shed consumer unit

[gsc]

Hi,

I am looking to have a she/garage consumer unit running from my house 10 way 100A consumer unit.

An electrician told me he will get an rcbo into my house consumer unit and then run armoured cable from that to the shed unit. I am just wondering if that sounds right and how you think he's going to connect it to my house consumer unit..

I am having the shed unit which is 25m away from house unit because I want outside lighting and power to run power tools.

Any advice is greatly received.

GSC

 

[Richard Burns]

From what you describe the electrician probably knows what he is doing, it is not how I would do it but it is a viable option.
If he can put an RCBO into a spare way on the consumer unit then he is good to go.

 

[NDG Elecs]

Yep agree with RB. It depends partly on matters such as earthing arrangement and the current consumer unit, if a high integrity type then all good to go. If it's not I would used a sub board to eliminate possible nuisance tripping in the future. Especially if the armoured cable is being buried underground.

 

[Spoon]

Hi gsc. Welcome to the forum. What power tools are you intending to use in the shed? What size RCBO is the electrician thinking of using?

 

[gsc]

Rcbo 40A according to the electrician... things like a table saw, drill, circular saw and bits like that. Also a pressure washer but all these will not be used at the same time...

He said he would put the rcbo next to the mains and connect it with a busbar...

I don't know much but didn't know if that was acceptable...???

Armoured cable was going to be 6mm and running 40m.... He looked at all my things I would use including lighting and thinks it won't go over 6kw ever...

Does that sound acceptable?

Thank you for your help and advice because I would rather have other electricians agree with his method haha...

GSC

 

[Guest77]

Hi,

I am looking to have a she/garage consumer unit running from my house 10 way 100A consumer unit.

An electrician told me he will get an rcbo into my house consumer unit and then run armoured cable from that to the shed unit. I am just wondering if that sounds right and how you think he's going to connect it to my house consumer unit..

I am having the shed unit which is 25m away from house unit because I want outside lighting and power to run power tools.

Any advice is greatly received.

GSC

What do you do for a living?

 

[Darkwood]

As you have variable loading it must be assumed the rating of the rcbo is the load factor here for calculating volts drop even giving some diversity here the volts drop will not comply if referencing from the BS7671 and your the info supplied is correct, so no this is not designed correctly IMHO.

 

[Spoon]

There are different ways you can do this installation. People do things differently.
An alternative way would be to use a breaker in the house CU, as armoured cable doesn't need RCD protection. Then have a CU with RCD in the shed. This is also better in that if the RCD trips for any reason you don't have to go back to the house to reset it.
Also 6mm cable over 40 meters: depending on the manufacturers specs, its close to the 3% voltage drop allowed. I'm sure your electrician has got the manufacturers specs and worked all this out, so all should be fine.
Can I ask why you don't trust your electrician?

 

[telectrix]

There are different ways you can do this installation. People do things differently.
An alternative way would be to use a breaker in the house CU, as armoured cable doesn't need RCD protection. Then have a CU with RCD in the shed. This is also better in that if the RCD trips for any reason you don't have to go back to the house to reset it.
Also 6mm cable over 40 meters: depending on the manufacturers specs, its close to the 3% voltage drop allowed. I'm sure your electrician has got the manufacturers specs and worked all this out, so all should be fine.
Can I ask why you don't trust your electrician?

unless, of course, the house installation is TT.

 

[Darkwood]

There are different ways you can do this installation. People do things differently.
An alternative way would be to use a breaker in the house CU, as armoured cable doesn't need RCD protection. Then have a CU with RCD in the shed. This is also better in that if the RCD trips for any reason you don't have to go back to the house to reset it.
Also 6mm cable over 40 meters: depending on the manufacturers specs, its close to the 3% voltage drop allowed. I'm sure your electrician has got the manufacturers specs and worked all this out, so all should be fine.
Can I ask why you don't trust your electrician?

Manufacturers specs may give a different max load for cable but the voltage drop for a 70c rated cable 6mm would be the same I would have thought as coppers has a fixed resistive value at any given size whether you reference from the manufacturers or the BS7671 and will only change if the temperature rating of the cable was different.

 

[Spoon]

unless, of course, the house installation is TT.

Sorry tel, forgot about that.

 

[Guest77]

Yeah Tel has to chuck in a spanner haha

 

[Spoon]

Manufacturers specs may give a different max load for cable but the voltage drop for a 70c rated cable 6mm would be the same I would have thought as coppers has a fixed resistive value at any given size and will only change if the temperature rating of the cable was different.

I think it changes darkwood. Regs say 7.3. Eland say 7.9

 

[Darkwood]

I think it changes darkwood. Regs say 7.3. Eland say 7.9

Hmmm ! ... you sure the cable your reference isn't 90c rated ... as 7.9 is the mA/m figure for that?... manufacturers may give a different load value to the BS7671 but they cannot change the natural resistive value of copper as its a fixed constant at a given temp' and size regardless where you source the information.

 

[Spoon]

Hmmm ! ... you sure the cable your reference isn't 90c rated ... as 7.9 is the mA/m figure for that?... manufacturers may give a different load value to the BS7671 but they cannot change the natural resistive value of copper as its a fixed constant at a given temp' and size regardless where you source the information.

Sorry darkwood, you are correct, the spec sheet I had was for 90c.
Looks like the 6mm is not good enough for the 40 meter run then.

I think I may stop posting today.... just can't get thing right......

 

[Guest77]

6mm2 isn't enough on this occassion if a 40 amp design current, but a 20 amp supply may actually be adequate lol, but what I liked about your initial post was your question regarding why the op doesn't trust his spark, I like to know the answers to those questions, and asked what he did for a living as well, and I wasn't being sarcastic, I genuinely would like to know.

 

[Darkwood]

Sorry darkwood, you are correct, the spec sheet I had was for 90c.
Looks like the 6mm is not good enough for the 40 meter run then.

I think I may stop posting today.... just can't get thing right......

We all do dont fret... just wondered how Elend cables had managed to change the laws of Physics - a first since Einstein did it

 

[Spoon]

Just to say to the OP. The voltage drop for 6mm over 40 meters is not recommended. For 37 meters it's ok.

 

[gsc]

I hope I explained okay...

The House CU is a 10 way split load with 2 RCDs.. running different circuits... He said he would plug the RCBO (40A) into the mains switch of the House CU as there is a spare way and connect it via the busbar. Then run the armoured cable above ground to a CU with RCD on the shed...

It's the bit about the RCBO I am worried about... is that the correct way or is it possible that it could be an issue?

Thanks again..

Also MDJ I am a computer technician but I hope you aren't asking that question as a way to make me feel bad for asking if its safe...

GSC

 

[Spoon]

We all do dont fret... just wondered how Elend cables had managed to change the laws of Physics - a first since Einstein did it

haha... At least it's nearly Friday.