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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Electrical ground again posted by Leopold Nenning on March 29, 2002 at 07:50:00:
This question is asked so many times at this forum. Many uninformed persons believe that "isolated ground" (IG) means simply installing a separate rod in the ground and running a wire to one's equipment, which is downright dangerous. A link I have provided in the past titled "The Hows and Whys of Isolated Grounding" providing details of isolated grounding is no longer active. In the absence of that resource, see the explanation of IG below.ISOLATED GROUNDING EXPLAINED IN A NUTSHELL:
The grounding in a branch circuit consists of two elements or segments:
(a) The Equipment Ground, which is the means by which the equipment/device being operated on a circuit [connected equipment] is grounded to (the single main household ground). The purpose of the equipment ground is to shunt any electrical fault (short) occuring in the connected equipment safely to ground.
(b) The System Ground, which is the [collective means] by which the receptacle box, metal receptacle grounding strap or yoke and metal conduit/armor containing the insulated circuit conductors are grounded to the main household ground. The purpose of the system ground is to shunt any electrical fault occuring in the circuit wiring safely to ground.In a standard ground circuit, the Equipment Ground and System Ground are one and the same. In an isolated ground (IG) circuit, the Equipment Ground and System Ground are separated.
In an isolated ground circuit, the equipment ground consists of an insulated (isolated) wire that is connected on the equipment end to the grounding pin(s) of the receptacle and on the service end, to the main grounding bus of the electrical panel. This equipment ground therefore does not come into any electrical contact with any of the components of the system ground as described above, except at the point where they all terminate at the grounding bus in the main supply panel.
In an isolated ground receptacle, the grounding pin(s) and ground terminal are separated/insulated from the metal grounding strap or yoke. In a standard ground receptacle, the grounding pin(s) and ground terminal are connected to the metal mounting strap or yoke. It is the separation/insulation of the “equipment†ground from the “system†ground that gives an isolated ground circuit its name.
Therefore, “isolated ground†does not mean a connection to a separate ground rod., which is a dangerous undertaking.
When the grounding pins of a receptacle are isolated, this is indicated by a green triangle on the face of the receptacle. The green dot on the face means that the receptacle is hospital grade. Usually, IG receptacles are also always hospital grade. While orange is a popular color for HG/IG receptacles, they also come in other colors.
One other thing is, in order for an IG circuit to be properly implemented, it should be done with metal conduit, either EMT tubing or type MC (metal clad) cable, which is a flexible armored cable with redundant grounds (one [insulated] for the equipment ground and the other [bare] for the system ground). The metal serves as an RF shield. The flexible armor, because of its spiral form, by itself cannot adequately serve as a system ground of low enough impedance, hence the need for a redundant [bare] ground wire in continuous physical contact with the armor. The thin, bare aluminum wire seen in BX cable (a.k.a. type AC cable) also serves a like purpose of reducing impedance.
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Follow Ups
- Re: Electrical ground again - Glen B 11:14:57 03/29/02 (1)
- Re: Electrical ground again -- Thanks - Leopold Nenning 13:27:02 03/29/02 (0)
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