Supplemental grounds for sensitive electronic equipment?

[Martin B]

If any one has ran into a similar situation I would appreciate any advice.


I was told that some one needed a "ground wire pulled". As soon as I read the service request one of my eye brows went up. I get to the job, which is a medical research laboratory and and it seems that a maintenance guy spotted something he didn't like so he reported it.



A research doctor has assembled several sensitive testing and measuring instruments (sorry I don't know what they do) on a rolling cart about 4' wide by 6' tall. All these 120 volt instruments are plugged into one 12 outlet power strip. I checked voltage with my meter and there Is 120 volts between hot and neutral AND hot to ground. According to my contact "they have been using it for years".



When looking at the back of the cart, there are several green wires that are either connected directly to exposed grounding lugs from the backs of the equipment or just taped with masking tape to the tops of these instruments that all run to a ground bar bolted to the rolling rack. This ground bar has an 8 AWG conductor that is connected to it that is stretched across the floor and is temporarily clamped to a hose faucet.



l guess my question is,,, should I even be concerned with the supplementary grounds that the research Dr. has assembled and temporarily clamped to the hose faucet? It seems that the equipment is plugged into a electrical outlet that has a good equipment ground. I'm not sure installing a isolated ground would help anything.

Thank you,
Martin

 

[mpoulton]

The type of equipment and how it's being used is important here. If it's "normal" equipment without any unusual electrical aspects to it, then the EGC is fine and the extra grounding is nonsense. The only need for supplemental grounding conductors is generally for certain radio frequency applications and certain types of sensors or measurement devices which rely on extremely low level voltage signals referenced to the surrounding environment. In those instances, the required supplemental grounding is really more like equipotential bonding or shielding. If the researcher were doing that sort of thing, they'd be plenty sophisticated enough to know what sort of special arrangements are needed. In short, this is probably all unnecessary.

 

[iwire]

If any one has ran into a similar situation I would appreciate any advice.


I was told that some one needed a "ground wire pulled". As soon as I read the service request one of my eye brows went up. I get to the job, which is a medical research laboratory and and it seems that a maintenance guy spotted something he didn't like so he reported it.



A research doctor has assembled several sensitive testing and measuring instruments (sorry I don't know what they do) on a rolling cart about 4' wide by 6' tall. All these 120 volt instruments are plugged into one 12 outlet power strip. I checked voltage with my meter and there Is 120 volts between hot and neutral AND hot to ground. According to my contact "they have been using it for years".



When looking at the back of the cart, there are several green wires that are either connected directly to exposed grounding lugs from the backs of the equipment or just taped with masking tape to the tops of these instruments that all run to a ground bar bolted to the rolling rack. This ground bar has an 8 AWG conductor that is connected to it that is stretched across the floor and is temporarily clamped to a hose faucet.



l guess my question is,,, should I even be concerned with the supplementary grounds that the research Dr. has assembled and temporarily clamped to the hose faucet? It seems that the equipment is plugged into a electrical outlet that has a good equipment ground. I'm not sure installing a isolated ground would help anything.

Thank you,
Martin

There is nothing wrong with what they are doing.

I doubt it helps anything but it is not dangerous or a code violation.

 

[jtinge]

Supplemental grounds for sensitive electronic equipment?

There is nothing wrong with what they are doing.

I doubt it helps anything but it is not dangerous or a code violation.

Would only be a problem if they drove an independent ground rod that was not bonded to the rest of the grounding electrode system and connected all their grounding conductors from the cart to it instead. I have seen this done in research labs and industrial shops where the user is trying to eliminate noise and ground loops. This usually results in a tutoring session on the purpose of grounding and bonding and explaining why their configuration violates code and is a safety hazard. But for the configuration described in the OP I don't see a problem adding the extra bonding conductors.

 

[mike_kilroy]

The type of equipment and how it's being used is important here. If it's "normal" equipment without any unusual electrical aspects to it, then the EGC is fine and the extra grounding is nonsense. The only need for supplemental grounding conductors is generally for certain radio frequency applications and certain types of sensors or measurement devices which rely on extremely low level voltage signals referenced to the surrounding environment. In those instances, the required supplemental grounding is really more like equipotential bonding or shielding. If the researcher were doing that sort of thing, they'd be plenty sophisticated enough to know what sort of special arrangements are needed. In short, this is probably all unnecessary.

Nice reply! I especially like the acknowledgement "If the researcher were doing that sort of thing, they'd be plenty sophisticated enough to know what sort of special arrangements are needed. " They certainly have learned how important that extra ground wire is! I have been involved with many 'sensative' machines where that extra ground wire solved that high freq noise issue! The researchers probably realized quickly that that little 120v ground pin has basically infinite resistance to ground at the hi freq noise they were arguing with!

So I can only assume your last line, "In short, this is probably all unnecessary." referred to the electrician who called the "cops" on them? Funny!