Advice on garage supply

[Sparks321]

Hi i'm looking for some advice, i have been to look at a job to wire a garage. In the garage will be 3 double sockets and 3 lights. What my idea was is to run a 6mm 3core swa from a non rcd protected way on 40amp mcb to 40amp rcd double switch in a 2way garage unit which will be feeding a 20amp radail and 6amp lighting circuit. The length of the swa will be approx 22m run under the floor cavity and out to garage.

 

[Spoon]

Have a look at this mate... It might help.

 

[Sparks321]

I'm feeding a sub main board so my max power will be dependent on how many amps the sockets and lights pull.

 

[Spoon]

But you are fitting a garage CU with a 20A breaker for the sockets and a 6A for the lights. According to your post #1.

Did you look at the Youtube video? Do you understand it?

 

[hightower]

So you can work out what lights you are installing and their related current. Can't really do that with sockets, so got to work off the protective device rating.

 

[telectrix]

guys, i think we are in danger of over complication here. 6.0mm cable is more than adequate for the load and to comply with volt drop. it don't even need a calculation as it's what i would call well over the required parameters. obviuously, testing should be carried out, both dead and live, to confirm.tin hat on

 

[DPG]

OP, do you have calibrated test equipment? And what certs will you be issuing to the customer?

 

[Sparks321]

Yer this is what am sayin, i would rather oversize the cable for anythin extra in future aswel but without going over the top and as long as the fuse rating are adequate protection all should be good. Not had chance to watch video will look when i get home. Yes i get you gotta take volt drop into account but it is a straight forward install which seems to be getting made complicated. This question may sound stupid but say i ran a 4mm in and put on a 32amp mcb could that feed the 40amp rcd board?

 

[Spoon]

guys, i think we are in danger of over complication here. 6.0mm cable is more than adequate for the load and to comply with volt drop. it don't even need a calculation as it's what i would call well over the required parameters. obviuously, testing should be carried out, both dead and live, to confirm.tin hat on

Not over complicating things mate, just teaching the OP on cable cals. He says he need brushing up on it.

 

[telectrix]

agree with that. every installation should be designed so as to be adequate, but not over the top, esp in industrial where choice of cable size could have a huge cost difference, but what i;,m saying, is in OP's situation, the cost differential between , say 2.5mm, 4mm, and 6mm, is so small as to be negligible compared with the overallcost of the job.

 

[DPG]

Yer this is what am sayin, i would rather oversize the cable for anythin extra in future aswel but without going over the top and as long as the fuse rating are adequate protection all should be good. Not had chance to watch video will look when i get home. Yes i get you gotta take volt drop into account but it is a straight forward install which seems to be getting made complicated. This question may sound stupid but say i ran a 4mm in and put on a 32amp mcb could that feed the 40amp rcd board?

Not being funny, but if it is so straightforward an install, why do you need advice on it, and why can you not do the calcs?

Your question about the 4mm/32A breaker - is this a straightforward install?

I know this post might come across as being a bit arsey, but you are presumably doing paid work for a customer here.

 

[DPG]

Not being funny, but if it is so straightforward an install, why do you need advice on it, and why can you not do the calcs? Forum members aren't making it over complicated - they are just asking some basic questions.

Your question about the 4mm/32A breaker - is this a straightforward install?

I know this post might come across as being a bit arsey, but you are presumably doing paid work for a customer here.

 

[hightower]

it is a straight forward install.

And yet here you are asking for advice on it. Can't be that straight forward....

This question may sound stupid but say i ran a 4mm in and put on a 32amp mcb could that feed the 40amp rcd board?

Provided the rated current of the RCD main switch is equal to or greater than the expected load on the distro circuit (and therefore protective device rating at main board) I can't see what the issue would be with that.

 

[MDJ]

but it is a straight forward install which seems to be getting made complicated.

It is straight forward to us fella, but you seem to be in a right mess over it.

 

[Sparks321]

Basically it was reassurance that what i was doing was the best way as everyone always has a different way and a cheaper way of doing things.

 

[Richard Burns]

From what you describe without having seen the site it would seem to be the most appropriate method of installation.
There may be cheaper ways of doing things but they can often be significantly more dangerous.
With the load you anticipate the voltage drop should be OK on 6mm² and probably OK on 4mm² unless the garage lighting circuit is huge. 6mm² will allow future expansion if required, whereas the 4mm² would limit you to about what you have already planned.
Make sure you have a quality installation of the SWA especially if run underground so that it will last for years and not need repairs.
Using a local RCD is useful and having a core for the earth is also handy, just in case of armour problems. Remember it is more dangerous to run SWA rather than another cable type if you do not earth the armour properly.