Fire Pump Fed From Utility & Generator

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GamecockEE

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I'm working on a project where I need to be able to feed an electric fire pump from the utility and provide stand-by(legally required per IBC-2003(403.10.2)fora high rise project. I want to use ground fault protection on the service, although some may suggest utilizing several 800A mains. Problem I am running into is parallel paths back to the neutral point which foul up my ground fault sensing. I am using 4-pole transfer switch. The only way it seems to work is if I use another utility transformer to feed the fire pump.
What do you folks see being used out there that addresses this type of issue? Thanks for the advice!
 
Re: Fire Pump Fed From Utility & Generator

Problem I am running into is parallel paths back to the neutral point which foul up my ground fault sensing. I am using 4-pole transfer switch.
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Why would there be parallel paths if you are using a 4 pole transfer switch?
Don
 
Re: Fire Pump Fed From Utility & Generator

Problem I am running into is parallel paths back to the neutral point which foul up my ground fault sensing.
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I am with Don. This sounds strange. Does this problem occur under normal condititons or only when you are on the generator?
 
Re: Fire Pump Fed From Utility & Generator

I want to use ground fault protection on the service
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Why? Normally one would go with a fire pump controller with service entrance rated xfer switch and wire straight to the utility xfmr secondary. Also, you can't feed the fire pump from a disconnect in a switchboard.

The only way it seems to work is if I use another utility transformer to feed the fire pump.
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Why? you can use one POCO xfmr and run service entrance to your switchboard and a separate service entrance to the fire pump controller / xfer switch.

How bout them gamecocks! Gonna get a little tougher without Mr. Newton. Its just not fair! If its not the law hauling away the players its the injuries. Oh well too bad Spurier can't put on a uniform. Then yall would show em.
 
Re: Fire Pump Fed From Utility & Generator

Sorry to take so long to get back with you folks. I had a doctor's appointment, and then an appointment to carry my daughter deer hunting.

Let me see if I can try to paint you a better picture of what I'm trying to do. The fire pump service is 3 phase with a grounded conductor for the return of fault current to the utility source. The grounded conductor is bonded to the transfer switch frame in the normal source position. I am planning to use a separate service for the fire pump fed off the utility transformer, just as SCEPE suggested.

The generator is set up as separately derived system. Neutral will be grounded to the generator frame and the GEC at that point. It will feed a distribution panel, that in turn will feed emergency, legally required stand-by, and possibly optional loads as well through transfer switchs. The fire pump transfer switch is fed from this panel for it's stand-by source, and an EGC is carried with the phase conductors for return of fault current to the generator.

The problem appears when the transfer switch is in the Normal (Utility source)position and I put a line to ground fault elsewhere on the system. Fault current flows across this EGC between the generator distribution panel & fire pump transfer switch and gets back into the grounded conductor by the bond to the frame of the transfer switch, instead of completely flowing to the main panel as it should.

In looking at this, I have just had a thought. Would it be permissable instead of making a hard connection with the EGC from the Generator distribution panel to the frame of the fire pump transfer switch, to tie this conductor to the Generator source side of the fourth pole? The frame of the transfer switch will continue to be bonded to the common pole as I have tried to describe above I realize the conduit needs to be non-conductive.

For you folks out there. I'm using the IEEE Orange book diagrams for a separately derive source, a main service, and a 4 pole transfer switch. What I have added is the fire pump transfer switch and a generator distribution panel. I do have a sketch but don't have a clue as to how to post it on this site. Would be happy to fax to someone for a look.

For SCEPE, When it rains it pours, But I have already seen worse, and every dog (oops, I mean rooster) has its day. I just hope to live long enough to see it again! Go Cocks!
 
Re: Fire Pump Fed From Utility & Generator

gamecock,
i've got to think about your reviesed post but I wanted to get in a comment about what is really important...Football.

Congrats on a big win at Tenn. One thing I've learned over the years is you can never predict the gamecocks. When your sure their gonna beat Navy or the Citadel they find a way to lose. When your sure their gonna lose to #23 Tenn, they find a way to win. As for my Tigers, they deserve to loose by 21. Awefull, just plain awefull.
 
