Garage MCB/SWA

[Tony Gallagher]

I have trawled through numerous prior advices on this subject but can't quite find matching variables so please excuse me for taking you over old ground again. The bulk of the work will be done by a Canadian relative at the end of this month. (He built the garage last year). He is very competent but I am concerned by the differences in specification and practice. I will certainly be more confident if his proposals compare favorably with any advice that you are able to give me.

I need to power up my new garage (30M2) which incorporates a study+WC & basin+a sink in the garage area. I also intend to replace the house CU but I will use a local spark once the garage job is done. At the moment I have an overcrowded fusebox.

The maximum load iwould derive from:
LIGHTS Internal lighting say 400W...External lighting say 500W
STUDY 3Kw heater/computer/printer/scanner/copier
CLOAKROOM Instantaneous water heater 5.5Kw
GARAGE A second instaneous water heater5.5Kw/several 13a outlets for domestic power tools inc.,extension to lawnmower etc. and a small chest freezer at 5oow.
TOTAL: 20KW RATIONALISED TO c.10KW

The builder has already buried 5m of 3 core SWA from a point in the house's floor void which is 6m from the main CU.. I do not know what size the cable is. It looks substantial and imeasures 15mm dia??

QUERIES
1) Should the freezer to be excluded from RCD?
2) Should the sockets be on a ring or radial and/or separate for study and garage?
3) What to do with the two 5.5KW water heaters. By their nature they will be used minimaly and for a matter of seconds. They will both be within 2.5m of the location of the CU?
4) Can you guys tell from the 15mm., dia., of the SWA whether it is sufficient or should I chop a piece off to ID the rating accurately (got a feeling I know the answer)?
5) I was thinking of using a galvanised junction box at each end of the SWA with glands. At the garage end the box would be adjacent to the CU...What size cable should I use between the two?
6) On the house side would 10mm T&E be sufficient over the 6m run?
7) Given that the armour will be connected to earth should the core wire also be used? Isn't there an issue in running two earths in close parallel?
8) What size RCD ?


I hope that I am not stretching your patience with this lot.

Many Thanks in advance

Tony

I am in Scotland (Differs from part P)
Ihe property is PME

 

[Taylortwocities]

You should get someone who is truly competent to plan and install this. The loads you are proposing are the equivalent of a small house. Is your existing supply sufficient for the existing & propsed loads?

You say 'rationalised' to 10KW. Do you mean diversity?? If so you might know that you do not apply diversity to instantaneous water heaters so you've got 11Kw before you start!.

500W outside lights: is this Glasgow airport?

The SWA will have the size of the cores written on the outside sheath. Have a good look. 3 core 4mm SWA is around 15mm dia.

 

[Adam_151]

know that you do not apply diversity to instantaneous water heaters so you've got 11Kw before you start!.

Perhaps the OSG tables don't exactly comply with reality in this instance, I reckon that if they did get run together, then it wouldn't be for long, and if everyone was cleaning their hands in the garage after working on the car then theres not going to be many people in the house, running heavy applicances there.

I reckon the OP could get away with it if he:

A) Used a 16mm SWA submain from a 1361 60A switchfuse
B) Dropped the water heaters down to 4kw units
C) Has a 100A service and doesn't have electric shower


@OP, might be worth asking the DNO for a quote for a second service in the garage just for comparison, it would be a better way of doing things, and if its not daylight robbery it would pprobably be what you ought to go for

 

[Taylortwocities]

I agree, but if he has only 4mm that max 42A if its XPLE SWA.
If there is mains water pressure I'd put in a small Megaflo (70litre maybe) heated by its immersion. Then its only 3KW for all the hot water.

 

[davy_owen_88]

I agree, but if he has only 4mm that max 42A if its XPLE SWA.
If there is mains water pressure I'd put in a small Megaflo (70litre maybe) heated by its immersion. Then its only 3KW for all the hot water.

A small 15l unvented water heater would be ideal in this case where the only water used is for handwashing/dishes etc.

2kW and you don't need an unvented ticket to install it either.

 

[sparkydude]

a 15mm diameter cable is not substantial if thats the overall diameter of the outsside of the cable, probably is only a 4-6mm cable inside in which case 32-40A MAX loading If however each core is 16mm then not a problem with your proposed loadings,

Nick

 

[Tony Gallagher]

Hi Guys,
Sorry I’m slow getting back. NTL replaced my cable on Wednesday and I lost my connection within an hour of them leaving. They finally got it sorted yesterday.

Thanks for all your responses. Hopefully you will stay with me for a bit
Longer.....I’ll buy you a couple of pints if you’re ever around Glasgow.

TTC: My Canadian cousin, who will be installing this, is fairly competent. (He is a municipal building inspector and a Fred Dibnah like DIY fanatic). As for the planning, I do think we need some help particularly as UK & Canadian specs and practice appear to be oceans apart. If I don't have it figured out for him he will research it himself before starting. I would like to have that groundwork prepared.

Adam_151: You are spot on. I really don’t expect my bill to go up very much at all following this as almost all of the new usage is simply relocating from the house to the garage. My wife and I live alone except for our son who moves in whenever he is skint - which can be often and prolonged. I am disabled and the reason that the facilities are being put in is to reduce unnecessary to-ing and fro-ing for pees etc. My biggest draw on the power will be the 3Kw heater in my new study which is 8M2 and very well insulated.

There is one 8.5Kw shower in the house.
The supply is 100A
NICK: The SWA markings are (600/1000v 3/6 10237m)....So only 6mm right??
The proposed 500w outside light was a PIR flood but it’s a bit unsuttle anyway so I’ll use a pair of lanterns with 25w low energies.
I agree that the two water heaters are OTT. As the smallest unvented type that I have found is 7Ltrs., and keeping that hot for very occasional use is impractical, I could fit one 5.5Kw inline instantaneous type that can serve two draw off points.
I have a 50mm duct buried which could take a separate supply from the house CU (10metres) to run, the 3Kw heater, the study sockets and the freezer - total 4Kw. Or I could run new SWA and start over.

So! What do you think?
1) Should the freezer to be excluded from RCD?
2) From the above markings is the SWA a 6mm., Is it reasonable to run a separate cable for 4Kw or will I abandon the buried SWA and start again? Hmmm, probably?
3) Is a 32A mcb + 6mm T&E OK for a 5.5KW water heater. By it’s nature it will be used minimally and for a matter of seconds. It will be within 1m of the CU location?
4) I was thinking of using a galvanised junction box at each end of the SWA with glands. At the garage end the box would be adjacent to the CU...What size cable should I use between the two?
5) On the house side would 10mm T&E be sufficient over the 6m run from the new junction box to the CU?
6) Given that the armour will be connected to earth should the core wire also be used? Isn't there an issue in running two earths in close parallel? 7) What size RCD ?

Thanks,
I hope that you are still there.

Tony