rated at 7.4kW of that total.

Based on the power rating, I think it might be cheaper to just get takeaway every night

 

[Taylortwocities]

Thats 70amps at full whack!!!. Did you share that figure with your electricians? Should you warn UK power that they need a new power station dedicated to you?
Blimey, mate. Luckily electricity is so cheap at the moment.

3-phase.

 

[flameport]

1 - the advantage is that it spreads the load across all 3 phases, and the size of cable required between the consumer unit and the cooker will be smaller in cross sectional area but have more cores in it.

2 - if one phase fails and the others don't, then anything that uses 3p will not work properly or at all. Some devices could be damaged, but that's not particularly likely with a cooker.

 

[JohnW2]

Thats 70amps at full whack!!!.

Yes, it is something like that (nearer 65A at 230V if the 16.24 kW is at 240V) ... or 28A after diversity - and even that only if all parts of the cooker (presumably including at least two ovens) were being used simultaneously

3-phase.

One could use 3-phase but, at least in theory, one could use a 32A single-phase circuit.

I would think that any advantages of using a 3-phase supply would be pretty minimal.

Kind Regards, John

 

[Colin Brenton]

Do you have a single phase DB or a three phase DB (or both) in the house? Within easy-ish reach of the kitchen? What (if any) cabling is in place already?

I'd guess at going single phase from what's been said so far, but the above might throw some other options up.

Cheers,
Colin

 

[JohnW2]

Do you have a single phase DB or a three phase DB (or both) in the house? Within easy-ish reach of the kitchen? What (if any) cabling is in place already? I'd guess at going single phase from what's been said so far, but the above might throw some other options up.

Valid questions but, as I've implied, the decision needs to consider the perceived 'advantages' of using 3-phase which, as I said, I suspect are minimal.

Like the OP, I have a 3-phase supply, with all three phases easily available to my kitchen but if I had an electric cooker (which I don't), even a large one, I don't think I would personally dream of supplying it with a 3-phase supply.

Kind Regards, John

 

[phykell]

Thats 70amps at full whack!!!. Did you share that figure with your electricians? Should you warn UK power that they need a new power station dedicated to you?
Blimey, mate. Luckily electricity is so cheap at the moment.

3-phase.

I'll be cooking on my log burner (Esse Bakeheart stove) after the October price hike

 

[phykell]

1 - the advantage is that it spreads the load across all 3 phases, and the size of cable required between the consumer unit and the cooker will be smaller in cross sectional area but have more cores in it.

2 - if one phase fails and the others don't, then anything that uses 3p will not work properly or at all. Some devices could be damaged, but that's not particularly likely with a cooker.

OK - I was just looking at the cables and I believe they're both 6mm T&E so they should handle the power using 3-phase or single phase just fine. It would be interesting to see the wiring inside the appliance and based on what's been said here, I'm going to drop the manufacturer an email to ask for more information regarding the potential failure of one of the phases.

 

[phykell]

Do you have a single phase DB or a three phase DB (or both) in the house? Within easy-ish reach of the kitchen? What (if any) cabling is in place already?

I'd guess at going single phase from what's been said so far, but the above might throw some other options up.

Cheers,
Colin

The consumer unit (CU/DB) is located roughly 20 metres away from the cooker and there are two (2x) 6mm T&E cables running from the consumer unit to the cooker.

 

[winston1]

OK - I was just looking at the cables and I believe they're both 6mm T&E so they should handle the power using 3-phase or single phase just fine. It would be interesting to see the wiring inside the appliance and based on what's been said here, I'm going to drop the manufacturer an email to ask for more information regarding the potential failure of one of the phases.

If it is wired as 3 phase failure of one phase just means that those parts of the cooker on that phase won’t work. Of course if wired as single phase and that phase fails none of the cooker will work.

 

[plugwash]

I see a number of downsides to wiring a 3 phase supply for a domestic cooker.

1. Space in the distribution board. A 3 phase MCB takes up 3 times as much space as a single phase one.
2. RCD protection, most brands don't do a 3 phase RCBO as-such. Schnider do a "Vigi" unit which clips onto the size of a MCB and effectively turns it into a RCBO, but it's expensive and means your MCB+VIGI combination takes up 6 modules of space! Now strictly speaking cookers don't need to be RCD protected, but if the cable is concealed in a wall or partition then practically it needs to be either RCD protected, run in steel conduit, or run in a cable type like SWA that incorporates an earthed metal layer.
3. Local switching. While i'm not sure if it's a regulatory requirement, the normal expectation in the UK is that cookers will be provided with a local switch/isolator. In a domestic kitchen, the expectation is that said switch will be a flush mounted accessory matching the others in the kitchen. Practically every range of accessories will offer DP plate switches and Cooker control units, TP+N plate switches are far more esoteric.

 

[JohnW2]

If it is wired as 3 phase failure of one phase just means that those parts of the cooker on that phase won’t work. Of course if wired as single phase and that phase fails none of the cooker will work.

You seem to be assuming that the loads (e.g. heating elements) within a cooker supplied with 3-phase are all wired as single-phase loads (i.e. P-N). Is that necessary the case (I have no idea)? If not, then I would imagine the behaviour if one phase were lost would be less predictable, wouldn't it?

 

[plugwash]

Given that the manufacturer gives the option of wiring the cooker as single phase, I think it's reasonable to assume there are no loads wired P-P.