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Posted By Topic: Welder

May 01 2018 21:27

I need to install a socket outlet in a mechanics workshop for a welder. The welder comes with a 15 a plug on it. he said it blows fuses very quickly and also cooked his generator which has 15a outlets. I’ve looked the model up it’s a strata advancemig 250. It says maximum input current 40a. And 15% duty at 250a on mig. Why do they put a 15a plug on the welder? I’m thinking of using a 25a socket and 25a breaker. Is a d curve breaker the right option or stick with a c? What’s the best option for setting this up? I don’t have much experience with welding. Thanks guys

May 01 2018 23:20

"Blows fuses" isn't very specific. Without knowing what they mean, it's hard to say.

It says it is 15A input. The 40A peak might only be for a fraction of a second.
It will probably run on a 15A socket just fine. If you use a suitable size cable on the circuit and protect it with a 20A circuit breaker, it should be ok. The worst that might happen is that the plug might burn out. But even that would be unusual.

May 01 2018 23:30

"Why do they put a 15a plug on the welder?"

Bloody wonder that they did that Nick, not uncommon to find welders pull 20+ amps with a 10Amp plug fitted and a tag that says the 10Amp plug is for "display purposes" and the user is responsible for sorting out the correct plug for the item.

On the welder, there should be a rating plate. That should state what supply voltage it requires, and it's I effective, most welders rated at 250A have an Ieff of 19-20A.

Manual for item says 9.4Kva generator required to feed it, what was rating of "cooked" one?

May 02 2018 08:33

If you read some of the applicable standards 60974-1 BS, EN AS etc you will see the use of I(eff) which they define as “maximum value of the effective input current, calculated from the rated supply current (I1), the corresponding duty cycle (X) and the supply current at no-load (I0) by the formula…..” so they are, in effect giving you a thermal rating, accepting that things will get hot but have an enforced cool down period.

If all products sold in NZ are actually rated using this method or just print the standard and an arbitrary value I can’t say.

Putting on a generator as in the original post, it can pull up to the max current until it gets too hot (duty cycle limit) or in this case the generator limits it through some means OC protection (or smoke).

For the wiring, connectors the effective thermal load is as stated but the supply must be able to supply the max current (depending on output setting of course) in bursts.


May 02 2018 10:40

As/NZS 3760 appendix J might help clarify things.

May 02 2018 10:47

This welder is an invereter welder it can handle a range of input voltages 90-275 AC or DC.
40A maximum input current at 90V minimum voltage gives 3.6KW.
At 230V 15A gives 3.45KW.
It's possible if the generator was sized correctly that it was on it's way out anyway and was operating below 230V causing current draw above 15A that the generator was rated for.


May 02 2018 10:50

There is also the possibility that harmonics from the DC switching fed back into the generator and destroyed it.

May 02 2018 11:28

The manufacturer specifying 9.4kva should be a hint as to input requirements. 250A output with a weldign voltage of 20V (mig) is 5kW (it's DC). This is telling you that you will need more than this of real input power (kW, let alone kVA). 15x230 is <<5000

Thermally it behaves like a load that consumes I(eff) over a long period, but it is a 9.4kVA load when delivering full wick.

May 02 2018 11:34

See example of manufactures guidance here, this is our 275A single phase welder.

May 02 2018 11:41

ok, not able to be read, the name plate rating is 95A @ 230V and they (Lincoln) specify protection by a 150A superlag fuse or equivalent.

May 02 2018 13:07

"The manufacturer specifying 9.4kva should be a hint as to input requirements." Yes for a generator.

It says input power supply just above that 230V AC 15A 50/60Hz

250A output at 26.5V duty cycle of 15% which gives us 6625W this is not the input required it is output for 15% duty cycle

Duty cycle the ratio of time during which welding current flows to the standard period of 1 minute.

15% @250A means you can run a bead for 9 seconds. Any more than that and you will trip the overload or cook the generator due to heating of the winding (increased resistance). After 9 seconds of welding the welder should be allowed to cool for 51 seconds before commencing welding again.

AS/NZS 3000:2007 C2.5.2.1 (a) (i) applies to arc welders which is What a MIG/Tig is C2.5.2.1 (a) (ii) applies to resistance welders which is how you get >5KW not applicable for this type of welder.

This welder is a slightly above average mig nothing special. It should run on a 15A socket with no issue unless you start abusing the duty cycle rating.

The generator it cooked obviously had no OC protection for the socket and the duty cycle was exceeded.

AS/NZS 3000:2007 C2.5.2.2 ARC Welding Machines (a) Individual machine The maximum demand of an individual arc welding machine shall be deemed to be 100% of the RATED PRIMARY current.

Which is 15A in this case.

The 40A is there to ensure that it is not run @ a supply voltage of <90V, if it was it would exceed the 40A maximum current rating when used on its highest setting 250A.

I used to use both types of welder everyday as a professional welder.

May 02 2018 13:14

The duty cycle on the Lincoln 275 square wave is 40% because it's a far better machine, as a result the input current requirements are far higher.

The Strata has 250A @15%. No welder worth their salt would buy one to weld at 250A it will not last. You might get away with it for a short period if you observe the duty cycle cool down period and weld periods. It's a marketing ploy.

May 05 2018 20:00

I have one of these welders, and it runs happily off a 15amp socket/20amp breaker.

The reason for the 40amp input current rating is that they're a 'Hot Start' welder, meaning that for 0.5 a second on startup they draw up to the 40 amps to provide a strong arc to prevent sticking.

They're a Very good welder, and if its tripping breakers then there's something wrong with it.