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#126732 - 10/24/06 01:54 PM Transformer secondary neutral bonding
poorboy Offline
Member

Registered: 06/02/05
Posts: 128
Loc: Central Maine
Found a condition which I questioned on a job yesterday. A 120/208 panel was fed from a dry type xformer. The ground had been run from the 480/277 panel and bonded to the xformer frame, and a ground was run from that point to the building steel. 3 hot legs(X1-X2-X3) and a neutral(X0) went from the xformer to the 120/208 panel, where neutrals and grounds were together but NO GROUND WIRE WAS RUN FROM THE NEUTRAL/GROUND STRIP TO ANYWHERE! Am I correct that the ground from the xformer case to steel should instead be from the 120/208 volt panel neutral strip to steel? I am unsure what X0 terminal actually is but thought there was no physical connection between it and ground.

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#126733 - 10/24/06 02:29 PM Re: Transformer secondary neutral bonding
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Poorboy, the XO tap (neutral Tap) must be grounded, this point is where the windings of a Wye are common.

The grounding can take place at the XO tap itself or the neutral/ground bar in the panel (only four conductors between the transformer and the panel, no EGC) but if there are any conductive paths between the two, it can not take place at both.

The primary side can provide the bonding for the transformer frame as you described, or if you do ground the XO tap in the transformer, you can tie both the primary and secondary bonding together at this point.

Roger

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#126734 - 10/26/06 07:03 PM Re: Transformer secondary neutral bonding
Almost Fried Offline
Member

Registered: 09/04/06
Posts: 104
Loc: Madison County, Ark. USA
I have been inside at least 100 dry types in Wal Mart elect. cages for one reason or another and found that the missing bond from XO to ground was almost to be expected. All transformers state on a tag attached to the terminal strip or somewhere plainly visible within the enclosure that XO MUST be grounded in most applications. I have gotten on a plane and flown 1400 miles to handle a crises and fixed it with the bronze lugs and #2 green I always carried. If that bond is not made, the neutral point (XO) is floating relative to the building steel and you can have (in my experience), as much as 45 volts between bldg. steel and the neutral of a receptacle. What this means to a computer that has a logic level of <3 volts and zero, is confusion;it cannot tell the difference between ones, zeros, and ambient electrical levels. The bonding of this terminal secures a point of reference for the transformer and all the distribuited wiring downstream.

On a lighter note, I learned to always look underneath these dry types as they almost always have loose hardware under them that was kicked there by the crews building the service. I have found bundles of allthread, big flex connectors, lots of bronze, etc., so always check under them when working on a dry type; you may even find the tag that says "bond this terminal to system ground to avoid floating neutral conditions"...

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#126735 - 10/27/06 03:12 AM Re: Transformer secondary neutral bonding
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Fried, did you look to see that the bonding was not done at the first panel the transformer served?

That is as Roger mentioned also a code compliant way of doing it.

Though having been on th receiving end of many prebuilt electric rooms I would not be surprised if there was mistakes made.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#126736 - 10/27/06 06:31 AM Re: Transformer secondary neutral bonding
Almost Fried Offline
Member

Registered: 09/04/06
Posts: 104
Loc: Madison County, Ark. USA
iwire; Yes. I had worked for a consulting engineer as a Designer for a year before I started my Maintenance/Repair chapter; said eng. firm designed the distribution systems in the various stores so I had a well versed perspective before I started digging into the repair end of the process.

I had a procedure developed where I opened up everything, measured everything to verify visual clues, then figured out how to fix it. I have seen every possible combination of intelligence/stupidity/incompetence/lack of experience that those 425 stores could serve up and subtle things like bonding of transformers was all too common and not addressed in drawings or specs. Ya just gotta have the experience to run a job of that magnitude without really screwing up something.
I would get complaints such as the customer had touched a gondola simultaneously with touching a bldg. column and received a shock, complained to a manager, who touched the same gondola and column; guess what? he was zapped too! So I was dispatched to the location, did my little dance, sure enough, voltage from store fixture to steel. A cheap extension cord serving some lighting display on the gondola had become pinched between two cases such that the cases had 120 volts above the neutral of the adjacent hard wired receptacle, 30+/- volts to bldg. steel. So this is an example where the floating neutral possibly saved someone's life? there was just enough capacitance between the system and the building to cause the customer to feel the juice, not enough to hurt them but if it had been grounded properly, maybe the breaker would have tripped. Anyway, many similar situations occurred because of improperly bonding of said XO terminal.

