Air Compressor Wiring Help

[TexTJ209]

Howdy,

I'm looking for some clarification on how to properly set up wiring for an air compressor I'm looking at adding to my home garage. I've done a ton of searching here and elsewhere and haven't come to any real conclusions.

The air compressor is the Harbor Freight 60gal 5hp 230v one, which the manual states needs a 40A breaker. Simple enough you'd think.

But my house was built in 1964 and has an old Square D QO split bus panel, model #QO-12-306. With a little breaker reorganization I should be able to fit the 2 pole breaker in (slots 9&11 I think?), but I believe since this house doesn't have a ground, what is the best correct way to go about getting this wired up?


Thanks in advance for any help y'all can provide!

 

[510ebl]

http://gens.lccdn.com/GeneracCorpor...-model-5796.png?width=768&height=480&ext=.png

 

[510ebl]

Seriously though... do you already have a subpanel installed somewhere?

 

[TexTJ209]

Nope, just this one panel. Eventually I'm going to have the main panel upgraded to a more modern unit, but due to the cost that probably won't be any time soon.

 

[wyliesdiesels]

Howdy,

I'm looking for some clarification on how to properly set up wiring for an air compressor I'm looking at adding to my home garage. I've done a ton of searching here and elsewhere and haven't come to any real conclusions.

The air compressor is the Harbor Freight 60gal 5hp 230v one, which the manual states needs a 40A breaker. Simple enough you'd think.

But my house was built in 1964 and has an old Square D QO split bus panel, model #QO-12-306. With a little breaker reorganization I should be able to fit the 2 pole breaker in (slots 9&11 I think?), but I believe since this house doesn't have a ground, what is the best correct way to go about getting this wired up?


Thanks in advance for any help y'all can provide!

Ew split bus panel! Get rid of that thing! Fast!

Now you have 2 separate questions- how to wire the AC and what to do about the ground.

First, wiring for motor circuits is sized @ 125% of NEC table FLC. For a 5HP(28FLC) motor this means 35a wire- either #10 THHN in pipe or #8/2 NM-b.

If the wire run is pretty long then u eill want to upsize to compensate for voltage drop.

U will need a disconnect if the AC is farther than 50' and not within sight of the panel.

It will need to be hardwired unless u can find a recepticle and plug rated for 5HP or more.

U will need a starter if the PS isnt rated for 5HP or more.

Second, IM not sure what youre getting at about the house not being grounded. Is this panel your main service panel? If so, the EGC(ground) for the compressor would go on the neutral bar.

 

[pattenp]

The ground for the new 240V circuit goes to the neutral bar. Grounds and neutrals can share the same bar in the main service panel.

 

[TexTJ209]

The ground for the new 240V circuit goes to the neutral bar. Grounds and neutrals can share the same bar in the main service panel.

Gotcha, that helps! I think based on reading that the air compressor may have a four wire hookup. Two hots, neutral and a housing ground.

Ew split bus panel! Get rid of that thing! Fast!

Now you have 2 separate questions- how to wire the AC and what to do about the ground.

First, wiring for motor circuits is sized @ 125% of NEC table FLC. For a 5HP(28FLC) motor this means 35a wire- either #10 THHN in pipe or #8/2 NM-b.

If the wire run is pretty long then u eill want to upsize to compensate for voltage drop.

U will need a disconnect if the AC is farther than 50' and not within sight of the panel.

It will need to be hardwired unless u can find a recepticle and plug rated for 5HP or more.

U will need a starter if the PS isnt rated for 5HP or more.

Second, IM not sure what youre getting at about the house not being grounded. Is this panel your main service panel? If so, the EGC(ground) for the compressor would go on the neutral bar.

I plan on just hard wiring it, contemplated using a plug and receptacle but most stuff I saw recommended hard wiring it. The compressor will be installed in sight of the breaker box, both are located in the garage which is about a 24'x25'. The house (being older), doesn't have a ground rod outside that I've seen, and I was under the impression that the older 60s era stuff didn't actually use a ground, they only had the neutral bar. I may be way off in this stuff, I'm an MET not an EE. This is the main and only panel for the house.

And yeah, the split bus panel will hopefully be going away eventually. Any idea what a panel upgrade would run? It'd be super nice to actually have a real main disconnect instead of just the one 60A that shuts off the lighting breakers only.

 

[182RG]

Gotcha, that helps! I think based on reading that the air compressor may have a four wire hookup. Two hots, neutral and a housing ground.

3 wire. 2 hots and a ground. Single phase 230V motors don't take a neutral.

You should have the panel replaced with a new panel and a proper earth ground.

You can run ground to the neutral bar in the old panel since neutral/ground is shared.

In lieu of this, you can drive ground rods and establish an earth ground. Not exactly code, however. Your choice.

See link:

http://askville.amazon.com/living-h...nd-bus-bar/AnswerViewer.do?requestId=50272991

Sent from my iPad using Tapatalk

 

[Charles (in GA)]

Get a new 30 or 40 space panel installed. The panel and breakers are not that expensive, and judging from the looks of the existing panel, it should be a fairly easy swap.

Charles

 

[pattenp]

You can run ground to the neutral bar in the old panel since neutral/ground is shared.

In lieu of this, you can drive ground rods and establish an earth ground. Not exactly code, however. Your choice.

Sent from my iPad using Tapatalk

Earth ground and equipment ground are two different things. Fault current is not cleared via the earth ground. Bonding the EGC to the neutral at the main service provides the proper equipment grounding. The ground rods are for lighting strike grounding.

 

[Junkman]

If your electrician installs a new Square D panel that uses the QO breakers, you can re-use the old Square D breakers. You will need to purchase some GFI breakers for the bathrooms and the kitchen.
I am not an electrician, and my electrical knowledge is limited, however, I have learned a lot from this forum, along with some basic knowledge of Square D panels.
I recently had an Eaton panel installed in a property that I own, and the panel was under $60, and from memory, I think that the new breakers were about $5 or $6 each. The GFI breakers were about $15 or $20 each.