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Joined: Oct 2004
Posts: 806
mxslick Offline OP
An associate and I engaged in a debate over what would be considered a "dedicated" circuit.

He feels that one half of a multi-wire circuit (shared neutral, one grounding conductor) is a dedicated circuit. (The circuit in question runs to a resi bathroom. One leg powers the receptacles and the other leg a ceiling-mounted heater/fan.) He wants to remove the heater fan and power a "dedicated" receptacle in an ajoining room for a computer.

I disagreed, as I feel a true dedicated circuit has its own neutral and grounding conductor, each returning to the panel ideally without splices and/or taps.

Code issues aside, what do you guys think?


(edited to correct bad typing)

[This message has been edited by mxslick (edited 06-22-2005).]

Stupid should be painful.
Joined: Feb 2003
Posts: 687
I worked with some that felt a dedicated circuit could not have the nutral shared.

For me a dedicated circuit is one breaker connected to one thing. Got to charge more for it to cover the cost of the HR. Where with a general lighting circuit I might not charge for the circuit because I figure I make it up on all the openings.

Unless they specify it's not their business if I network circuits together. Granted I try to avoid motor loads with lighting and electronics.

Say I got 2 sump pumps that are to be on dedicated circuits. What differance is it to the HO if I network them?

Maybe it would make your partner happy if you called it something elce like a single load circuit.


Joined: Jul 2004
Posts: 9,677
Likes: 9
I would tend to agree that you might see some influence of harmonics from one side to the other on a multiwire circuit but that would be caused by the computer, not something that would hurt the computer.

Greg Fretwell
Joined: Oct 2004
Posts: 265
I don’t think its a code issue, but a specification issue. Plans rarely specify what dedicated means, so I use my judgment.

I go by 4 levels of circuits, each with increasing costs:
1. General - shared power, neutral, and ground
2. Dedicated - its own power, but shared neutral and ground (usually for a coffee pot or something like that)
3. Dedicated w/ own neutral - own power, neutral, but shared ground (I use this on alarms, phone equipment when IG isn’t spec’ed).
4. IG - own power, neutral and ground.

Joined: Mar 2005
Posts: 212
DMattox, when you install what you call an IG circuit, do you use the IG receptacle with the special symbol to indicate that it is IG? An awful lot of electricians do, even when they are terminating in a panel that does not have a true IG ground bar.

Joined: Jan 2005
Posts: 5,316
Cat Servant
It seems obvious to me that a "dedicated circuit" has a breaker serving that outlet, and no other. And, last I looked, the neutral has no connection to the breaker, so it doesn't come into the discussion at all.

That said, I consider using a dedicated neutral as a very important first step where there are power quality concerns- so very often a dedicated circuit will also have a dedicated neutral.
From a code standpoint, I see no problem with, say, the furnace and the laundry sharing a neutral- even though they are both dedicated circuits.

Joined: Oct 2004
Posts: 265
Gregtaylor, it depends.

There is nothing that requires the isolated ground to be connected to the switchgear ground, it is an option that the code allows. So if the customer is willing/wanting to pay for it, I will do it. However, installing an isolated ground outlet that has a seperate ground connected to the ground buss bar in a subpanel is a code compliant installation IMO.

I guess I should have a 5th option, IG with ground ran to switchgear. Though I've never had someone want to pay for it during a service call. [Linked Image]

Joined: Jul 2004
Posts: 9,677
Likes: 9
The code really does not address IG circuits with how you have to do it. It only relieves you of making load end connections to cabinets, raceways or boxes if the IG conductor is present. You still need them bonded, just not to your IG.
Where that initial IG bonding happens is a design decision (in NEC speak). Proper IG design dictates that the IG will bond to the same bus as the main bonding jumper and radiate from there "isolated". If you are not doing that you might as well save your IG money.
I can PDF up the design criteria from the IBM physical planning book if someone wants to see it.
It might also be noted that IBM officially withdrew the requirement for IG sometime in the 80s because it really wasn't fixing anything. Some computer folks still cling to the illusion that it helps.

Greg Fretwell
Joined: Oct 2004
Posts: 265
I totally agree that IG isn’t needed, unless you have specific testing or studio equipment. I try to steer people away from it if I have the ability to do so.

You say, "Proper IG design dictates...", I would disagree that an IG outlet ran to the nearest panel is rendered useless compared to one ran to the switchgear. It is just one step up the ladder.

Like I said in my original post, there are different levels of isolation/dedication. As you increase up the level, your isolation increase, however so does your costs, with a diminishing return in isolation. You could run 3/0 for your ground of an IG 120V/20A outlet all the way to the switchgear, most likely it would result in a cleaner ground; however it most likely would be a marginal increase over a dedicated ground to your nearest panel. It’s all a cost/performance analysis based on the application.

Joined: Jul 2002
Posts: 8,412
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My interpretation of a "dedicated circuit" would be a circuit that has no reference to any other circuit in the installation.
And is supplied from it's own dedicated Circuit-Breaker or Fuse and has it's own neutral.

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