Electrics to Garage!!

[dinga]

Sorry guys to start another thread on electrics to garage but I have trawled through the existing threads and really just want to clarify a few things before going any further

Basically I had a sparky over to quote me for installing electrics to the garage and this was on the pretence I ran the cable and got the parts for him from a shopping list he supplied. I have now installed a run of approx 40Mtrs (about half underground and half clipped to wall) of 3 core 4mm SWA from outside the house where the mains comes in off the street to inside of the garage, I have a 40Amp MCB for the existing CU in the house and an IP65 rated CU for the garage with a 40Amp RCD, 16Amp MCB for a couple of sockets and 6Amp MCB for the lights.

Basically....
1) has the sparky quoted the correct parts for the job as now looking at the forums it seems that a 6mm or even 10mm would be the prefered option over 4mm??
2) Can you connect the SWA directly to the Garage CU with a gland (he didnt specify metal)??
3) Its a fairly new house with a standard electric box on the front wall with a plastic pipe running into it and the electric boards cable terminating inside. Guessing he was going to run the cable into this box which im now dubious about? Not entirely sure why but im now nervous that he knows what he's talking about (with the original cable size quoted). can he bring a new cable into this box to get to the house CU or is this for the electric board use only??

Any comments before I ring another sparky and waist a little more money would be usefull? Thanks

 

[Spark123]

What are you paying the electrician for? He should be terminating it.
Ask him about the run, I know the DNO don't really like anyone putting items onto their boards etc.
A quick check for a 40A circuit over 40m using 2C XPLE SWA shows a 16mm to be the correct size when there is a lighting circuit.
Do you actually need a 40A circuit? For a 32A circuit a 10mm would be sufficient and for a 20A circuit a 6mm.
I suppose he could be relying on the downstream devices (16A and 6A MCBs) for overload protection, however, personally I wouldn't as anyone can add a circuit or up the MCB size in the garage. Protect the cable with the correct size at source is far better imo.

 

[tSpark]

If you give that exact distance it will be easier to tell, If no lights where involved 4mm might be ok to give you a 20 amp supply.

But one things for sure, A 40 AMP MCB IN YOUR EXISTING CU IS NO PROTECTION WHATSOEVER FOR 4MM OVER THAT DISTANCE

 

[ricicle]

A quick check for a 40A circuit over 40m using 2C XPLE SWA shows a 16mm to be the correct size when there is a lighting circuit.

 

[Spark123]

Yep - single phase you use 2 core calc even though you can use 3 core cable
Use a 3 core calc and some software calcs assume 3 phase.
As there is a lighting circuit involved then the VD should not exceed 3%

 

[dinga]

Im laying the cable but not terminating it. But the main reason im posting this is that im now worried about the fact iv burried the wrong cable for him to terminate i.e. a 4mm cable hence why I started the thread. I dont really want to be asking him about the job if he's already got me to spend over £100 on the wrong cable. I dont really want to be digging up the cable iv already laid to then bury another cable. What all your advice is saying is I cant run lights and sockets of this cable?

 

[j4m3s1984]

Hi, i would say your 4mm cable would be ok as it will carry up to 40amps, which you say your mcb in the house is rated to anyway. Not sure about him going thro the electric boards box, seems like he's taking an easy option to get into the house. Not sure if its allowed or not. You would normally dig a hole beside the house where you are running the cable and drill a hole thro the outer wall into the house under floor level. Then run it to your consumer unit under your floor.

 

[ricicle]

Yep - single phase you use 2 core calc even though you can use 3 core cable
Use a 3 core calc and some software calcs assume 3 phase.
As there is a lighting circuit involved then the VD should not exceed 3%

Sorry mis-read the post so it looked a little strange . I know where you're coming from

 

[tSpark]

Hi, i would say your 4mm cable would be ok as it will carry up to 40amps, floor.

NOOOOOOOOOOOOOOOOOOOOOO

40mtrs Voltage Drop??? Lights (ie 3%)

Dinga 4mm is not suitable for 40 amp at 40mtrs infact its probably only capable of about 20 - 22 amps with a voltage drop of about 10.5volts at that distance

 

[dinga]

tSpark I take it you think it wont be ok LOL. So next question, how can i do this with minimal expense, i really dont want to put another SWA in as it would mean digging up part of my garden

 

[tSpark]

This really depends on the exact distance, I mean its one thing to work what swa you need, but really even then, we dont know the length of the final circuits connected to the cu at the end of it, as this also has to be taken into consideration because of further voltage drop

As a very rough guide though working on a 20 amp demand over 40 mtrs with lights MINIMUM 6mm unfortunately and to be honest I would always put in a minimum of 6mm to garages or sheds like this

 

[j4m3s1984]

Your right tspark, i never even acknowledged the fact it was 40m, sorry dinga. Half asleep here.

 

[hairyben]

4mm's kinda winging it, 6mm woulda been better.

scrub the CU, feed the whole lot via a 20a mcb with the lights on a fused spur, then it's not a "lighting circuit"...

 

[tSpark]

That sounds a lot better HB

 

[dinga]

Look thanks guys, im glad something positive has come out of this. I really didnt want to dig up the cable and lay another one damaging my newly laid lawn. So before I go ringing a different sparky (Definately not going back to the other one now iv seen your comments) to use the 4mm 3 core he should use a 20Amp MCB in my house CU and as the cable is at the meter cupboard on the front of the house can he terminate in that or should he be routing outside of it? What should then be in the garage? I know i ask alot of questions but looks like iv already been burned and want to know whether he agrees with your cencus before I pay anybody.