Wire size and type?

[magrahamkp08]

I recently just purchased a new Quincy air compressor. It's a 5hp 240v single phase motor. They recommend a 60amp breaker but don't specify wire size. will 10ga be sufficE? I only need to run about 5' or so.

Secondly. I picked up an old south bend lathe. I plan on using a 30a breaker and 10ga wire. What wire type should I be getting to run 100' of it in metal conduit from the pa el box to my phase converter?

Thanks for the assistance.

 

[pattenp]

You should use #8 copper for the compressor.

Edit: If using THHN wire in conduit you can get by with #10, but #8 gives you a better margin on ampcapacity. If using any NM in the circuit it needs to be #8.

 

[G_P]

10ga can only be installed on a 30 amp max breaker. Put 10ga on a 60 amp breaker and if there is a problem, the wire will burn before the breaker can trip.

 

[wildstyle]

My 80 gallon DeVilbiss with a 5hp baldor on it is only 27amps full load. 60 seems huge for a compressor. I'm running mine on a 30 amp breaker on 10/2 wire.

 

[pattenp]

NEC requirements are different for motors. 5HP motor per NEC is 28A X 1.25 = 35A. That is #8 NM or #10 THHN in conduit. The 60A breaker is fine. Breaker for motor loads can be oversized.

 

[wyliesdiesels]

I recently just purchased a new Quincy air compressor. It's a 5hp 240v single phase motor. They recommend a 60amp breaker but don't specify wire size. will 10ga be sufficE? I only need to run about 5' or so.

Secondly. I picked up an old south bend lathe. I plan on using a 30a breaker and 10ga wire. What wire type should I be getting to run 100' of it in metal conduit from the pa el box to my phase converter?

Thanks for the assistance.

5HP is 28a FLC so #8 NM or #10 THHN.

Does the compressor have a starter?


For the lathe we need more info...What voltage and HP? Assuming 3 phase...

10ga can only be installed on a 30 amp max breaker. Put 10ga on a 60 amp breaker and if there is a problem, the wire will burn before the breaker can trip.

Its a little more complicated than that. #10 NM is max 30a. #10 THHN is 35a..

Regardless, motor circuits are different. In a motor circuit, the breaker is only for short circuit and ground fault protection. The overload(red button on motor), overload relay(starter), or fuses in disconnect provide overcurrent protection for motor and wire....so breakers can be oversized and need to be because of in-rush currents....

Wire is sized @ 125% NEC FLC table...

Breaker can be MAX 250% NEC FLC table...

Compressor must be hardwired if over 3HP...

My 80 gallon DeVilbiss with a 5hp baldor on it is only 27amps full load. 60 seems huge for a compressor. I'm running mine on a 30 amp breaker on 10/2 wire.

10/2 wire is undersized. Read above

EDIT: Pattenp beat me to it!

 

[magrahamkp08]

Good to know. It is currently 10 thhn so I will leave it at that. Yes the air comp has a starter.

Any recommendations for running 100' of wire for my lathe. 100' of 10ga thhn seems really expensive and unnecessary.

 

[wyliesdiesels]

Good to know. It is currently 10 thhn so I will leave it at that. Yes the air comp has a starter.

Any recommendations for running 100' of wire for my lathe. 100' of 10ga thhn seems really expensive and unnecessary.

Did u read my post? How many HP is the lathe and what voltage does it run on?

 

[wildstyle]

Different in Canada? That's the way an electrician wired it at my last place and how I wired it at my new place

 

[wyliesdiesels]

Canadian code does vary from US code... Just the reason why i dont comment on canadian code questions...

 

[Norcal]

If NM cable is used the ampacity is limited to the 60 degree column, and if overload protection is provided the fuse or circuit breaker is just for short circuit protection on a motor circuit.

 

[wyliesdiesels]

Wok wok. Theres a few parrots in here!

Norcal, it sure would be nice to have a sticky outlining basic motor circuit wiring...seems like we repeat this same thing a few times a week!

 

[wildstyle]

Mine also has a Square D magnetic starter on it as well....not sure where that comes into play?

 

[magrahamkp08]

3.5hp 3 phase 240v. I am using a phase converter to get 3 phase

 

[C96]

Its a little more complicated than that. #10 NM is max 30a. #10 THHN is 35a..

Actually, the allowable ampacity for #10 THHN is 40

 

[wyliesdiesels]

Mine also has a Square D magnetic starter on it as well....not sure where that comes into play?

It means your motor doesnt have built in overloads and/or the pressure switch isnt rated for the HP of the motor...

3.5hp 3 phase 240v. I am using a phase converter to get 3 phase

That motor will have an FLC of approx 11a. So 125% of that is 13.75a...simple math gives us approx 4300 cir mils which we would use #12, since #14 is only 4100 cir mils. This is calculated with 3% voltage drop. So #10 is more than adequate.

If youre thinking that #10 seems too small at that length, then u have to remember that youre using a 3phase motor so the FLC is lower. For a 240v single phase 3.5HP motor the FLC is closer to 20a!

Actually, the allowable ampacity for #10 THHN is 40

Thats the 90* c ampacity and is for derating purposes only!

 

[Norcal]

Actually, the allowable ampacity for #10 THHN is 40

That is Home Depot advice and VERY wrong.

 

[C96]

Thats the 90* c ampacity and is for derating purposes only!

Quoted you out of context (my bad), just stating a fact about its allowable ampacity rating.

That is Home Depot advice and VERY wrong.

Lol.. Don’t know what Home Depot is advising, but what I have stated is correct and basically a direct quote from NEC Table 310.15(B)(16)

 

[Norcal]

Quoted you out of context (my bad), just stating a fact about its allowable ampacity rating.



Lol.. Don’t know what Home Depot is advising, but what I have stated is correct and basically a direct quote from NEC Table 310.15(B)(16)

You cannot use the 90 degree column for sizing conductors as there is no equipment rated for 90 degree use, you only use it for derating.

 

[C96]

You cannot use the 90 degree column for sizing conductors as there is no equipment rated for 90 degree use, you only use it for derating.

I understand the purpose of the table, I was simply commenting on the fact that #10 THHN has an allowable ampacity of 40. The comment was not meant to imply anything other than that.

 

[pattenp]

I understand the purpose of the table, I was simply commenting on the fact that #10 THHN has an allowable ampacity of 40. The comment was not meant to imply anything other than that.

 

[C96]

 

[C96]

 

[wyliesdiesels]

Wow! Thx for the laugh. I almoat pissed myself!