Cable size for Oxford welder

I had a 180 amp oil cooled welder sat in my workshop , fitted with a blue round pin plug (32a?) ,only the underground armoured cable feeding my workshop ring , is a piddly 2.5mm ..from a fusebox 50ft away . This is feeding a consumer unit in my workshop to which i fitted a ring and light circuit....The largest load is a 2hp motor on a lathe and a SIP 140amp buzz box welder. I was a little reluctant to use the oxford welder ,I thought it might be too much for the wiring although i did try it out at low power with a fly lead plugged in to a 3 pin metalclad socket .. no bang or fire !! A friend now has the welder .. and wants to use it in his outbuilding that has a consumer unit , that is fed with a 16mm underground cable 200 meters from the house supply .. The cable was run for lighting , and a couple of sockets for horse clippers / kettle .. I suggested having a dedicated blue socket fitted a so it can be plugged in . Will it be safe ? Volt drop issues ? Was i wise not to use it in my workshop on the 2.5mm?

At idle ,does a transformer welder use the same amount of juice as when its pushing a 4mm rod ?

Edited By Hacksaw on 24/07/2016 00:27:42

Edited By Hacksaw on 24/07/2016 00:35:40

At idle, the current used will be only transformer losses -although these welders were not designed for maximum efficiency at idle! Think here of the different amounts of heat produced when welding! If the welder had to dissipate the arcing current when idle it would soon melt!

There will be tables on the net giving maximum power and maximum distances for the cable run. I assume you really mean 16mm^2 conductors. That is a large cable, easily able to transmit a few kW over that distance. The tails on your meter are likely that size - good for 100A in that use.

Look at the rating plate on the welder. I doubt it will be more than 6kW and likely only 4 1/2. And that would be flat out. Voltage drop for the welder would only mean a slightly reduced welding current/voltage requiring a higher setting on the machine. Look at the consumer unit rating - that will have a supply rating and will likely include a 45A cooker breaker.

Common sense should prevail with only the welder in use as a high current userat the time, of course.

Cable size calculator **LINK**

Sorry, much as I understand the rationale, if anyone with slightly dodgy wiring tries to follow that tip they could end up with a house fire, so I have had to delete it.

FWIW its the switch on surge that is the biggest problem. I use an extension lead for my arc welder or it pops the breaker half the time. The MIG is better behaved.

Neil

Cable sizes are quite critical to get right and we (UK) are not allowed or supposed to do alterations to home wiring outside small jobs like change a socket outlet unless you are qualified to do so. The garage/workshop is on a 16mm2 supply, sub 10m cable run, to consumer unit which may seem a bit of over kill but did not want to be find the cable was too small at a later date. I've seen some really dodgy supplies to workshops and I have been guilty in the past, twin and earth is not really the cable to use outside, bigger is better.

Hi, not withstanding the common sense approach ref wiring sizes, I have an Oxford oil cooled and in my old shop it tripped the breaker every time if I forgot to turn the welding current down first it's called inrush current, a transformer can be considered similar to a big capacitor as in it needs ' filling' with lots of little wigglies as you turn it on, once on I never had any trouble welding.

.

Look up the differences between B, C and D type breakers. - The correct selection is designed to overcome this problem of initial inrush.

But first the supply to the workshop has to be adequate. No easy fix for that one other than to put ones hand into thy pocket and dig deep for correct sized copper.

Nick

Mark C just so its clear some work on the electrics fall under part P of building regulations see **LINK**

The wire won't reach to my workshop I use one or other of two RCD domestic sockets at front and back of house, each is on a normal ring main (small welder suitable for 13A plug - it's never blown a 13A fuse) and I don't want to reduce the day to day protection.

I have got a higher capacity 32A spur in the workshop (which in turn is on VERY hefty copper for up to 40A from the main box) (these amperages are approximate - I can't be bothered to go and check, but it was all done to the regs as of 2002)

Neil

Neil

Hi Hacksaw,

My advice would be for your friend to get an Electrician with current knowledge (no punn intended) to assess the installation. There are too many unknowns for anyone here, and I mean no disrespect to anyone, to provide solid answers to your specific questions (and I include myself, electrician working to 15th edition a few years ago).

Ideally any electric cable installed should have a fuse or circuit breaker rated to protect it. ie the 16mm SWA cable should have been installed with an appropriate protective device allowing for potential volts drop over the 200m that you mention. The potential volt drop is usually factored in when a circuit is designed and the cabling and equipment is chosen for the installation. If overloaded, the over current device would break the circuit before damage to the cable occurred. I'd doubt whether the 16mm cable would have any issues, a problem that seems to be posted in a number of forums relates more to not having the 32amp blue plugs installed and standard 13amp 3 pin plugs blowing fuses.

