Garage Feed from House

[Magnet]

Ok thanks for all your help ,just another question , if I am putting the 4mm2 cable in I thought it may be a good idea to put a 10mm2 cable into the loft at the same time in case the shower will be upgraded to a higher wattage , now it is a 8,5KW with a 6mm2 cable supplying it , I juts thought that it  would be better to do that  now and either leave it terminated into a Henley block or coiled up enough to reach the shower at a later date ! .

 

[binky]

good thinking, just don't terminate the 10mm into a consumer unit so it can't be 'energised'.

What sort of load are you expecting to use in the garage? Entire houses are often on a 60A main fuse

 

[Magnet]

good thinking, just don't terminate the 10mm into a consumer unit so it can't be 'energised'.

What sort of load are you expecting to use in the garage? Entire houses are often on a 60A main fuse

Just a couple of sockets and the clothes dryer that's it , it is running off the upstairs 2.5mm2 ring main at the moment ( for the last 20 years ) ,but I just wanted to run the feed for the garage on its own mcb  from a 16A/20A mcb from the 63A Volex RCD shower unit  ( the shower is on a 50A mcb ) I have already in place  , but it seems that is not a good idea ! , I understand that 4mm2 would be a good choice though .

 

[Lurch]

I just wanted to run the feed for the garage on its own mcb  from a 16A/20A mcb from the 63A Volex RCD shower unit  ( the shower is on a 50A mcb ) I have already in place  , but it seems that is not a good idea

I don't think there is anything wrong with that idea particularly, I think the issue was with you connecting everything up and/or the 2 RCD's in series issue. If the garage is protected by the RCD in the shower unit you don't need one in the garage.

Get your electrician to pop round for a look before committing to anything as there are a few ways to do the job.

 

[Evans Electric]

Magnet , the reason I mentioned an isolator is,    sub-mains like yours to a separate building should have the option of being isolated .  

However they change the Regs every month these days so I'm probably talking out of my ass.  

A rotary isolator also gives you something to gland off  the SWA .  

As the others said , I'd get the cable in and let your sparky connect it.      

 

[Magnet]

Magnet , the reason I mentioned an isolator is,    sub-mains like yours to a separate building should have the option of being isolated .  

However they change the Regs every month these days so I'm probably talking out of my ass.  

A rotary isolator also gives you something to gland off  the SWA .  

As the others said , I'd get the cable in and let your sparky connect it.      

OK , just purchased the  3core 4mm2 swa , question Evans Electric ,when you mentioned about it being able to be isolated , could not the 63A RCD switch in the Volex shower unit be used as a isolator , if there was a need to isolate the garage supply ! .

I am asking this in case I don't need to purchase a rotary isolator , I am sure if the Sparky was going to supply one it will cost more than I could purchase on my own , He did however not mention anything to me about getting a isolator switch , I said to him I would purchase the cable and whatever was needed , all he come back to me was a garage unit and the cable .

I could ask him again ,but I don't like to repeat myself to him , next time I call/message him is when I have the cable in .

cheers 

 

[Lurch]

could not the 63A RCD switch in the Volex shower unit be used as a isolator , if there was a need to isolate the garage supply ! .

You could, but then you can't use the shower either. Better than not being able to use anything at all though so up to you, not a requirement to have the isolator but a convenient individual isolator means you can keep the shower working if there is a fault in the garage.

I said to him I would purchase the cable and whatever was needed , all he come back to me was a garage unit and the cable .

Glands, cleats, adaptable boxes.... ?

I could ask him again ,but I don't like to repeat myself to him , next time I call/message him is when I have the cable in .

I would rather you called me with any queries before I turned up rather than turn up to find missing/incorrect parts, but then he doesn't sound like the sort of person who is all that bothered either way.

 

[apprentice87]

Look, the lenght of the entire circuit from the CU to the last socket is 25 metres..

Anyone else tried calculating what Zs will be.. 32A "b" curve.. Hmmmmm

john..

 

[Lurch]

Why?

 

[apprentice87]

Well, if you had a 32a "B" curve protecting the 4mm, [and you had 3 core] and a 20a "B" curve protecting the 2.5 at the point it joins the 4mm, [presumably a CU in the shed or whatever] it would be ok, [assuming Ze of 0.8] but god only knows what the op is planning.. [cannot be arsed to do the calcs for 2 core 4mm!!]

john..

 

[Evans Electric]

OK , just purchased the  3core 4mm2 swa , question Evans Electric ,when you mentioned about it being able to be isolated , could not the 63A RCD switch in the Volex shower unit be used as a isolator , if there was a need to isolate the garage supply ! .

I am asking this in case I don't need to purchase a rotary isolator , I am sure if the Sparky was going to supply one it will cost more than I could purchase on my own , He did however not mention anything to me about getting a isolator switch , I said to him I would purchase the cable and whatever was needed , all he come back to me was a garage unit and the cable .

I could ask him again ,but I don't like to repeat myself to him , next time I call/message him is when I have the cable in .

cheers 

Hi Magnet ,  I don't wish to complicate your job , sounds like you're getting there.   As I said above , as far as I know  a sub-main would need a double pole isolator , what you describe would isolate the shower too , as Lurchio has said.

A 40A  X 4 pole rotary isolator would cost you around  £19  inc VAT  and as I said , the SWA can be terminated to it.  

I don't know if its a Regulation or a Code of Good Practice  ...its something I've always assumed was necessary   .   Its up to you how you do it  . 

 

[Lurch]

if you had a 32a "B" curve protecting the 4mm, [and you had 3 core] and a 20a "B" curve protecting the 2.5 at the point it joins the 4mm, [presumably a CU in the shed or whatever] it would be ok

From what I can gather that is what the OP is planning, hence my query.

There's an actual electrician involved now so might as well just leave it up to him to worry about now!

 

[apprentice87]

Yes, i expect they will get it sorted!!

john..

 

[Magnet]

Well, if you had a 32a "B" curve protecting the 4mm, [and you had 3 core] and a 20a "B" curve protecting the 2.5 at the point it joins the 4mm, [presumably a CU in the shed or whatever] it would be ok, [assuming Ze of 0.8] but god only knows what the op is planning.. [cannot be arsed to do the calcs for 2 core 4mm!!]

john..

 

[Sidewinder]

Beety,

Where did you get that calc from?

There are a few glaring errors there for compliance with BS7671

 

[Magnet]

View attachment 7576

No idea what this is saying or meaning , Ime only wanting to put a cable to my garage from my house .

 

[Tony S]

I've got a headache  Guinness

 

[Magnet]

Beety,

Where did you get that calc from?

There are a few glaring errors there for compliance with BS7671

Like what !

 

[Sidewinder]

Where did the calc come from?

I'll give you one to start, operating temperature 75 deg C.

Can't use 75 deg C unless the connected equipment is rated @ 75 Deg C, most isn't.

Now you answer next as to where the calc came from.

 

[Tony S]

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