Wiring a welder into mains power box

Discussion in 'Electricians' Talk' started by WelderCrafts, May 24, 2020.

  1. WelderCrafts

    WelderCrafts New Member

    Greetings to all
    Need some advice on adding a seperate power supply for my welder.
    Roughly what size wire would I need for a 300 amp welder and what size circuit breaker would I need or could I use a rewireable fuse?
    Thanks in advance
  2. Bob Rathbone

    Bob Rathbone Screwfix Select

    Rewireable fuses are obsolete, use a circuit breaker. You do not specify the input current or loading of the welder, how long the cable run will be or what the installation conditions will be. I suggest you employ an electrician for this job as your knowledge of electrical installation seems very weak.
  3. unphased

    unphased Screwfix Select

    Morning, can you supply some more information. What type of welder is it? Are there any specifications for it? Make?
  4. Bazza

    Bazza Screwfix Select

    Indeed. Some welders are 3-phase, and that’s a different can of worms.

    is there a rating plate ? Photo please.

    make and model too would help.

    and how far from the supply do you want to use this. Distance is a big factor.
    WelderCrafts likes this.
  5. MGW

    MGW Screwfix Select

    I have worked on 25 volt plus one volt per 25 amp so 300 amp 37 amp approx, so 11.1 kW so around 50 amp single phase at 230 volt or 28 amp with 2 phases, standard welding transformers don't use 3 phase, a welding inverter may use 3 phase. So in real terms a welder of that size can't be used in domestic premises, yes you can fit a 63A socket and wire to a single phase supply but a standard consumer unit will not take a 63A MCB or fuse, the old loadmaster did, but even then your looking at the welder dipping the supply voltage and most supply agreements for domestic will not permit the use of a welder that big.

    So the unit will be in commercial premises, the safety aspects don't stop, the old Oxford oil filled transformers have long since gone, two reasons one cancer producing oils, which cost a fortune to dispose of, and the earth which to protect is required, and can result is building earth wires melting, in the old days welding shops had minimum of 35 mm earth wires so they would not burn out with stay welding currents.

    So heath and safety rules come in, even type of fire alarm etc. I know where I work, welding is restricted to certain areas, it is not as simple as having the supply. Large 300 amp welders were the norm where I worked, but unless doing coded welding on thick wall pipe lines and the like, normally a 160 amp is ample, and the large 300 amp welding transformers and inverters are not often seen today.
    WelderCrafts likes this.
  6. Nicholbe

    Nicholbe Member

    MGW, welders do vary a fair bit now, I have a 200 amp ( 135 60%) which has a 13 amp plug fitted.

    As above request , a few more details are required to allow help.
  7. WelderCrafts

    WelderCrafts New Member

    Appreciate the replies
    The welder is a Sip 300 dual voltage 240 / 400 volts
    I'm looking to run it off a 240 volt domestic mains I wouldn't be running it to its max. 120amp would be my maximum use.
    Max length of wire I would like to use would be 2 meters
    I attached a photo of the specs
    Thanks again

    Attached Files:

  8. Nicholbe

    Nicholbe Member

    Suggest you google the actual model number, similar sip 300 amp is listed at 45 amp breaker being required.
    Some models have better PF correction and better voltage tolerance that allow high voltage drop / longer leads.
  9. MGW

    MGW Screwfix Select

    So 37 to 62 amp with output 164 to 300 amp, all on the plate, so you may get away with a 32A outlet with a type C MCB/RCBO for your 120 amp, it really depends on in rush, with a welding inverter you may get away with 13A at 120A output, the inverter stops inrush and produces a smoother output so welding voltage can be reduced, but with a simple welding transformer unless supplied with 32A MCB or above it will likely trip on inrush.

    I find welding with an inverter feels like welding with DC, it is AC with 50/50 heat where DC is 25/75 heat but they feel so smooth, when you think this [​IMG] was the old 300 amp welding sets of the 1980's you realise how much power they needed, the 4 cylinder Perkins or Ford engine was rated around 50 HP. Its a big industrial unit at 300 amp, it was never designed to sling over your shoulder and jump off a helicopter with, this [​IMG] however can be plugged into a 13A socket, and light enough to carry over your shoulder, it is an inverter, not a simple transformer, and at £138 likely cheaper than getting the supply put in for the one you have, and easier to use.
    WelderCrafts likes this.
  10. WelderCrafts

    WelderCrafts New Member

    I've tried Google but seems to be an old model couldn't find any info or manual for the welder
    Thanks anyway
  11. MGW

    MGW Screwfix Select

    You can likely use one of these [​IMG] they are not too expensive Screwfix £11.29 but the problem is it needs wiring back to consumer unit on it's own dedicated supply, so you need a socket where ever your going to use it, I have only shown a 32 amp version, to get the full out of the welder would need the 63A version. That becomes more expensive one linked here at £68 which is why I question is it worth it, your looking at £80 for plug and socket plus cable and work involved and the far better inverter is not that much more, and can be used anywhere.

    Ebay is full of cheap old welding sets, there is a good reason.
    WelderCrafts likes this.
  12. Nicholbe

    Nicholbe Member

    Good comments MGW,

    Perhaps Welder craft could confirm , is the welder you have a stick or MIG ?
  13. WelderCrafts

    WelderCrafts New Member

    Appreciate the advice I have an inverter but only use it for light
    Appreciate all the valuable information you've shared.
    I have a small transformer based flux cored MIG welder which I use for small repairs I also have an inverter ( Cemont Colt 150) I tend not to use it for any heavy welding.
    Was wanting to get this beast up for all the donkey work as it welds like a dream.
    The plug that is on it is a 13amp to 16amp fly lead converter # 13 amp plug to 16amp socket was using the welder with it in the garage but once you flick the switch on it sets off the breaker only way to get it to stay on was to turn the welder on whilst the power from mains is off then switch mains back on and I'd have no issues with it tripping the breaker.
    The circuit breaker it is connected to has multiple sockets thus I wanted to wire a dedicated circuit for just the welder.
    Another conclusion would be that the switch on the welder has issues causing the breaker to trip.
    Thanks once again for all the advice.
  14. Teki

    Teki Active Member

    That would seem plausible - worn switch contacts.

    Given that someone has plugged the welder into a 16A socket to 13A plug lead further suggests that it should really be plugged into its own dedicated circuit.
    WelderCrafts likes this.

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