Long post and questions!!! (sorry)

[Doc955]

Hello all,

I've recently moved into a house which has an old style 6 way fusebox, circuits arranged thus:

40A Cooker.
6A CH pump/boiler/controls
30A Sockets (study, hall, beds 1 & 2)
30A Sockets (lounge/diner, kitchen, utility, beds 3 & 4) Single socket in garage is also spurred off this ring.
6A lights (upstairs)
6A lights (downstairs, bathroom & garage).

There's also a seperate single 45A fuse/switch unit for the shower.

We're doing the kitchen soon so I'm replacing the fusebox with a split load CU. I'm keeping most of the circuits as they are except I'll be putting the kitchen/utility on its own ring and running a separate feed for the garage.
Additionally, the shower (10kW) is on 6mm cable, so I'll be replacing that with 10mm.
Also the meter tails are currently 16mm so I'll be wanting to replace these with 25mm!

My questions are:

1) Who is responsible for the cabling from the master fuse to the meter and from the meter to the CU/fusebox? Is it the distribution company or me? I tried phoning them but was told by the robot to 'call back later', so I did, and was told to 'call back later' so I used the online enquiry. They'll get back to me within 10 working days............

2) Will the shower need a seperate RCD or can I just take it to a 50A MCB on the RCD protected side of the board (80A, 30mA RCD)?

3) I'm going to need at least 6 double sockets in the garage, I will probably be using some fairly heavy equipment in there (MIG welder, pillar drill, lathe - although not at the same time!!) as well as having the usual bits and bobs plugged in (freezer, phone, radio etc). My thoughts are to have a separate CU for the garage, fed by 6mm T+E cable direct from the CU (effectively using the CU as a junction box) and have a RCD and a 32A MCB ring for the sockets and a 6A MCB for the lights (6x36W flouro). Would this be OK or is there a better(correct!) way of doing it?
Also, should the sink/pipework in the garage be earthed back to the (garage) CU?

4) What size cable should I be using from the CU to the earth point? AT present it's 6mm.

Advice much appreciated.

(I will be notifying BC about this BTW )

 

[mdbalson]

The DNO is responsible for the DI tails from the Service head to the Meter.
The Consumer is responsible for the DI tails from the Meter to the CU.

2) Will the shower need a seperate RCD or can I just take it to a 50A MCB on the RCD protected side of the board (80A, 30mA RCD)?

You could put the shower on a 50A RCBO on the Non-RCD side of the CU, If you did that, then if the shower tripped the RCD it would ownly be the shower that goes off & not every thing else which is on the RCD side of the CU.

3) I'm going to need at least 6 double sockets in the garage, I will probably be using some fairly heavy equipment in there (MIG welder, pillar drill, lathe - although not at the same time!!) as well as having the usual bits and bobs plugged in (freezer, phone, radio etc). My thoughts are to have a separate CU for the garage, fed by 6mm T+E cable direct from the CU (effectively using the CU as a junction box) and have a RCD and a 32A MCB ring for the sockets and a 6A MCB for the lights (6x36W flouro). Would this be OK or is there a better(correct!) way of doing it?
Also, should the sink/pipework in the garage be earthed back to the (garage) CU?

What is the distance from the House CU to the Garage

What is the wattage of the of the welder

The garage would be a submain from the house CU

4) What size cable should I be using from the CU to the earth point? AT present it's 6mm.

By this do you mean the main earth cable from the service head to the CU, if so then you need to use a piece of 16mm Green/Yellow cable.



Matt

 

[Doc955]

Thanks for the quick reply Matt.

The DNO is responsible for the DI tails from the Service head to the Meter.
The Consumer is responsible for the DI tails from the Meter to the CU.

Thanks, that's what I thought.

You could put the shower on a 50A RCBO on the Non-RCD side of the CU, If you did that, then if the shower tripped the RCD it would ownly be the shower that goes off & not every thing else which is on the RCD side of the CU.

Good point! I should have enough spare space on the board to do that.

What is the distance from the House CU to the Garage

What is the wattage of the of the welder

The garage would be a submain from the house CU

The garage is integral to the house, probably about 15m cable run from the main CU to where the garage CU would be.

The welder's not huge, 100A. Not sure of the power draw.

By this do you mean the main earth cable from the service head to the CU, if so then you need to use a piece of 16mm Green/Yellow cable.



Matt

Yes, the main earth. I'll use one of the old meter tails and just shrinkwrap it in green/yellow.

 

[ban-all-sheds]

My thoughts are to have a separate CU for the garage, fed by 6mm T+E cable direct from the CU (effectively using the CU as a junction box)

Absolutely not!

If you're using 6mm² T/E is must come off a 32-45A breaker (depending on installation method), not directly from the CU incomer. Not that there would be a satisfactory way to connect the cable anyway.

The alternative would be to split the tails and take a feed via a switchfuse to the garage CU.

Whereabouts in the UK are you? Are you aware of Part P, if it applies?

Also, should the sink/pipework in the garage be earthed back to the (garage) CU?

