Protection against corrosion

[rustynails]

Hi all,

Do I really need 16mm SWA to supply an external garage with a 63A 16A Power 6A Lighting unit? Maximum demand would be 100% of 16 + 40% of 6 which = 18.4 rounded to 19. Current carrying capacity of 16mm is 64A although its like £7pm. Or am I getting confused. Should I be saying that the maximum demand is 63A?

It's a TT installation which will have the garage distribution circuit protected by a 32A MCB and then downstream the 63A breaker in the garage has a 30ma RCD protecting the sockets. Upstream there will be a 100ma Time Delayed RCD which will be fitted inside the consumer unit, making the RCD the main switch.

 

[malcolmsanford]

First off RN what do you envisage being plugged into these sockets that is going need 19amps of load? That is totally over the the top unless your using a welder???

With just a 32amp MCB protecting your sub main, the 63amp part of your clacs are a little superfluous don't you think?

The 63amps is the rating of the load the RCD can withstand, in the same way an 100amp Double pole switch is rated at 100amps .............but rarely does 100amp go through one

Now a more realistic loading in this set up IMO would be 4-8amps maximum at any one time .............so what size cable do you think you will need.

Once you size a cable on your load, length of run, installation method etc, add say 3-4 more amps for the just in case factor/anything that you might want in the future/perhaps you want a heater in there in the chilly months .

 

[rustynails]

Re: SWA size for garage sub..again!

First off RN what do you envisage being plugged into these sockets that is going need 19amps of load? That is totally over the the top unless your using a welder???

No welder, but sometimes I use a Table Saw, Mitre Saw although never usually at the same time.

With just a 32amp MCB protecting your sub main, the 63amp part of your clacs are a little superfluous don't you think?

Yes

Now a more realistic loading in this set up IMO would be 4-8amps maximum at any one time

Fair enough, but the lighting circuit powers 7/8 tubes as well. I appreciate not much more.

so what size cable do you think you will need.

Maybe 16mm was a little over the top, going on what you have just said and looking at table 4d4a in the regs I could use 6mm 38A CCC minimum with a 32A MCB, which could be a 20A MCB given what you've just said. My only question would be, is 6mm cpc enough? I guess 10mm would be more substantial.

Once you size a cable on your load, length of run, installation method etc, add say 3-4 more amps for the just in case factor/anything that you might want in the future/perhaps you want a heater in there in the chilly months .

Length of the run is approximately 18m. 60% buried.

:smiley2:

 

[malcolmsanford]

1. Unless it's a commercial type saw/mitre what are you look looking at watt wise 700/1000?

3. If fluorescent tubes then what 7/8 X 24watt or even 56watt that would be 448watts at the upper level and most likely HF so really 2/3 amps maximum

4. You can lay your pension/mortgage/and everything you own if your LIVES are 6mm then your 6mm CPC will be sufficient. But you could always use the Adiabatic

5. Even if you take it your permanent load is 15amps, remember we use Ib and not In then your vd on a 6mm cable @ 18mts would be less than 2 volts. So 6mm would be fine IMO

 

[Knobhead]

I've got to be missing something, corrosion ? ? ? ?

 

[Des 56]

I've got to be missing something, corrosion ? ? ? ?

There must be something about the username that sort of links to it

 

[amo]

I've got to be missing something, corrosion ? ? ? ?

Probably being the swa cable mentioned maybe ??