Three phases in single domestic kitchen grid box. OK or not?

[Mark42]

I'm fitting a small kitchen in my remote office/workshop with a limited, existing, supply (3 phase/20A MCB on a long 4 x 10mm SWA).
I need to think carefully about diversity and load balancing.
My proposed solution is to install individual final circuits for every appliance (Small hob, Small oven, Extractor, 2kW stored water heater, fridge, microwave). Each from a separate RCBO, none over 16A, loads spread equally across the phases.
For neatness, I'd like to put all the local DP isolation switches into a single, deep, 6-gang grid enclosure.
This means there'd be both 400V in the box, and multiple sources of supply. If this is noted internally, is it OK? I don't want scary labels on the outside of the switch plate.
What do you reckon?

 

[Strima]

If all from the same supply problem. No need for labels. As long as conductors are identified correctly all is good.

If all phases are from the sameD DB then it’s the same supply.

People tend to be scared of three phase. It is always wise to be wary but it’s not the devil.

 

[davesparks]

With a 20A MCB protecting the distribution circuit any 16A MCB installed downstream of it will be more of a formality than actually doing anything useful.

The regulations require that where the nominal voltage to earth exceeds 230V, and wouldn't normally be expected to, a label stating the maximum voltage present be fitted. So there is no requirement to fit any such label for the grid switch you are proposing, however it is sensible to provide some warning for anyone working on it in the future as it is unusual and could catch someone by surprise.

Why do you need local DP isolators for the appliances?

 

[Risteard]

I'm fitting a small kitchen in my remote office/workshop with a limited, existing, supply (3 phase/20A MCB on a long 4 x 10mm SWA).
I need to think carefully about diversity and load balancing.
My proposed solution is to install individual final circuits for every appliance (Small hob, Small oven, Extractor, 2kW stored water heater, fridge, microwave). Each from a separate RCBO, none over 16A, loads spread equally across the phases.
For neatness, I'd like to put all the local DP isolation switches into a single, deep, 6-gang grid enclosure.
This means there'd be both 400V in the box, and multiple sources of supply. If this is noted internally, is it OK? I don't want scary labels on the outside of the switch plate.
What do you reckon?

A 400V label isn't required as Uo (voltage to Earth) doesn't exceed 230V.

 

[naylorpd]

Many modern hobs can be connected to two phases of a 3 phase supply, if it helps when balancing the loads. The hob is likely to be the largest power consumer. Give or take, the hob on 2 phases and oven on the third is likely to be fairly balanced in itself, ignoring other appliances.

 

[MJPD29]

It's fine. You'll find 3 phases at light switches and grid switches in many places.

 

[Mark42]

Thanks everyone for the helpful replies.

Many modern hobs can be connected to two phases of a 3 phase supply, if it helps when balancing the loads. The hob is likely to be the largest power consumer. Give or take, the hob on 2 phases and oven on the third is likely to be fairly balanced in itself, ignoring other appliances.

Yup, oddly enough I today downloaded the manual for the old hob I have in my store, which has exactly that - a two phase connection option (but not three). It has two induction zones.
So perhaps if the hob goes on L1 and L2, and the immediately adjacent oven on L3, they could be protected by a standard, cheap, three phase MCB, or RCBO as if they were one appliance. Why not?

It's fine. You'll find 3 phases at light switches and grid switches in many places.

Thanks, and agreed.
But usually protected by a single 3P breaker, not three or more single phase RCBOs potentially all over the DB? That's the complication which made me think about it.

With a 20A MCB protecting the distribution circuit any 16A MCB installed downstream of it will be more of a formality than actually doing anything useful.

Agreed, but I hoped it might provide a bit of discrimination, and prevent a 200m walk if the main supply 20A MCB trips. I also want to use RCBOs locally, to introduce the earth leakage protection which is not present on the distribution supply.

Why do you need local DP isolators for the appliances?

I don't really understand. Why wouldn't I? I always though it was standard practice!

 

[MJPD29]

Thanks everyone for the helpful replies.


Yup, oddly enough I today downloaded the manual for the old hob I have in my store, which has exactly that - a two phase connection option (but not three). It has two induction zones.
So perhaps if the hob goes on L1 and L2, and the immediately adjacent oven on L3, they could be protected by a standard, cheap, three phase MCB, or RCBO as if they were one appliance. Why not?


Thanks, and agreed.
But usually protected by a single 3P breaker, not three or more single phase RCBOs potentially all over the DB? That's the complication which made me think about it.


Agreed, but I hoped it might provide a bit of discrimination, and prevent a 200m walk if the main supply 20A MCB trips. I also want to use RCBOs locally, to introduce the earth leakage protection which is not present on the distribution supply.


I don't really understand. Why wouldn't I? I always though it was standard practice!

You can find them wired off seperate breakers when wired in singles, possibly 3 banks if lights fed from the different phases all off 3 separate 10a mcbs In a switch bank

 

[Taylortwocities]

I don't really understand. Why wouldn't I? I always though it was standard practice!

Having a array of isolation switches for everyone (including grid switches) the sort of thing that kitchen fitters and designers think you ought to have. But there is no regulation that says you must have them.
personally, in your situation, I would put in a larger CU And split out your circuits at that point.