Isolated Ground

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bwyllie

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MA
I am working on a project where Hospital Grade AC cable was installed for all the IG branch circuits. The tenant will not accept this and will only accept a 4-wire branch circuit(1-Hot, 1-Neutral, 1-IG & 1-EGC) all #12AWG. The agree what we gave them will work and is code compliant but they say their requirments for the space dictates 4 wires. Anybody ever run into this before or any opinions. What are peple's thoughts on the armor vs wire for an EGC.
Oh yeah, the tenant is a US Government office...our tax dollars hard at work!!!!
 
Re: Isolated Ground

Where do you get your IG's? You should have used 12/2MC with a separate IG conductor (yellow/green). That's probably what they are talking about.
 
Re: Isolated Ground

You should probably check the spec's that the engineer placed on the project, if it was called out to have four conductor than you should install it. If it is not calling for it than you can tell the tenant what you have installed is code compliant and if they want four conductor you will do it for additional cost.
 
Re: Isolated Ground

I should also add that you should read 99' 250-146(d). My opinion is that you are not code compliant.
 
Re: Isolated Ground

Do not use cable like this:
ac90.jpg


Stack it like this:
nm310_im2.jpg


Use connectors like this:
560-dc2.gif


Be sure the armored able has enough conductors plus an insulated green ground.
 
Re: Isolated Ground

sjaniga,
Why is it not code compliant? The jacket is the method to ground the raceway system and box (from the FPN). The hospital AC cable has an insulated EGC.
 
Re: Isolated Ground

Ron, you are correct, sorry I read the post incorrectly. guess it all hinges on what the original specs were.
 
Re: Isolated Ground

Does the NEC and UL recognize the armor of the AC cable as an equipment grounding conductor?
 
Re: Isolated Ground

Bwyllie, yes. See 250.118(9)

Roger
 
Re: Isolated Ground

What was specified? Did it satisfy minimum NEC requirements?. If the specification meets minimun NEC requirements, exceeds the NEC requirements, and under contract, guess what??

[ September 02, 2003, 09:45 PM: Message edited by: dereckbc ]
 
Re: Isolated Ground

I understand that what was specified must be installed, what I don't fully understand is the reason, besides "because it is what was specified". How much of a better ground is a conductor vs the armor? Also, in the spec if it says a equipment ground wire and the contractor installed hospital grade AC cable using the armor as the ground wire, as recognized by NEC, does that not qualify or is that too techinical?

[ September 02, 2003, 10:28 PM: Message edited by: bwyllie ]
 
Re: Isolated Ground

bwyllie
The problem is not whether or not the armor of the cable is a good ground or not it is the isolated ground that they want because the armor of the A/C cable can come-into contact with other grounded metal in it long run back to the panel. this would cause multi-point grounding and can cause noise in the ground wire which can disrupt computers and other sensitive electronics that are subject to unwanted noise in the grounding.
 
Re: Isolated Ground

thanks, I hope at sometime someone will have a definite finding of the use of IG, wether it is useful or just a waste of money.
 
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