We have a so-called electrician that considers motor frame grounds to be an unnecessary evil he can't be bothered with. His negligence even applies to 480 volt fan motors on wooden cooling towers. These "unneccessary" frame grounds are in fact the only grounds to be found on the fan tower motors because the conduit is coated in PVC and is merely strapped to the grounded aluminum cable tray.

The NEC clearly states the need for industrial motor frame grounding in addition to conduit grounds but this guy claims that power plants don't fall under NEC jurisdiction. So I'd like to know what code covers power plants so I can maybe convince this guy and/or his boss that he needs to get with the program.

 

I don't claim to be a power station expert but I think your sparky is crazy. Of course your motors need to be grounded, at the very least through the motor cable/conduit
Roy

 

Sparky your "electrician's" statement that power plants are excempt from NEC rules is correct, but requires clarification.

Most Utilities are exempt, until their practice runs afoul of NEC requirements, especially in a law suit!

I was personally involved in a case where the Utility (plantiff) sued a Controls Vendor (defendant) for $800,000,000, for loss of the Utility's boiler resulting from an explosion, during light-off. Because an NEC recommentation was essentially ignored, the Utility was held responsible for about $700,000,000 of the loss, while the Vendor was held responsible (resulting from the 'deep pockets' rule) for the balance!

Regards, Phil Corso ([email protected])

 

I'd suggest your electrician be prompted to research the specific citations supporting his case. I can't think of any circumstances (outside of certain testing procedures) where a motor frame shouldn't be grounded, but many cases where an ungrounded motor frame led to electrocution.

 

I've heard this argument before, that NFPA doesn't apply to power plants, or that the foundation bolts are grounded and so re-connecting the ground leads is unnecessary.

It's common sense that says that for everyone's safety, including his own, that motor frames and conduit should be grounded.

If the motors are ungrounded as installed by the constructor, then there's something we're missing here. If he's just refusing to re-connect an existing ground lead to an existing ground lug on the motor frame or conduit, then your safety representative should be having a very serious conversation with this person. And anyone else who might come in contact (normally or accidentally) with these motors as it's their safety that he's affecting.

Perhaps he should spend every break and lunch period seated on one of the running, ungrounded motors. Or, that he has to physically touch each running ungrounded motor with his tongue to determine if there's a ground in the stator before anyone else touches the motor for any reason.

 

Nothing in the code requires an external frame ground AFAIK. Perhaps you can point out where that is to be found in the code.

It is perfectly acceptable to use the conduit as the grounding means, and is quite common.

If what you are suggesting is the conduit is not bonded, that is by itself a code violation.

He is mostly right about power plants not being subject to the NEC though most utilities have adopted most of the code as an internal standard.

 

ANSI/IEEE Standard 141 (Red Book) addresses the necessity of equipment grounding. I also believe that ANSI C2 "National Electric Safety Code" has been adopted by most utilities, so you may want to check that standard. I am not familiar with it, however.

 

I think your "So-called electrician" is not worthy of the title. Unless special precautions are taken, even the continuity of conduit can be questionable. If he insisted on practicing the trade in the manner that you describe, he should be allowed one occurrence in which to learn. The second occurrence of such a flagrant disregard for safety would clearly demonstrate that he is untrainable. Most organizations have no need for folks like that.

 

I agree, just because power plants are exempt does not mean that it would be SAFE to not follow it. It also does not exempt them from OSHA safety rules etc. You still cannot blatently ignore safety. I had a similar issue involving steam safety and an individual who said it was not an issue. My answer like another writers was to have this supervisor stand by the tank while I "failed" the valve, Of course he refused and we fixed the situation.

I think that someone should "manage" this individual and lay down the law.

Dave Ferguson
Control Systems Engineer

 

Ask the electrician to put a voltmeter between the motor frame and earth ground while the motor is running.  If there is truly no ground attached to the motor frame, then dangerous voltages may be present.  The motor can act as a transformer and energize the frame. 

Another potential issue is current traveling through the bearings if the motor frame is not grounded, but the motor shaft is grounded.  This can damage your bearings, especially if the use a variable speed drive.

Bill Sturm

Abbeytronics LLC

 

Sorry to rise up this old message, but I have a question involving a current grounding design so I need you expert experience on that matter.

In my current grounding design I have grounded every MV and LV motor frame (NEC 250.112(C) and 430.242) by means of sized grounding conductor which is laid all along all the cable trays of the plant.

The case is that the vendor has provided a grounding terminal inside the terminal box and our client is claiming us to explain via the NEC why this terminal is not connected/bonded since the NEC 430.12(E) seems to require also the connection to the grounding terminal of the motor terminal box.

My understanding is that because the box is in permanent metallic contact with the frame, there is no need to connect/bond this terminal since the box is already being grounded via the frame.
The closest reason I have found in the NEC is NEC 250.136(A) "equipment secured to grounded metal supports" [equivalent to OSHA 1926.404(f)(8)(iii)], but ir refers to the metal supports/racks.

I would be very thankful if someone could help me.
Thanks in advance.

 

Valen... the grounding lug within the motor's JB, is a just a convenient means of grounding the frame when the GroundING conductor is installed with the "TEE" leads!

If the conduit is a legit "GroundING" method, the the lug is superfluous!

Regards,
Phil Corso

 

Thank you Phil for your prompt answer.

This is also my understanding, but I would like to find any section in the NEC that could state that it is not necessary to use the superfluous lug when the motor frame is already being grounded by equipment grounding conductors.

FYI: power cable is entering to the box by means of cable gland, not conduit. Equipment grounding cable is installed all along the cable trays; this cable is connected to grounding electrode (main grounding grid mesh) every 30m.

Could you please support me in this sense?
Thanks a lot in advance. Appreciate your interest.

 

Valen,

please provide some construction detail.

Cable size, insulation,rubber-sheathing, metal-shield, termination-fitting, EGC size in tray, periodic bonding to EGC, etc?

Phil

 

Valen... pic(s) will help. Send to: [email protected]

Phil

 

Hi Phil,

At this time I am not at the office so I can't post further details, meanwhile you could check the thread I posted in Mike Holt forum.
http://forums.mikeholt.com/showthread.php?t=170885

Hope this helps to understand. If more information is necessary I will send it to you by email (by the way, thank you for your interest and help).

The EGC cable installed at cable trays is MCM #250 (calculated by IEEE80 and NEC), same size than the power cable which is 3F3W without grounding conductor.

MV power cable is 5kV 133% MV105 and shielded, and 600V XHHW-2 without shield for LV cable of 480V system.

EGC is bonded each 30m to grounding electrode (grounding grid mesh of the plant). This cable is used to ground frame motors, enclosures, conduits, etc.

Please let me know if you need any other information.
Thank you again.

 

Valen... If I have correctly interpreted your query, I can present a legal argument that will illustrate why the external EGC-conductor does not have to be connected to the internal grounding-lug.

Please contact me at [email protected] to discuss details.

Phil

 

Valen,

Please see my reply over on Mike Holt's forum...

 

Dear Phil,

Thank you very much for you invaluable help and interest.

Best regards

 

Valen... you're welcome!

Were you able to come to an amicable agreement with your client?

Phil Corso