Lessor Of Two Evils

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dereckbc

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Thought I would throw this out. I have found myself in an uncomfortable situation for which I have no control.

In my company there are about 42 cell sites. Each site is identical. Each site is equipped with a generator snout for emergency power. All sites have manual transfer switches that do not switch the neutral. All sites are single phase 240/120. 39 of the sites use a 3-wire generator snout, while the other 3 use 3-wire. The portable generators are 36 KVA and have the neutral bonded to the frame.

I have lost my case with money managers to change out the 3-wire snouts with 4-wire. My delimma is no to choose the lessor of two evils which are:

1. Leave the bond in the portable gensets to at least provide some solid bonding between N-G, and grit my teeth over the non switched neutral in the MTS.

2. Close my eyes and do as told and say nothing else, either way is a violation IMO

The contractor wrote a letter to my management stating he wanted a letter to release him of liability. I refused to write such letter and would have no part of it. My management wrote him a letter informing him they had utility status and would bear the risk. Only good thing my name is not on the letter.

What do you think?
 
Re: Lessor Of Two Evils

So, if there is a ground fault (phase to case fault) while the generator is connected, is there a path back to the source that will cause the overcurrent protection to trip?

Eric Stromberg, P.E.
 
Re: Lessor Of Two Evils

Only by the metal-to-metal connection at the snout. The plug from the genset is 4-wire (L1-L2-N-G) with a another converter plug/recpt to 3-wire. I put a good fight stating everything needed to be 4-wire with a SG bonded coonection using 4-wire snout. Money folks do not want to spend the cash to convert the sites.
 
Re: Lessor Of Two Evils

Dereck,
If the neutral is not switched at the transfer switch, you would have a fault clearing path via the main bonding jumper at the service equipment. I don't see a big problem with the parallel path caused by the neutral being bonded at both the service and the generator, especially with a portable unit.
Don
 
Re: Lessor Of Two Evils

I think that I would chose option #1.This is an interesting situation I'll have to give it some more thought to see the safety issue.
Do you have a code section that states this as a violation?
Could you clarify this sentence in your op?
39 of the sites use a 3-wire generator snout, while the other 3 use 3-wire. The portable generators are 36 KVA and have the neutral bonded to the frame
 
Re: Lessor Of Two Evils

Originally posted by bassphisher:
Could you clarify this sentence in your op?
39 of the sites use a 3-wire generator snout, while the other 3 use 3-wire. The portable generators are 36 KVA and have the neutral bonded to the frame
My Bad. 39 sites have 3-wire (L-L-N, no ground) the remaining 3 have 4-wire (L-L-N-G). The violation is no EGC at the snout to bond the genset frame. Hope that clears up any confusion.
 
Re: Lessor Of Two Evils

Originally posted by don_resqcapt19:
Dereck,
If the neutral is not switched at the transfer switch, you would have a fault clearing path via the main bonding jumper at the service equipment. I don't see a big problem with the parallel path caused by the neutral being bonded at both the service and the generator, especially with a portable unit.
Don
Don the neutral is NOT switched. Since there will not be a EGC other than the metal-to-metal contact made at the snout is why I am considering leaving the bond in the genset, even though I know it does not comply. It would at least provide a fault clearing path in the event of a L-G fault in the genset.Do you agree with this theory?

[ February 17, 2006, 10:44 AM: Message edited by: dereckbc ]
 
Re: Lessor Of Two Evils

Dereck: I don't understand why there is a problem. The N-G bond at the generator should be removed. Here is the fault clearing path:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Start at generator's phase conductor,</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To transfer switch (now selected to "generator"),</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To load,</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To fault point within load (phase conductor to load's external metal parts),</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To EGC connection at load's external metal parts,</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To ground bar at "normal source,"</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To N-G bond at "normal source,"</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To neutral wire at "normal source,"</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To connection of neutral wire at transfer switch,</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To neutral wire of generator at transfer switch,</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">To neutral of generator windings.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">You are now back to the source, and the generator breaker should trip.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">Am I missing something? Do I presume incorrectly that the two neutral wires (i.e., from normal and generator sources) are connected to each other at the transfer switch?
 
Re: Lessor Of Two Evils

Charlie, I am not concerned with faults beyond the snout. My concern is faults between the snout and genset. For eaxample a fault in the generator itself.

The cable that leaves the genset is 4-wire and is terminated with a 4-wire plug. From the 4-wire plug there is a converter to 3-wire. The converter is just a 10-foot cable with a 4-wire recept on one end, and 3-wire plug on the other. The only EGc connection is what ever gets made by metal-to-metal contact at the connection points. In other words no made or SG from the missing 4th pin.

Hope that helps. Maybe I am just a worry wort. One way or the other I see a code violation and safety issue and trying to find the lessor of two evils.
1. Shut up (myself) and let the 3-wire go as is.
2. Pitch a fit and have the electrician leave the second bond in the genset.
 
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