Wire today for air compressor in the future

[Belgarion]

Hello all!

First of all, thank you to all of the forums supporters for all of the advice given on these GJ boards. I have been reading hundreds of posts and have learned a great deal from some of you, so thanks!

Now, I am looking for opinions from the GJ experts.

I am in the process of gutting my 2-car attached garage and replacing some very, very scary wiring that was done by the previous owner. While this is my first real foray into wiring, I am a fast learner.

My question is "what is the best way to prepare for a future air compressor, or maybe a mini-split A/C, on the far wall from my (yet-to-be-installed) new sub-panel?".

The reasoning here is that while I have the walls down to the studs and running all of the lighting/outlets, I also have 50+ feet of left-over 6-3 NM cable that I am thinking might come in handy someday. The garage is 28 feet wide and the vehicles fit close to the house, so the far wall would be the only place I would ever put anything permanent. I will start a thread with some before & after pics when I am getting close to buttoning up the walls.

The sub-panel I am installing is a Square-D QO132M100C being fed by 2-2-2-4 AL SER.

Should I just install a 50 amp break and run to a second, small sub-panel on the far wall? Or maybe a disconnect of some kind?

Any opinions/thoughts/advice would be GREATLY appreciated.

Thank you in advance!

 

[A_Pmech]

Welcome!

Regarding the air compressor, I would use your 6/3 to install a 50A receptacle in the location of the proposed air compressor.

Mini split indoor units are powered by the outdoor unit. If you forsee having a mini split, I'd install an outdoor disconnect at the proposed location of the outdoor unit. Remember, you have to run power and refrigerant to the indoor unit at time of installation, so plan your location accordingly to minimize what you have to tear out.

 

[Norcal]

Run a 3/4" conduit to your planned compressor location, leaves lots of options for the future.

 

[Belgarion]

Welcome!

Regarding the air compressor, I would use your 6/3 to install a 50A receptacle in the location of the proposed air compressor.

Mini split indoor units are powered by the outdoor unit. If you forsee having a mini split, I'd install an outdoor disconnect at the proposed location of the outdoor unit. Remember, you have to run power and refrigerant to the indoor unit at time of installation, so plan your location accordingly to minimize what you have to tear out.

That is a good point on the mini-split. I guess the 50 amp receptacle would make more sense, but I thought I read on these boards that the > 3HP air compressors need to be hardwired?

Thanks for the "welcome"!

 

[Belgarion]

Run a 3/4" conduit to your planned compressor location, leaves lots of options for the future.

I would prefer to keep the wire in the walls/ceiling joists. Unless you are suggesting the conduit in the walls?

 

[yeldogt]

My shop is large - and I have a second panel at the far end +65 ft away from the main. At the time did not know where I wanted everything -- and I was not going to run a lot of dedicated wires -- so I ran one for a 50amp sub. The wires in that area are all surface conduit -- so a bit easier in my case.

A/C units don't require the amps of a just a few years ago my older 4ton only has a 10g -- think I ran a 10g for my compressor and that was overkill.

What you are running into is a common problem -- we all end up with a couple of extra lines.

It maybe easier to simply spend the $100.00 on some wire and run a couple extra vs the cost of the second panel and breakers.

My 2 ton A/C has a 12g running to it -- That is easy and cheap. Just run it to a disconnect for a future mini. Take some pictures of the location for future reference. The need a 3" hole.

 

[pattenp]

Technically a compressor with a motor that is rated more than 3HP should be hardwired. The reason being is plugs and outlets that you would normally use have a max of a 3HP rating.

That is a good point on the mini-split. I guess the 50 amp receptacle would make more sense, but I thought I read on these boards that the > 3HP air compressors need to be hardwired?

Thanks for the "welcome"!

 

[Belgarion]

Technically a compressor with a motor that is rated more than 3HP should be hardwired. The reason being is plugs and outlets that you would normally use have a max of a 3HP rating.

You hit the nail on the head pattenp.

My thought is that I may want to hook up a beefy air compressor a year or two down the road. But, since I have all of this 6-3 wire sitting around with no intended purpose AND I have all of the walls down to the studs, now would be a good time to run that wire from the garage sub-panel to the far wall, before I insulate & sheet rock.

