Flexible Wire or Strap 250.138

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whuyckjr

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I was recently asked to ground a piece of cord and plug connected equipment by running a ground wire from the faceplate screw on a stainless steel duplex recepticle cover to the metal case on the equipment. According to 250.138 an equipment grounding connection can be made using a flexible wire when connected to an equipment grounding conductor. However, I do not believe that a face plate screw meets the requirements for an equipment grounding conductor (250.118). Secondly, I beleive there is a requirement for a #10 screw treaded into a metal box for bonding (dont recall the code number).

The equipment has a three wire molded cord that includes the grounding conductor plugged into 120vac 20amp recepticle, that is wired properly and passes a circuit test. The owner claims that the equipment is failing a current leak test and needs to pass such test for safety. the equipment is a sign in kiosk with a touch screen display in a lobby waiting area.

Anyone have any advice on this subject? Thanks.
 
whuyckjr said:
I was recently asked to ground a piece of cord and plug connected equipment by running a ground wire from the faceplate screw on a stainless steel duplex recepticle cover to the metal case on the equipment. According to 250.138 an equipment grounding connection can be made using a flexible wire when connected to an equipment grounding conductor. However, I do not believe that a face plate screw meets the requirements for an equipment grounding conductor (250.118). Secondly, I beleive there is a requirement for a #10 screw treaded into a metal box for bonding (dont recall the code number).

The equipment has a three wire molded cord that includes the grounding conductor plugged into 120vac 20amp recepticle, that is wired properly and passes a circuit test. The owner claims that the equipment is failing a current leak test and needs to pass such test for safety. the equipment is a sign in kiosk with a touch screen display in a lobby waiting area.

Anyone have any advice on this subject? Thanks.
Click to expand...

This is just my opinion based on experience. First, since you have a grounding conductor already, providing additional connection to ground via the cover plate screw doesn't violate anything that I am aware of. That said, I don't think it will accomplish anything either unless there is in fact a problem with the aforementioned ground. I think further investigation needs to be done to find out what the actual concerns and facts are regarding this current leak test. If too much current is leaking to ground then the ground is doing what it is supposed to do.
 
The Difference

The Difference

I didn't think a second ground would make a difference either, but the leakage current without the second ground is 600 microamps and with the second ground is zero. I too suspect a problem in the molded cord but the end user wants this complete as requested. I'm just looking for some input and advice. It just looks hack to me.
 
whuyckjr said:
I didn't think a second ground would make a difference either, but the leakage current without the second ground is 600 microamps and with the second ground is zero. I too suspect a problem in the molded cord but the end user wants this complete as requested. I'm just looking for some input and advice. It just looks hack to me.
Click to expand...
That doesn't make electrical sense. By adding the second grounding conductor, you are decreasing resistance to ground, but only insignificant amount if the cord-and-plug ground has not been compromised. The leakage current to ground should remain relatively the same or increase.

The only way leakage current would decrease is if the leakage current being measured is not through the circuit and grounding conductors (e.g. clamping around all the conductors including grounding). Such a decrease would indicate compromised grounding through the equipment cord. Could be connection of grounding conductor to the receptacle, the receptacle, the plug to receptacle contact, the cord wire to the plug prong connection, the cord's grounding conductor, the cord's grounding conductor connection to the chassis, or any combination thereof. You mentioned the circuit tests good, but may not account for the ground prong to receptacle contact.

That said, running the separate grounding conductor is a violation, IMO. 250.138 says by one of the methods, (A) or (B), not both. While a compromised cord ground can be construed as removing (A) from the section's application, I don't believe (B) is intended to be used as a remedy for faulty cord and plug connection.
 
Meter used

Meter used

The leakage is being measured using a Fluke Meter designed for such testing. I do not know the model number. The Fluke plugs into the wall outlet and the equipment then plugs into the Fluke and the measurement is returned. This test equipment is owned by the end user.
 
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whuyckjr said:
The leakage is being measured using a Fluke Meter designed for such testing. I do not know the model number. The Fluke plugs into the wall outlet and the equipment then plugs into the Fluke and the measurement is returned.
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The only Fluke I could find that measures that way is this one:

http://www.flukebiomedical.com/biom...a620-electrical-safety-analyzer.htm?PID=55976

That would exclude the separate grounding conductor from the measurement if just the equipment plug was connected. Was the separate grounding conductor connected by way of one of the other connections?
 
Fluke meter

Fluke meter

Now that you point the exclusion out, you are right. While the Fluke meter is different than the one you posted, it is generally the same. When they tested leakage with the separate ground attached the separate ground was not connected through the meter and would then be excluded from the test measurement, therefore the measurement would be inaccurate. I will bring this to their attention. Thanks.
 
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