Disconnect opens the neutral

[johnny watt]

article 514.11

What is the purpose of requiring the EMO disconnect to open the neutral (grounded and ungrounded conductors) for a gasoline dispensor ?
Does this requirement possibly introduce more of a hazard than it is attempting to address?

 

[GoldDigger]

article 514.11

What is the purpose of requiring the EMO disconnect to open the neutral (grounded and ungrounded conductors) for a gasoline dispensor ?
Does this requirement possibly introduce more of a hazard than it is attempting to address?

As long as the ungrounded conductors are all opened at the same time as the neutral, it does not create any additional risk.
And the EGC is never interrupted, so the equipment remains bonded to protect against a fault from other sources.

The risk to leaving the neutral connected is that in the event of a lost neutral upstream (serving equipment which was NOT served by the disconnect in question) there could be voltage imposed on the neutral, which would then still be able to generate sparks or heat through a fault to "earth" in the form of either ground electrodes or an EGC.

 

[don_resqcapt19]

Even without any open neutral or other problems, if you touch the neutral to the raceways or other metallic objects that are connected to the EGC or have any other path back to the system neutral, you may create a small arc. This arc is driven by the voltage drop on the grounded conductor downstream from the main bonding jumper. This may or may not have enough energy to ignite any gasoline vapors in the area. The requirement to disconnect all of the circuit conductors, including the grounded conductor, removes this risk.

 

[GoldDigger]

As long as the ungrounded conductors are all opened at the same time as the neutral, it does not create any additional risk.
And the EGC is never interrupted, so the equipment remains bonded to protect against a fault from other sources.

The risk to leaving the neutral connected is that in the event of a lost neutral upstream (serving equipment which was NOT served by the disconnect in question) there could be voltage imposed on the neutral, which would then still be able to generate sparks or heat through a fault to "earth" in the form of either ground electrodes or an EGC.

Take a look at the video which Mike Holt posted in this thread http://forums.mikeholt.com/showthread.php?t=157853&highlight= for several good examples of potential problems, not even looking at the more common sorts of problems that don has brought up.

 

[johnny watt]

Thank you for the responses.
I have observed that when service people work on dispensers and pumps they do not shut off breakers most of the time. But when they do, they do not shut off the EMO but only an individual breaker, which does not open the neutral.
Also, sometimes they use a receptacle on the building or other location that is not neutral switched and run a chord to the dispensers when servicing.

I guess what I see is that the majority of the time that there is potential explosive fumes (filter changes and meter changes or fuel being unloaded), the neutral is left in tact. But once every few years that there is a surface spill large enough to warrant hitting the EMO switch (assuming the attendant stops the entire station instead of the pump stop on the register), then the neutral is opened. If the EMO is hit then we have a potentially invisible hazard because the canopy lights are out too.

But I am thinking the more likely is that an EMO doesn't get hit, if ever, until after the fire/explosion. And then they are in the dark from the canopy lights being cut.

I have seen three separate stations where the pump and tanks were upgraded, and that neutrals were mixed up. You can point to the electrician but it wasn't the same company that did it. The problem came when the main panels are feeding existing signs, areal lights, air machines and whatnot, and then the upgrade required more circuits for the signs, or one switched and the other 24/7. They ran a second circuit from the gas panel to a device that already had a first circuit coming from the main panel and then ran separate neutrals but did not keep them straight when they re-landed them and tied them together in one case.

 

[don_resqcapt19]

Thank you for the responses.
I have observed that when service people work on dispensers and pumps they do not shut off breakers most of the time. But when they do, they do not shut off the EMO but only an individual breaker, which does not open the neutral.

Every breaker I have ever seen for a gas dispenser was of the type that opens both the ungrounded conductor and the grounded conductor. The EMO is only required to kill the power, that is open the ungrounded conductors. It is not required to open the grounded conductor.

Also, sometimes they use a receptacle on the building or other location that is not neutral switched and run a chord to the dispensers when servicing.

There is no requirement that circuits, other than the dispenser circuits, have a means to disconnect the grounded conductor.

I guess what I see is that the majority of the time that there is potential explosive fumes (filter changes and meter changes or fuel being unloaded), the neutral is left in tact. But once every few years that there is a surface spill large enough to warrant hitting the EMO switch (assuming the attendant stops the entire station instead of the pump stop on the register), then the neutral is opened. If the EMO is hit then we have a potentially invisible hazard because the canopy lights are out too.
But I am thinking the more likely is that an EMO doesn't get hit, if ever, until after the fire/explosion. And then they are in the dark from the canopy lights being cut.

The EMO is only required to kill the power to the dispensing equipment, not to the lighting or any other equipment. There is no requirement that the EMO open the grounded conductor.

I have seen three separate stations where the pump and tanks were upgraded, and that neutrals were mixed up. You can point to the electrician but it wasn't the same company that did it. The problem came when the main panels are feeding existing signs, areal lights, air machines and whatnot, and then the upgrade required more circuits for the signs, or one switched and the other 24/7. They ran a second circuit from the gas panel to a device that already had a first circuit coming from the main panel and then ran separate neutrals but did not keep them straight when they re-landed them and tied them together in one case.