Re: Fire Pump Fed From Utility & Generator

In studying this, I think my issue is with the proper grounding and bonding of the fire pump transfer switch. When fed from the normal source(utility xfmr) the transfer switch would be considered a separate service and grounded accordingly. When fed from the generator, the xfer switch is no longer a service, but feeder equipment and should be grounded like a feeder. The grounding electrode becomes a supplemental electrode bonded to the EGC of the generator feeder conductor at the time the transfer switch changes over to stand-by power. As I was asking SCEPE this week-end, Is it permissable by code to allow the fourth pole of the transfer switch to switch between the grounded conductor of the normal source and the EGC from the Generator Feeder Panel? Any feed back would be helpful.
Note: to Don_ The fault current is flowing from the EGC that runs with the Generator conductors & flows back to the utility xfmr via the fire pump
grounded conductors.

[ November 01, 2005, 04:20 PM: Message edited by: GamecockEE ]
 
Re: Fire Pump Fed From Utility & Generator

Note to SCEPE, or others out there. Have you had a chance to think on this one? Ask me some more questions to see through this puzzle.
 
Re: Fire Pump Fed From Utility & Generator

GamecockEE
Note: to Don_ The fault current is flowing from the EGC that runs with the Generator conductors & flows back to the utility xfmr via the fire pump grounded conductors.
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Where is the main bonding jumper for the service and the system bonding jumper for the generator in relation to the transfer switch?
Don
 
Re: Fire Pump Fed From Utility & Generator

Don, the main bonding jumper is located in the main service panel, between the neutral and the equipment ground bar. The Generator bonding jumper is between the neutral of the gen-set & the frame of the generator. The Fire pump transfer switch is three-pole, no neutral. There is a grounded conductor back to the utility for fault current flow when in the normal position, and an EGC with the gen-set feeder conductors. There are other transfer switchs, Emergency & Standby. Those will be four pole.

What I'm simulating is a line to ground fault in the Emergency section of the distribution scheme. The fault current is capable of taking two paths back to it's source, because it can flow through the grounding of the fire pump transfer switch which interconnects the utility service to the Gen-set.

Don, how should the Fire pump transfer switch be grounded, since in the normal position it is a separate service fed by the utility & in the Stand-by position it becomes a feeder off the generator? Thanks for batting this around with me.
 
Re: Fire Pump Fed From Utility & Generator

Gamecock,

At Last I think I have a handle on what you are talking about. Your original post said a 4 pole transfer switch and that was stumping me. I saw a good article from ASCO on pretty much the exact scenario you are talking about. It was faxed to me by a supplier and I cant find it on their web site. It was titled "Do 3 pole transfer switches provide for adequate isolation and ground fault sensing of today's normal and emergency systems" Asco Facts Vol5 Num 7.

The solution they advocate is using a 4 pole xfer switch with overlapping neutral contacts.

If you want, send me a private message with fax # and I will send you a copy.
 
Re: Fire Pump Fed From Utility & Generator

GamecockEE
What I'm simulating is a line to ground fault in the Emergency section of the distribution scheme. The fault current is capable of taking two paths back to it's source, because it can flow through the grounding of the fire pump transfer switch which interconnects the utility service to the Gen-set.
Click to expand...
The two paths won't be a problem as long as they combine on the load side of the ground fault sensor.
Don
 
Re: Fire Pump Fed From Utility & Generator

What kind of ground fault sensing are you using? (direct or residual)
 
Re: Fire Pump Fed From Utility & Generator

Don, the two currents combine at the neutral of the utility transformer, upstream of the ground
fault sensing device in the main service panel. I'm thinking that I may need a zero-sequence ct in the fire pump xfer switch, that will work in combination with the sensor in the main service panel, so that all the fault current can be accounted for.
 
Re: Fire Pump Fed From Utility & Generator

Engy, I'm thinking I'm not really sure which type just yet. More or less trying to establish the locations of where it needs to be sensed, and preventing unnecessary trips.
 
Re: Fire Pump Fed From Utility & Generator

I think you have a conflict with 695.3(B)which requires a second source if the utility is not deemed reliable and a source that complies with 695.3(A). Since you are not in a multi-campus bldg you can't use feeder sources in 695.3(B)(2).

One of your sources has to be utility connection as specified in 695.3(A)(1), which requires a seperate service or tap ahead but not w/in the same section as the service disconnect.

Designers here will start at the UGPS section and go one way to normal service and then the other way to the fire pump service. From the fire pump service it goes directly to the fire pump controller which has integral XFR equipment.
 
Re: Fire Pump Fed From Utility & Generator

Larry, the primary service for the fire pump will originate at the secondary terminals of the utility transformer, and will feed the fire pump transfer switch as separate service. The Stand-by source will be the on-site Gen-set. The stand-by power requirement is coming from the IBC for high-rise buildings.
 
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