It would be interesting to know how much current a welder e.g. 180amp would actually pull from the supply. Anyone know ?

Ed.

If like me you had built your own house ( twice now) then you would have built the garages first so you could store tools & important gear.

Then you would have had the electric meter & supply placed in the garage so you could use electricity for the works & run the house supply from there when ready.

That way the workshop & garages do not have the problems others have . Called forward planning !!

It's a common misconception that transformers have an inrush surge current at first turn-on. In fact, the primary of the transformer is simply an inductive load, so the peak current resulting from energising it part way through the cycle can never exceed the normal peak magnetising current. It's just basic electrical theory as taught at school.

You might argue that connecting the primary when the secondary is loaded could explain this problem but that's not normally the cause and even then it's not an "inrush surge" issue so much as a "reflected load". And that shouldn't exceed the normal rated current anyway.

What DOES cause transient currents at turn-on is remanence ie residual magnetism in the cores due to the random timing of last disconnection (when the switch was opened) and random timing when the primary is next connected (switch turned on again). If the correct conditions occur, the core magnetisation is additive (volt seconds on the winding), the transformer cores can saturate and you get a very high transient current - essentially a short circuit on the primary winding. The typical saturation margin on the magnetisation current is surprisingly low.

Fitting a high current type C or D MCB can help to some degree but isn't always the answer, given what is actually happening. The ideal solution is a soft start circuit - usually a phase controlled triac or a timed resistor / relay. The latter is simpler but not straightforward, as you need a low enough resistance to drive the magnetising current close to where it should be but high enough to prevent saturation. You can also control (delay) the turn-on and turn-off events so that the flux is always controlled.

Murray

In practical terms:

I have owned an Oxford welder for more than 40 years, and I can tell you that it will require a heavier-than-domestic wiring feed, and appropriate trips (see Nick_G's post).

In a previous workshop, I began with a 16 amp industrial-style socket wired into its own fuse at the fusebox, but had endless trouble with the earth arrangements, so abandoned that temporarily many years ago. Using the welder via a 13A domestic plug into a good quality 13 amp socket for short welds the socket face plate soon had burn marks on it, and it got very hot if welding over a metre or so at a time. You can't really run more than about 110 amps with this setup. The 2.5mm2 wiring leading to the socket also got hot, which is a potentially serious problem.

So I would caution you not to begin by using a domestic wiring arrangement with this welder, but to install a proper high capacity fuse, thicker wiring and an industrial plug. Domestic wiring is a definite fire hazard.

I also have a large capacity fire extinguisher in the workshop, but that would not be much good if the wiring in the walls overheats.

One other problem is that when the welder is switched on there is a significant surge which can trip a domestically-rated fuse. The more often the fuse trips, the more prone it is to tripping. It's a cycle of despair relieved only by taking note of the differences between types and ratings of breakers (see Nick_G's post).

I'm hoping to add a different type of welder shortly, but it is clear that any welder capable of welding anything other than thin sheet (car body thickness) will draw more current than can safely be delivered via 13 amp domestic fuses and cables. The specs on many models make this clear, and I note that at least one manufacturer will not supply a 13A plug for their more capable welders.

Having said all that, the Oxford is a robust welder capable of heavy duty. I have not had a moment's bother with mine, despite miles of welding.

Marcus

Some helpful answers here ! Thanks. My friend is wealthy.. I'll advise him to get his sparks to fit a blue plug and dedicated cable into the consumer unit . He wont be welding much anyway ..

Marcus, I agree ,those old Oxfords weld lovely , and all day long without cutting out !

Probably cheaper to sell the Oxford (unless he was going to use the single point carbon brazing setup) and buy a 120 amp MIG. So much easier to use, runs off 13 amp plug etc etc.
And he won't do his back in moving the thing about.
BobH

Cable calculator :- www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html?cable=Twin_Earth&application=clipped_direct&max_perct_volt_drop=5&ambient_temp=25&no_circuits=1&circuit_layout=bunched&power=5&power_units=1000&voltage=230&length=50&submit=Calculate+Min+Cable+Size

Others are available

Frank

Edited By Neil Wyatt on 25/07/2016 21:46:18

I respect your care and attention Marcus, but the qualification on thickness of metal is not correct. I have a 150amp commonly supplied, basic MIG welder (Clarke) that runs through a 13amp domestic plug and fuse, and I can fully weld 6mm steel that is butted, vee groove. I have even joined items onto 10mm plate by working from both sides, although probably not a fully penetrating weld. Whether it really delivers 150amps is another matter, but it's called a '150 turbo' !!

Norm

Edited By norm norton on 26/07/2016 22:04:15