redundant grounding

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liquidtite

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I recently switched companies that I work for so I coudnt see the end result,the last job that I was on was in a hospital were we had redundant grounding.I was woundering when you bring your redundant grounding conductor to the panel it has to be on a ground bar that's not bonded to the pane?.And if so what makes it a ground do you have to get a ground from a seperatly derived system or transformer.Or are the two egc,s bonded together in the panel?
 
517.13 has the specific requirements but the short version is that it only applies to branch circuits and the redundant EGC is only required to go as far as the panel supplying the branch circuit.
 
then I wounder why the guy I was working with made me identify the redundant ground and make shure that's the one that terminates to the tail on the hg receptacle
 
iwire said:
How many 'wire' EGCs were at the outlet?
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And are you sure that you had a redundant ground EGC rather than an isolated ground EGC?
If it really was just a redundant ground, then it should not really have mattered which was which as long as each of the two was terminated to a different point on the receptacle and both ran independently all the way back to the ground bar of the panel that fed the circuit.
If there were more than two wire EGCs, then it would potentially matter which was which. And it would matter which one was the redundant ground in that it might not be connected to as many outlets and would be less likely to end up carrying fault current originating somewhere else. As I understand it, the two ground paths should be kept separate (or at least redundant) from the receptacle all the way back to the panel. (But see following definition, which muddles things a bit.)

517.2 (2011):
Patient Equipment Grounding Point. A jack or terminal that serves as the collection point for redundant grounding of electrical appliances serving a patient care vicinity or for grounding other items in order to eliminate electromagnetic interference problems. [99:3.3.141]
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as contrasted to 250.96 (2011):
(B) Isolated Grounding Circuits. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, an equipment enclosure supplied by a branch circuit shall be permitted to be isolated from a raceway containing circuits supplying only that equipment by one or more listed nonmetallic raceway fittings located at the point of attachment of the raceway to the equipment enclosure. The metal raceway shall comply with provisions of this article and shall be supplemented by an internal insulated equipment grounding conductor installed in accordance with 250.146(D) to ground the equipment enclosure.
Informational Note: Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system.
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The first may be required in hospital patient care areas, while the second may be used in lab areas or for other sensitive electronics. Its usefulness when other wiring has been done correctly has been debated.
 
As Bob points out, 517.13 spells out the requirement. This is not an isolated ground, it is a wire and a raceway combined (joined together) to assure a low impedance path to the source.

Roger
 
When we speak of 'redundant grounding', we mean a wiring method that employs a sheath or raceway which is itself an EGC, and additionally an insulated copper wire within. There is no need for two wire-type EGCs. And two green wires do not satisfy the requirement for the cable sheath or raceway to qualify as a grounding conductor.

As mentioned in previous posts, if two wire-type grounding conductors were used, and one was kept carefully identified, it seems likely that those particular circuits may have been isolated grounds. The receptacles typically used with those circuits, however, are not permitted to be installed in patient care areas per 517.16, where 'redundant grounding' generally is. :eek:
 
im new to hospital work all branch circuits are in conduit the only circuits that had two grounds were for critical care.the recepicals for the cc were orange and had a tail off of it ,the ears were isolated from the tail .One ground gets bonded to the 1900 box the other is spliced to the recpepical.
 
liquidtite said:
so is what I described isolated or redundant and what is the difference thanks for your time
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I sounds to me in your post #10 that you are describing an isolated ground receptacle. Isolated ground receps. are not allowed in patient care areas. Maybe missing some info here.
 
liquidtite said:
im new to hospital work all branch circuits are in conduit the only circuits that had two grounds were for critical care.the recepicals for the cc were orange and had a tail off of it ,the ears were isolated from the tail .One ground gets bonded to the 1900 box the other is spliced to the recpepical.
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In addition to the orange color, there should be a green dot or triangle or other symbol. That should tell you what the receptacles actually are. Or you could look at the part number or the box it came in.
A white receptacle with an orange triangle or an orange receptacle with a green triangle indicates isolated ground.

This link shows what the Pass and Seymour versions look like.

A green dot indicates Hospital Grade, which includes requirements for better grounding than a standard outlet but does not specifically imply redundant grounding. Redundant grounding is accomplished by supplying one ground path through the raceway connected to the device yoke and the other through a separate ground wire (not just a jumper from the raceway ground) connected to a ground terminal screw on the receptacle. This can technically be done with any receptacle which bonds the yoke to the ground screw, but for hospital use in a patient care area a Hospital Grade receptacle needs to be used.

There has been quite a bit of discussion about whether IG receptacles can be used in patient care areas, and the authoritative answer seems to be no.
http://www.ecmag.com/section/codes-standards/safety-takes-precedence
 
The plugs were orange and I think they had a green triangle on the them .on the back it did say isolated.i installed them in a room were their were patient lifts and I was told patients would be keep their .only a few recepticals were isolated .
 
liquidtite said:
The plugs were orange and I think they had a green triangle on the them .on the back it did say isolated.i installed them in a room were their were patient lifts and I was told patients would be keep their .only a few recepticals were isolated .
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Well, for an isolated ground receptacle, it certainly does matter which ground wire you use, since the whole idea is to provide a direct ground wire back to the panel or some other special point, and not have any other equipment use that ground wire.

As mentioned, there may be special equipment in the area that is thought to need an isolated ground, but putting those receptacles in a patient care area may not be accepted by the AHJ regardless of that "need." An isolated ground receptacle, by design, does not satisfy the requirement for redundant grounds.
 
I used the wrong terminology then ,so when you bring the two Egcs too the panel ,one Egc is bonded to panel and the iso ground I'm assuming is terminated to a ground bar that's not bonded to the panel so how does that ISolated ground have a path to ground .?does it get a ground from transformer or seperate system?
 
liquidtite said:
I used the wrong terminology then ,so when you bring the two Egcs too the panel ,one Egc is bonded to panel and the iso ground I'm assuming is terminated to a ground bar that's not bonded to the panel so how does that ISolated ground have a path to ground .?does it get a ground from transformer or seperate system?
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Exactly how it gets bonded to some sort of earth reference will depend on the system design. If the current carrying conductors are coming from a transformer (to provide noise isolation from the main system), then the isolated ground wire should go to the point where the grounded conductor of that SDS is bonded to ground.
If the current carrying conductors form either a balanced or an ungrounded system, then it gets more interesting, and I would want to have an engineer or EC lay out exactly what is intended.
 
liquidtite said:
The plugs were orange and I think they had a green triangle on the them .on the back it did say isolated.i installed them in a room were their were patient lifts and I was told patients would be keep their .only a few recepticals were isolated .
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If this area is a Patient Care area the wiring method is incorrect. Before the 2011 there was an article 517.16 that seemed to allow it but, without an exception to 517.13 it was wasted ink and was removed from the code.

Roger
 
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