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thatshimman 11-16-2011 01:36 PM

Wiring subpanel
I have a millermatic 140 and a Morgan air compressor that requires 240v. Would it be safe to say that a 100 amp subpanel with a 60amp breaker from the main allow me to utilize both devices simutaneously? That sounds like overkill to me.

Bmacdona 11-16-2011 02:58 PM

It's going to depend on the size of your compressor motor. a 3hp single-phase motor @240v will draw somewhere around 18A or so. You'll need to check the data plate on the motor itself for HP/amperage draw. The 140 will pull about 15A@115V and you'll also want to take into consideration anything else that you'll be running off the panel....lights, fans, heaters/AC, etc. If after adding up all the numbers, you're comfortable with the 60A breaker (that it also gives you room for expansion), then it shouldn't be a problem. You'll probably want to consider oversizing the feed wire, depending on the actual distance between the boxes.

timothale 11-16-2011 07:19 PM

starting load.
In my old shop I had a100 amp sub panel. 145 ft from house main panel to shop. The distance from the main panel to the sub panel determines the wire size needed. I used the minimum size per code calculation and the lights used to go dim when someone was welding and the 5 Hp air compressor kicked in. In the new 40 x 120 ft shop my son who is an electrical contractor put in a new feed from the power pole and a 200 amp main panel, 42 circuit and added a 60 amp sub panel next to the lift. seperate feeds to all of the bigger machinery, welder. lathe, mill. chop saw,etc , only 6 general use outlets per circuit breaker. . The wood side got feeds for planer, table saw, turret saw, sawdust colledtor. etc and the lights don't dim.

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