I have constructed a garage apartment above my existing garage. Before starting construction, I installed a 100-amp square D sub panel in the garage.

The neutral and ground bars are separated in the sub panel.

He is the question-- The furnace and condensor are fed by 60-amp and 30-amp circuts, respectively. The furnace has a 6/3 with ground feeding it and the condensor has a 10/3 with ground feeding it. Each has a cut-off box. I understand that the black and red wires are the hots. Is is safe to connect the white wire to the boxes making sure that the white wire at the sub is attached to the neutral bar? Or, do I hook up the bare neutral at both ends?

Thanks

 

I'm guessing that you are referring to the Equitment Grounding Conductor in the Branch-Circuit cable when you describe "a bare Neutral".

Most condensor/compressor Branch-Circuits are 2-wire, 240 volts, and do not have a Neutral connection.If the blower/furnace section is equipped with 120 volt loads then the Branch-Circuit cable supplying power to this equiptment requires a Neutral conductor. All Neutral connections must be "Ground-Isolated", i.e., not in contact with the metallic surfaces
of equiptments and enclosures.

Good Luck & Enjoy the Experience!!!!!!!!!!

 

I mistakingly wrote bare neutral when I meant bare ground. Your answer makes great sense. Regarding the airhandler/furnace that is in the attic of the apt., I need to check to see if it is 240/120. As I appreciate this, the neutral in this situation splits the power and provides a pathway back. Since the unit is 100% electric, I am assuming it is not 240/120.

He is a dumb question. Why is it that the condensor (which is wired for 240) does not require a neutral connection and only a ground?

Thanks and I am enjoying the experience. The cool thing about the addition is that it is out of the way and not an inconvenience. I get to it when I can and I don't feel pressured to get it done. Truly enjoyable.

 

It's hard to explain why it doesn't need a neutral. It's kind of like asking why a car doesn't need a rabbit.

It only takes two wires to complete a circuit -- one coming and one going. A 240-volt circuit has two wires and has no need for a third. A 120-volt circuit also has two wires and no need for a third. The only circuits that need three wires are ones that provide both 240 and 120, and these are really providing two separate power supplies.