2 consumer units or 1?

pappasmurf · 5 Apr 2021

Had an Electrician come round and recommend using 2 consumer units on a complete re-wire of a 6 bedroom house. 1 consumer unit (Wylex 19 way) was for the complete house and the other consumer unit (Wylex 5 way) was to be dedicated for the kitchen area only, with the fridge and freezer having their own ring main from this 5 way consumer unit. Can anybody tell me as to the reason of why he decided to go down this route of separating the kitchen with another consumer unit? He did tell me but I seem to have forgotten. Is it because of maybe some sort of interference from the condensers from the fridge and freezers? I have myself since then configured a list of the RCBO distribution within the 2 consumer units. See below for the RCBO configuration of each Consumer Unit...

Main Consumer Unit (Wylex 19 Way) :-

1. Immersion Heater

2. Ground Floor Ring Main (Ex. Kitchen)

3. 1st Floor Ring Main

4. 2nd Floor Ring Main

5. Air Conditioning (SWA 2.5mm T&E)

6. Boiler (Spur)

7. Through Lounge Lighting

8. Downstairs Hallway/Porch/Dining Lighting

9. 1st Floor Hallway Lighting

10. 2nd Floor Hallway Lighting

11. Bedroom 1 Lighting

12. Bedroom 2 Lighting

13. Bedroom 3 Lighting

14. Bedroom 4 Lighting

15. Bedroom 5 Lighting

16. Bedroom 6 Lighting

17. Ground Floor Shower Lighting

18. 1st Floor Shower Lighting

19. 2nd Floor Shower Room (New Loft) Lighting

Kitchen Consumer Unit (Wylex 5 Way) :-
1. 45A Cooker (Not really Needed, but put in anyway)

2. Kitchen Ring Main

3. Fridge/Freezer Ring Main

4. Kitchen Lighting

5. Spare (Possible Bell Transformer)?

333rocky333 · 5 Apr 2021

Not much scope for Expansion there, maybe a 3 phase commercial board fitted with a Single phase conversion kit maybe a better solution

flameport · 5 Apr 2021

pappasmurf said:
some sort of interference from the condensers from the fridge and freezers?

No.
There is no reason to have some of the circuits in a separate consumer unit.
It's just a metal box, it makes no difference to anything.

As for the rest - do you really want 14 individual lighting circuits?
Why rings?
Why the fridge/freezer on a separate circuit?
Why the boiler on a separate circuit?

JohnW2 · 5 Apr 2021

pappasmurf said:
.... 7. Through Lounge Lighting
8. Downstairs Hallway/Porch/Dining Lighting
9. 1st Floor Hallway Lighting
10. 2nd Floor Hallway Lighting
11. Bedroom 1 Lighting
12. Bedroom 2 Lighting
13. Bedroom 3 Lighting
14. Bedroom 4 Lighting
15. Bedroom 5 Lighting
16. Bedroom 6 Lighting
17. Ground Floor Shower Lighting
18. 1st Floor Shower Lighting
19. 2nd Floor Shower Room (New Loft) Lighting ....

That really isn't necessary. Even for a large house, two or 3 (or perhaps even 4) lighting circuits is generally more than enough, particularly in these days of LED lighting which means that any one room will only use a tiny fraction of what is available from a standard 6A lighting circuit.

Kind Regards, John

ericmark · 5 Apr 2021

If not using RCBO's I can see reason so 4 RCD's not two, but with RCBO's see no reason.

SUNRAY · 6 Apr 2021

In another thread Sunray said:
Sorry, no beer this time.

The CU fitted in 2016 seems to have been a good quality total rewire and much of the decorating has not been done so chases are still visible.

The other side of the wall are a column of 3x12 way CU's, first is filled with a main switch and 10x6A RCBOs, the next has 12x6A RCBOs and the 3rd has 3x6A RCBO making a total of 25. one for each light switch in the building, each perfectly labelled with Dymo.

Sure enough the appropriate RCBO was half cocked, I just had to turn it off and on and get out as fast as the smell could propel me, dropping the mask, gloves and blue over shoes in the wheelie bin by the gate.

Not often I speak to God but I thanked him on that one.

https://www.diynot.com/diy/threads/light-not-working-after-blown-bulb-replaced.548260/#post-4676477

bernardgreen · 6 Apr 2021

Having separate RCBOs for each bedroom does have some benefits.

If all the lighting is on one RCBO ( or MCB ) then when a lamp goes pop and trips the MCB all the rooms lose their lights.

Separate RCBOs also provide some isolation between any Switched Mode devices ( dimmers, LED drivers ) whose high frequency switching may cause them to interact with each other leading to unstable operation.

