Morris Minor Owners Club

In the spring I want to run a power cable from house to garage, I posted a while back will an associated issue. This time I am trying to add the amperage of all likely plant that I will be using, although not all at the same time. Hopefully I have attached a picture of details of two welders I have, and to show my ignorance on the subject would be grateful to know if there is enough info there to determine the current in amps each would draw. This will of course assist me in selecting whether to use SWA cable of 6mm or 10mm.[frame][/frame][frame][/frame]

The MIG tells you it can draw as much as 32 amps, so the 6mm will be fine - especially as the draw won't be continuous.

Thanks, and I presume the arc welder rated at 100 amps is the output. The info says it can be run from a 15 amp socket.

Hi Les, here is a cable size calculator , https://www.tlc-direct.co.uk/Technical/ ... eDrop.html

Thanks Richard, I do have that particular calculator but not sure what temperature to enter, trying different values makes a lot of difference to the cable size, also number of circuits, I'll be wanting power and lights but assume I can split the light circuit when in the garage, therefore only needing one SWA cable running underground? The more I delve into this the more questions I find, for example SWA or SWA- Xlpe.

easy get a qualified electrician to do it
also check your insurance policy as doing it yourself may invalidate your insurance in the event of a claim

Don't forget the law changed a while back, the only electrics you can do yourself now are extensions run from existing power outlets. You can still do it yourself but must get the installation commissioned by a qualified electrician if my understanding is correct. I will stand by to be corrected

Probably wise to consult an electrician. When I extended the garage in 2014 and put in extra wiring it needed a dedicated consumer unit to meet the latest regs. Didn't cost a fortune and all certified to cover insurance requirements.

I will be getting someone qualified to replace the consumer unit and whatever is needed in the garage but wanted to dig the trench and bury the cable in preparation. Thought it a good plan to do the boring part myself, not sure an electrician would be too keen on digging a 20 metre run.

I had some similar work done last year. When the electrician came round to do the quote and it was agreed he left me two reels of cable and a couple of weeks for me to run it through to the shed and garage. He just connected up to the consumer units at each end and charged for the cable saving a few £'s labour. Both happy as I saved money and he didn't have to crawl through small loft spaces.

That sounds like a plan for you Les.

Les,

With the added information about a 20m cable run and I would guess that you would like a heater to run at the same time as the welder to keep you cosy, a 6mm cable is not big enough. I would suggest that a minimum of 10mm cable will give you a bit of headroom for future 'expansion'.

The TLC calculator with SWA, 20m underground, 30°C with 8kW load shows 10mm, but if you increase the load up to 11kW, i.e. MIG welder, heater and some lights, then a 16mm cable is required. For the same load and using a SWA XLPE or Hituf cable drops it back to 10mm (just).

Thanks for that Richard, I had decided on 10 mm, now I need to consider your thoughts. I find it difficult to reconcile the fact that the ring main I have installed around the garage has been run in conventional 2.5 t&e. Yet I need such a large cable to get the power to it. I suppose that's the trouble with not knowing too much about the subject.

It's only that MIG welder that is taking a large current -and then only for short bursts at high power....They are rarely used at full power. But obviously it should not be plugged into your 'ring main' - put in a dedicated high rated socket for that MIG.

Get the electrician round for advice, he'll be the one signing off the work. Just tell him what will be used in the garage/shed and he will advise accordingly. I would only be worrying about the cable size if it was me making the decision, you don't want to put something in that the electrician says it not up to the job or overkill.....
FYI I had a dedicated 16A socket put in for my welder.

Les,

The ultimate capacity of the ring main is 2 x 2.5 T&E as the feed to any socket can be from 2 directions around the ring. The main reason for the 'spur' single feed cable size is the current capacity required and that it is underground - distance only seems to kick in at >70m.

The TLC calculation jumps from 4mm to 10mm when the kW capacity increases from 6kW to 8kW, which does seem a bit disproportionate, even allowing for the power loss increasing as the square of the current in the cable.

I would think that an electrician would suggest 10mm for the feed cable, but worth checking.

Les, talk to the sparks who is going to sign the work off! (S)he's the only person that matters here!

Yes I've now concluded that's right. Initially it was my idea to get the donkey work out the way so it was virtually a matter of new consumer units and connecting but it's getting too involved, and probably not worth risking any difference of opinion with an electrician.

Don't give up Les, wait to see what the electrician says. I don't see anything difficult in asking what cable to put in and if they will supply it, although they may want to see the cable in the trench to check it is deep enough etc before it is covered in. Get a few quotes as I found each electricians opinion was different.
Ask how much they charge for digging a 20mtr trench. That may decide if you pick up the spade or leave it in the shed.

Thanks, can't get cracking until around March, so time to explore all these options.