Welder / Wiring for Small Garage

[NoSmoke]

When running 240vac the current load is shared by both hot legs so factor that into your wiring choice. For example if welder pulls 30 amps each leg supplies 15 amps so wiring can be determined by that and wire run length.
wire it and use welder for 240vac and forget about using it with 120vac IMO.

That is incorrect. Each leg carries the full 30 A.

 

[DaBear3428]

The answer to your requirements is in the printed information under the voltage/amps chart. It states that the power cord is 240v 50 amps.
Good luck plugging that 50 amp cord into a 30 amp receptacle. If you replace it with a 30 amp plug—bye bye bye to your warranty.
The chart also shows in the last column 34 max amps.
I would do 1 central 50 amp plug centered on the non 30’ wall and build up 1 50 amp cord to be able to reach several feet out of the bay doors (50 feet?).

you can install a 50a outlet on any size wire you want, the circuit breaker needs to be 50a or less, the load has to be less than the wire size but nothing stopping you from installing upgraded components as long as they meet/exceed the requirements.

 

[DaBear3428]

You shouldn't use 8/3 for a 30 amp breaker, the coded size for 30 amp is # 10 wire, any size larger than that with a 30 amp breaker could cause a problem. It would take longer for a breaker to trip

actually it would trip faster under a fault condition and be the same otherwise, as others have stated other than making it fit and cost considerations, no problem, in fact it is sometimes required to meet voltage drop requirements.

 

[NoSmoke]

Why would the breaker take longer to trip with larger wire? I would think if anything it would trip faster as the larger wire would allow greater current under a short condition.

 

[YardBikeBob]

Yes. It will be fine.

 

[cavedweller29]

I did something similar but ran 2 ga for about 40 feet. I put in a 100 Amp sub-panel with the idea that I would rather have extra capacity in case plans change later on. I have an 80 gallon compressor and a Lincoln 255 mig machine on it. it is going to obviously cost more but I have flexibility for later on.

 

[MAX-24-Dean]

I'm guessing that a #12 extension cable would be OK to use on a 30 amp welder because of the duty cycle. I think it would be frowned on for the building wiring because of the potential of hooking up a constant 30 amp load.

Good post, The duty cycle hasn't been discussed much in this thread. Duty cycle is the reason that the manufacturer has written in the manual that #12 conductors rated for 75 degree C is the minimum size required for the installation.

From memory after reading in the manual the duty cycle for the Multi-Handler at 240 Volt AC and 170 DC output is approximately 20%. (looked it up, See section 4-11)
Duty cycle for welders is always based on a 10 minute time of use. So for the 20% duty cycle the welder would be off for 80% of the time, and on for 20% of the time. Hence the smaller conducter size allowed by the manufacturer.

Once again, Manufacturers written instructions supercede the NEC.

In the Manufacturers Manual for these welders there is a note (Section 5-9)that says,
5-9. Input Power Extension Cord Data
Use extension cord only for temporary wiring. Remove extension cord immediately after completing the project.

Cord Type Minimum Conductor Size Number of Conductors

Heavy Duty (Hard Usage) 12 AWG (4 mm2) 3

. Read OSHA Standard 1910.334 for more information on the use of cord and plug connected equipment. Read National Electrical Code (NEC) Article 590 for more information on temporary wiring.

Input 17 2018-11
Maximum Cord Length
50 ft (15 m)

Heavy Duty (Hard Usage) cord is rated for 600 Volts. So Cord type would need to be type SO cord or type ST cord.

 

[MAX-24-Dean]

I understand that the breaker protects the wiring of the circuit.

Where would I find chart that shows # 8 copper can handle 55 amps? I thought # 6 was only rated for 50 amps.

The attached has an ampacity table for conductors and gives us a flow chart to help comply with code, the flow chart is base on Electrical Theory. More going on here than there is room in this thread to explain. "Physics at work" is the best short explanation.

 

[MAX-24-Dean]

Duty cylce note from section 4-11 in manual.


Duty Cycle is percentage of 10 minutes that unit can weld at rated load without overheating.

If unit overheats, output stops. Wait fifteen minutes for unit to cool. Reduce amperage or duty cycle before starting to weld again.

NOTICE − Exceeding duty cycle can damage unit and void warranty.

 

[MAX-24-Dean]

#12 is 20 amp rated not 30.

True, except the code has to give allowance for Physics/Theory. One example would be motor loads. Breakers for motor loads need to be sized to allow for the inrush of current. So the NEC allows for breakers to be sized at approximatley 250% of motor running amps. As long as the conductor size has sufficient ampacity to serve the running amps load plus 125%, the breaker can be larger than the running amp by up to 2.5 times. (My paraphrase, Not code verbage cause I'm not taking the time to look it up.)

If you look at Art 630 of the NEC for overcurrent protection of welder conductors, the verbage is basically that conductors supplying welders shall be protected by an overcurrent device rated no more than 200% of the conductor ampacity.
So a 20 amp rated conductor could have a 40 amp breaker protecting it.
There is a formula for calculating this in 630.12.B



For inverter resistance welders. You would use Art 630.31.A, basically states that the conductor ampacity shall not be less than 70% of the rated primary current for seam welders and automatically fed welders that can be adjusted for different values of primary current and duty cycle. And not less than 50% of the rated primary current if there are other circumstances.
There are to many variables to go into here.

At least for the last 25 years of doing electrical drawings the minimum conductor sizes for welders was given in the operators manual for each welder. See attached sheets that have been previously posted showing this. I have never placed an approved stamp on a one line drawing without looking at the engineered data in a welders operators manual. The engineering calculations are placed in the operators manual, so I never bother with figuring it out. It has become thier liabilty.

I did at times have to have pictures of nameplate data sent, so I could size conductors and overcurrent protective devices.

From the welders manuals in this thread. One manual stated the minimum counductor size being a #14, the other manual stated the minimum conductor size as being #12. Both manuals stated that a "hard service cord" of #12 conductors were the minimum for an extension cord for up to 50 feet in length. The manuals also had the sizes for overcurrent protection provided.