No.

Where does the water supply pipe enter the property?

(I will be notifying BC about this BTW )[/quote]

 

[Doc955]

Absolutely not!

If you're using 6mm² T/E is must come off a 32-45A breaker (depending on installation method), not directly from the CU incomer. Not that there would be a satisfactory way to connect the cable anyway.

The alternative would be to split the tails and take a feed via a switchfuse to the garage CU.

OK, fair enough. So if I were to take a single cable feed from a 40A breaker to the CU in the garage, that would be OK for a 32A ring and a lighting circuit? 6mm cable would be suitable for the feed, yes?

Whereabouts in the UK are you? Are you aware of Part P, if it applies?

Well aware of part P, the work will be notified to local BC. I just want to make sure that I know what I'm going to do before I start (I thought that was a reasonably good idea!)

No.

Where does the water supply pipe enter the property?

The rising main comes in in the downstairs loo, which is between the kitchen and the garage. There's an earth point there already from when the new boiler was installed which is bonded back to the service head.

 

[Doc955]

Boing.

Anyone have any other comments?

 

[JohnD]

yes, it's too long. see if you can make a shorter post.

 

[securespark]

Do you really need a 32A ring in the garage? Would a 20A radial do?

Does a 40A breaker discriminate against a 32A?

 

[ban-all-sheds]

OK, fair enough. So if I were to take a single cable feed from a 40A breaker to the CU in the garage, that would be OK for a 32A ring and a lighting circuit? 6mm cable would be suitable for the feed, yes?

As observed, 32A seems like a lot for a garage. 6mm² will be OK, as long as it doesn't encounter any thermal insulation.

Well aware of part P, the work will be notified to local BC. I just want to make sure that I know what I'm going to do before I start (I thought that was a reasonably good idea!)

Apologies for that - not only did I miss that you'd already said that, I left it dangling at the end of my post in an improperly bracketed quote..

The rising main comes in in the downstairs loo, which is between the kitchen and the garage. There's an earth point there already from when the new boiler was installed which is bonded back to the service head.

No need to bond the water pipe in the garage then.

 

[Doc955]

Thanks for the reply.

Do you really need a 32A ring in the garage? Would a 20A radial do?

Probably don't need 32A at the moment but I may well need the extra capacity in the future. I suppose if I make sure the cable from the CU to the garage CU is capable, then it's not going to be a huge job to upgrade from a 20A radial to a ring in the garage itself.

Does a 40A breaker discriminate against a 32A?

Not quite sure what you mean. As I understand it, the 32A MCB in the garage is there to protect the socket circuit. Wheras the 40A at the main CU is there to protect the cable going to the garage, which also has to carry the supply for the 6A (although it will only be drawing about 1 amp)lighting circuit. If there's a fault in any of the equipment in the garage the 32A should always trip unless there's a fault in the cable between the main CU and the garage CU.

 

[Doc955]

As observed, 32A seems like a lot for a garage. 6mm² will be OK, as long as it doesn't encounter any thermal insulation.

I suppose I could run it initially as a 20A spur and upgrade the MCBs if I wanted to convert to a 32A ring in the future.

The cable goes from the consumer unit straight into the first floor void, then across the kitchen (in the floor void) then across the utilty room (in an insulated loftspace) before it gets to the garage. I'll make sure it's routed clear of the insulation.

Apologies for that - not only did I miss that you'd already said that, I left it dangling at the end of my post in an improperly bracketed quote..

As they say on the bike forums:- 'poor obs'.

Thanks for your input chaps, it's much appreciated.

 

[ban-all-sheds]

Does a 40A breaker discriminate against a 32A?

Not quite sure what you mean.

What he means is if there is a fault which causes a fast trip, will the 32A breaker trip before the 40A one.

Answer is probably "no guarantee" - i.e. a fault on the garage socket circuit might trip the 40A breaker, not the 32A one.

If there's a fault in any of the equipment in the garage the 32A should always trip.

No guarantee.

 

[Doc955]

Answer is probably "no guarantee" - i.e. a fault on the garage socket circuit might trip the 40A breaker, not the 32A one.

So worst case scenario would be that the 40A trips and the lights go out too instead of just the sockets going off. Not ideal, granted, but not a total disaster.

What's the solution then? A type C breaker at the main CU?

edit: Just read the thread you started on discrimination, I think I'll run the garage sockets on a 20A radial with a 40A MCB at the main CU and see how it goes.

 

[RF Lighting]

So worst case scenario would be that the 40A trips and the lights go out too instead of just the sockets going off. Not ideal, granted, but not a total disaster.

It might be if you are operating a rotating power tool, something happens and all the power goes off. While in the dark you table saw your arm off.

 

[Space cat]

Since the garage is part of the house, do you really need a separate CU for it. You could give it its own ring and lighting circuit from the main CU.
Is there any regulation that I don't know about that says otherwise?

I suppose one advantage of a CU actually IN the garage is that you wouldn't have to come back into the house covered in oil and sawdust - or worse - to reset a breaker.