Workshop electric problems!

[Zebsport]

Hi Guys,

After helping building my brothers workshop he's now done the electrics. Please don't shoot me down about Part P, i have explained this several times to him.

He asked me to take a look (i'm not an electrician) to see what I thought. In the workshop he's got an 40A RCD CU, with 6A for lights, 16A for sockets and a 32A feed to his 3hp air compressor (yet to be switched on).

This all seems fine (perhaps higher amp RCD?) but the problem arose when I checked the supply from his house. He's taken this from a spare 32amp mcb on the RCD 63A side of his house CU. This already has 3 x 32A (sockets) and a 50A (shower) on it plus his new 32A for workshop. So here comes the question!
1. Should he increase the house RCD to 80A and change the mcb to the workshop for a much higher rating?
2. He now has 2 RCD at both ends is this bad practise?
3. Would it make sense to remove feed from the house CU, split the tails (there is an isolator switch on the incoming) and have the feed straight down to his work shop. Totally seperate from the house CU.

Any advice much appreciated,

Cheers Zeb

 

[sparkwright]

The main question here is what size cable has been used to feed the workshop?

 

[sparkwright]

Does the compressor need a 32 amp supply? How many kW is it rated at?

 

[sparkwright]

What type of cable has been used to supply the workshop? SWA? How has it been installed?

Are they any spare non-RCD ways in the house consumer unit?

 

[Zebsport]

The cable to the workshop I think its 16mm. In fact slightly larger than the cable coming in to the house from the lane! His pal bought it around on his way home from work, and cut it of a wooden drum on his trailer.

If you need more info i'll give him a ring

thanks for quick reply

 

[Zebsport]

Air compressor 3.0hp 2.2 kw. I'll find out if the cable is SWA, give me 10 minutes.

 

[sparkwright]

If SWA, have both ends been properly terminated with cable glands; and is the armouring connected to earth, preferably at both ends?

If he can do pictures, even better.

 

[sparkwright]

Air compressor 3.0hp 2.2 kw. I'll find out if the cable is SWA, give me 10 minutes.

The air compressor only needs to be on a 16 amp breaker in 2.5 mm cable. What size cable was used for this circuit?

 

[Zebsport]

the cable is not SWA its been put in condulit and in a trench about 4ft down. Its about 120ft from house to workshop and he put an extra earth rod at workshop end.

 

[dingbat]

the cable is not SWA its been put in condulit and in a trench about 4ft down. Its about 120ft from house to workshop and he put an extra earth rod at workshop end.

Here we go then! Stand by for the 'c' word!

 

[sparkwright]

Is the earth wire is the cable used as well? Or does the earth only come from the earth rod? If so, has he done any tests to confirm he has a decent earth here?

 

[Zebsport]

thanks Sparkwright we will change air compressor to 16 amp breaker will leave cable as 2.5mm twin and earth.

 

[sparkwright]

Stand by for the 'c' word!

Is the 'C' word what I think you mean?

 

[Zebsport]

the earth both runs back to the house CU and is earthed at the workshop end via an earth rod.

 

[sparkwright]

thanks Sparkwright we will change air compressor to 16 amp breaker will leave cable as 2.5mm twin and earth.

You don't want a radial circuit in 2.5 mm cable on a 32 amp mcb.

I take it the sockets are wired in 2.5 mm. I assume they are a radial circuit; and not a ring circuit.