Garage Rewire

[vwes59]

For a change its nice to have a clean slate to work to. Client wants their garage rewired (and boy does it need it!) so they can have the following:

Washing Machine, Tumble Dryer, American Fridge/Freezer, Outside socket, outside lights, workshop tools all 13A type such as circular saw etc.

Garage already has a 6mm cable connected back to the house consumer board via a 32A MCB and is RCD protected.

The existing cabling is a real rats nest and just isn't suitable for purpose, so its all being ripped out along with the old Wylex rewireable fuse board which just hasn't been wire correctly - I suspect multiple DIY'ers over the years have just added things into it.

Anyway I digress. My thoughts were this.

New consumer unit with a 63A main switch (7 available ways), existing 6mm cable terminated into it.
All cables can be clipped direct as it's in a garage with an open truss roof so loads of room to run cables neatly.
All the "kitchen" type appliances on a 4mm radial to a 32A MCB.
Workshop appliance(s) on a 2.5mm radial to a 20A MCB. This should be adequate to deal with any inrush current.
Outside socket on it's own 2.5mm radial to a 20A MCB.
Indoor lights on a 1.5mm 6A MCB
Outdoor lights on a 1.5mm 6A MCB

Giving the client an extra 2 ways if necessary for expansion.

Yes I suppose I could put the kitchen appliances on a ring, but its extra cabling and given I can do clipped direct I can do a 4mm radial on a 32A breaker (4mm is 37A clipped direct).
Could I get away with a 16A MCB for the tools ? Well, perhaps given they aren't industrial grade tools, just the ones you would get from a DIY store, but I want to allow for any inrush current, a 10A would probably trip.

Yes it would be better to tap off the incoming tails via a Henley block, but there is no isolator switch which means pulling the 100A fuse if I wanted to do it - just seems too much for this particular job.

If I've worked this all out correctly, the 6mm cable back to the 32A MCB should be more than adequate unless everything was running at the same time at full load all the time, which is highly unlikely. I suppose I could up it to a 40A MCB, but I don't think its necessary.

Just wondered what other peoples thought were on this.

 

[Pete999]

For a change its nice to have a clean slate to work to. Client wants their garage rewired (and boy does it need it!) so they can have the following:

Washing Machine, Tumble Dryer, American Fridge/Freezer, Outside socket, outside lights, workshop tools all 13A type such as circular saw etc.

Garage already has a 6mm cable connected back to the house consumer board via a 32A MCB and is RCD protected.

The existing cabling is a real rats nest and just isn't suitable for purpose, so its all being ripped out along with the old Wylex rewireable fuse board which just hasn't been wire correctly - I suspect multiple DIY'ers over the years have just added things into it.

Anyway I digress. My thoughts were this.

New consumer unit with a 63A main switch (7 available ways), existing 6mm cable terminated into it.
All cables can be clipped direct as it's in a garage with an open truss roof so loads of room to run cables neatly.
All the "kitchen" type appliances on a 4mm radial to a 32A MCB.
Workshop appliance(s) on a 2.5mm radial to a 20A MCB. This should be adequate to deal with any inrush current.
Outside socket on it's own 2.5mm radial to a 20A MCB.
Indoor lights on a 1.5mm 6A MCB
Outdoor lights on a 1.5mm 6A MCB

Giving the client an extra 2 ways if necessary for expansion.

Yes I suppose I could put the kitchen appliances on a ring, but its extra cabling and given I can do clipped direct I can do a 4mm radial on a 32A breaker (4mm is 37A clipped direct).
Could I get away with a 16A MCB for the tools ? Well, perhaps given they aren't industrial grade tools, just the ones you would get from a DIY store, but I want to allow for any inrush current, a 10A would probably trip.

Yes it would be better to tap off the incoming tails via a Henley block, but there is no isolator switch which means pulling the 100A fuse if I wanted to do it - just seems too much for this particular job.

If I've worked this all out correctly, the 6mm cable back to the 32A MCB should be more than adequate unless everything was running at the same time at full load all the time, which is highly unlikely. I suppose I could up it to a 40A MCB, but I don't think its necessary.

Just wondered what other peoples thought were on this.

Don't think the 6mm or the 32A mcb will be adequate for the supply.

 

[GBDamo]

What's the feed to the garage in?

Attached or detached garage?

Could do with some selectively.(personally I prefer discrimination, it's a word that doesn't get a lot of use these days?)

Really comes down to what is likely to be used together. If you got washer/dryer/fridge& tools cycling together you could challenge the 32A feed.

Me, I'd go for something like...

