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#29552 - 09/19/03 06:40 AM Gasoline shutdowns  
walrus  Offline
Joined: Jul 2002
Posts: 680
Bangor Me. USA
I work in a lot of locations in which the fire suppression folks have a shutdown that is supposed to stop the flow of gas when the fire suppression pull box is pulled. The way they do it is, interupt the neutral going to the coils of the relays for the pump motors. They use a normally closed relay that opens when the pull station is pulled. It works but is it right????

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#29553 - 09/19/03 06:55 AM Re: Gasoline shutdowns  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
hmmm, maybe it's just my personal experience walrus, but i've been used to contactor controlled subpanels in gas stations.....

#29554 - 09/19/03 07:30 AM Re: Gasoline shutdowns  
electure  Offline

Joined: Dec 2000
Posts: 4,260
Fullerton, CA USA
This is the way many factory wired motor starters work with relationship to the overload relays.
On an ungrounded control circuit this might be OK, but on a control circuit using a grounded conductor I don't like it.
There is the potential for a ground fault between the coil(s) and the contact that is used to interrupt them to render the shutoff (or tripped O/L) totally inoperable.
Under normal operation, this ground fault could go undetected indefinitely. The first sign could be that the shutoff doesn't work when called upon to do its (important) job.
This situation could be compounded by multiple starters/relays wired in conjunction with each other...S [Linked Image]

#29555 - 09/19/03 04:08 PM Re: Gasoline shutdowns  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
That type of installation appears to be a violation of 430.73.


#29556 - 09/19/03 06:44 PM Re: Gasoline shutdowns  
walrus  Offline
Joined: Jul 2002
Posts: 680
Bangor Me. USA
I always thought that switching the neutral like that wasn't right but wasn't 100% sure why.

I have some contactor controlled installs but few and far between. The reason they shut down the neutral is because there is several relays controlling several pumps but only one neutral to all relays. Easy?....

I'm involved in a location that has no shutdowns and they want to put one in. No chance they spring for the money to put in a contactor,although I'm thinking shunt trip?? and a contactor might be cheaper.
Any other suggestions???

#29557 - 09/20/03 01:02 AM Re: Gasoline shutdowns  
wa2ise  Offline
Joined: Nov 2002
Posts: 782
Oradell NJ USA
This can only work if all the pumps are fed by the same voltage and phase. If the pumps are on 2 or three phases (each pump using only one phase), and you break the neutral, the pumps would still have voltage across them. Only if each pump draws the same current would they split up the supply voltages evenly. In any event you wouldn't get shutdown.

If everything is fed by one voltage/phase source, then you could put that contactor on the supply wire, and leave the neutral alone.

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