This subpanel for the house is protected by a 2-pole 60 amp breaker at the main. I want to add a 15 amp 220v circuit in my garage to run a jointer. It currently has a 3 phase motor hooked up to a 220v phase converter.



I know I have the space, but is there any code limit on the number of circuits or amps? All of the current circuits are for pretty small stuff. The biggest things that would pull from this are probably the washing machine and disposal.

The first thing I'd do is check the wiring running to this sub-panel and see what it's rated for.

No limit on number of circuits but limited by lower of either upstream breaker or wire size. Residential load calcs are pretty low outside of appliances and HVAC. Looks like you have all 20A singles outside the existing 2P for the motor. Doesn't look like much load.

What's the motor? Will it run at the same time as your jointer? If not, they are considered non-coincident load and you only have to count the bigger of the two. You might have a net zero increase.

UnderoosAg said:

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No limit on number of circuits but limited by lower of either upstream breaker or wire size. Residential load calcs are pretty low outside of appliances and HVAC. Looks like you have all 20A singles outside the existing 2P for the motor. Doesn't look like much load.

What's the motor? Will it run at the same time as your jointer? If not, they are considered non-coincident load and you only have to count the bigger of the two. You might have a net zero increase.

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Don't have an existing 2-pole. The 3 phase motor with phase converter is what is on the jointer right now. I don't plan to run more than one tool at a time, so I'm not too worried about drawing too much power.

I'm just wondering if there's a code calculation or something that says I can only have a total of x amps of breakers in the panel because it is protected by a y amp breaker or has z gauge wiring to it. It sounds like I can have as much as I want and long as the expected load is less than 80% of the upstream breaker, which would be the case here.

Ah, I read the "it currently has..." as the panel currently has, not the jointer.

Quote:

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I'm just wondering if there's a code calculation or something that says I can only have a total of x amps of breakers in the panel because it is protected by a y amp breaker or has z gauge wiring to it. It sounds like I can have as much as I want and long as the expected load is less than 80% of the upstream breaker, which would be the case here.

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There are calcs, and the lesser of the y breaker or z wire is you limiting factor. The 80% thing is a *******ized rule of thumb. There is no 80% rule in the NEC. Article 240 says you have to size a breaker to 100% of the non-continuous load plus 125% of the continuous load. That got morphed into keeping loads at 80% as to not worry about it, but it's not a hard and fast rule.

Using 2500sqft for your house. Adjust as needed.
2500** x 3 VA/sqft = 7500 VA
small appliance 2 x 1500 VA = 3000 VA
laundry 1 x 1500 VA = 1500 VA
disposal 1 x 1200 VA = 1200 VA
built in microwave 1 x 1800 VA = 1800 VA (another assumption)
dishwasher 1 x 1500 VA = 1500 VA (another assumption)
(you only need to worry about permanently connected appliances)
Total = 16500 VA

First 8000 at 100% = 8000 VA
Remainder at 40% = 0.4 x 8500 = 11,400 VA = 47.5 A.

You theoretically have 12.5A of load to play with if the 60A worth of wire holds true. From a more practical perspective, could you run two vacuum cleaners at the same time in your house during an average day with the TV on, lights on, etc? That's about what that jointer would use.

Got it. Sounds like I'm probably good.