Wire size check sparkies.

[Possum]

7.5hp 3ø motor, 22 full load amps, 40 ft. one way.
22 x 1.25 = 27.5 amps = 10 AWG?
What should I use for a ground? Can I run this in 1/2" EMT?

Thanks in advance.

 

[Gooch]

7.5hp 3ø motor, 22 full load amps, 40 ft. one way.
22 x 1.25 = 27.5 amps = 10 AWG?
What should I use for a ground? Can I run this in 1/2" EMT?

Thanks in advance.

#10's will be fine. If it's 480v you could actually use #12.

as for the ground it is based off the breaker/fuse.

but as long as you're using a Inverse-time breaker or time delay fuses you'll be fine with a #10 ground aswell.

also asuming you're using THHN single conductor, you can get it in 1/2" emt.

 

[Aceman]

I don't know whether your motor is 208v or 230v? But either way, #10 THHN would work. It will fit in 1/2" but I'd recommend 3/4" emt.

 

[electrican]

7.5hp 3ø motor, 22 full load amps, 40 ft. one way.
22 x 1.25 = 27.5 amps = 10 AWG?
What should I use for a ground? Can I run this in 1/2" EMT?

Thanks in advance.

Green wire!

 

[Possum]

Thanks for the responses fellas. Its 230V and yes I will be using THHN. It will be fed from a three poll 30A breaker and the lathe has a built in disconnect and fuses. So no reduced ground?

 

[Gooch]

Thanks for the responses fellas. Its 230V and yes I will be using THHN. It will be fed from a three poll 30A breaker and the lathe has a built in disconnect and fuses. So no reduced ground?

that 30A breaker will trip alot.


Just so we are clear, you have a 240V 3phase service?

 

[Possum]

Yes, fed from phase converter. Am I not sizing the breaker correctly? I thought the breaker would have to protect the wire. I had it temporarily setup with 12 awg on a 20 amp and didn't have any trouble. I just moved it to its final location and wanted to get it right. There are no codes in my area FYI.

 

[Gooch]

Yes, fed from phase converter. Am I not sizing the breaker correctly? I thought the breaker would have to protect the wire. I had it temporarily setup with 12 awg on a 20 amp and didn't have any trouble. I just moved it to its final location and wanted to get it right. There are no codes in my area FYI.

NEC will allow up to a 60 Amp breaker, but if you're not having any issues with it tripping then it's fine.

The breaker is protecting the wire, from short circuits, not overcurrents. if the motor is overloaded and thus causes an overcurrent the overloads will trip. the breaker is there for short circuit and ground fault protection only.

 

[Possum]

Good to know. I did some searching and found this - "Breaker cannot be larger than ampacity of wire, except for motors and a few other loads." - and then gives a 175% figure. Is this what code states?
Thanks for all the input.

 

[fefarms]

Given a circuit dedicated to supplying a motor, the motor controller (at the motor end)provides overcurrent protection for the supply wires. The code allows the selection of a breaker of as large as 175 percent of the ampacity of the supply wires. If there are then problems with nuisance tripping the code allows further upsizing to 250 percent.

The need for any of this upsizing will depend on how difficult the load is to start. For machine tools like lathes and mills you won't need much if any. Motors driving air conditioning systems or conveyor belts will need a fair amount. Air compressors will be somewhere in the middle.

 

[wyliesdiesels]

Good to know. I did some searching and found this - "Breaker cannot be larger than ampacity of wire, except for motors and a few other loads." - and then gives a 175% figure. Is this what code states?
Thanks for all the input.

175% FLC is actually the max size for dual element fuses. A breaker can be a max of 250% FLC...

Given a circuit dedicated to supplying a motor, the motor controller (at the motor end)provides overcurrent protection for the supply wires. The code allows the selection of a breaker of as large as 175 percent of the ampacity of the supply wires. If there are then problems with nuisance tripping the code allows further upsizing to 250 percent.

The need for any of this upsizing will depend on how difficult the load is to start. For machine tools like lathes and mills you won't need much if any. Motors driving air conditioning systems or conveyor belts will need a fair amount. Air compressors will be somewhere in the middle.

Thats not what the code says. See T430.52. It states a max size of 175% FLC for dual element fuses and 250% FLC for inverse time breakers....

 

[Norcal]

If not NM cable, you get to use 310.16 ampacities for motors. You cannot reduce the grounding conductor w/ 10 & 12 AWG 12 requires a 12 AWG EGC, 10 requires a 10 AWG EGC.

 

[hidollartoys]

7.5hp 3ø motor, 22 full load amps, 40 ft. one way.
22 x 1.25 = 27.5 amps = 10 AWG?
What should I use for a ground? Can I run this in 1/2" EMT?

Thanks in advance.

Is this "table amps" or what is on the nameplate? Code requires you to use "table amps" for conductor sizing. Sorry dont have a code book in front of me but I think it is table 430.250.

 

[wyliesdiesels]

Is this "table amps" or what is on the nameplate? Code requires you to use "table amps" for conductor sizing. Sorry dont have a code book in front of me but I think it is table 430.250.

yes, 22a IS table amps for 7.5hp 230v rated motor. Yes, the table is 430.250

 

[Aceman]

Why are you digging up 2 year old threads Wylie?

 

[wyliesdiesels]

Why are you digging up 2 year old threads Wylie?

To correct the misinformation in case someone stumbles on it. Why do u ask? Is it against the rules or does it bother u?

 

[foolishpride]

Why are you digging up 2 year old threads Wylie?

Wylie is very bored!

 

[wyliesdiesels]

Wylie is very bored!

good guess!!

 

[Aceman]

To correct the misinformation in case someone stumbles on it. Why do u ask? Is it against the rules or does it bother u?

Neither.

I just didn't realize you were on a personal crusade to right all the wrongs on the electrical forum. If that's the case.....

175% FLC is actually the max size for dual element fuses. A breaker can be a max of 250% FLC...

Thats not what the code says. See T430.52. It states a max size of 175% FLC for dual element fuses and 250% FLC for inverse time breakers....

Actually, that's only the half of it. Those are the maximum table values, but if they do not correspond to a standard breaker size you can pick the next breaker size up. And you are allowed to go past that maximum table value.

On top of that, if that previously chosen fuse size blows on startup of a motor, you can now use 225% as the absolute maximum instead of 175%.

For example, 22 amps x 225%=49.5 amps.

You must round down, instead of up like before which gives you a 45 amp fuse.

A breaker is the same story.

22 x 250%=55 amps=60 amp breaker.

You are allowed to round up to the next breaker size. Now if it trips you are allowed an absolute maximum of 400% for loads 100 amps and less, but you must round down.

22 x 400%=88 amps=80 amp breaker.

Is this "table amps" or what is on the nameplate? Code requires you to use "table amps" for conductor sizing. Sorry dont have a code book in front of me but I think it is table 430.250.

yes, 22a IS table amps for 7.5hp 230v rated motor. And the correct table is T430.52 not .250!

I don't see why you are trying to correct him here, he listed the right table for motor amps.

 

[wyliesdiesels]

I don't see why you are trying to correct him here, he listed the right table for motor amps.

Yes, youre right. I dont know how i did that one....