Motors

[wmeek]

If you have a 20HP three phase motor that has a nameplate of 46A do you use table amps of 54A or nameplate amps in determining the overcurrent for the breaker.
46A x 250%= 115A go up to 125A
54A x 250%= 135A go up to 150A

Also when determing the disconnect size do you use table amps or nameplate
46A x 115%= 52.9A up to 60A
54A x 115%= 62.1A up to 100A

 

[david luchini]

Per 430.6(A), you would use the table value of 54Amps for determining conductor size and OCPD size. You would use the nameplate amps for sizing the overload protection.

The 150A would be the maximum allowable c/b size, but nothing prevents you from using a smaller c/b.

 

[wmeek]

So do you think if you went with a 100A breaker that it would be sufficient
Also what about the disconnect size

 

[david luchini]

So do you think if you went with a 100A breaker that it would be sufficient
Also what about the disconnect size

I see no problem with a 100A breaker (as long as it does trip on inrush at motor starting.)

The disconnect size is also sized based on the table amps value. See 430.110 for sizing requirements. I think you'd need a 100A disconnect.

 

[wmeek]

Thanks David

I havent had much experience om motor branch circuits

 

[wmeek]

I have another question about the size of so cord needed. I have 54A x 125% = 67.5A
I am using a #4 Thhn conductor in condiut to a 100A disconnect. I will be using so cord from disconnect to this chop saw, because it is on a mobile stand. If using a so cord at 54A x 125% = 67.5A, It looks like you need a #2 per 400.5(A) of the 2008 NEC. Would this be a code compliant install.

 

[jumper]

I have another question about the size of so cord needed. I have 54A x 125% = 67.5A
I am using a #4 Thhn conductor in condiut to a 100A disconnect. I will be using so cord from disconnect to this chop saw, because it is on a mobile stand. If using a so cord at 54A x 125% = 67.5A, It looks like you need a #2 per 400.5(A) of the 2008 NEC. Would this be a code compliant install.

You cannot hard wire the saw to the disconnect using SO cord.

 

[wmeek]

Thanks for that info. But is #2 So cord correct size for this. I will use a receptacle instead.

 

[wmeek]

Trying to size a SO cord for this saw. Its a 20hp 240V 3 phase.
54A x 125% = 67.5
Using table 400.5(A) column (A) in 2008 Code is a #2 conductor the proper size for this application. Going to run approx. 25' and attatch a 60A ( per 430-109(F) pin an sleeve type receptacle and cord cap.
Would this be code compliant.

Thanks

 

[Cow]

Trying to size a SO cord for this saw. Its a 20hp 240V 3 phase.
54A x 125% = 67.5
Using table 400.5(A) column (A) in 2008 Code is a #2 conductor the proper size for this application. Going to run approx. 25' and attatch a 60A ( per 430-109(F) pin an sleeve type receptacle and cord cap.
Would this be code compliant.

Thanks

Without looking at your cord size, I bet the pin and sleeve connectors you need will be 100 amp to meet the HP rating of your motor. With that said, I bet you'll have 1-2k in just the cord/pin and sleeves connecting this chop saw. Are you sure they can't live with flex and unhooking some wires if they ever need to move it? I also can't picture how you'll physically fit #2 cord in a 20HP peckerhead.

 

[wmeek]

Manufacture of the saw says the starter enclosure will accept the #2 SO cord. My customer wants to be able to roll the saw out in the driveway of their shop to cut these 2 1/2- 3" wire rope cables. I understand that it will be costly , I was just wanting to know if I have it all figured correctly.