Induction???

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I recently removed two disconects and a small panel replacing them with an 3 phase,800 amp panel with main. The new panel is located adjacent to old switchgear(1952) and is fed by parrallel runs of 500, 500 neutral and 1/0 ground. It is connected by two 3 1/2 inch nipples just off the floor. The two sets enter the switch gear where in two feet the grounded conductors and the equipment grounds run up 5 feet and over two feet to be lugged on the neatral bar. The hot legs continue two feet on the bottom to be lugged to the bus bar there.
The Problem is the inspector felt that seperating the conductors like that created induction problems, a danger, as they would create heat.
Induction was not on my mind at all. The
switch gear is an enclosure and I can do pretty much what I want with the wires. Induction doesn't create heat as much as it creates Noise which may interfear with sensitive electronic equipment down the line, but not in this case. I understand that keeping the wires together minimizes the fields but it is not as important as practicality "In an enclosure"
Even sillier to me is that the ispector wants me to measure the amp draw of everything to see if there may be a problem, ballancing issue. One measures induction with an occiliscope right? Anyone care to enlighten me on any of this I would apprecitate it.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Re: Induction???

I am not completely certain that I understand the configuration. Are you saying that:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">(1) 3 hots, 1 neutral, and 1 ground enter an enclosure by way of one conduit, and
    (2) 3 hots, 1 neutral, and 1 ground enter the same enclosure by way of a second conduit, and
    (3) Once inside, the 2 neutrals and the 2 grounds go one way (basically, they go up), and
    (4) The 6 hots run horizontally towards the bus bars (basically they are close to each other)?</font>
<font size="2" face="Verdana, Helvetica, sans-serif">In other words, is the Inspector concerned about the hots running in different directions from the ?non-hots?? If that is the case, the Inspector?s concern is unfounded. The magnetic field generated by a Phase A conductor will reach its peaks and its valleys at different times than will the magnetic fields of the other two phases. But if you keep all three phases close to each other, the three fields tend to cancel each other out. You only run into induction (and heat) problems when you put (for example) two or more Phase A conductors close to each other (for example, in the same conduit) and separated from the other two phases (for example, in different conduits). That is because the magnetic field generated by each of the two Phase A conductors will add up, and because the fields from the other phases are not close enough to cancel it out.

As far as ?balancing currents? is concerned, that is driven by the way the loads are connected, not by how the source is connected. If you had one phase conductors much longer than the other two, that might have an influence on the balancing of currents. But the situation you are describing will not have an influence on the balancing of currents.
 
Re: Induction???

there is two 3 1/2" nipples with 3 hots 1 neutral and one ground in each. I agree with you. One would not run a hot and a neutral through seperate raceways to feed something, this is not what I am doing. Switch gear is an enclosure not a series of raceways. If induction is going on it is inducting into a grounded enclosure. Whatever rules (and the inspector was not specific) that require a neutral to lay alongside the hot or hots does not apply here. I would like to know what code referance he may be talking about. And as far as the balancing, of course. I guess I am looking for confirmation that the inspector is well... an *(&^ or has an axe to grind. On top of it, he insisted on a 350 mcm (he did the math) bonding jumper between switch gear and neutral bar. Though none was evident I have no reason to think the origianl installers would have not put one in. I would think that end of it would have been grand fathered. perhaps they brought the grounding electrode to the transaformer in the adjacent room, allowed in an lateral service and all...right? and why would any such jumper need be larger than 3/0? Just looking to make sure I am not missing anything.
 

brian john

Senior Member
Location
Leesburg, VA
Re: Induction???

Just:

While you installation does seem to be OK from a code standpoint. Do not assume that induction can not be a problem inside a metallic enclosure. Have seen many instances of hot conductors and structural supports (we perform IR) where the phase conductors were routed through a piece of equipment with metallic structural supports separating the conductors with the supports.
 

karl riley

Senior Member
Re: Induction???

I see no Code problem here.

Yes, higher magnetic fields are created wherever conductors of a circuit are separated, as they are in a breaker box. And induction creates some level of heat in nearby metal. But not to the level that requires a Code change.

As a point of interest, if a client is concerned about the higher magnetic field which surrounds most breaker cabinets for a few feet, usually locating the box so it is not on the other side of a wall where, say, a bed is on the other side solves any concern.

For some very concerned clients one can install a Siemens box which routes the neutrals with the hots and lands them on a bus near the hot's breaker. But once again, there is no Code involvement here.

Karl
 

karl riley

Senior Member
Re: Induction???

Pierre, my attention has been taken up with figuring out how not to loose my money in the market. I am getting an intense education.

Also playing in tennis leagues down here in Naples. Tough life!

Karl
 

luke warmwater

Senior Member
Re: Induction???

Originally posted by karl riley:
Pierre, my attention has been taken up with figuring out how not to loose my money in the market.
Karl
Mr. Riley, Karl if I may, a wise man told me the only guaranteed way not to lose money in the market is not to put it in.
But for me the allure of making money is too tempting!
Naples sure sounds nice right about now. And I am soon off to Lake Mary, and then St. Augustine, a nice break from this dreary weather that brings out the worst drivers.
Todd
 
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