Swa cable size for welder

[Mrstauf]

Hi

Im going to be running power to my new garage and want to size cable large enough to run a small welding set rated at 140 amp

The run of swa from the house to garage is 100m, and if i size that at 140amp it comes out at 70mm cable!! But the welding set is a 13a 3 pin plug type, and even manufacturers say you can run it off a 2.5mm extension lead up to 25m long, so should i actually size it off the mcb it will be feeding (20amp) as that comes in at 10mm, or could i even get away with 6mm? As 90% of time all it will be powering is lights

Ta

 

[Iggifer]

Ignore the amp rating of the welder, it is irrelevant in this calculation.

If it runs off a 3-pin plug as per MI, then assume the load as 3kW.

If you were to JUST have the welder, and say 10w of LED lighting, you MIGHT get away with 6mm, but why chance it? You're already going to be spending £270 ish on 100m of 6mm, why not just spend the extra £100 and get 10mm, then you can happily run the welder, boil a kettle and have enough fluorescent battens to make the welding safe.

100m is a LONG run! Jealous of your garden!

 

[PrenticeBoyofDerry]

Probably 6.0mm would do, but I be tempted to throw 10mm in.

 

[Mrstauf]

Ok thanks,

Yes think i may as well go for 10mm to be on safe side,

It is a long run! Its an old farm house and its a long path up to garage, very steep and very annoying!

 

[ericmark]

As a general rule 25 volt plus a volt per 25A so 140A will need 31 volts so ohms law supply at 230 volts approx 19 amp.

So at 20A and 100 meters a 10mm² cable will give a volt drop of 8 volts over the amount for lights but under the amount for power so likely to be good enough as long as lighting selected which will stand a little over normal volt drop.

With 6mm² volt drop at 20A would be around 13.2 volt over the permitted volt drop but likely a inverter welder would still work OK. Using either HF florescent or LED lights likely these would work on that volt drop so likely there would not be too much of a problem although not strictly complying.

With a TN-C-S supply with an ELI of 0.35 likely at the garage with 6mm² you will still have an ELI of 1.01Ω so one should get away with it even if not strictly to the rules.

As an electrician I would have to work out volt drop and as a result at 16A and with 10mm² cable I would get 6.24 volt drop so within the 6.9 volt allowed but as a DIY'er I know with LED lights with a 20A MCB and 6mm² cable I would get away with it. You have to decide.

Note with a non inverter welder the strike amps are much higher and you may have a problem with a B16 MCB in fact even a B20 MCB may not hold. Using a C20 MCB the ELI would not be good enough but with a RCD that should not really be a problem. Again for an electrician having to sign an electrical installation certificate this may present a problem but as a DIY'er likely you would not worry.

 

[JohnW2]

As a general rule 25 volt plus a volt per 25A so 140A will need 31 volts so ohms law supply at 230 volts approx 19 amp.

That 'general rule' may give reasonable estimates in some cases, but since the OP's welder apparently comes with a 13A plug (and instructions that it can be used with a 25m 2.5mm² extension lead) suggests that it is 'way out' in this case.

Kind Regards, John

 

[ban-all-sheds]

Im going to be running power to my new garage and want to size cable large enough to run a small welding set rated at 140 amp

Have you applied for Building Regulations approval yet? If so, what did you say, or by default allow your LABC to assume, would be the way that compliance with Part P would be achieved?

You can't promise one thing then do another - they don't like that, and people have had completion certificates withheld as a result.

Also, you should read this regarding permission from your DNO to use the welder:

//www.diynot.com/diy/threads/welding-socket-needed-for-17th-edition-board.417054/#3236375

 

[Mrstauf]

Thanks again for replys

Building regulations approval? Electrician who if fitting it will be registering it with building control if thats what you mean, im just digging the trench and laying the cable!

Shouldn't need permission for the welder, its just a 13amp plug in job, doesn't need its own socket

 

[ban-all-sheds]

Electrician who if fitting it will be registering it with building control if thats what you mean, im just digging the trench and laying the cable!

In which case he will have to say that he did all of the work, so the only person you can ask about the cable to use is him. And you also need to confirm what he wants to do about checking your trench etc - does he want to inspect it before the cable goes in, or before it is backfilled etc.

Shouldn't need permission for the welder, its just a 13amp plug in job, doesn't need its own socket

Did you actually read that topic, and this: http://www.enwl.co.uk/docs/default-...nce-for-interference-with-supply.pdf?sfvrsn=5 ?

 

[ericmark]

As a general rule 25 volt plus a volt per 25A so 140A will need 31 volts so ohms law supply at 230 volts approx 19 amp.

That 'general rule' may give reasonable estimates in some cases, but since the OP's welder apparently comes with a 13A plug (and instructions that it can be used with a 25m 2.5mm² extension lead) suggests that it is 'way out' in this case.

Kind Regards, John

I am sure you know it takes well over 13A to blow a 13A fuse. Also set to 100A many welding sets will run on 13A there it nothing forcing one to run the set at maximum setting.

With an inverter welding set most of the spikes are removed and it does not really upset other users of the DNO supply and unless some one complains the DNO is unlikely to know you have a welding set.

With other types it can cause large dips on the supply and also mains born interference. All it takes is for a neighbour to complain they may be unaware the problem is caused by you and blame the DNO.

 

[JohnW2]

I am sure you know it takes well over 13A to blow a 13A fuse.

I do, but I don't believe that any responsible manufacturer would put a 13A plug on something if they knew that it's running (not starting) current was 19A or 20A, would they?

Kind Regards, John

 

[ban-all-sheds]

Firstly, we don't know that this is made by a responsible manufacturer - I've not looked, but I'd be pretty confident making a bet that there's flaky Chinese tat on sale on eBay.

Secondly, we don't know that the welder originally came with a 13A plug on it.

Lastly, it might be that it's a C&N welder, specced down to the point where at some pathetic duty cycle and setting which actually makes it next to useless it scrapes in for connection via a 13A plug.

//www.diynot.com/diy/threads/welding-socket-needed-for-17th-edition-board.417054/page-3#3237452

 

[westie101]

All it takes is for a neighbour to complain they may be unaware the problem is caused by you and blame the DNO.

Who will investigate and if they find you are responsible can disconnect your supply.