Mig Welder OCPD sizing?

[factoryrat]

I have three Miller Invision 354 MP DC Inverter Arc Welders. Input Voltage 460 V, 3-phase. The nameplate says: INPUT = 11.5kw and 18.9 amps. How do I calculate OCPD size and wire size if I want to put all three welders on one circuit? And what size OCPD and wire size would be needed if I was to run an individual circuit to each mig welder?

I have an existing 60A circuit (OCPD = 60A & feeder wire size is #6) not being used for anything else. I have one of the three new welders hooked up to this circuit now. There is a fused disconnect at the welder which is fused at 40A. I was wondering if from the existing 60A circuit I can connect the other two mig welders?

With these new welders I received an owner?s manual. The manual has a page that shows a table. I believe the table indicates each one of the welders should be protected by 15A Time-Delay fuses. This seems small to me and because I do not know how to calculate the correct sizes I'm confused. If I am reading this right ? Can I use the 60A feed and run it to each welder where I?d have a disconnect with 15A fuses to protect the mig welder?

Believe it or not I am an electrician but have never calculated circuit protection for mig welders before. I would appreciate any information anyone could give. Thank you.

 

[raider1]

Take a look at 630.11 (A) and (B) for determining the ampacity of the supply conductors for an individual welder or a group of welders respectively. Also look at 630.12 for the requirements for overcurrent protection for the welder and the supply conductors.

Chris

 

[factoryrat]

630.11(A)
Does this mean I take the nameplate 18.9A and multiply it by .78
(18.9 x .78 = 14.74A). I have no I eff listed on the nameplate.

630.11(B)
14.74A + 14.74A + (14.74x85%) = 42.01A
So I need a feeder that can handle 42.01 amps. The #6AWG can do that.

630.12(A)
200% x 18.9A = 37.8A
Does this mean that each welder would need to be protected by 40A Time Delay Fuses?

Thanks for reply Chris. I was aware of the code sections you mentioned but I am unsure how to interpretate it and apply it. Any further help would be appreciated.

 

[raider1]

630.11(A)
Does this mean I take the nameplate 18.9A and multiply it by .78
(18.9 x .78 = 14.74A). I have no I eff listed on the nameplate.

Correct if you have a duty cycle of 60

630.11(B)
14.74A + 14.74A + (14.74x85%) = 42.01A
So I need a feeder that can handle 42.01 amps. The #6AWG can do that.

Correct.

630.12(A)
200% x 18.9A = 37.8A
Does this mean that each welder would need to be protected by 40A Time Delay Fuses?

You can use one overcurrent device for the conductors that feed multiple welders and this overcurrent device can be used to protect the welders as long as the overcurrent device does not exceed 200 percent. In this case that would be a 35 amp breaker or fuse. Or you can install a larger overcurrent device to protect the supply conductors and individual overcurrent devices to protect the welders.

hope this helps,
Chris

 

[Bob NH]

I have three Miller Invision 354 MP DC Inverter Arc Welders. Input Voltage 460 V, 3-phase. The nameplate says: INPUT = 11.5kw and 18.9 amps. How do I calculate OCPD size and wire size if I want to put all three welders on one circuit? And what size OCPD and wire size would be needed if I was to run an individual circuit to each mig welder?

I have an existing 60A circuit (OCPD = 60A & feeder wire size is #6) not being used for anything else. I have one of the three new welders hooked up to this circuit now. There is a fused disconnect at the welder which is fused at 40A. I was wondering if from the existing 60A circuit I can connect the other two mig welders?

With these new welders I received an owner?s manual. The manual has a page that shows a table. I believe the table indicates each one of the welders should be protected by 15A Time-Delay fuses. This seems small to me and because I do not know how to calculate the correct sizes I'm confused. If I am reading this right ? Can I use the 60A feed and run it to each welder where I?d have a disconnect with 15A fuses to protect the mig welder?

Believe it or not I am an electrician but have never calculated circuit protection for mig welders before. I would appreciate any information anyone could give. Thank you.

You need to consider the difference between protecting the circuit (the breaker must not exceed the ampacity of the wires) and protecting the welders. The welder manufacturer doesn't want you to have overcurrent protection greater than 15 Amp Time-delay fuses.

If you are going to run them off one circuit, you should have a fused disconnect for each one that will have the 15 Amp Time-dealy fuses to protect the welder.

The welders probably have a duty cycle rating. That duty cycle rating is taken into consideration when designing the circuit and the overcurrent protection.

 

[factoryrat]

Yes, I do have a duty cycle of 60%.

Chris and Bob please help me understand what you are saying. Are you saying I can supply the three welders with a single circuit protected by 35A time delay fuses? And are you saying I have to protect each individual welder with 15A Time Delay fuses (as stated in owners manual)? As I said earlier - one welder is hooked up and is presently protected by 40A fuses. If I am understanding you guys correctly this individual welder is not being protected by the 40A fuses?

I have a hard time with this because the welder?s power cord is a factory supplied SOOW cord, 4 - #8AWG wires. It doesn?t make sense for the Miller Co. to supply these large, copper, power conductors if I am suppose to use only 15A Fuses ahead of them.

I am at home now and do not have the owners manual and other pertinent data here to read over. I will read more tomorrow while at work.

I do appreciate your responses Chris and Bob. I feel I am learning from this exchange.

 

[Bob NH]

The manual (4-5 Electrical Service Guide) says input at rated output is 15 amps. The manual also says that maximum recommended fuse size is 15 Amp time delay or 20 Amp standard fuse, and consult factory if using a circuit breaker. The same table also recommends minimum 14 AWG wire.

However, 3-1 Specifications says the RMS Amps is 18.9 at rated output. No explanation of the difference.

It is pretty clear that you can run three welders on a 60 Amp circuit.

Considering the fuse sizes recommended in the manual, you may be putting the welder at risk if you use 40 Amp fuses for each welder.

 

[factoryrat]

Looking again at the owner?s manual I can see why they supply the (4 cond. #8AWG) power cord. The welder can be hooked up for different voltages and the lower voltages require more input current.

I know the rating plate says 18.9A but the owners manual says @ 460V, 3 phase, that the input amperes at rated output equals 15A.

That is what Chris is saying.

I?m going to go with the 15A Time Delay fuses at each welder disconnect and use the 60A feeder for the supply of all three welders.

If I can find a phone number I might call the Miller company tech support. Thanks again.

 

[factoryrat]

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Thank you so much for your knowledgeable help - I have learned quit a bit from this exchange and I do appreciate it - Thanks again.

 

[factoryrat]

I called Miller Welding Tech Support and the gentleman I talked with said the 15A Time Delay fuses were the proper size for this unit when hooked up to 3-phase 460V power. #14 AWG conductors are adequate.

It seems small to me - but what seems right is not always right.