Question on sub-panel for new shop

[JoeEngler]

I have seen a lot of questions on sub panels for remote shops. I just wanted to put all my information and see if my planning is correct. First the building will be a metal building.

• The building is about 45 feet from the house.
• The plan is to run (3) #4 wires and (1) #6 for ground
• 2 Grounding rods that will be placed at least 6 feet apart.
• 60- or 70-amp breaker in the house to feed the sub-panel
• Currently it looks like it will (4) 110v breakers and (3) 220v breakers
• 3 - 20 amp for outlets (110v)
• 1 – 15 amp for lighting (110)
• 1 – 20 amp for air compressor (220v)
• 1 – 25 amp for mini spilt (220v)
• 1 – 30 amp for welder (220)

Now for the big question, I bought a square-d sub panel that is MLO 86428. However, after reading several posts, it seems that I need a disconnect in the garage. I think my choices are going to be.

• Add a main breaker to the purchased panel
• Back feed a breaker with a hold down
• Return the panel and buy one with a main breaker
• Install a separate disconnect.

If I use a main breaker, I have heard it should be a higher amperage then the breaker in the house. The logic I read was that this would make sure the breaker in the house stays the breaker and the one in the garage at a higher amperage would not trip is this correct?

Sorry if I’m asking the same question someone else may have. I have searched a lot a just want to make sure it is correct and not have to have the inspector come back several times and burn more money.

 

[sparky 1971]

The easiest, most cost effective thing is going to be return the panel and buy a 100 amp main breaker panel. Don't worry about the fact that it's 100 amp, it's just a disconnect. The breaker in the house is your ocp.

 

[Terry D]

I also agree, return the panel and get a 100 amp main breaker.

 

[pattenp]

For a 60 to 70 amp feeder breaker, #6cu thhn in conduit is sufficient. 60A only needs a #10cu egc, 70A will be #8cu egc. But, nothing wrong with the sizes you stated.

 

[JoeEngler]

For a 60 to 70 amp feeder breaker, #6cu thhn in conduit is sufficient. 60A only needs a #8 egc, 70A will be #6 egc. But, nothing wrong with the sizes you stated.

Thanks, if I stay with #4 I could use a 90A breaker in the house or use #6 and keep it at 70A?

 

[JoeEngler]

The easiest, most cost effective thing is going to be return the panel and buy a 100 amp main breaker panel. Don't worry about the fact that it's 100 amp, it's just a disconnect. The breaker in the house is your ocp.

Seems like the logical thing to do. I will return and buy the panel with the 100A main breaker

 

[yatg]

You've already filled up 10 slots of the 12 slot panel you speced.
Doesn't leave much room for expansion.
For $99 you can get a main panel, 30 slots, and it includes a few breakers you can use.

Square D Homeline 200 Amp 30-Space 60-Circuit Indoor Main Breaker Qwik-Grip Plug-On Neutral Load Center with Cover - Value Pack HOM3060M200PQCVP - The Home Depot

Upgrade your power system with Square D Homeline 30-Space 60-Circuit Indoor Main Breaker Qwik-Grip Plug-On Neutral Load Center with Cover - Value Pack.

www.homedepot.com

 

[Terry D]

For a 60 to 70 amp feeder breaker, #6cu thhn in conduit is sufficient. 60A only needs a #8 egc, 70A will be #6 egc. But, nothing wrong with the sizes you stated.

For a 60 amp circuit, #10 copper is good for the EGC. A 70 amp circuit, #8 copper is good for the EGC. The sizes you posted is for aluminum.

 

[pattenp]

For a 60 amp circuit, #10 copper is good for the EGC. A 70 amp circuit, #8 copper is good for the EGC. The sizes you posted is for aluminum.

Oops.... yep, had aluminium on the brain. Will fix.

 

[pattenp]

Thanks, if I stay with #4 I could use a 90A breaker in the house or use #6 and keep it at 70A?

Yes.