More Corner Grounded Delta Q's

[biggladant]

I have been going over threads on 3 phase corner grounded systems but I am still confused on a few things. On a 3 pole fusible motor disconnect does the grounded phase have to be sluged or is a fuse also ok? If it does have to be slugged is it a NEC requirement? I also have the same question for motor overloads.The system I am working on is 480 Volt and currently all the disconects have three fuses. Thanks

 

[john m. caloggero]

Re: More Corner Grounded Delta Q's

Hi Bigg, According to the Section 240.22 of the 2002 NEC, NO overcurrent device in the grounded conductor UNLESS it opens all of the ungrounded conductors and the grounded conductor simultaneously.
John C

 

[don_resqcapt19]

Re: More Corner Grounded Delta Q's

John,
You have to add the next part of that section, which permits the use of fuses in the grounded conductor for motor overload protection.
Don

 

[biggladant]

Re: More Corner Grounded Delta Q's

Thanks for your replies, I am not useing fuses for overload protection and I will make sure that there are overload units in each phase, if there is not any safety factors other than NEC 240.22 I think i will leave this existing system alone and not worry about the fuses in each phase but I will let the customer know about it. Does this seem like the right thing to do? Thanks Again for the replies.

 

[kiloamp7]

Re: More Corner Grounded Delta Q's

Yes, but that is where the fuses serve as running overload protection , right?

That is seldom the case, right?

Usually the running overload protection are "heaters" in the motor starter.

 

[kiloamp7]

Re: More Corner Grounded Delta Q's

Sorry, big. Your post beat mine.

My comment was about don_r statement above.