Maybe I should have asked the question "How do you have your electrical runs going from your sub-panel to your 5HP air compressor?"

Sorry, I know this is not the most intuitive thread to read.

 

[pattenp]

For my compressor I ran NM in the wall to the general location of the compressor and brought it out into a surface mounted disconnect box. I then used flex conduit from the box to the compressor.

 

[A_Pmech]

Horsepower rated receptacles are available to at least 40 Hp 1ph 240v.

Failing that, replace the 50a receptacle with a section of SO cord and a wall plate with strain relief if you install a compressor.

 

[pattenp]

Correct me if I'm wrong, but I don't think code allows flexible cord to be used in this manner for equipment. It needs to have a plug. NEC 400.7(A)&(B)

Horsepower rated receptacles are available to at least 40 Hp 1ph 240v.

Failing that, replace the 50a receptacle with a section of SO cord and a wall plate with strain relief if you install a compressor.

 

[wyliesdiesels]

Horsepower rated receptacles are available to at least 40 Hp 1ph 240v.

Failing that, replace the 50a receptacle with a section of SO cord and a wall plate with strain relief if you install a compressor.

The only receptacles I've seen that are rated for more than 3hp are expensive pin and sleeve units. Prepare to shell out some serious dough for those!

Correct me if I'm wrong, but I don't think code allows flexible cord to be used in this manner for equipment. It needs to have a plug. NEC 400.7(A)&(B)

That's my understanding of it.

 

[A_Pmech]

Correct me if I'm wrong, but I don't think code allows flexible cord to be used in this manner for equipment. It needs to have a plug. NEC 400.7(A)&(B)

In my opinion, 400.7(A)(7) (vibration isolation) is wide open to interpretation and not subject to the cord-and-plug requirements of 400.7(B)

My interpretation of 400.7 is they're trying to keep people from wiring buildings with SO cord. They figure if you need a flexible cord on it, you'll probably have a plug on the end of the cord anyway, so it's an easy way to exclude "permanent wiring" possibilities.

The only receptacles I've seen that are rated for more than 3hp are expensive pin and sleeve units. Prepare to shell out some serious dough for those!

Only if you're crazy enough to buy new! I buy as much of my commercial electrical stuff used. I'll let the big guys get raped by the likes of Hubbel and Square-D.

 

[Belgarion]

For my compressor I ran NM in the wall to the general location of the compressor and brought it out into a surface mounted disconnect box. I then used flex conduit from the box to the compressor.

Yes pattenp, that sounds like what I am thinking about. Run the wire in the wall to a surface mounted box now and be ready for the future <whatever> on that side of the garage.

So:

• 6-3 CU NM w/ground cable
• connected in the sub-panel using a 30 amp QO230 breaker
• running into a Square-D 30 Amp 240-Volt Two-Pole Indoor General Duty Fusible Safety Switch with Neutral on the far wall

I will be ready for something along the lines of a 3HP (maybe more?) air compressor, but the wall wire can handle 50 amps so a simple breaker change and disconnect upgrade and I could do more.

Does that sound about right?

Thanks!

 

[pattenp]

This is the disconnect I used. You don't need the neutral so it can be wire nutted off in the box.
http://www.homedepot.com/p/Square-D...de-Overcurrent-Protection-QO200TRCP/202353314

 

[pattenp]

In my opinion, 400.7(A)(7) (vibration isolation) is wide open to interpretation and not subject to the cord-and-plug requirements of 400.7(B)

My interpretation of 400.7 is they're trying to keep people from wiring buildings with SO cord. They figure if you need a flexible cord on it, you'll probably have a plug on the end of the cord anyway, so it's an easy way to exclude "permanent wiring" possibilities.

If that's the case, how do you explain this?
http://ecmweb.com/code-basics/flexible-cords-cables-and-fixture-wire

 

[Belgarion]

Thank you pattenp!

Not to be a pain, but the disconnect you referenced is 60 amp. Should I go with a 50 amp breaker since it is 6-3 cable? Is there a downside to using the 60 amp disconnect on 50 amp wire? I am assuming "no", since the 50 amp breaker will trip before the disconnect ever gets 60 amps.

 

[pattenp]

The 60 is the amp load rating of the disconnect switch. The disconnect switch is not a breaker and provides no over current protection. Also that 60A disconnect switch carries a 10HP rating.

