Sewage Pumping Station Wet Well

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KeeganPeters

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I found a discussion from back in 2007 about a Sewage Pumping Station Wet Well. The discussion is linked below.

http://forums.mikeholt.com/showthread.php?t=91513

I'm not an Electrical Engineer and was hoping someone could clarify what was discussed in that thread. The NEC 501.15(B)(2), Exception 2 what applies for an open air termination for an explosive environment?

We are trying to install a quick disconnect panel that us Meltric plugs next to our pump station wet well. The power and control cables will run first to a concrete vault. The wet well and the vault will be located directly next to each other with less than a foot of 12"dia pvc sch pipe in between. The concrete vault top will be half grate and grated stand for the panel. The power and control cables will run through the wet well to the vault through the grated stand to the bottom of the panel.

We have been having a discussion with our electrical engineer about this item. He says the code is very clear that you need a seal off when leaving an explosive environment. We would like to avoid a seal off because they would make the Meltric plug useless. Would the grated control panel stand be adequate to meet NEC 501.15(B)(2), Exception 2?
Thanks
 

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Sewage Pumping Station Wet Well

rbalex said:
Let's start with the elementary question: "Why aren't the well and vault Division 1?"
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Yeah the well and vault would be a Division 1 if we didn't get the 12 air exchanges per hour. If we did get the 12 air exchanges per hour and the vault and well were classified as Division 2, would the exception be applicable?
 
Are you exhausting those 12 air changes through the panel?
Are you using conduits between the vault in the panel?
 
rbalex said:
Are you exhausting those 12 air changes through the panel?
Are you using conduits between the vault in the panel?
Click to expand...

We would likely have another pipe in the well that the fan would blow into the well. There would be another pipe gooseneck pipe to act a vent, but I guess some of the gasses would vent out of the vault to the panel.

There would be conduit between the vault and well. The cables would run bare though the vault and the grated panel stand. There would be no conduit between the vault and the panel.

I found this figure. Best I can tell, we are more then 0.5 feet from the lid of the vault and are now in a unclassified division if we removed the fan.
 

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KeeganPeters said:
We would likely have another pipe in the well that the fan would blow into the well. There would be another pipe gooseneck pipe to act a vent, but I guess some of the gasses would vent out of the vault to the panel.

There would be conduit between the vault and well. The cables would run bare though the vault and the grated panel stand. There would be no conduit between the vault and the panel.

I found this figure. Best I can tell, we are more then 0.5 feet from the lid of the vault and are now in a unclassified division if we removed the fan.
Click to expand...
Permit me to assure you that, with 12 air changes/hour, the design as described will exhaust gases through the panel. A boundary seal is the least of you problems since your original diagram indicates vents through the panel front and sides and the entire installation is in Division 2. Section 501.15(B)(2) Exception 2 doesn't apply because there is no boundary.
 
KeeganPeters said:
I found a discussion from back in 2007 about a Sewage Pumping Station Wet Well. The discussion is linked below.

http://forums.mikeholt.com/showthread.php?t=91513

I'm not an Electrical Engineer and was hoping someone could clarify what was discussed in that thread. The NEC 501.15(B)(2), Exception 2 what applies for an open air termination for an explosive environment?

We are trying to install a quick disconnect panel that us Meltric plugs next to our pump station wet well. The power and control cables will run first to a concrete vault. The wet well and the vault will be located directly next to each other with less than a foot of 12"dia pvc sch pipe in between. The concrete vault top will be half grate and grated stand for the panel. The power and control cables will run through the wet well to the vault through the grated stand to the bottom of the panel.

We have been having a discussion with our electrical engineer about this item. He says the code is very clear that you need a seal off when leaving an explosive environment. We would like to avoid a seal off because they would make the Meltric plug useless. Would the grated control panel stand be adequate to meet NEC 501.15(B)(2), Exception 2?
Thanks
Click to expand...

Will the cables be located below the control panel and vented below control panel? Also, control power and motor pump power shouldn't share the same conduit. If it's vented below control panel, we'll typically seal off the pvc conduit with duct seal. That would be an acceptable seal off in this application.
 
You might not be able to use the cord plugs below the panel. I can't find anything that states you can. Art. 501.140 (2014 NEC) mentions that the cord shall be continuous.
 
chris1971 said:
Will the cables be located below the control panel and vented below control panel? Also, control power and motor pump power shouldn't share the same conduit. If it's vented below control panel, we'll typically seal off the pvc conduit with duct seal. That would be an acceptable seal off in this application.
Click to expand...
Did you review the design drawing shown in the OP?
 
rbalex said:
It's pretty clear that the vault vents directly into (not below) the control panel.
Click to expand...

Imo, that wouldn't be acceptable. Typically, we'll bring the pump power in a conduit below the control panel, the float switches in another conduit below the control panel. The conduits are cut, bell ends installed and the pipes are sealed below the control panel panel with duct seal. We then enter the control panel with cord grips.
 
chris1971 said:
Imo, that wouldn't be acceptable. Typically, we'll bring the pump power in a conduit below the control panel, the float switches in another conduit below the control panel. The conduits are cut, bell ends installed and the pipes are sealed below the control panel panel with duct seal. We then enter the control panel with cord grips.
Click to expand...


Thats what I typically see. Except, I usually visit pump stations a few months/years after they have been put in and during the first pump or float swap out the pipe sealant is removed and never reinstalled.
 
Saturn_Europa said:
Thats what I typically see. Except, I usually visit pump stations a few months/years after they have been put in and during the first pump or float swap out the pipe sealant is removed and never reinstalled.
Click to expand...

That's typically what happens when a pump or float switch is replaced.:lol:
 
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