My consumer unit as I want it

Cashman · Mar 19, 2021

Hi Guys,

I have designed the attached unit to replace the existing ones that are separate (1 =House/1 Outdoor shed and lighting)
I think it looks better all in one with 2 main Switches. Is this OK?
Appreciate our comments ,Cheers.

DPG · Mar 19, 2021

Why 2 main switches?
You don't get 63mA and 80mA RCDs. I think you are confused with the maximum operating current.
Outside lighting on a 16A MCB - maybe a bit OTT?
I would go for a full RCBO unit with an SPD.

Dave OCD · Mar 19, 2021

I think you'd be better off with a single 100a main switch then use individual RCBOs for all circuits. This would provide better discrimination in the event of an earth fault on any final circuit.

Dave OCD · Mar 19, 2021

Beaten to it by Daz, fastest finger first. ?

Cashman · Mar 19, 2021

DPG said:
Why 2 main switches?
You don't get 63mA and 80mA RCDs. I think you are confused with the maximum operating current.
Outside lighting on a 16A MCB - maybe a bit OTT?
I would go for a full RCBO unit with an SPD.

The 16A MCB is wrong . It is 6 A, sorry. 2 Main switches because I want Shed and outdoor lighting be separate)

Dave OCD · Mar 19, 2021

You'll achieve that with RCBOs.

Cashman · Mar 19, 2021

Cashman said:
The 16A MCB is wrong . It is 6 A, sorry. 2 Main switches because I want Shed and outdoor lighting be separate).

I have made another mistake in writing. These are 80A,63 A and 40A RCDs

Cashman · Mar 19, 2021

Dave OCD said:
I think you'd be better off with a single 100a main switch then use individual RCBOs for all circuits. This would provide better discrimination in the event of an earth fault on any final circuit.

Yes, RCBOs are better, I will have more space as well.

DPG · Mar 19, 2021

Cashman said:
Yes, RCBOs are better, I will have more space as well.

Makes sense to include an SPD as well.

Cashman · Mar 19, 2021

DPG said:
Why 2 main switches?
You don't get 63mA and 80mA RCDs. I think you are confused with the maximum operating current.
Outside lighting on a 16A MCB - maybe a bit OTT?
I would go for a full RCBO unit with an SPD.

I have uploaded the revised image. I will have a small consumer unit in the shed being fed from here. I am not sure if it is wise to feed the shed CU from a a RCBO in this main CU!?

DPG · Mar 19, 2021

Cashman said:
I have uploaded the revised image. I will have a small consumer unit in the shed being fed from here. I am not sure if it is wise to feed the shed CU from a a RCBO in this main CU!?

I think you would be best to get an electrician to give you a quote for this work. This will also ensure the necessary notification side is done.

pc1966 · Mar 19, 2021

Cashman said:
I am not sure if it is wise to feed the shed CU from a a RCBO in this main CU!?

That is a very wide question as it depends on what the shed is for, etc.

In the majority of cases (lights & couple sockets) just take it from a RCBO and it is fine.

In the minority of cases (used as a workshop, or big loads like a heated sex pond) then you might want it fed from a separate fuse-switch off the supply tails, but then you have to be sure the cable is safe without RCD protection (so in effect SWA all the way) and the garage CU then has to have a RCD or all-RCBO.

Cable requirements can also be influenced by the earthing arrangement for the supply and any extraneous metalwork at the shed such as metallic water pipes, etc.

But in all of these cases it is not DIY work, and in England and Wales it falls under Part P of the building regulations as notifiable work. Your best plan is to find a good electrician locally who is registered with one of the competent person schemes like NICEIC as they can do the necessary initial design and finally notify their own work without the fees building control normally charge to test & inspect.

Cashman · Mar 19, 2021

DPG said:
I think you would be best to get an electrician to give you a quote for this work. This will also ensure the necessary notification side is

pc1966 said:
That is a very wide question as it depends on what the shed is for, etc.

In the majority of cases (lights & couple sockets) just take it from a RCBO and it is fine.

In the minority of cases (used as a workshop, or big loads like a heated sex pond) then you might want it fed from a separate fuse-switch off the supply tails, but then you have to be sure the cable is safe without RCD protection (so in effect SWA all the way) and the garage CU then has to have a RCD or all-RCBO.

Cable requirements can also be influenced by the earthing arrangement for the supply and any extraneous metalwork at the shed such as metallic water pipes, etc.

But in all of these cases it is not DIY work, and in England and Wales it falls under Part P of the building regulations as notifiable work. Your best plan is to find a good electrician locally who is registered with one of the competent person schemes like NICEIC as they can do the necessary initial design and finally notify their own work without the fees building control normally charge to test & inspect.

The shed is wooden and I will have a CU with a 6A mcb for lighting in there and a 16 Am mcb for a single socket. That is it. I do not think that is a problem at all.

brianmoooore · Mar 19, 2021

Even if you go with your isolator for outside circuits idea, I don't see the reason for the second mains switch. The third RCD will serve this function.

pc1966 · Mar 20, 2021

I agree with @brianmoooore that you would be far better putting in a couple of double-pole switches for the outdoor stuff if you want a means of isolating them.

If they are off RCBOs then you won't have the risk of an outdoor fault tripping other indoor things, however, I would still prefer to have a simple and accessible means of isolation or control over external PIR lights or a shed/outside sockets just for peace of mind.

Is your shed already wired up?

I ask because if you are only needing sockets and some lights, then having a feed from something like a 20A RCBO could go to the sockets in the shed directly, and then a FCU with a 3A fuse would allow you to control some LED striplights or similar without the need for a 2nd CU.

However, if you have plans for more stuff in the future then having a small CU to wllow separated protection (to a degree) is a good idea. Remember though you won't get any meaningful selectivity between a 20A RCBO and a 16A, or even 6A MCB in the event of a hard fault, both would trip on the magnetic part.

My consumer unit as I want it

Cashman

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