You can find code violations in all types of installations, gas stations are no exception. Remember that 1/2 of all electricians were in the lower half of their class.

 

[iwire]

Don, go take a look at the code wording.

Most of the stations I have serviced use standard single pole breakers in the panels.

For the required disconnect they use a separate multipole switch because they have to kill three circuits to each dispenser. Lights, power and some sort of control circuit between the pumps under ground and the dispenser.

That said, I agree with you that the NEC cannot make people use the correct switch when servicing the pumps.

That seems more like a proper training issue than a code issue.

 

[johnny watt]

I apologize for my terrible memory but it completely slipped my mind that every station I have worked on did in fact have switched neutral breakers for the dispensers and submersibles. Only the older stye dispensers had a second power circuit leading to them for lights, all of the newer Wayne and Gilbarco dispensers I have seen were only fed with a single power circuit. I think about ten years ago they started incorporating a dispenser hook isolation board instead of hooking all the hook switches directly together to trigger the submersible.

All of these stations use a dedicated fuel panel fed by a contactor which interrupts the neutral and two hots when the EMO switch is pushed. Maybe that is their way of dealing with the dispenser hook circuits, tank monitor sensors and whatever else might be running to the sumps? But then that seems like it makes the switched neutral breakers redundant.

[514.11 ] Disconnects for dispensing stations need to allow for rapid response to a hose breakage or other event that creates a fuel-related fire or explosion hazard:

(A) Each circuit leading to or through a dispenser (including equipment for remote pumping systems) must have a clearly identified and readily accessible switch (located remote from the dispenser) to disconnect simultaneously all conductors of the circuit (including the grounded neutral conductor). You can?t use single-pole breakers with handle ties.

Sounds to me like the simultaneous requirement is circuit specific and it would be okay to have a separate breakers to turn off each separate circuit if so desired?

The only other thing I am wondering about is what "leading to or through a dispenser" means. Is there a rule that says the dispenser sump is the dispenser? And if the canopy lighting conduit comes up through a pull hole in the canopy column two feet away from a hose, would you say it is running to the dispenser, being so close?

 

[don_resqcapt19]

Don, go take a look at the code wording.

Most of the stations I have serviced use standard single pole breakers in the panels.

For the required disconnect they use a separate multipole switch because they have to kill three circuits to each dispenser. Lights, power and some sort of control circuit between the pumps under ground and the dispenser.

That said, I agree with you that the NEC cannot make people use the correct switch when servicing the pumps.

That seems more like a proper training issue than a code issue.

It has been some time since I worked on on, but the ones I worked on used the neutral switching breaker.
With all of the additional circuits now used, I can see the cost effectiveness of a multipole disconnect switch. Still not sure how they disconnect the data and other non-power circuits.

That being said, I don't see any requirement that the device used for the emergency shut-down has to open the neutral.

 

[texie]

I apologize for my terrible memory but it completely slipped my mind that every station I have worked on did in fact have switched neutral breakers for the dispensers and submersibles. Only the older stye dispensers had a second power circuit leading to them for lights, all of the newer Wayne and Gilbarco dispensers I have seen were only fed with a single power circuit. I think about ten years ago they started incorporating a dispenser hook isolation board instead of hooking all the hook switches directly together to trigger the submersible.

All of these stations use a dedicated fuel panel fed by a contactor which interrupts the neutral and two hots when the EMO switch is pushed. Maybe that is their way of dealing with the dispenser hook circuits, tank monitor sensors and whatever else might be running to the sumps? But then that seems like it makes the switched neutral breakers redundant.



Sounds to me like the simultaneous requirement is circuit specific and it would be okay to have a separate breakers to turn off each separate circuit if so desired?

The only other thing I am wondering about is what "leading to or through a dispenser" means. Is there a rule that says the dispenser sump is the dispenser? And if the canopy lighting conduit comes up through a pull hole in the canopy column two feet away from a hose, would you say it is running to the dispenser, being so close?

Under the 2011 rules, you are right, a switched neutral breaker is not needed as you are going to achieve neutral disconnection through the contactor with all the other circuits. In the old days when we only switched the power to the dispenser and EPO was not used, a switched neutral breaker was the norm.
The problem with the contactor solution is how do you also switch the data, video, credit card data, etc. along with the power conductors? A contactor does not lend itself to do this kind of switching. I am aware that Square D has come up with a product that will switch everything to a dispenser in a manner compliant with 2011 NEC although I have not seen one yet. Not sure if there other companies doing this. I can tell you that without a product such as the Square D that I mention, I don't know how you can met the rules in 514 for the 2011 edition as a contactor won't work to switch all the low data/electronic stuff.
As to the case of the canopy or other conduit coming up nearby, I don't think this is an issue as it is only a raceway passing through the classified area, but not through the dispenser.
Here is a link to the SqD unit. It looks like a fairly complex piece, but given what it claims to do I can see why: http://www.schneider-electric.us/documents/product-site-support/LVDD-V-HO.pdf
I can tell you that there are an awful lot of stations out there built under the 2011 NEC that are not compliant with the 514 disconnection rules.