how to connect the following?

[sparkymarky123]

ok guys i'm an aircraft electrician so i have little knowledge of domestic electrics (honesty check )

Info: I have run 20 metres of 6mm swa to my garage from a 13a spur off house ring main. (This is protected at the house c.u by the existing 32a mcb 30a split load mccb for the existing ring)
The swa is terminated in a junction box at the garage to take 2.5mm t&e around the garage. The 2.5mm goes in through the garage wall straight into a double power socket then into a 3 amp switched fcu to run two lights- a PIR flood outside and a 6ft fluorescent tube.

1) does this all sound ok so far? I hope so dont want to buy anything else!!!

2) how would you connect the lights? i have bought loads of 2.5mm t&e as i thought that would be for the lighting but now realise i would have been better with 1mm or 1.5mm. BUGGER! still going to try using the 2.5mm though as i have bought it now.
(N.B i have also put a double gang light switch on the wall- a 2 way one) I have no idea how to wire the lights so that the pir has a permanent live so that it will work all the time and how to wire the flourescent tube so that it is switched............... i've seen about a million ways to wire lights on the net but none yet that cover my installation!

thanks for any help!!!!!!!!!!!!!!
mark

 

[Guest112]

why have you used 6mm swa from a 13A spur?

 

[Paul.M]

Looks like your out of your depth on this one, the same if I tried to rewire a plane.

This work could be done in a much better way, all you need is a domestic electrician and a few more parts. Post up your location and I'm sure one of the lads can help you out with this.

 

[sparkymarky123]

I used 6mm swa as I wanted a 20a fused spur off the main (as i may use a compressor etc and after calculating the volts drop i wanted to keep the volts drop fairly low over the 20+ metres run) but the guy at the electrical factors said no a 13a spur rather than a 20a.............. thinking i should have stuck to my guns !

my location is truro, cornwall.................. any help appreciated and yep fully appreciate my skills as an aircraft electrician are worthless when it comes to domestic

 

[Paul.M]

why have you used 6mm swa from a 13A spur?

Is it because he found it laying around at work?

Can you take the swa to the cu or run a new circuit from the cu in the house to the swa?

 

[Paul.M]

Ok scrap my last post.

To tap into the ring main using a 13A fsu and 6mm swa is not against the regs but there are better ways of doing it.

 

[sparkymarky123]

Hi paul, no i went and bought it It wasnt through a lack of trying to "borrow" some from work though

in response to your question, yep i was originally going to run from the house c.u but it is at the opposite end of the house and just too much hassle trying to run it all the way through the house- hence the spur method as i'm using a socket which is right next to the house rear door, leading out to the garage.

i realise that would be a better way though

i know i'll only have 2.83A of lighting (hence the 3amp fcu)
but will occasionally use a compressor and heater which could end up being around 4000 watts total, i.e 17a

Vd would then be 18m x 19.83A x 7.3 / 1000 = only a 2.6 vDrop, well within the 4%/(3% lighting) but of course, you have to add that v.drop to whatever the length is of the ring i have spurred off (assumedly!) which i dont know the value of so thought it best to play safe and go for 6mm......

 

[Paul.M]

Could you tell us what you are planning on powering in the garage? You could be over loading the house ring.

 

[sparkymarky123]

Ok scrap my last post.

To tap into the ring main using a 13A fsu and 6mm swa is not against the regs but there are better ways of doing it.

I'm thinking of going back to the shop and getting the 20A spur i wanted so i can appliances in the garage and hence the reason for choosing the 6mm in the first place. Yep I would've gone smaller than 6mm if only using a 13a spur as it does seem overkill.

 

[sparkymarky123]

yep sure. lighting= 1x PIR flood (500w)
1x fluorescent (60w)
= 2.83A lighting

 

[Guest112]

he mentioned he wants to run a compressor in his garage

 

[sparkymarky123]

power= 1 x lead lamp 60w
1 x compressor (occasional use only) 2115 w (so 9A)
1 x heater (occasional use only) 1500w (so 6.38A)

so: power total = 15.38A (plus nominal lead lamp)
+ lighting total= 18 A total load

which is why i wanted a 20a spur......... I think i'm going back to get the guy to change the 13a spur box for a 20a so i can actually use what i want in the garage

 

[Paul.M]

If you need 20A in the garage you've not got much left on the house ring. Get some one in to help you with this, I'm sure one of us can get a cable from the cu to your garage a lot easier than you think.

 

[sparkymarky123]

so...........i think that leaves 14A spare on the downstairs sockets ring (32a mcb) in the house before its overloaded.

I only run tv/sky box in normal use on this downstairs socket ring (about 600 watts use according to the electricity monitor which obviously is only a couple of amps) as when i'm in the garage i wont be using kettle/toaster (which if on together could take me over the 32a limit by my calculations).

am i on the money or a mile off??? thought i'd worked out loads/overloads and volts drops etc ok, but as a newbie am always ready to be shown the light!

 

[sparkymarky123]

yep no worries, anyone live in the cornwall vicinity on the forum?

 

[Engineer54]

power= 1 x lead lamp 60w
1 x compressor (occasional use only) 2115 w (so 9A)
1 x heater (occasional use only) 1500w (so 6.38A)

power total = 15.38A (plus nominal lead lamp)

which is why i wanted a 20a spur, think i'm going back to get the guy to change the 13a spur box

Will you ever use the compressor and heater at the same time?? Also, the compressor only runs for what, 3 or 4 minutes at a time? The only thing i can see being in anyway restrictive is the starting current of the compressor, you may need to change the ring circuit B type MCB for a C type. Other than that i can't see a problem with your present loading...

 

[Guest112]

nothing sounds wrong really but not best practice having a 20a spur off a ring isnt the best option as your putting a heavy load on one point of the ring whuch isnt recommended

 

[Paul.M]

Your not a million miles off but in my opinion your leaving it to chance that your not going to be using to much current.

Good point from E54 about using a type C rcd and from Peter D.

 

[sparkymarky123]

thanks for the replies guys engineer54- i wouldn't have to run the compressor and heater at the same time but it would be preferable in order to dry spray paint.
Paulm- i see what you're saying actually. even just using kettle could take me over the 32a limit. iots a 3kw kettle so 13a on top of the 18a= 31a. getting near isnt it! i will only use the compressor and heater maybe once/twice a month but see what you're saying...........

 

[Engineer54]

I reckon the 13A supply from the FCU will be fine, not the best practice. Far better to run a 6mm T&E from the CU to connect to the 6mm SWA on a 25A/32A MCB then onto a 3 way garage CU. A bit more cash to dish out, but better all round...

The main point is, that compressors only run for a very short period to compress the air, then shut off until the pressure drops to a set level, before starting up again for another short period...