isolated ground

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richig

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in order the isolated ground system to work properly its should come from service ground bus or seperately derived ground and insulated from common ground noises. its like second neutral originated from x0 but not to be used for normal ac return path. isolated ground panelboard should have separate insulated isolated ground bus in addition to common ground safety bus that is usually bonded to casing of the panelboard.
 
if you disregard the word "neutral" it actually sounds like an fairly accurate "isolated ground" description, does it not ?
As with Iwire, I'm still unsure of the intent of the post.

I believe it was richig's first post. Hopefully as he reviews the forum, he will clarify a bit for us.
 
Yep, sounds like he has given a decent description of an isolated ground. Since he didn't ask a question, I'll ask one. Let's say the equipment which "needs" the isolated ground has a metal case. And the metal case is attached to a building column. Did we not just defeat the entire purpose of the isolated ground? For the isolated ground to be effective, wouldn't the non-current-carrying metal of the equipment need to be isolated from the building structure and be grounded only by the isolated ground wire?
 
crossman said:
Yep, sounds like he has given a decent description of an isolated ground. Since he didn't ask a question, I'll ask one. Let's say the equipment which "needs" the isolated ground has a metal case. And the metal case is attached to a building column. Did we not just defeat the entire purpose of the isolated ground? For the isolated ground to be effective, wouldn't the non-current-carrying metal of the equipment need to be isolated from the building structure and be grounded only by the isolated ground wire?
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Yep, and is the big flaw of IGR. Also if it is interconnected to any other equipment that uses a ground cable like a signal circuit (eg coax or RS-232) using ground is compromised. IGR is antiquated :rolleyes:
 
I was stoked to see an article in November's EC&M magazine pertaining to IG - but was a little disappointed at the buckshot nature of the article. "Too short does nothing, and too long doesn't help much. Somewhere between too long and too short is a good length." :D

Of course, I was more annoyed at the circuit breaker article - I was tempted to write in and ask for a technical explanation of how the square footage of a building factors into the available fault current calculations. :roll:

Can't complain too much though, it's free. :)
 
We use to pay for this magazine and maybe it is just me but I think it was a better mag in those days. But then candy bars use to be a nickle, kids were better back then and the good old days maybe they weren't really that good?
 
Brian,
We use to pay for this magazine and maybe it is just me but I think it was a better mag in those days.
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It was far better then, and in the very early days it accepted no advertising.
Don
 
Don I seem to remember the lack of advertising, EC&M was a major influence on my early learning and understanding of grounding. What upsets me is I paid for the mag out of pocket from my first year in the trade, which I did not mind, and now I have trouble getting my guys to get the mag for free, much less read it.
 
Speaking of isolated ground circuits, here's a good example of how not to do isolated grounds. I took this picture a few weeks ago at a customer's location. Each of these three THHN's originated at the IG terminal of an isolated ground receptacle and terminated on its own ground rod. If a ground fault were to occur within the cord-connected equipment, the overcurrent device would surely never trip. A supreme hazard, which I was not able to adequately explain to the customer in a way that they would permit me to change it and make it proper. (sorry about the poor quality picture. I left my camera behind, so this was from my phone)

isolatedgroundviolation.jpg
 
I'm not quite sure if you were making a joke, Brian - but I think Marc was saying that the isolated grounds were not in physical contact with the neutral of the system. I think the picture of the rods was to punctuate the point.
 
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