 

[Belgarion]

Your help is VERY much appreciated. Thank you pattenp!

 

[wyliesdiesels]

Yes pattenp, that sounds like what I am thinking about. Run the wire in the wall to a surface mounted box now and be ready for the future <whatever> on that side of the garage.

So:

• 6-3 CU NM w/ground cable
• connected in the sub-panel using a 30 amp QO230 breaker
• running into a Square-D 30 Amp 240-Volt Two-Pole Indoor General Duty Fusible Safety Switch with Neutral on the far wall

I will be ready for something along the lines of a 3HP (maybe more?) air compressor, but the wall wire can handle 50 amps so a simple breaker change and disconnect upgrade and I could do more.

Does that sound about right?

Thanks!

With NM 6/3, u could use upto a 7.5hp motor. Wire for motors is sized at 125% of FLC. Breaker can be max 250% of FLC

 

[A_Pmech]

If that's the case, how do you explain this?
http://ecmweb.com/code-basics/flexible-cords-cables-and-fixture-wire

Their illustration isn't all-encompassing of what 400.7 allows v. disallows.

 

[pattenp]

If you read the info at the link provided it seems straight forward to me that if you use flexible cord to provide power to utilization equipment that a plug is required. This it what my understanding is, or what I recall from many moons ago in electrical class. Oh well, not worth burning brain cells over.

Their illustration isn't all-encompassing of what 400.7 allows v. disallows.

 

[A_Pmech]

If you read the info at the link provided it seems straight forward to me that if you use flexible cord to provide power to utilization equipment that a plug is required.

I read my copy of the NEC on the bookshelf.

What you say is 100% correct, but with the exceptions noted in 400.7!

As I read it, when used as a means of vibration isolation under any conditions, cord can be used without a plug and receptacle connection just like an elevator or control pendant. Since compressors vibrate a lot, that was my angle.

What I've always found humorous about that section is the fact that the NEC tried to limit the use of SO cord to equipment connected with a plug, presumably to preclude it's use as "permanent" building wiring. Yet, in doing so they created a situation where, under most circumstances, you're forced to add another failure point in the circuit by using a plug and receptacle to use some SO.

"We're from the NFPA and we're here to help."

But yes, you're right, it's not worth arguing about.

 

[Charles (in GA)]

Thank you pattenp!

Not to be a pain, but the disconnect you referenced is 60 amp. Should I go with a 50 amp breaker since it is 6-3 cable? Is there a downside to using the 60 amp disconnect on 50 amp wire? I am assuming "no", since the 50 amp breaker will trip before the disconnect ever gets 60 amps.

The disconnect simply needs to have AT LEAST the amp capacity as the rest of the circuit. It CAN HAVE MORE without any issue. Its not a circuit breaker, its a simple on off switch.

Charles

 

[Norcal]

Thank you pattenp!

Not to be a pain, but the disconnect you referenced is 60 amp. Should I go with a 50 amp breaker since it is 6-3 cable? Is there a downside to using the 60 amp disconnect on 50 amp wire? I am assuming "no", since the 50 amp breaker will trip before the disconnect ever gets 60 amps.

Fusible & non-fusible safety switches come in 30,60,100,200,400 & so on ampere ratings so for 50A a 60A has to be used.

If you wanted to use a 400A switch the only limitation is the wire range of the lugs of the switch.

 

[Belgarion]

Thank you for the clarification on the disconnect switches.

Question: In what situation would you opt for a fusible disconnect switch versus a non-fusible disconnect, which is what I am getting?

I imagine the difference is merely that the fusible will "blow" the fuse after a certain amount of amperage so, in theory, you could put a 50 amp fuse in a 60 amp disconnect and it would blow the fuse before reaching 60 amps? Is it that simple, or am I missing the point?

 

[Norcal]

A 60A fusible safety switch will accept 35-60A fuses, the fuses installed determine when a fault clears, not the switch.

 

[Aceman]

Question: In what situation would you opt for a fusible disconnect switch versus a non-fusible disconnect, which is what I am getting?

If you have a properly sized breaker ahead of the disconnect there is no reason to get a fused disconnect. It doesn't hurt to have a fused disconnect, but it's not required.

 

[Belgarion]

Thank you both for the explanations.