Some more 220V wiring questions

[1wheeldrive]

So, I am another guy getting ready to wire up a 220V circuit for my air compressor.

Compressor is 5HP. rated for 20 something amps, seems a 30A might be enough but I am thinking a 40A breaker. The wiring run is a bit under 50Ft. I am thinking 8AWG or maybe 6 would be better?

If I run surface mounted EMT, can i run stranded wire all the way into the breaker in the panel? Or do I need to transition to solid wire? I am thinking of just cutting a hole in the drywall next to the breaker panel and running the conduit right into one of the panel knockouts.

OR would it be better to just run a short section of vertical EMT off the panel to the attic and use romex across the attic above the ceiling to another short vertical EMT to drop down to the compressor? No conduit needed for the romex above the ceiling, right?

The panel is flush mounted into an outside walll or I would just drop romex thru the wall from above and skip the conduit but it might be hard to access the top of that outside wall to drop the wires in...

The compressor will be hardwired, transitioning to flex conduit to connect at the compressor.

Any advise is GREATLY appreciated. Thanks!

 

[sberry]

If you pipe it and use single conductors you can use 10 for 5 hp. If you use a cable you need 8. It can be ran same wire all the way, say stranded, no need to change and actually prefer to run it uninterrupted.
Under 50 ft and in view of the panel and it doesn't need disconnect. Breakers from 30 to 50 with 40 being ideal.

 

[mike93lx]

you could run romex the whole way, including in conduit where needed for protection. just need it to be large enough to not overfill and allow for easy pulling.

IMO, If you can run conduit, do that and use stranded wire. it will be a lot easier to work with than anything solid.

pictures would help

 

[wyliesdiesels]

If using emt, then #10 THWN is code compliant for 5hp.

If youre gonna use cable, such as NM-b then you need #8.

Also how far away is the panel and is it within sight of the compressor?

 

[HIG]

If using emt, then #10 THWN is code compliant for 5hp.

If youre gonna use cable, such as NM-b then you need #8.

Also how far away is the panel and is it within sight of the compressor?

I hope I can jump in, what size breaker would you use?

Why is 10ga okay to use in EMT conduit but 8 ga required for Romex, does it have to do with Conduit Fill and heat?

Thanks, Steve

 

[Norcal]

I hope I can jump in, what size breaker would you use?

Why is 10ga okay to use in EMT conduit but 8 ga required for Romex, does it have to do with Conduit Fill and heat?

Thanks, Steve

NM cable must be sized from the sixty degree column so to get a minimum of 35A, 8AWG must be used because 10 AWG NM cable is only 30A and for motors 10 AWG THHN is 35A, 8 NM is 40A. As to what breaker, 40 or 50A is good, still less then the maximum.

 

[matt_i]

I would just keep running conduit in the attic above the joists. Use LBs to turn corners and drop down. Get a helper to fish wires. Get this done before the dead of summer hits (!)

 

[wyliesdiesels]

I hope I can jump in, what size breaker would you use?

Why is 10ga okay to use in EMT conduit but 8 ga required for Romex, does it have to do with Conduit Fill and heat?

Thanks, Steve

No nothing to do with conduit fill and heat...

Has to do with ampacity temperature limitations.

If you ran romex through conduit, it would still have same limitations..

Need an understanding of Article 240 and table 310.15(B)(16)

NM cable is limited to 60°c ampacity despite having 90°c rated conductors
THWN is sized @ 75° ampacities unless derating is involved then you start with 90°c ampacity and derate from there....

EDIT: Forgot to answer your breaker question. Id go with a 40a breaker but code allows up to 250% of the table FLC, which, for a 5HP motor, would be 70a.

 

[1wheeldrive]

thanks for the input, the panel is within direct sight of the compressor btw for the guy who asked. Off to buy some wire and emt!

Although 10 AWG is sufficient with a 40A breaker, would there be any problem running 8 or even 6 in case I need to upgrade later? Just cost and a little harder to work with right? Its a 50ft run from the panel.

 

[mike93lx]

thanks for the input, the panel is within direct sight of the compressor btw for the guy who asked. Off to buy some wire and emt!

Although 10 AWG is sufficient with a 40A breaker, would there be any problem running 8 or even 6 in case I need to upgrade later? Just cost and a little harder to work with right? Its a 50ft run from the panel.

No problem with up sizing the wire

 

[HIG]

NM cable must be sized from the sixty degree column so to get a minimum of 35A, 8AWG must be used because 10 AWG NM cable is only 30A and for motors 10 AWG THHN is 35A, 8 NM is 40A. As to what breaker, 40 or 50A is good, still less then the maximum.

Wow, it's going to take a lot to try and understand this!! I do not see NM or NM-B listed in Table 310.15(B)(16), I do see under the 60 degree column TW and UF listed. Is this the same as non metallic Romex? TW and UF are just the type of insulation?


So if I needed 60 amps:


NM (Romex) - I would need 4 AWG (70 amps)

or

THHN - I would need 6 AWG (75 amps)

What derates NM cable, length of run, if it's run through conduit or a tight hole or space, ambient temperature?

Thanks, Steve

 

[HIG]

No nothing to do with conduit fill and heat...

Has to do with ampacity temperature limitations.

If you ran romex through conduit, it would still have same limitations..

Need an understanding of Article 240 and table 310.15(B)(16)

NM cable is limited to 60°c ampacity despite having 90°c rated conductors
THWN is sized @ 75° ampacities unless derating is involved then you start with 90°c ampacity and derate from there....

EDIT: Forgot to answer your breaker question. Id go with a 40a breaker but code allows up to 250% of the table FLC, which, for a 5HP motor, would be 70a.

Thank you.

 

[Bert_]

I would just keep running conduit in the attic above the joists. Use LBs to turn corners and drop down. Get a helper to fish wires. Get this done before the dead of summer hits (!)

NO LB's IN THE ATTIC. The next person to try and pull wires into it will wonder what spawn of satan put the LB up there that somebody now has to crawl up and find. Use 90's or whatever bend in the attic and keep all your pull points accessible from below.

 

[teamextreme]

NO LB's IN THE ATTIC. The next person to try and pull wires into it will wonder what spawn of satan put the LB up there that somebody now has to crawl up and find. Use 90's or whatever bend in the attic and keep all your pull points accessible from below.

 

[wyliesdiesels]

Wow, it's going to take a lot to try and understand this!! I do not see NM or NM-B listed in Table 310.15(B)(16), I do see under the 60 degree column TW and UF listed. Is this the same as non metallic Romex? TW and UF are just the type of insulation?


So if I needed 60 amps:


NM (Romex) - I would need 4 AWG (70 amps)

or

THHN - I would need 6 AWG (75 amps)

What derates NM cable, length of run, if it's run through conduit or a tight hole or space, ambient temperature?

Thanks, Steve

You could use 6/3 nm-b for 60a IF the load is 55a. Otherwise, yes you will need #4.

But using THWN would be cheaper.

Where are you running this wire? If outside or underground, then NM is a no go...