Fusible Switch Circuit

ezridermnFebruary 2, 2011


I want to wire an electrical circuit in my home to run a small Miller TIG welder. The welder rating is 230v at 20amps. The max standard circuit breaker/fuse is designated at 30amps. Their recommendation is to use a 30amp fusible switch between the source and the machine. They also designate a minimum 14 gauge conductor size. (which sounds lite to me)

Specifics to my home. The main panel (200 amp service) is located about 75' from the location of the 230v outlet to run the welder.

My primary question relates to configuring the circuit to use a fusible switch per their suggestion. Do I put a 30amp breaker in the main panel, then run wire to a 30 amp fusible switch located near the welder and then make the connection to the outlet from there.

If that isn't the correct configuration I would appreciate it if you could tell me what is the right way to do it.

Also, I would like to know what gauge wire I should use to carry the 20 amp load over 75' to the welder.

Thanks in advance for your help!


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The 30 amp breaker is the "fusible switch", no additional required. Article 630 in the NEC permits electric welders to be on circuits with apparently undersized wire (tables in the Article show the sizes) in cases where the duty cycle is below 100%. Your welder might be only 20%. Some of the imports are only 6%. 20% means what one can weld 2 minutes out of very 10 and the welder is permitted to cool for the other 8 minutes. The conductors also cool during that time. I would use #12 for the application. #10 would be better but not necessary.

    Bookmark   February 2, 2011 at 11:18AM
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"Article 630 in the NEC permits electric welders to be on circuits with apparently undersized wire"

Welding equipment, induction motors, and hermetic compressors are have there own code sections.

The wires are not undersized, but based on the characteristics of the equipment.

This equipment contains built in thermal overload protection, so all the breaker is doing is protecting the feeder against short circuits.

The low duty cycle of many welders allows plenty of time for the wires to cool off.

General purpose circuits (15 and 20 amp, 120 V) feeding multiple loads and used many times in every installation are designed with extra margin (#14 wire at 15 amps, #12 at 20 amps) to ensure safety.

    Bookmark   February 2, 2011 at 5:18PM
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Hey Guys. Sounds like I now know what I need to know. Thanks for the help!

    Bookmark   February 3, 2011 at 9:53AM
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