517.13 and Isolated Power System. Clarification

M

marcosgue

Senior Member
Location
Tampa
Occupation
Electrician
Is clear the two conditions in 517.13 that in Patient Cares Spaces, including OR, the use of wiring method shall be qualify as equipment grounding conductor and beside that every circuit from the isolated panel shall be run with green wire type equipment grounding conductor which is connected to grounding terminals of receptacles, metal boxes, device boxes.
The fact is the PM assistant was doing grounding test and mandate to disconnect the ground pigtail saying that specifically in OR is no allow to bond the metal box with the equipment grounding conductor running with the circuits originated in the Iso Panel.
I believe he's wrong and violate 517.13b.
My question is why to bond the metal boxes to provide an effective ground fault current path if there's no neutral in the Isolate power system and is not allow the operation of overcurrent device.
Any input and clarification is appreciated.
Thanks in advance
 
Roger are you saying that for equipotencial purposes is not required to bond the metal boxes to the equipment grounding conductor?
I understand that Health care facilities also have to follow nfpa 99 but if this true how to conciliate NEC 517.13 with NFPA 99 6.3?
That means in ORs it's no require to bond the metal device boxes to the equipment grounding conductors coming from the isolation panels inside the room?
what cuold be the argument to provide a low impedance fault current path if there's no way to return the fault current back to the source and open the overcurrent protection device?
 
The egc is not for clearing faults in an Isolated Power System. You could connect one leg to the egc and it simply becomes an end grounded winding, it would take a second fault to cause any damage. The LIM would go into alarm. I don't know where the tester is coming up with a requirement to lift the wire egc for commissioning though.
 
The equipotential between all devices has to be less than .1 ohm. That is the reason for the low impedance grounding
 
Thank you Roger to clarify me, but still I don't understand why disconnect the equipment bonding jumper for all devices metal boxes to perform the equipotencial grounding testing? This is a requirement from nfpa 99?
We use grounding integrity tester Hampden model MVO-1-PB
Could you tell me how to access or purchase nfpa 99?
 
I have never disconnected or seen any testing company (we used SQ D field services most times) disconnect the Equipment Bonding Conductor for any commissioning. You can buy or view NFPA 99 from the NFPA website.

NFPA 99 Code Development

Stay informed and participate in the standards development process for NFPA 99
www.nfpa.org www.nfpa.org
 
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