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#126737 - 10/27/06 06:49 AM Re: Transformer secondary neutral bonding
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Almost.....don't worry I fully understand the importance of a properly bonded SDS.

 Quote:
I have seen every possible combination of intelligence/stupidity/incompetence/lack of experience...


Naw...there is always some new way to screw up a job.

 Quote:
Ya just gotta have the experience to run a job of that magnitude without really screwing up something.


I agree.

Oh I have to ask....

When you where in a state you did not have a license in you just directed the a licensed electrician from the area how to do the work?

I ask because I have had to be 'the licensed guy' for out of state ECs trying to work in Walmarts.






[This message has been edited by iwire (edited 10-27-2006).]
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#126738 - 10/28/06 07:15 AM Re: Transformer secondary neutral bonding
Almost Fried Offline
Member

Registered: 09/04/06
Posts: 104
Loc: Madison County, Ark. USA
Re: out of state licenses for Wally World work
For the repair end of the business I never had a problem with local authorities, probably because of the quick response to diagnosis & repairs. When we were installing specific equipment, there was a job or two in Illinois where we were required to have a local union sparky stand by with screwdriver in hand, he could not do anything constructive as he was not knowledgeable of the energy management equipment, but had to be paid for political purposes.
I had a couple of men in a store in Lousiana installing some power for sattelite receivers that were snitched off by a store employee with ties to city hall; soon thereafter I received a stern letter from the city of W. Monroe demanding that I show up in court and pay something like 7-800 bucks for two counts of Performing Elec. work without a license and two counts of performing elect. work without a permit but they would waive half of the attempted extortion if I sent them a check...so somewhere in a database in that Parish is an 1988 misdemeanor charge of the above...
We had unmarked vehicles and kept a low profile, mostly. Since the work was site specific for us it was impractical to involve the locals because they, in most cases, would have had no idea about the systems we were servicing.

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#126739 - 10/31/06 02:51 AM Re: Transformer secondary neutral bonding
poorboy Offline
Member

Registered: 06/02/05
Posts: 128
Loc: Central Maine
Very interesting stuff, AF. I am going to remember your username for future reference. The experience you have had is a valuable resource...that's what I like about this site. As common as they are, transformers still represent only a tiny percentage of any given electrician's work, and several years may pass between installations of them. The codebook is not a "how to" manual, so many have nobody to ask when questions arise. Also, retail store jobs usually have very aggresive schedules, causing a hurry-up attitude where these things slip by.

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#126740 - 10/31/06 03:05 AM Re: Transformer secondary neutral bonding
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
 Quote:
I received a stern letter from the city of W. Monroe demanding that I show up in court and pay something like 7-800 bucks for two counts of Performing Elec. work without a license and two counts of performing elect. work without a permit but they would waive half of the attempted extortion if I sent them a check.


Why do you feel your above the law?

Its' not extortion, it is a fine for breaking the law.

 Quote:
We had unmarked vehicles and kept a low profile, mostly. Since the work was site specific for us it was impractical to involve the locals because they, in most cases, would have had no idea about the systems we were servicing.


In this area that is known as intentionally breaking the law.

And I am not talking union rules, actually state laws.

The reason 'Wally world' finds it impractical is because they are incredibly cheap and don't want to deal with those pesky licenses, permits or inspections.

If I see unlicensed work going on I may also 'snitch it out' and I have zero ties to city hall.

My beef is I put a lot of effort to getting and keeping my license and out of state contractors have no right breaking the rules I must follow.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#126741 - 10/31/06 04:02 AM Re: Transformer secondary neutral bonding
Eddy Current Offline
Member

Registered: 09/26/06
Posts: 112
Loc: Ontario,Canada
I agree with iwire on this one. I don't think it is bettering our trade at all if you have to sneak around to do a job. Local rules may not be known to an out-of-town'r. Also things like not grounding the tranny might be caught in time if there was an inspection.

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