Wire Sizing Help

[mikeyboy]

I have to run a power cable from a Weld Control to a weld transformer on the end of a robot.

The weld control has a 300A SCR. Do I have to run wire rated for 300A to the end of the robot?

The weld control will have about a 8% duty cycle. When welding it will only take about 140A normally.

I am not sure how to factor in the duty cycle into the cable size. Any help would be appreciated.

 

[jrwb4gbm]

There is wire designed specifically for welding. It is a lot more flexible and sized by the manufacturer for a given application that includes the amps and duty cycle. Perhaps you really need to consult your robot and/or welding supplier for this. Having said this, my best guess would be that if you were to use #2AWG motor lead wire, it should handle the current and duty cycle, if the length is reasonably short.

 

[controlled]

There is wire designed specifically for welding. It is a lot more flexible and sized by the manufacturer for a given application that includes the amps and duty cycle. Perhaps you really need to consult your robot and/or welding supplier for this. Having said this, my best guess would be that if you were to use #2AWG motor lead wire, it should handle the current and duty cycle, if the length is reasonably short.

Out of curiosity, how did you come up with using 2awg

 

[jrwb4gbm]

Out of curiosity, how did you come up with using 2awg

Just a guess based on the statement about 140 amps being the normal load. #2AWG THHN is rated in that range with the free-air rating being higher than that and in conduit not quite that high. It should be a conservative guess based on the 8% duty cycle. Motor or welding lead type wire is designed for a higher ampacity than THHN insulated wire for a given wire gauge.

 

[bluebyu]

I don't think it requires special "welding wire" for the primary side of the transformer.

Roman Manufacture web site may be of help,
http://www.romanmfg.com/resources_faqs.html

 

[mikeyboy]

Refernecing Roman Transformers FAQ's I have detiremined the following.

72KVA Transformer x 50% duty cycle x 1000 = 36000VA
----------------------------------------------------- = 53A continuous
480V primary voltage x 1.41 = 676.8V

Considering the above I should be able to use a 4AWG and be ok.

Thanks everyone for your input.:site: