Sewer wet well conduit for submerged pumps.

JoelWEdwards

New User
Location
City of Lakeland Water utilities
Occupation
electronic technician
I am an electronic technician for the City of Lakeland Water Utilities.

We are interested in finding out how to obtain an exemption in the NEC 501.15 (4) Class 1 Division 1 Boundary. Our situation is this. We have 185 sewer wet wells in the city. They have a rigid aluminum conduit that is open in the wet well with a pump lead coming out of it going to a submersible pump that is submerged in sewage. We have a junction box that is between the motor control cabinet and the pump. When the pump has to be pulled for maintenance and rebuilt the conduit seal off has to be busted out and that puts pieces of concrete in the conduit and then the pump wire won’t come out because it is trapped or snagged in the conduit from the concrete. We want to put a C body condulet in the conduit just before the EY seal off so that we can open it, block it off with rags and keep any concrete from going down into the underground part of the conduit run. Our city inspector says we can not do this because of what is stated in 501.15. Having to bust up a concrete pad and rip conduit apart underground because of this we find to be unacceptable. What are your thoughts?
 

kwired

Electron manager
Location
NE Nebraska
This has topic has come up before. My opinion is it is not a classified area. If the gasses in the wet well are thick enough to be explosive you have bigger problems to solve than some wiring.
I kind of have to agree that it probably isn't concentrated enough, but I am not allowed to classify it either.

Nothing prohibits junctions within the classified boundary, problem is your sealing fitting is likely the first thing in the line outside the boundary which is allowed and there is no easy place to put a junction within the boundary.
 

tom baker

First Chief Moderator
Staff member
what works for us is to have a sleeve into wet well sleeve (PVC) extends up and out to side of liftstation building. Sleeve is open ended about 12" below SS J-Box, pretty large, 18 x18 inches, that has terminal blocks in it. No seal needed, any fumes from wet well dissipate out thru end of sleeve. You could pack some duct seal into end of sleeve. I may be able to get some pictures. If you like this I can get you in touch with the WWTP maintenance department send me a PM
 

rbalex

Moderator
Staff member
I am an electronic technician for the City of Lakeland Water Utilities.

We are interested in finding out how to obtain an exemption in the NEC 501.15 (4) Class 1 Division 1 Boundary. Our situation is this. We have 185 sewer wet wells in the city. They have a rigid aluminum conduit that is open in the wet well with a pump lead coming out of it going to a submersible pump that is submerged in sewage. We have a junction box that is between the motor control cabinet and the pump. When the pump has to be pulled for maintenance and rebuilt the conduit seal off has to be busted out and that puts pieces of concrete in the conduit and then the pump wire won’t come out because it is trapped or snagged in the conduit from the concrete. We want to put a C body condulet in the conduit just before the EY seal off so that we can open it, block it off with rags and keep any concrete from going down into the underground part of the conduit run. Our city inspector says we can not do this because of what is stated in 501.15. Having to bust up a concrete pad and rip conduit apart underground because of this we find to be unacceptable. What are your thoughts?
I am assuming you wish an exemption from Section 501.15(A)(4). Other than the two Exceptions listed, there is none.

The issue then is how to properly transit the boundary. Tom Baker's suggestion is excellent. There are, however, two cautions. When leaving the sleeve open recognize that a small radius ckassified envelope will still exist around the exterior penetration. Second, the cable used to cross the boundary must be installed per Section 501.15(D). There are several cable options listed in Section 501.10(A) and at least one of the Section 501.15(D) Subsections will apply. Common to all of the options is the cable end must be sealed at the terminations in the classified location. [Section 501.15(D)(1)]
 

kwired

Electron manager
Location
NE Nebraska
I am assuming you wish an exemption from Section 501.15(A)(4). Other than the two Exceptions listed, there is none.

The issue then is how to properly transit the boundary. Tom Baker's suggestion is excellent. There are, however, two cautions. When leaving the sleeve open recognize that a small radius ckassified envelope will still exist around the exterior penetration. Second, the cable used to cross the boundary must be installed per Section 501.15(D). There are several cable options listed in Section 501.10(A) and at least one of the Section 501.15(D) Subsections will apply. Common to all of the options is the cable end must be sealed at the terminations in the classified location. [Section 501.15(D)(1)]
Doesn't that cable pass completely through the classified area with no fittings? The pump end is under water, wouldn't that be outside the classified area? Sort of no different than running one piece of RMC with no couplings or other fittings through a classified area but both ends are outside the classified area - no boundary sealing needed, no vapors causing the classified area are supposed to be able to get inside.
 

tom baker

First Chief Moderator
Staff member
One other detail. Where the sleeve is installed on the outside of the electrical bldg, there is a ss u shaped shield over the sleeve, from ground to about 2" below the j box. Pump cable goes into j box with a cgb connector
 

rbalex

Moderator
Staff member
Doesn't that cable pass completely through the classified area with no fittings? The pump end is under water, wouldn't that be outside the classified area? Sort of no different than running one piece of RMC with no couplings or other fittings through a classified area but both ends are outside the classified area - no boundary sealing needed, no vapors causing the classified area are supposed to be able to get inside.
Good point - so what NEC Section are you citing?
 

rbalex

Moderator
Staff member
Yes - but those Exceptions only apply to conduits, not cables AND the conduits must extend at least 12" beyond the boundary. Can this be guaranteed for cables at all times? EDIT ADD: I should have said, "Can this be guaranteed for cables at all times for this application?"
 
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kwired

Electron manager
Location
NE Nebraska
Yes - but those Exceptions only apply to conduits, not cables AND the conduits must extend at least 12" beyond the boundary. Can this be guaranteed for cables at all times? EDIT ADD: I should have said, "Can this be guaranteed for cables at all times for this application?"
Can't necessarily even be guaranteed at all times for conduits when it comes to maintenance and repairs.

I'd have to read through things a little more carefully, but just didn't make sense to me to seal the motor end of the cable to prevent gas from transfering through the cable when it is supposed to be submerged in the water during normal operation and on top of that already has a seal that is supposed to keep the water out of the motor. Then aren't many of those submersibles oil filled with connections immersed in the oil on top of that?

I haven't worked on a ton of those but seems they all were somewhat like I described.
 

tom baker

First Chief Moderator
Staff member
This has topic has come up before. My opinion is it is not a classified area. If the gasses in the wet well are thick enough to be explosive you have bigger problems to solve than some wiring.
I saw an explosion in a wet well that threw the manhole cover across the street. I admit it was from gasoline someone poured down the sewer. NFPA 820 calls it a classified area
 

oldsparky52

Senior Member
My 2 cents.

The units I've wired came with one 2" opening in the side of the wet well structure for electrical wiring entry. I would extend a piece of 2" PVC to under the control cabinet but not attach it to the control cabinet, and keep the conduit low enough that it does not leave the "classified" location. Since the conduit does not leave a classified location, then a conduit seal is not required since it does not cross a boundary.

The cables come through the conduit then in free air to the control cabinet that is installed above and out of the classified location. The cable comes installed with the pump or the float switch and is long enough to get to the control cabinet w/out any splices. I believe the cable is of a type that does not pass gases, so it is allowed w/out seals.

When a pump or switch goes bad, you disconnect the cable in the control box, pull it out of the cabinet, pull the cable into the wet well (with a pull rope to pull in the new cable), pull out the bad pump or switch, then pull the cable back into the control cabinet and connect.

This crap of needing x-proof seals is BS as far as I'm concerned. This whole system is set up to not need splicing and to be able to replace pumps/switches w/out breaking seals.

501.140(A)(3) allows the cable to be extended w/out splicing.

To the OP, IMO you are dealing with a crappy installation. Since you have 185 of these, IMO someone needs to get with the electrical inspections department and the engineers and see if you can't come up with a remediation plan to these poor installations.
 
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kwired

Electron manager
Location
NE Nebraska
My 2 cents.

The units I've wired came with one 2" opening in the side of the wet well structure for electrical wiring entry. I would extend a piece of 2" PVC to under the control cabinet but not attach it to the control cabinet, and keep the conduit low enough that it does not leave the "classified" location. Since the conduit does not leave a classified location, then a conduit seal is not required since it does not cross a boundary.

The cables come through the conduit then in free air to the control cabinet that is installed above and out of the classified location. The cable comes installed with the pump or the float switch and is long enough to get to the control cabinet w/out any splices. I believe the cable is of a type that does not pass gases, so it is allowed w/out seals.

When a pump or switch goes bad, you disconnect the cable in the control box, pull it out of the cabinet, pull the cable into the wet well (with a pull rope to pull in the new cable), pull out the bad pump or switch, then pull the cable back into the control cabinet and connect.

This crap of needing x-proof seals is BS as far as I'm concerned. This whole system is set up to not need splicing and to be able to replace pumps/switches w/out breaking seals.

501.140(A)(3) allows the cable to be extended w/out splicing.

To the OP, IMO you are dealing with a crappy installation. Since you have 185 of these, IMO someone needs to get with the electrical inspections department and the engineers and see if you can't come up with a remediation plan to these poor installations.
Some will say you did basically same thing as adding a vent stack to an underground fuel tank, and there is a classified area near the vent opening on those so at least need to keep the end of it far enough away for that sort of situation
 

oldsparky52

Senior Member
Some will say you did basically same thing as adding a vent stack to an underground fuel tank, and there is a classified area near the vent opening on those so at least need to keep the end of it far enough away for that sort of situation
Okay, that distance is usually 3', so keep the conduit 6" above grade and the bottom of the enclosure 42" above grade and I think that takes care of that technicality.

Now, if that fuel tank is diesel, would that 3' still be applicable? What is the classification (flash point) of the atmosphere in that sewer pit?

You can also seal that conduit with ductseal that would basically force any venting through the pit vent.

Reason has to come into play here sometime. (I hope)
 

oldsparky52

Senior Member
I've described my methodology for this installation before on this site, and AFAIK, no one ever shot it down, but no one ever blessed it either.

I would love it if someone would say, "yea, I agree". :)

I NEED VALIDATION! (personality flaw)
 

kwired

Electron manager
Location
NE Nebraska
I will admit that some inspectors are not reasonable.
I will second that.
I've described my methodology for this installation before on this site, and AFAIK, no one ever shot it down, but no one ever blessed it either.

I would love it if someone would say, "yea, I agree". :)

I NEED VALIDATION! (personality flaw)
I like your installation description, especially with added information in post 16.

IMO if tank mentioned there contained diesel you have no classified location, flash point is too high.
 
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