Questions on machine tool install - feeder, xfmr, wiring, grounding/bonding

[4eyedbuzzard]

Hi, hoping for a bit of help. Today at work, a fairly large new lathe that's been sitting unused for months suddenly became a crisis and my illustrious management team (the same geniuses that buy 208V equipment in a facility with 480V distribution) is now in a rush to fire it up by Friday.

Info sent from manufacturer and local rep is 208/220 3Ø 45KVA. The sum of all motors (I physically looked) is 32KVA. But nameplate is stamped 208/220 3Ø 65KVA. Made in Taiwan, of course, with, IMO, poor electrical documentation. Note - It is extremely doubtful the machine will ever run anywhere near full load current as it's overkill for the work being performed. That said...

A 480/208 45 KVA delta/wye xfmr has already been set by others, primary wired with 3x #6 thhn and #10 ground in 3/4" EMT and greenfield, fused at 50a. As there will be no secondary OCPD other than the lockable machine main disconnect/OCPD, I sized the secondary conductors for the full xfmr rating of 45KVA, 125amps at 208V (75°C), running 3x #1 thhn and a #6 ground in 1 1/4" EMT. There is no neutral connection at the machine itself. Does this seem correct?

My understanding is the EGC from the machine, the supply side ground, the xfmr frame/enclosure all connect at the same point/lug and be connected to X0 at the xfmr secondary via system bonding jumper. Correct?

All conductors on both primary and secondary to be run in EMT/greenfield and with ground wire as well. No concentric knockouts will be used, secondary is under 250V, so I don't believe grounding locknuts or grounding bushings are required. Correct?

Any help or comments on the above is really appreciated.

Thanks!

 

[Little Bill]

Bump

 

[electrofelon]

Hi, hoping for a bit of help. Today at work, a fairly large new lathe that's been sitting unused for months suddenly became a crisis and my illustrious management team (the same geniuses that buy 208V equipment in a facility with 480V distribution) is now in a rush to fire it up by Friday.

Info sent from manufacturer and local rep is 208/220 3Ø 45KVA. The sum of all motors (I physically looked) is 32KVA. But nameplate is stamped 208/220 3Ø 65KVA. Made in Taiwan, of course, with, IMO, poor electrical documentation. Note - It is extremely doubtful the machine will ever run anywhere near full load current as it's overkill for the work being performed. That said...

A 480/208 45 KVA delta/wye xfmr has already been set by others, primary wired with 3x #6 thhn and #10 ground in 3/4" EMT and greenfield, fused at 50a. As there will be no secondary OCPD other than the lockable machine main disconnect/OCPD, I sized the secondary conductors for the full xfmr rating of 45KVA, 125amps at 208V (75°C), running 3x #1 thhn and a #6 ground in 1 1/4" EMT. There is no neutral connection at the machine itself. Does this seem correct?

My understanding is the EGC from the machine, the supply side ground, the xfmr frame/enclosure all connect at the same point/lug and be connected to X0 at the xfmr secondary via system bonding jumper. Correct?

All conductors on both primary and secondary to be run in EMT/greenfield and with ground wire as well. No concentric knockouts will be used, secondary is under 250V, so I don't believe grounding locknuts or grounding bushings are required. Correct?

Any help or comments on the above is really appreciated.

Thanks!

You need a GEC for the SDS per 250.30(A)(4). As long as the machine disconnect has appropriately sized fused,then it looks ok to me.

 

[ActionDave]

Hi, hoping for a bit of help. Today at work, a fairly large new lathe that's been sitting unused for months suddenly became a crisis and my illustrious management team (the same geniuses that buy 208V equipment in a facility with 480V distribution) is now in a rush to fire it up by Friday.

Info sent from manufacturer and local rep is 208/220 3Ø 45KVA. The sum of all motors (I physically looked) is 32KVA. But nameplate is stamped 208/220 3Ø 65KVA. Made in Taiwan, of course, with, IMO, poor electrical documentation. Note - It is extremely doubtful the machine will ever run anywhere near full load current as it's overkill for the work being performed. That said...

