COMMUNITY FORUM

masterofnone1

07:58AM | 12/10/07
Member Since: 10/14/07
4 lifetime posts
Bvelectrical
I have a 60 amp Junction box with 13 breakers in it already with two slots still available it is a General electric box wired Hot with no "Main Breaker" The main breaker is in the buddy box I wired from my main house breaker box, so in reality I have two Buddy boxes off my main house breaker box. My question is

Can I wire a Double poll 30 amp Breaker off my general electric Box to Run a Heavy duty Machine that calls for / 230 Volts / 19 amps / 60 Hz / Single phase / to run? Or do I need to wire a 220 volt service? If someone knows the answer and would be so kind as to call me at (919) 681-5558 I am Clinton / I am being pushed to buy this machine or not, it is at a really good price but I do not want to buy something I cannot get wired with what service I have available.

Please help.

Billhart

05:03AM | 12/11/07
Member Since: 04/25/05
1915 lifetime posts
"I have a 60 amp Junction box with 13 breakers in it already with two slots still available it is a General electric box wired Hot with no "Main Breaker" The main breaker is in the buddy box I wired from my main house breaker box, so in reality I have two Buddy boxes off my main house breaker box."

First it is not a junction box, but rather a sub-panel.

And by the way you need to run 4 wires to a sub-panel (2 hots, neutral, and ground) and the neutral bus isolated from the ground bus. On some panels you can do that by just removing a strap. On other you also need to by a ground bus bar kit.

And you did not give any clues of the load on that sub-panel or what is is wired for.

But if you have 2 open slots next to each other then you can install a 2 pole breaker to supply the motor. If the slots are not next to each other then you can rearange the exisitng ones.

If you are questioning the 230 volt requirment the standard supply in the US is 120/240 volts, NOT 110/220.

However, the standard for rating motors is 230 volts. And yes is to works fine on 240 systems.

masterofnone1

05:44AM | 12/11/07
Member Since: 10/14/07
4 lifetime posts
Thank you. I will do as you sugested to my "Subpannel" :o)

TimBonham

10:02AM | 12/11/07
Member Since: 01/09/07
197 lifetime posts
"Can I wire a Double poll 30 amp Breaker off my general electric Box to Run a Heavy duty Machine that calls for / 230 Volts / 19 amps / 60 Hz / Single phase / to run?"

If your motor only needs 19A, I would use a 20A double-pole breaker rather than a 30A one. You can use smaller (cheaper) wires to the motor that way. And if this is a single use circuit just for that motor, there is no need (and it's not a good idea) to provide that much excess capacity. If it shorts out, you want the breaker to blow sooner rather than later.

Billhart

11:29AM | 12/11/07
Member Since: 04/25/05
1915 lifetime posts
Look at the section of code on Motor circuits.

The circuit wiring needs to be rated at least 125% of the operating current.

The motor, it'self is protected by either internal overload protection or protection in the starter.

For a dedicated circuit the circuit overload protection can be much higher than the breaker can be much larger that "normal". I don't have time to look it up, but depending on the typie of overload device it can be 175 or 225% of normal operating current.

Common breakers have a 2 modes for triming. One is a time inverse heating element and bi-metalic trip. The other is a magnetic trip. For "shorts" the magnetic trip will be what protects the wiring and it is near instaneous.

CH and SQ D both show this in the breaker curves.

If this is not a dedicated circuit the 125% rule still holds, but the breaker is limited to the nominal size based on the wire size.

For home workshop these rules are often ignored and it works out OK. Except for air compressors most home workshop motors start with limited load so the starting current and time is fairly low.

They are used on a relatively low duty cycle.

And wiring with modern insulation can care more current than the size of the breaker allows for the #14, 12, 10 sizes.
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