Medical Equipment Grounding question

[pierre]

Roger
This question is for anyone who may have experience with this type of installation - I know that Roger has extensive experience, so maybe he can help.


An electrician called yesterday and mentioned he saw the medical equipment installers install a grounding conductor from the 'shell' of an MRI to a ground rod without bonding to the premises grounding electrode system. Have you seen this done before, do you know anything about this type of installation?

Thanks in advance!!!

 

[jim dungar]

Re: Medical Equipment Grounding question

I have not seen this on an MRI, but have seen it on other "intelligent" equipment. This is a misguided intention to reduce "noise".

It is wrong and not per code. All ground rods must be bonded together (no book at home for article).

 

[iwire]

Re: Medical Equipment Grounding question

Originally posted by jim dungar:
It is wrong and not per code. All ground rods must be bonded together (no book at home for article).

Jim I believe you are thinking of 250.50

"If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system. "

250.58 Common Grounding Electrode only applies to separate services

That said this would be considered a Supplementary Grounding Electrode.

250.54 Supplementary Grounding Electrodes.
Supplementary grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.56, but the earth shall not be used as the sole equipment grounding conductor.

It does not have to be bonded to the other electrodes although it can not be the only grounding means.

I agree it will not do what they want it to.

 

[pierre]

Re: Medical Equipment Grounding question

Until recently, I have had no experience with this method. I am told that the installation with the exclusion of bonding the "shell" grounding electrode from the system grounding electrode system is vital for this equipment to work properly I really do not know if this is true, and I do not want to be responsible for the improper operation of this equipment by making an uninformed decision. I am still confused.

 

[roger]

Re: Medical Equipment Grounding question

Pierre, this is not correct if in fact there's no connection to the premises grounding system.

There should be a single grounding point where all EGC's from inside the shell will connect and from here they will connect to the buildings grounding system.

There will be a dielectric connection of the metallic raceways from inside to out.

As Bob said, a supplementary grounding electrode could be allowed, but would serve no purpose.

Roger

 

[pierre]

Re: Medical Equipment Grounding question

Hello Roger
I knew you would know the answer to this. Thank you.
Do you know of any links to information, or drawings/schematics?
I just did a google search and got very frustrated.
Would I use 517.19(C) and/or (G) as my basis for this type of installation?

What about a reference in NFPA 99?

Not bonding the shell of this equipment to the system grounding scheme is potentially dangerous, is it not?

Again, Thanks

[ June 26, 2005, 09:05 AM: Message edited by: pierre ]

 

[roger]

Re: Medical Equipment Grounding question

Pierre, I have some drawings at work, if you will PM me with an address, I'll mail you some notes off of the manufacturers plans.

517.19(C)/(G) wouldn't really apply, these sections are referring to an old ground jack reference point that is rarely used anymore.

The fact is, the grounding is no different in these rooms than in any other room with the exception of entering the room and the isolation between metallic raceways.

Not bonding the shell of this equipment to the system grounding scheme is potentially dangerous, is it not?

Absolutely

Roger

[ June 26, 2005, 09:25 AM: Message edited by: roger ]

 

[stud696981]

Re: Medical Equipment Grounding question

Pierre,

I have heard of this as well, BUT IT IS WRONG. This is an idea of someone who does not work in the electrical trade and thinks they are making an "isolated ground."

Hopefully the inspector notices this as it will be the reason to fail the inspection.

 

[iwire]

Re: Medical Equipment Grounding question

Originally posted by stud696981:
Hopefully the inspector notices this as it will be the reason to fail the inspection.

Hey 'Stud' Pierre is the inspector.

A good one that is not afraid to seek others opinions before making snap judgments.

I can assure you he understand that the earth is not an acceptable ground fault path.

 

[steve66]

Re: Medical Equipment Grounding question

Pierre:

Here is a link to some typicall medical systems installations drawings:

http://www.gehealthcare.com/company/docs/siteplanning.html

MRI's usually have a main ground stud which would have to be tied to the buildings grounding electrode system.

However, the sheild for the room is usually designed by a third party, not by the manufacturer of the medical equipment. I just say a note on one drawings that said:

Maximum sheild resistance to ground - 1000 ohms.

That leads me to believe that some sheilds may not be tied directly to ground. I think in general the sheilding people know what they are doing. But ask to see the sheilding drawings if you still have doubts.

 

[roger]

Re: Medical Equipment Grounding question

Pierre, here are some pictures of the single point grounding.

The first two pictures are inside the room, this bar is located below the RF filters, the EGC's will leave a jbox at the filters and land on this bar

This next picture is on the outside of the room where a connection to the building EGC will take place.

Roger

 

[pierre]

Re: Medical Equipment Grounding question

"Hey 'Stud' Pierre is the inspector.

A good one that is not afraid to seek others opinions before making snap judgments.
"


Bob
Flattery always wins friends Thanks

As an inspector, I do see work/installations that I am not sure about. So I seek help. What better place than here. I remember when I got started in this industry, getting correct answers was very difficult to say the least. Now with a little patience and a post, the answers are a mouse click away.

This situation is the perfect example of "losing the ego". I swallowed my pride and told the installers that I would seek out other info before I let this pass (we do this all the time, don't worry). It did not seem safe, and I want to make sure.

The fear of not knowing and making a mistake is worse than making a mistake and not knowing it.

My daughter spent almost 2 years in the medical machines of wonder and her safety was in the hands of other people.

Now other people are depending on me for their safety - people I may never meet - and I take that responsibility as being of the utmost of importance.

Thanks to Roger and Steve66 for the great help. I appreciate it. This is what it is all about!!!