20A radial for washer/fridge (MI/load permitting)
20A radial for Dryer.
20A radial for sockets.
6A lights.

All in 2.5mm² or 4mm² depending or routings, obviously not the lights.

If possible I'd like to get the feed off an RCD and use an RCBO board in the garage.

Would need to see it in the flesh to be sure though.

 

[MJPD29]

What's the feed to the garage in?

Attached or detached garage?

Could do with some selectively.(personally I prefer discrimination, it's a word that doesn't get a lot of use these days?)

Really comes down to what is likely to be used together. If you got washer/dryer/fridge& tools cycling together you could challenge the 32A feed.

Me, I'd go for something like...

20A radial for washer/fridge (MI/load permitting)
20A radial for Dryer.
20A radial for sockets.
6A lights.

All in 2.5mm² or 4mm² depending or routings, obviously not the lights.

If possible I'd like to get the feed off an RCD and use an RCBO board in the garage.

Would need to see it in the flesh to be sure though.

You won't need rcbo board for garage if there's rcd protection at source. There will be no point as you won't achieve distribution between 30ma devices.

 

[vwes59]

Garage is attached to the house, and the feed is 6mm T&E from the house consumer board (from 32A MCB) to the Wylex board in the garage, approx 10m run clipped direct currently. MCB in the house is protected by an RCD which I've tested and works.

Yes, I agree with the possibility of further protecting the circuits with RCD's or RCBO's (I wouldn't have downstairs lighting on the same RCD as the downstairs sockets for example), but you wouldn't know which RCD/RCBO would trip in the event of a fault in this case. I'm sure I've read somewhere you can "force" the issue, but I can't remember where I read it.

The absolute max load that could be seen in the garage is 42A, but that's only if everything was running at a full load 24x7 and most of the appliances are temp controlled, or would only run at full tilt for short periods, so I applied diversity according to the OSG, but yes belt and braces I could run a new 10mm cable from a 40A MCB.

 

[timhoward]

It feels a little bit close for comfort.
Quick calculation - washing machine 3000w, tumble drier 2500w, fridge 200w, freezer 200w = 25 amps assuming they are all modern relatively efficient appliances.
Are outside lights halogen - they could add a couple of amps.

You won't need rcbo board for garage if there's rcd protection at source. There will be no point as you won't achieve distribution between 30ma devices.

Agreed - with additional note that if a fridge/freezer is in garage it would be good to know in house if something in the garage is causing tripping. I'd stick with RCD in house and MCB's in garage.

 

[telectrix]

what's the earthing arrangement at the house? if it's PME then the cpc in that 6mm ain't gonna cut it as a bonding conductor.

 

[GBDamo]

You won't need rcbo board for garage if there's rcd protection at source. There will be no point as you won't achieve distribution between 30ma devices.

Thinking more along the lines of nuisance tripping and losing everything in the house for something in the garage, especially with O/S lights and sockets.

 

[vwes59]

House is TNS, and all lights both inside and out are/will be LED. As for the wattage requirements, have taken the values from the manufacturer from everything both in place and planned, along with expected inrush currents from the workshop tools.

 

[GBDamo]

It feels a little bit close for comfort.
Quick calculation - washing machine 3000w, tumble drier 2500w, fridge 200w, freezer 200w = 25 amps assuming they are all modern relatively efficient appliances.
Are outside lights halogen - they could add a couple of amps.


Agreed - with additional note that if a fridge/freezer is in garage it would be good to know in house if something in the garage is causing tripping. I'd stick with RCD in house and MCB's in garage.

A fridge freezer will be in daily use and if on its own RCBO circuit nuisance tripping will be reduced to a minimum.

Having the lights go out to alert you to a garage fault is one way of doing it though.

 

[vwes59]

Just a quicky. I knew I'd read something about selectivity but in this case it would be really fiddly to get a selective RCD upstream of the board in the garage to agree with BS7671, and the board doesn't really allow me to get the MCB off the RCD and be independent. If I was going to do any of that, I'd get the DNO in to put in an isolator and just tap off the tails directly.

 

[Pretty Mouth]

I'd have it way more simple than you have planned:

Garage board
32A ring final for all the sockets
6A lighting circuit for all the lights
RCD protection at main house CU. It's all in the same building anyway.

I see no point in dividing the installation up further than this.

 

[telectrix]

if the 6mm is clipped direct, it does not, in itself, require RCD protection, so split the tails and fit a 40A MCB in it's own enclosure via henleys. don't faff about. get it right first time. seal fairy has loads of meter seals.