Garden Electric supply.

[Briansmad]

THIS is what i have decided to do. I have wired a 6mm twin and earth to a 40AMP RCD which has two trip switches both rated 16Amps one of these will power my 25049 3C1.5 XLPE/SWA/PVC cable into garden buried 450MM deep then drilled through house wall and wired to RCD. How many WATTS would this power after the 25 meter cable terminates??? Or what would be safe to us?? Also am going to get building inspector round to make sure rules are followed.

 

[ban-all-sheds]

The cable is safe on the 16A breaker, but volt-drop will limit you before you get to that. You've not said how long the internal 6mm² run is, so say around 12A - 2.75kW.

BTW - don't have 2 RCDs in series....

 

[Briansmad]

BTW - don't have 2 RCDs in series not sure what you mean by this? Cable run inside house is ten meters. House circuit breaker that i wired garden circuit breaker into is 32 amps. Stright wire from there into the 40Amp RCD for garden.

 

[Briansmad]

Also could somone please tell me the difference in cable size. I oppted for 6mm inside house because i thought it would allow me More watts to use outside. Would it of been the same on 2.5 mm Twin and earth?? If i bought 4mm SWA cable what diff would it make or is all this to do with voltage drop. Sorry if i ask to much.

 

[Briansmad]

Some info on my garden lights required? I have bought 4 X 15mm blue LED fittings each with 5mt cable, 12 volt indoor transformer, 6 way junction box with 10mt cable. THE only thing is i need to connect 2 * 10 meter cables together will i get the same voltage/amps after twenty meters instaed of ten?

 

[Briansmad]

Is there anyone out there that can help me with this hopefully fitting this tomorrow if weather okay. Also how do you terminate this swa cable. have seen things where it says the end needs sealing with some kind of compound.

 

[mapj1]

//www.diynot.com/forums/viewtopic.php?t=27081
read this thread for the lowdown on terminating SWA cables...
As regards cable selection, voltage drop is current times resitance, so if a cable is fat enough to not overheat, then the voltage drop is the next thing that limits its maximum length fo ra given cross-sectional area ande terminal load.
See the cable calculators in the reference section for the gory detail
The 16a MCB limits you to 4KW, but if you want less than 4% voltage drop ( the rather abitrary abount chosen as 'negligable' in the UK regulations, for situations where the makers of the equipment don't specify any other operating voltage range) then IF all the load is at the far end of the, then with 1.5mm cable you mention, you should probably aim to stay nearer 3Kw, as B-A-S suggests.
To be honest even if the voltage drop calculation is exceeded the worst that happens is that the lights dim a bit when a large load is connected. A problem in an operating theatre perhaps, not so much in the garden - its routinely seen that the garage lights flicker when the welder fires up, and no-one really looks that surprised and rushes out to fatten up the supply cables..

 

[ban-all-sheds]

BTW - don't have 2 RCDs in series not sure what you mean by this?

Apologies - I misread your post - I followed what appeared to be a sequence (with my emphasis):

I have wired a 6mm twin and earth to a 40AMP RCD which has two trip switches both rated 16Amps one of these will power my..cable into garden buried 450MM deep then drilled through house wall and wired to RCD

So I thought you had == T/E => RCD -> MCB == SWA ==> RCD

Cable run inside house is ten meters. House circuit breaker that i wired garden circuit breaker into is 32 amps. Stright wire from there into the 40Amp RCD for garden.

Also could somone please tell me the difference in cable size. I oppted for 6mm inside house because i thought it would allow me More watts to use outside. Would it of been the same on 2.5 mm Twin and earth??

Using 2.5mm² in the house would give you a bigger volt drop, but it would have made little practical difference - assuming the maximum load of 16A, your 15m of 1.5mm² SWA will drop 7V, and the 6mm² T/E about 1.2V. 2.5mm² T/E would drop 2.9V.

If i bought 4mm SWA cable what diff would it make or is all this to do with voltage drop. Sorry if i ask to much.

You would drop fewer volts or be able to carry more current. Have a play with the TLC calculator - it's designed to tell you what cable you need for a given load, so if you want to work out the voltage drop for a bigger cable, increase the length until the size you want pops up, then divide the volt-drop accordingly - e.g. if you're interested in a 20m run of something, and you have to take the length to 80m before the calculator spits out that size, divide the volt-drop it gives you by 4. When using the calculator for SWA always tell it that you've got 2-core cable even if you've got 3, or it will do 3-phase calculations.

However - you're now going to get the standard advice. A 15m trench, 450mm deep, properly prepared:

is probably not something you want to dig very often. What if you decide to have a sauna, or a hot tub? Or a bigger pool? I know the cable costs more, but installing 6mm² or even 10mm² SWA would mean you'd never have to do it again....

Some info on my garden lights required? I have bought 4 X 15mm blue LED fittings each with 5mt cable, 12 volt indoor transformer, 6 way junction box with 10mt cable. THE only thing is i need to connect 2 * 10 meter cables together will i get the same voltage/amps after twenty meters instaed of ten?

No, you'll get more voltage drop. Fortunately the current drawn by LEDs is quite small, so it won't be severe. ELV halogens are a nightmare for this - a 50W mains halogen draws a little over 200mA - the same brightness 12V bulb draws over 4A...

Try your LEDs and see if they look noticeably dimmer with the longer cable - if they do use a thicker one.

 

[Briansmad]

Thanks. Thats been a great help.