Having more than one sub consumer unit can reduce the amount of cable installation required. A main consumer unit as the single point of isolation with sub mains protected by MCBs feeding the sub consumer units which have RCD and MCBs ( or RCBOs ). It is easier to install a single 10mm² cable ( sub main ) than to run several cables all the way a single consumer unit for the whole house. .

Harry Bloomfield · 6 Apr 2021

pappasmurf said:
1 consumer unit (Wylex 19 way) was for the complete house and the other consumer unit (Wylex 5 way) was to be dedicated for the kitchen area only, with the fridge and freezer having their own ring main from this 5 way consumer unit.

Who's idea was it to use so many separate circuits? If it was his suggestion, I would be asking him if he had ever done a rewire before. 10 circuits for the lighting alone - wow, is this a castle? I would suggest maybe 4 lighting circuits at most should cover it.

There are advantages to having multiple circuits, in that a fault or need to isolate, means not all lighting is off, but that could partially be done by alternating lights on two circuits in an area, to retain some lighting.

sxturbo · 6 Apr 2021

If the price is reasonable then why not have so many circuits?

There is nothing wrong with what's been offered, over the top? maybe yeah, but will it cause you any issues functionally? Nope.

It will make it super easy to diagnose a fault though, not that there should be any faults after a re-wire.

pappasmurf · 6 Apr 2021

oi Harry, as I explained in the thread. "I" separated/planned these circuits in the consumer units!...so don't make me have to open up a can of whip ass on you!...its just to separate everything nicely for fault finding purposes with minimal disturbances to the other circuits!
I just need to know is it is wise to have 2 consumer units and why?

sxturbo · 6 Apr 2021

pappasmurf said:
oi Harry, as I explained in the thread. "I" separated/planned these circuits in the consumer units!...so don't make me have to open up a can of whip ass on you!...its just to separate everything nicely for fault finding purposes with minimal disturbances to the other circuits!
I just need to know is it is wise to have 2 consumer units and why?

It doesn't matter how many consumer units you have. Though may look a little silly if there are lots.

As someone else has said you could look at a commercial CU, but £££.

Having a seperate CU will make it neater and easier for wiring, you will have a substantial amount of cables going into the consumer unit from all the circuits you have requested.

The majority of what you have asked for would be halved if wired the traditional way, with a light circuit for each floor and a ring main for each floor, with kitchen seperate.

ETAF · 6 Apr 2021

You dont seem to have many spare for future
A lot of lighting as discussed , BUT what about
I assume all GAS cooking , I have 2 electric Ovens/microwave built in, each separately wired from CU being 16/20A and needing dedicate wiring.
HOB Electric ?
Are you having something like a Quooker heater in kitchen, or other types of heating appliance
Outside Lights, As so much lighting is seperate, i would have them seperate
Car Charging? - possibly if not now may be needed for future - fast charge or dedicated charger to CU - 13A socket takes hours to charge
Do you have Power for a Garage or outbuilding ?
Garden ? Outside power , for items in garage
Shower Power - you mention Lighting for shower rooms, but nothing to power the shower(s) themselves

AndyPRK · 6 Apr 2021

as said the amount of lighting circuits is bonkers.
1 per floor is plenty

JohnW2 · 6 Apr 2021

sxturbo said:
If the price is reasonable then why not have so many circuits? .... There is nothing wrong with what's been offered, over the top? maybe yeah, but will it cause you any issues functionally? Nope.

It's not "what has been offered" but, raher, what the OP is suggesting himself.

As you say, functionally there is nothing wrong with what was proposed and, as you go on to say, it would make any subsequent fault-finding easier. However, the main downside is the considerably greater about of cable (and installation of cable) required, particularly in the OP's 3-storey house.

Kind Regards, John

JohnW2 · 6 Apr 2021

sxturbo said:
It doesn't matter how many consumer units you have. Though may look a little silly if there are lots. .... Having a seperate CU will make it neater and easier for wiring, you will have a substantial amount of cables going into the consumer unit from all the circuits you have requested.

Particularly in a 3-storey house, and most particularly a very large one like mine, there are advantages in having multiple CUs - for example, final circuits can be kept to sensible lengths, not only saving cable and work but also meaning that both VD and Zs for the parts of the house most remote from the origin of the circuit (e.g. on the top floor) can be minimised by having large CSA distribution circuits feeding each CU.

I have probably gone OTT, but I have at least one CU per floor (4 floors, including the cellar), plus one for outdoor stuff, adding up to some 7 in total, all fed by 16mm² or 25mm² distribution circuits.

Kind Regards, John

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2 consumer units or 1?

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