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#99855 - 09/22/06 04:32 PM Fire Pump Transfer Sw.  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 822
Michigan
Service rated Transfer switch 480 V 3 phase.

Two feeds
One from Generator Breaker other from utility transformer (No breaker inbetween).

Both underground directly to transfer switch(service rated) Which has a breaker for Both incoming lines.

Generator feed is three phases plus Ground, Power co. feed I take it MUST be three phases plus Neutral. Even though neuutrals not to be used its required for grounding.
Thus you have an equipment Ground from Generator , AND a neutral from Power Co. Hooking to the same bar.& Neutral bar Must be tied to the case.
Any comments or Input???

Yoopers


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#99856 - 09/22/06 09:18 PM Re: Fire Pump Transfer Sw.  
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
Ernie- 3 phase from the generator for that voltage does not have to be grounded but it will have to have an equipment ground. look at 250.20(B). If the neutral conductor of the utility and the equipment grounding conductor are terminated in the transfer switch I think it would be best if the equipment grounding conductor from an ungrounded 480v. supply (generator) is tied to the enclousure of the transfer switch. I further think that the neutral of the utility supply should be tied to a bar in the transfer switch with a Main Bonding Jumper that is removable.


George Little

#99857 - 09/23/06 04:10 PM Re: Fire Pump Transfer Sw.  
tdhorne  Offline
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Joined: Mar 2001
Posts: 345
Maryland, USA
George
If that generator is wye connected wouldn't we be required to bring the neutral to the service disconnecting means and bond it pursuant to 250.24 (B). The reason that I bring that up is it is very common to use one generator to supply several emergency loads of which the fire pump is just one. In such a case the generator will be wye connected in order to supply the emergency lighting loads.
--
Tom Horne


Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

#99858 - 09/23/06 07:43 PM Re: Fire Pump Transfer Sw.  
George Little  Offline
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Joined: Jan 2004
Posts: 1,489
Michigan USA
Tom - If it were grounded I would agree with you based on your code reference of 250.24(B). But in the example Ernie cited their was no neutral load and based on the option to ground in 25020(B), he might not bond the wye SDS. If he did bond the system and also the utility Service he probably would end up with a 4-pole transfer switch with each system with it's own Grounding Electrode. (he could also use the same grounding electrode) but he would have to run the grounded conductor through a pole on the transfer switch.
IMHO or as I understand the code.


George Little

#99859 - 09/23/06 08:12 PM Re: Fire Pump Transfer Sw.  
Yoopersup  Offline
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Joined: Mar 2003
Posts: 822
Michigan
Both are 277/480 volt Y's thus I said Neutral required on Power Co.Service. Disconnect as its ist in Transfer Sw. But not from Generator as Breaker located at the Generator.


#99860 - 09/23/06 10:19 PM Re: Fire Pump Transfer Sw.  
George Little  Offline
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Joined: Jan 2004
Posts: 1,489
Michigan USA
Okay Ernie- Now that I understand what you have ie: 480/277v. for both the generator and the utility, you will need a 4-pole transfer switch to disconnect the SDS grounded conductor from the utility grounded conductor. Each will need a gorunding electrode and without the grounded conductor running through a pole of the transfer switch you'd be grounding your two systems in two places which is a code violation. Your first post only mentioned 480v generator which would lead me to think that the generator was running ungrounded single voltage.


George Little

#99861 - 09/24/06 08:29 AM Re: Fire Pump Transfer Sw.  
Yoopersup  Offline
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Joined: Mar 2003
Posts: 822
Michigan
Transfer Switch is Service Rated Fire Pump switch. As its 480 volt 3 Phase I;m sure theres no neutral prefusions at the transfer switch. I;ll check MoNday & see .


#99862 - 09/25/06 08:08 PM Re: Fire Pump Transfer Sw.  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 822
Michigan
Transfer switch 480volt 3 phase service rated
No neutral bar present.


#99863 - 09/25/06 09:33 PM Re: Fire Pump Transfer Sw.  
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
I think if it's single voltage - in other words, ungrounded straight 480v. you only need a 3 pole transfer switch. You will still be bringing an GEC from the generator to the transfer switch to ground the equipment. As I recall there is a need for ground indicator lights but I don't know where I saw that. Also typically ungrounded systems are Delta not Wye. You can check to see if you have any voltage between any of the 3 legs and Ground to find out if it's a grounded system. No insults intended Ernie cause I'm sure you already have done this. Also look in Soares Grounding 8th Ed. p. 43-51 for a brief overview of ungrounded systems and pictures too


George Little

#99864 - 09/27/06 08:38 PM Re: Fire Pump Transfer Sw.  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 822
Michigan
George]
The Generators a Y The power Co, Feeds a Y

Both 277/ 480.
Generator Neutrals Grounded at the Gen . Set
Power co. Requires a Neutral per Code Even thought its a 480 3 phase Because a Neutrals present at the transformer.
Thus it HAS to be brought in for Grounding purposes! The Question is Theres a EQuipment Gr. From Generator and a Neutral from Power Co. Service coming into a Transfer switch at the Fire pump set up from Ground only/


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