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#85497 - 07/10/03 06:04 PM Objectionable current
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
I would take 'objectionable'to mean that someone would complain, but they are not...

so here's the deal.........

240v open delta 3 ph pole mount x-formers feed pole mounted meter, load side had 2 runs (there is no main) to ...

a) poolhouse w/ 3ph panel & 3 ph 7.5 hp pump motor

b) lifegaurd shack/toilet/concession stand 20 cir 1 ph panel

now each building has a municipal H2O line, both metal, both used as a GEC.

there is also a chain link fence that circles the pool and travels from poolhouse to baywatch central

each is serving as a rather efficent noodle

any objections?

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#85498 - 07/11/03 05:47 AM Re: Objectionable current
Ron Offline
Member

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
Objectionable would mean that someone could get hurt from energized metal parts, or equipment/data failure due to the current.

Where is the neutral to ground bond located? Where is the service disconnect(s), is it the main breaker in the two panels you describe?
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#85499 - 07/11/03 05:58 PM Re: Objectionable current
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Steve, I will admit I am not that sharp, but my interpretation of what you're saying is there is no grounded winding. Right?

If that is the case, there is no objectionable current because there is not a circuit.


Roger

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#85500 - 07/12/03 03:04 AM Re: Objectionable current
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Is one phase of the open delta grounded?

If it isn't, there could still be stray currents flowing to ground due to capacitance.

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#85501 - 07/12/03 08:52 AM Re: Objectionable current
ElectricAL Offline
Member

Registered: 10/10/01
Posts: 615
Loc: Minneapolis, MN USA
 Quote:
b) lifegaurd shack/toilet/concession stand 20 cir 1 ph panel

I understand (assume) this panel to supply 120 V and possibly 240 V loads.

To me, Sparky is describing a 120 / 240 Volt 3 Ø 4 wire PoCo transformer bank with two service laterals, one 120 / 240 volt 1 Ø 3 wire, and one 240 volt 3 Ø 3 wire.

But since the question is about objectionable current, maybe that 3 Ø lateral is 120 / 240 V 4 wire? What say, Sparky?

As to the question. . .I personally object to the neutral current finding multiple return paths between the (in this case) two service neutral / ground bonding points and the transformer neutral terminal. . .but what's a code compliant sparky to do ??? And the chain link conductor makes the question all the more poignant.

Seriously.

[This message has been edited by ElectricAL (edited 07-12-2003).]
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Al Hildenbrand

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#85502 - 07/13/03 06:00 PM Re: Objectionable current
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
sorry to leave your q's unattended, i was off camping and dedicating my free time to contracting posion ivy.....


 Quote:
To me, Sparky is describing a 120 / 240 Volt 3 Ø 4 wire PoCo transformer bank with two service laterals, one 120 / 240 volt 1 Ø 3 wire, and one 240 volt 3 Ø 3 wire.

But since the question is about objectionable current, maybe that 3 Ø lateral is 120 / 240 V 4 wire? What say, Sparky?


yes & yes Al

 Quote:
Where is the neutral to ground bond located? Where is the service disconnect(s), is it the main breaker in the two panels you describe?

the MBJ's are in the panels of the two buildings, made to 'common' municipal h2o lines

 Quote:
Is one phase of the open delta grounded?

yes it is Paul, the traditional high leg, which was avioded in the lateral to the poolhouse

 Quote:
there is no objectionable current because there is not a circuit.

actually Roger, under a load ( like the 7.5 hp motor)there is notable voltage in the fence

but...i'm the only 'complainer' as yet.

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#85503 - 07/13/03 06:56 PM Re: Objectionable current
caselec Offline
Member

Registered: 04/14/02
Posts: 557
Loc: San Jose, CA
Steve

Did you mean to say that one of the phases was grounded or that the center tap of one of the transformers was grounded? If one of the phases was grounded then this would be a corner grounded delta system and the only voltage available at either panel would be 240V.

When you say there is a noticeable voltage on the fence do you mean you can feel it when the pump is on or your reading it with a tester? Assuming this is not a corner grounded delta system connecting any loads such as the pump that do not use the grounded conductor should not have any effect on the current flow seen on the water piping or fence.

Curt
_________________________
Curt Swartz

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#85504 - 07/13/03 07:33 PM Re: Objectionable current
ThinkGood Offline
Member

Registered: 08/07/02
Posts: 1084
Loc: Milwaukee, WI
sparky:

Re: the Poison Ivy--remember this thread?
http://electrical-contractor.net/ubb/Forum16/HTML/000008.html

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#85505 - 07/14/03 04:36 PM Re: Objectionable current
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Curt,
the voltages mimic a standard center tapped delta like this , i have 120/240 and a high leg of somewhere around 190 v's

how it is done with 2 x-formers i really can't say.....

and yes, you can meter voltage under a load bettween fence~GEC

as a matter of fact, i did up a new GEC in the pumphouse, and one can see (and even hear) a nice fat blue spark on removing/connecting it under said load.

i'm going back soon to install a nema3r stop/start, so maybe i'll probe it out for the sake of the thread.....

so we thus ajourn to 250.6(b)and items 1 thru 4

stumped? me too, i'm going out of my way to drag the state insp. there, i'll post his advice.

ps~ yes ThinkGood, i'm scrathin' like a hound here, but what father would'nt brave the wilderness given the request of a 'marshmallow stick' for his 11 yr old?

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#85506 - 07/15/03 05:24 AM Re: Objectionable current
ElectricAL Offline
Member

Registered: 10/10/01
Posts: 615
Loc: Minneapolis, MN USA
Sparky,

I woke up thinking about open wye - open delta transformer banks this morning, as well as a neighbor's open neutral.

Both of these will contribute neutral current to the grounding electrode systems of the concession stand and the pump building.

And also, the PoCo distribution grid primary unbalance current will be using the GES. The neutral to the buildings will be bonded by the PoCo at the transformer to the distribution grid neutral, if present.

So, I have a couple of questions. . .

1. Are there two (or three) PoCo primary (high voltage) conductors connected to the transformer primary windings?

2. What are the neighbors like?

Re. 1.: If there are only two high voltage conductors, the primary windings will be configured as an open wye. The wye neutral current will seek all available return paths to the generator (or substation), including the municipal water system.

Re. 2.: A neighbor with an open neutral and an unbalanced load will contribute to the current on the municipal water system. Depending on how your PoCo interconnects secondary neutrals between transformers, that neighbor's unbalance current likely is travelling from his neutral GES bond to the water pipe to the pool pump house service neutral to the pole to pole neutral that gets back to the neighbor's transformer.

Most PoCos make the secondary neutral (that they install from pole to pole) do triple duty as the primary neutral and as the interconnection of all their pole grounds (butt plates, ground balls, guy wire anchors, etc.).
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