50 amp supply to garage

SWA I should imagine.

 

Going to be a 50 metre run, that's quite long. Without any calculation, my gut feeling is 16mm 2 core or 10mm 4 core with the cores paralleled to give an effective 20mm. Do not use the earth from the house in the garage, I do not know the supply type you have, use a local earth electrode and a 30mA rcd in the garage CCU. Other solutions are available if you care to design the circuit fully.

 

Doesn't necessarily need an electrode in nearly all circumstances the house earth can be utilised.

 

I included a caveat to cover that possibility.

 

It does come in at 16mm I was thinking maybe 25mm when I first read it, nice one Bob

 

So, you need to go to a wholesaler and get a cut length of what you want, as long as you are convinced you have the right conductor size. Remember, “too long” is better than “too short”.

 

Maybe a good idea to ask your sparks-if you have one

 

With my “other hat” on, if you really do have a 8kW compressor, you should advise your DNO, as that is likely to take a couple of hundred amps on startup. They may wish to limit the number of starts the motor has per day, as well as the timing. In a residential area you could well be affecting the quality of a lot of your neighbour’s supplies. Alternatively, they may insist you have a three phase supply.

 

I had been considering putting my tin hat on and making a similar comment.

Disturbing loads, top of page eleven.
https://www.nationalgrid.co.uk/downloads-view-reciteme/231979#

 

Use 16nn 2 core, the provision of an earth over this length is an expensive and unnecessary extravagance. Go down the route of a local earth electrode and a local 30mA RCD, it will save money and give an installation that no one can criticise for being unsafe or risky.

 

The steel will still need to be the equivalent cpc required size and I doubt the cost savings will be significantly less once the cost of the rod, pit etc are included.

 

Providing the armour does not need to support main protective bonding derived from a TN-C-S system then the armour can be used as the cpc.

 

Yes, as is often the case with most SWA installs. It's just that I have a thing about distributing the house earth as disconnection times for the external installation, and the hot tub that comes later, may not be met.

 

I think you need to get up to date regarding disconnection times.

 

Have a look at soft starting. No high in-rush current. Plus I read that the compressor is 6 kw, which really roughly is about 30 amps. With soft starting, it's only the 30 amp running current that you need consider. Apart from fault current, means of earthing etc...

Only problem being is initial cost of soft start. But it's worth looking at.