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#202574 - 08/10/11 01:10 PM Dental Office  
harold endean  Offline
Member
Joined: Feb 2002
Posts: 2,233
Boonton, NJ
I have another one of those questions, that I might have seen here, but I can't remember if I did.?! smile

In medical offices sec. 517.13 requires effective grounding path for patient areas.

The question would be a dental chair.
1) Is redundant grounding required?
2) If the chair is fed from under the floor and it is PVC pipe, would you need 2 ground wires to have a double ground?


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#202575 - 08/10/11 01:37 PM Re: Dental Office [Re: harold endean]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,076
Estero,Fl,usa
I got a ruling here that the answer would be yes, no.

I was doing "draw" inspections for an engineering company and I questioned the redundant ground. It was escalated and they came back that a dentist chair was a patient care location.
I suppose your mileage may vary so I would ask the AHJ where you are installing this.

You still need a metallic wiring method for the first ground.

Quote
517.13 Grounding of Receptacles and Fixed Electrical Equipment in Patient Care Areas.
Wiring in patient care areas shall comply with 517.13(A) and (B).
(A) Wiring Methods. All branch circuits serving patient care areas shall be provided with an effective ground-fault current path by installation in a metal raceway system, or a cable having a metallic armor or sheath assembly. The metal raceway system, or metallic cable armor, or sheath assembly shall itself qualify as an equipment grounding conductor in accordance with 250.118.


In my case it was ruled that MC cable is not a redundant ground. "Medical" AC (with the green wire) is. Otherwise you are in metal pipe.


Greg Fretwell

#202577 - 08/10/11 02:32 PM Re: Dental Office [Re: harold endean]  
mikesh  Offline
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Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
The Canadian approach would classify a dentist chair as a patient care area and require an insulated ECG or "Bonding" wire as well as all other approved bonding methods like the raceway. No spiral cable armour is acceptable as a bonding method here. Cables like core flex where the armour is continous may. Further the panel supply also must have a copper bonding conductor so no aluminum feeders unless there is an internal copper bond wire.
Where an existing occupancy changes to a medical occupancy and the existing feeders have Aluminum bond wires we have given special permission to add an external, insulated bond wire if it can be installed to follow the existing feeder and still pass the required tests for VD and Potential rise as outlined in CSA standard Z-32.

Except for some differnces in the wiring material the US and Canadian rules follow the same criteria in setting the rules. Tested Volt drop and no potential differences between grounded metal points.


#202578 - 08/10/11 04:05 PM Re: Dental Office [Re: harold endean]  
HotLine1  Offline


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Joined: Apr 2002
Posts: 6,824
Brick, NJ USA
Harold:

I have to go with Greg on this. Metalic raceway with an insulated EGC installed. Or, HCF cabling.

I don't know if there is a PVC coated HCF cable, suitable for slab.




John

#202580 - 08/10/11 05:19 PM Re: Dental Office [Re: harold endean]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,076
Estero,Fl,usa
I am not sure what I would let them do if the RNC was already there in concrete. If this is new construction you would be using EMT with concrete tight connectors and off you go.



Greg Fretwell

#202588 - 08/11/11 10:48 AM Re: Dental Office [Re: harold endean]  
HotLine1  Offline


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Joined: Apr 2002
Posts: 6,824
Brick, NJ USA
"Existing" here goes into Rehab Subcode, which is presently under the 2005 NEC, until DCA completes a update/re-write. As there were no changes within the discussed article, metalic raceway method would be required, by the book.

A 'variation' may be requested by the EC or design professional, including the reason for requesting the variation. Thet are considered on a case by case basis.

My first comment to any party requesting a variation is 'would the correction or compliance cost less than the variation fees ($250)? If a yes answer, then 'why bother'?

I would be 'on the fence' with this topic; with the install of two (2) EGCs within the raceway (PVC) the intent of having two (2) ground paths is achieved. Is that not the intent of 517?



John

#202595 - 08/11/11 06:03 PM Re: Dental Office [Re: harold endean]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,076
Estero,Fl,usa
I was thinking I *might* say he could keep the two GGCs in the buried pipe, set a box and transition to a compliant raceway/cable at the first exposed opportunity (one EGC to the box/raceway, one extended as a green wire)

It is not really the letter of the law but I think it is a reasonable accommodation. I would certainly prefer seeing a new run that was totally compliant but I also understand chipping up the floor may not be possible.


Greg Fretwell

#202729 - 08/24/11 01:47 PM Re: Dental Office [Re: harold endean]  
harold endean  Offline
Member
Joined: Feb 2002
Posts: 2,233
Boonton, NJ
Sorry it took so long to get back here. First of all the job is existing and they are just changing the chair from being a left handed chair to a right handed chair.
Most likely there is already PVC in the ground.So then I guess you would have to have 2 grounding wires inside the pipe. 1 attached to the metal box where the circuit originates and one to the grounding wire inside that box.


#203197 - 09/14/11 09:06 AM Re: Dental Office [Re: harold endean]  
harold endean  Offline
Member
Joined: Feb 2002
Posts: 2,233
Boonton, NJ
What if the chair just plugs into a regular 3 prong outlet and there is no spot on the chair for any kind of a bonding ( redundant) lug?


#203198 - 09/14/11 09:51 AM Re: Dental Office [Re: harold endean]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,824
Brick, NJ USA
Harold:
The chair should have a 'green dot' (HCF-Hospital Grade) male cord cap. There is no redundant 'bonding' on the chair, or any other HCF utilization equipment that I am aware of that is cord & plug energized.


John

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