Grounding industrial XMFR's

[joepa]

When a 480-208/120 XMFR's installed in a building the ground must be reestablished via building steel, water pipe, ground rod. When a 480-208/120 XMFR's are installed on a industrial machine for control power, I've never seen the ground reestablished. The XO bond is there but the earth ground isn't. Can anybody clear this up for me

 

[ron]

Re: Grounding industrial XMFR's

250.30(A)(2) would apply to both scenarios.

 

[jtester]

Re: Grounding industrial XMFR's

Ron
I am not sure that I agree. When the transformer serves premises wiring, then it should be grounded. As part of an industrial machine it doesn't serve premises wiring as specified in 250.20(B), and then I suggest it doesn't have to be grounded.
Jim T

 

[don_resqcapt19]

Re: Grounding industrial XMFR's

Look at the exception to 250.30(A)(2) and 250.21(3).

 

[don_resqcapt19]

Re: Grounding industrial XMFR's

Jim,
I don't see where 250.20 restricts itself to premises wiring systems. Even if it did, if the control circuit extends beyond the "wiring internal to appliances, luminaires (fixtures), motors, controllers, motor control centers, and similar equipment", it would be "premises wiring".
Don

 

[ron]

Re: Grounding industrial XMFR's

Don,
Thanks for the reminder for exceptions. Many of the control transformers I have seen lately have been in excess of 1kVA. so I forgot.

 

[jtester]

Re: Grounding industrial XMFR's

Don
I agree with you that 250.20 does not restrict grounding to only those systems, but it clearly says when a system must be grounded. You certainly could ground the 480 to 120/208 transformer, and should if it has a neutral as a circuit conductor for example.
My point was that I don't see where 250.20 would require the machine transformer to be grounded unless there are extenuating circumstances.
Jim T

 

[petersonra]

Re: Grounding industrial XMFR's

As a practical matter, very few industrial control transformers (at least smaller ones) come with a ground lug anyway. I guess the fact that they are typically bolted to a steel sheetiron effectively grounds them anyway.

 

[don_resqcapt19]

Re: Grounding industrial XMFR's

Jim,

My point was that I don't see where 250.20 would require the machine transformer to be grounded unless there are extenuating circumstances.

I just don't see anything in 250.20 that says that the secondary of a 480/120 volt control transformer does not have to be grounded. It appears to apply to all systems where you can ground a secondary conductor and have a maximum voltage to ground on the ungrounded conductors of 150 volts or less. I don't see any exception for control transformers.
Don

 

[jtester]

Re: Grounding industrial XMFR's

Don
I'm a bit confused. If your reference to the requirement for grounding systems where the voltage to ground on the ungrounded conductors is 150 volts or less is 250.20(B)(1), then that does not seem to apply to all systems, only to premises wiring and premises wiring systems. Can you be more specific about the requirement for grounding the machinery transformer?
Jim T

 

[don_resqcapt19]

Re: Grounding industrial XMFR's

Jim,

If your reference to the requirement for grounding systems where the voltage to ground on the ungrounded conductors is 150 volts or less is 250.20(B)(1), then that does not seem to apply to all systems, only to premises wiring and premises wiring systems

Where does the code say that? I don't find anything that says 250.20 only applies to premises wiring systems.
Don

 

[rbalex]

Re: Grounding industrial XMFR's

Don,

I agree with Jim on this one. Section 90.2(A) with special emphasis on 90.2(A)(1) applies to the entire Code. Combining that with the second paragraph of 90.7 and the definition of Premesis Wiring excludes non-premises wiring from the NEC scope since it is not an installation and is covered by product standards rather than direct application of the Code. Product standards may be affected by the Code of course.

We went through a fairly lengthy debate on CMP14 with regard to "personal electronic devices" (hearing aids, pacemakers, wrist watches, etc.) none of which are approved specifically for classified locations, but all are routinely used in them even in Division 1. We concluded they are not "installations" and are not generally covered.

I do agree that any wiring that extends beyond the enclosure would be "premises" wiring.

 

[jtester]

Re: Grounding industrial XMFR's

Don
250.20(B) Alternating-Current Systems of 50 to 1000 Volts Alternating current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the folowing conditions:... or (D) Separately Derived Systems. which refers us to (B) in this case. 250.20(B) seems to limit its requirements for grounding to premises wiring.

 

[petersonra]

Re: Grounding industrial XMFR's

Originally posted by rbalex:
I do agree that any wiring that extends beyond the enclosure would be "premises" wiring.

So virtually every machine tool ever made is in violation?

 

[rbalex]

Re: Grounding industrial XMFR's

I was refering to the application in Don's second post: '...if the control circuit extends beyond the "wiring internal to appliances, luminaires (fixtures), motors, controllers, motor control centers, and similar equipment", it would be "premises wiring".'

[ December 22, 2004, 03:17 PM: Message edited by: rbalex ]

 

[don_resqcapt19]

Re: Grounding industrial XMFR's

Jim,
Sorry, I just kept reading right past those words.
Don