A 480/208 45 KVA delta/wye xfmr has already been set by others, primary wired with 3x #6 thhn and #10 ground in 3/4" EMT and greenfield, fused at 50a. As there will be no secondary OCPD other than the lockable machine main disconnect/OCPD, I sized the secondary conductors for the full xfmr rating of 45KVA, 125amps at 208V (75°C), running 3x #1 thhn and a #6 ground in 1 1/4" EMT. There is no neutral connection at the machine itself. Does this seem correct?

My understanding is the EGC from the machine, the supply side ground, the xfmr frame/enclosure all connect at the same point/lug and be connected to X0 at the xfmr secondary via system bonding jumper. Correct?

All conductors on both primary and secondary to be run in EMT/greenfield and with ground wire as well. No concentric knockouts will be used, secondary is under 250V, so I don't believe grounding locknuts or grounding bushings are required. Correct?

Any help or comments on the above is really appreciated.

Thanks!

I don't know what you mean by " As there will be no secondary OCPD other than the lockable machine main disconnect/OCPD" but you should have secondary overcurrent protection.

You are correct about the system bonding jumper and XO. No extra grounding bushing or locknuts are required.

edit to add, Electrophelon is right, about the GEC.

 

[electrofelon]

I don't know what you mean by " As there will be no secondary OCPD other than the lockable machine main disconnect/OCPD" but you should have secondary overcurrent protection.

Yeah I was a little concerned by that. To elaborate, the issue is the secondary conductors need protection. You have several options in 240.21(C), usually (2) or (6).

 

[4eyedbuzzard]

You need a GEC for the SDS per 250.30(A)(4). As long as the machine disconnect has appropriately sized fused,then it looks ok to me.

Yes. Understood. And I've been trying to explain this (GEC and other NEC requirements (especially the concepts of grounding and bonding to people who think that if you buy 90°C wire you can size conductors based solely upon that, without regard to ambient temp, derating for conductor fill, etc. I LOVE my job! 8~/

Checked two other similar installations (xfmr's supplying power to machine tools) in the plant and of course there is no GEC run on either. Unfortunately, chances are it will stay that way whether I point out the problem or not. Anyway, MY install isn't going to follow the "we've always done it this way approach". The nearest building steel is approx 15' overhead (nothing lower, all encased in masronry) and I am looking for suitable routing for a #6 GEC. Thanks for the reminder.

 

[4eyedbuzzard]

Yeah I was a little concerned by that. To elaborate, the issue is the secondary conductors need protection. You have several options in 240.21(C), usually (2) or (6).

Yes. I was assuming 240.21(C)(2)+(6) would allow me to satisfy the xfmr secondary conductor rule requirement but wanted some confirmation. I'm thinking it's okay and that I don't need a (pretty expensive) separate fusible disconnect in between the transformer and the lathe. Secondary conductors are exactly 25 ft to the disconnect switch/breaker at the machine (I had to move the xfmr a bit closer to the machine). The breaker is adjustable trip (set to lowest setting 112 amps) and is only accessible to qualified personnel as both the switch/breaker and the enclosure door are lockable and would seem to comply with 240.6(C)(3) conductors and 450 (B)(3) transformer.
Thanks for the reply.

 

[electrofelon]

Checked two other similar installations (xfmr's supplying power to machine tools) in the plant and of course there is no GEC run on either. Unfortunately, chances are it will stay that way whether I point out the problem or not. Anyway, MY install isn't going to follow the "we've always done it this way approach". The nearest building steel is approx 15' overhead (nothing lower, all encased in masonry) and I am looking for suitable routing for a #6 GEC. Thanks for the reminder.

Well the GEC really doesnt do anything anyway. As long as the SBJ is properly made up the supply EGC will ground the system just fine. That requirement is silly IMO. I am not saying dont follow the rules, but dont loose sleep over it if it is out of your control.

 

[4eyedbuzzard]

Well the GEC really doesnt do anything anyway. As long as the SBJ is properly made up the supply EGC will ground the system just fine. That requirement is silly IMO. I am not saying dont follow the rules, but dont loose sleep over it if it is out of your control.

Yeah. Understood. The counter argument is that my facility has an ongoing problem of allowing one bad practice here, another one there, and so on, that leads to/reinforces a culture of poor craftsmanship. Usually, it's more just annoying than anything else. Occasionally though, it's dangerous. I'm trying slowly to change it bit by bit.

Thanks again for taking the time to reply.