Originally Posted By: jfarsetta
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Ground loops is a term most widely used/referred-to in the computer or data center environment.
To Joe M's point, the notion of providing an isolated neutral back to the service entrance panel helps ensure a true "single-point ground". In most computing equipment applications, it is a manufacturer's requirement. It helps eliminate loops, and is a safety consideration.
Ground loops can be nasty things, providing an unclear path. Receptacles designed for use in an IG engironment are orange in color, and are marked with a black triangle on the face. The mechanics of the receptacle provides no bond between the metallic mounting hardware attached to the receptacle face and the ground lug. The receptacle mechanically and electrically bonds to the metallic box and to the safety ground within the cable or as part of the cable sheathing (BX). A separate insulated conductor is contained within the wire and returns to an isolated bus bar within the serving panel. Isolating transformers are utilized in commercial applications, and the neutral is separate all the way back to the switchgear.
This scenario is a bit different than what we see in a typical residence, in that normal receptacles provide mechanical and electrical bonds between the cable ground, the ground lug, and the receptacle frce and housing. Even the screw hole for mounting the faceplate is part of the grounding system.
Again, isolated grounds are foreign to most residential applications. Isolated neutrals within a subpanel are a code requirement, unless powered from a dedicated transformer. In that case the panel is considered to be like a main panel. Joe M mentioned the "ground loop" and I thought I'd jump in, seeing as how I've designed the electrical distribution for about 250 data centers around the US and Canada.
BUt back to the point (what was the point anyway?!). Oh, yeah... Joe M is correct in his assessment of what havoc a true ground loop can cause. Remember, though, that circuit breakers trip for one reason and one reason only: HEAT. It cant detect a short, ground loop, over current, or anything else. Any electrical malfunction can cause some sort of breaker overload, causind a rapid and sometimes severe jump in the generation of heat within the breaker. This is what causes it to trip. The exceptions to this rule pertain to GFI and arc-fault breakers, which are now required on bedroom circuits in new construction. Gosh, what a long answer to a question that no one really asked... Nevermind...
Illigitimi Non Carborundum
"Dont let the bastards grind you down..."