Chassis Ground Where Service Enters Machine

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fifty60

fifty60

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I have equipment (roughly the size of a small refrigerator turned on its side, it is not a refrigerator however) that is cord and plug connected to a 20A 120V outlet. The cord enters the rear of the machine, and is routed inside the equipment approximately 3.5 feet and then lands inside a UL 467 grounding terminal block.

Someone is telling me that the NEC requires a separate chassis ground at the point the electric service enters the machine. I agree the equipment has to be connected to the equipment grounding conductor, which it is, but I do not see any where in article 250 that requires that this be done at the point cord enters the machine. Even if it did say this, what advantage is there to cutting my listed cord that early in the circuit, and then running MTW the rest of the way to the power and grounding terminal blocks.

Where in 250 does it say "at the point the electric service enters the machine"? I think my obligations under article 250 are to connect the machine to the equipment grounding conductor (near the supply TERMINALS and not the point of entry), and then the exception under 250.114...
 
He may be talking about what is pointed out in 250.4(A)(2). This appears to not be the Equipment Grounding Conductor, but the connection to earth for lightning and other surge type protection. I do not see anywhere else in 250 that talks about this. The rest of 250 seems to cover what is required from 250.4(A)(3-5).

Is 250.4 saying that equipment needs an equipment grounding conductor back to the main service AND a separate grounding strap?
 
fifty60 said:
at the point the electric service enters the machine.
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Let's replace that word with "supply"; unless I'm highly mistaken, there is no "service" as defined by the NEC involved since it's cord/plug connected.

You mentioned UL- is this a listed piece of equipment? If so, and unless the instructions say otherwise, the EGC in the cord should be all that's required and once that enters the cabinet, the NEC no longer matters.
 
The equipment is not UL listed, but has been UL field tested in the past. What is NEC 250.4(A)(2) trying to say? Is this requiring a grounding strap for ESD?
 
There are times when someone has a way of doing things that they feel is correct and so they ,,over time ,,believe it to be code.
If you can show that the frame and the ground lug are connected,electrically then id say you re right.
 
The inspector is referencing OSHA Regulations 1910.304, in particular:

1910.304(g)(4)(i)
For a grounded system, a grounding electrode conductor shall be used to connect both the equipment grounding conductor and the grounded circuit conductor to the grounding electrode. Both the equipment grounding conductor and the grounding electrode conductor shall be connected to the grounded circuit conductor on the supply side of the service disconnecting means or on the supply side of the system disconnecting means or overcurrent devices if the system is separately derived.

1910.304(g)(5)
Grounding path. The path to ground from circuits, equipment, and enclosures shall be permanent, continuous, and effective.

Does this vary from state to state? Is the manufacturer required to provide this or is the installer of the equipment?
 
fifty60 said:
The inspector is referencing OSHA Regulations 1910.304, in particular:

1910.304(g)(4)(i)
For a grounded system, a grounding electrode conductor shall be used to connect both the equipment grounding conductor and the grounded circuit conductor to the grounding electrode. Both the equipment grounding conductor and the grounding electrode conductor shall be connected to the grounded circuit conductor on the supply side of the service disconnecting means or on the supply side of the system disconnecting means or overcurrent devices if the system is separately derived.

1910.304(g)(5)
Grounding path. The path to ground from circuits, equipment, and enclosures shall be permanent, continuous, and effective.

Does this vary from state to state? Is the manufacturer required to provide this or is the installer of the equipment?
Click to expand...
the terms "service" and "system" have very specific meanings within the NEC (and likely referenced by OSHA).

It is unlikely you have either unless you are supplying some kind of transformer within your equipment. In that case, it could be a separately derived system and might need a connection to the grounding electrode system.
 
fifty60 said:
The equipment is not UL listed, but has been UL field tested in the past. What is NEC 250.4(A)(2) trying to say? Is this requiring a grounding strap for ESD?
Click to expand...

If it was field tested in the past, that was only good for that specific installation. Just got done with a presentation with a rep from a NRTL, and a field evaluation is only for that specific piece of equipment at that location. It is not equal to the listing of a product.
 
Yes, I agree that is the case Packersparky. My reference to UL field tests was meant to convey that the same equipment has been inspected by UL before, and the above was never mentioned. I believe what is going on is that the OSHA inspector is trying to get us to install an grounding electrode conducter connection (not and EGC safety ground) to the equipment. Am I obliged to do this for 120V cord connected lab equipment?

I think interrupting the equipment grounding conductor where the 20A supply enters the equipment so that a grounding electrode conductor can be installed in the same terminal, and then running the EGC the rest of the way to the panel is not safe, but just adds another place where the EGC can fail.

I think if I could better understand what NEC NEC 250.4(A)(2) is trying to say, and what obligations I have for fulfilling NEC 250.4(A)(2), I would better understand what I have to do vs what they are wanting to do..
 
fifty60 said:
Yes, I agree that is the case Packersparky. My reference to UL field tests was meant to convey that the same equipment has been inspected by UL before, and the above was never mentioned. I believe what is going on is that the OSHA inspector is trying to get us to install an grounding electrode conducter connection (not and EGC safety ground) to the equipment. Am I obliged to do this for 120V cord connected lab equipment?
Click to expand...

It might be required if there is a transformer inside this unit that creates an SDS.
 
Is this a factory supplied cord & plug that came as part of the equipment ?

It may just be me, but it sounds a whole lot like we are mixing oranges with apples here.
As zbang points out the term "service" as referenced in the NEC would be in no way applicable to a
piece of equipment supplied by a 20amop cord & plug.
Unless I am very mistaken, if this equipment has a factory cord and plug, NEC rules are not involved. If it has a listing or field elvaluation by UL or amny other NRTL, I don't see where any inspector would even be involved unless they wanted to challenge the listing agency.
 
fifty60 said:
The inspector is referencing OSHA Regulations 1910.304, in particular:

1910.304(g)(4)(i)
For a grounded system, a grounding electrode conductor shall be used to connect both the equipment grounding conductor and the grounded circuit conductor to the grounding electrode. Both the equipment grounding conductor and the grounding electrode conductor shall be connected to the grounded circuit conductor on the supply side of the service disconnecting means or on the supply side of the system disconnecting means or overcurrent devices if the system is separately derived.

1910.304(g)(5)
Grounding path. The path to ground from circuits, equipment, and enclosures shall be permanent, continuous, and effective.

Does this vary from state to state? Is the manufacturer required to provide this or is the installer of the equipment?
Click to expand...

That kind of describes same requirements that are in NEC - but for services not for utilization equipment on a branch circuit.


250.4 is "general" grounding and bonding requirements for everything and there may be more specific requirements for certain conditions. You really need to keep these general items in the back of your mind then go down to 250 part VI for equipment grounding for your application.
 
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