50 amp supply to garage

Mr PEA

Mr PEA

New Member
I plan on purchasing a new compressor which requires a 45amp supply.
So to air on the side of caution I want to run a 50amp supply from my house to my garage at the end of my garden.
The cable will run 10m from the consumer unit to reach outside, then 25m underground ( within a buried pipe) then a further 10m within the garage.
What cable is recommended?
 
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.
 
Bob Rathbone said:
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.
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It does come in at 16mm I was thinking maybe 25mm when I first read it, nice one Bob :)
 
So, 16mm SWA 3core ?
Sadly Screwfix only list 25m in 16mm
Will my sparky fit that in the consumer unit?
 
Mr PEA said:
. . . Sadly Screwfix only list 25m in 16mm
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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”.
 
adgjl said:
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”.
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Hopefully someone more intelligent can confirm that. But from what I've been reading on various posts within the forum I think that 16mm is more than adequate. In fact I thought I'd kind of concluded 10mm should be fine but a few of you here advise not. As I said i know nothing really.
 
techie said:
Maybe a good idea to ask your sparks-if you have one
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Haven't got one yet. I've been given contacts, which I'm waiting to hear back from. In the meantime I'm just researching really.

Further thought..
Would it be easier to join the SWA cable to regular cable once within the house? Routing the SWA through the house will be very difficult ?
 
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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.
 
adgjl said:
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.
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I get your trail of thought but it's 6Kw and has "Sequentially starting motors allow the unit to be run from 230V single phase power supply (45Amp minimum)"
 
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.
 
Bob Rathbone said:
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.
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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.
 
Refuse to Bend said:
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.
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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.
 
Bob Rathbone said:
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.
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I think you need to get up to date regarding disconnection times.
 
Mr PEA said:
I plan on purchasing a new compressor which requires a 45amp supply.
So to air on the side of caution I want to run a 50amp supply from my house to my garage at the end of my garden.
The cable will run 10m from the consumer unit to reach outside, then 25m underground ( within a buried pipe) then a further 10m within the garage.
What cable is recommended?
Click to expand...

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.
 
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