Conduit Seal between XP JB and Non-XP Control Panel - Sewage Lift Station

[zapit480v]

Hi,

I'm new to the site, although I have used it several times to look up information.

I found a topic related to my question but it was "closed" and I couldn't post another comment regarding it.

Here is the TITLE of the thread and below is my question.

I have wired (in my past life as an electrician) and designed at least a hundred sewage lift stations and have never been questioned by the AHJ until today.


I have a submersible pump sewage lift station wet well (CL1, DIV1 location) and an outdoor NEMA 4X control panel (CP) installed outdoors above grade approximately 5' from the wet well. Two (2) pump cable (480vac, 3-phase), level transducer cable (connect to IS barrier in CP) and back-up float cables (connected to warrick IS relays in CP). There is a seperate conduit for each pump cable, the level transducer (IS) and the floats (IS) for a total of four conduits from the wet well to the control panel. The horizontal below grade conduits from the wet well to the CP are Rigid PVC and enter the wet well 24" below grade and are converted to RMC 24" below grade to above grade for termination to the CP. Where the RMC emerges above grade I specify an XP Crouse-Hinds type GUAC conduit body on all conduits for splicing cables. Above the XP conduit body I specify an XP conduit seal. Above the XP conduit seal and into the CP they can us a standard malleable conduit body, ie. LB, jake 90.. The reason for the seal after the XP JB is to allow the maintenance personnel to change pumps, transducers or floats without having to break seals to do so.

The AHJ wants the XP conduit seal located first, above grade, as the RMC emerges from below grade ahead of the XP GUAC conduit body for cable splicing forcing maintenance personel to break the seal. My question is what is the code reference allowing me to do as I described above rather than what is described in 501.15(A)(4).

Attached is a typical elevation design, it is for a 3 pump station rather than the 2 pump station I described, but same principle.

Thanks,

zap​

 

[rbalex]

Where have you established the Division 1 boundary?

 

[mcnut]

Sealed Motors

Sealed Motors

The motors are sealed from the factory, so there is a seal ahead of the XP j-boxes. The seal off is required where it it shown in the drawing, leaving the Class I Div I area. This would be 501.15(A) (1) and (4).

510.15(A)(1) exception 3 is what I think you are looking for to discuss with the AHJ.

 

[zapit480v]

I just got off the phone with the AHJ. I used the following sections (eventhough very ambiguously defined) and explaination to get his blessing and make him understand the intent of the installations design.

1. 501.10(A)(1)(a) exception 1 - Horizontal PVC 24" below grade and omitting the 2" encasement per 514.8 exception 2, most of our client don't want metal in the wet well because it rots so quickly.
2. 501.10(A)(1)(a) exception 2 - RMC from 24" below grade to above grade attached to the horizontal PVC.
3. 501.140(A)(2) & (3)
4. 501.140(B)(4)

Explaination to AHJ: The intent is to maintain Cl. I, Div. 1 integrity in the conduit system housing the cables from the wet well to the seal by installing the conduit per the sections above and providing an XP JB for splicing of cables ahead of the XP conduit seal making the seal my hazardous location barrier. I also explained from my experience that many times those maintaning these systems will break a seal to replace a component and never replace the seal because it is a pain to replace the component next time around. We agreed, the NEC is very ambiguous in this area and the potential for not replacing a removed seal during future maintanence activities would pose a greater potential risk than the designed installation which allows for the easy removal and installation of future components without jeadordizing the integrity of the original installations XP conduit seals was in everyones best interests.

Hope this helps the next person that may get inthis situation.

Thanks,

zap

 

[zapit480v]

This has always haunted me because the NEC doesn't really address this particular installation very well.

Any other thoughts?

 

[rbalex]

If you have made the aboveground seal your barrier, how have you addressed Section 500.5(B)(2)(3)? That is, there should now be a Division 2 envelope identified.

 

[zapit480v]

rbalex - I spoke to the AHJ about your concern regarding the Div. 2 envelope. We discussed NFPA 820, Table 4.2 (collection systems) Row 16; extent of classification column "entire room or space", per figure A.4.2.(c), ventilation NNV or A, we both interpret this to mean the extent of the Div. 1 hazardous ratings to be contained inside of the wet well itself with a Div. 2 envelope of 3' radius around the vent and 3' from the edges of the hatch by 18" high. The AHJ is not interpreting the seal to be the boundry, he is still iterpreting the point where the RMC emerges from below grade to be the boundry per 501.15(4) and allowing the XP JB to be a part af a "suitable raceway" per 501.140(A)(2)&(3) allowing for future maitenance flexibility and to maintain the seal during future maintenance activities or electrical components in the wet well.

I don't want to just get my way with the AHJ. I've been doing this for years, but if I am doing it wrong for the sake of making life easy for the maintenance personell and maintaining the original design itegrity of the seal during future maintanance activities I would like to know so I can correct my typical design. Please elaborate your interpretation (thoughts) on or experience with this matter rather than just providing a code reference from the book of interpretations (NEC).

Thanks,

Rich D.

 

[rbalex]

First let’s consider the “exceptions” within 501.15(A)(1)(a)Exception - they don’t apply. That is, your installation isn’t “…subject to…” the scope of either Article 514 or 515. So, if the underground PVC raceways are considered to be in a Division 1 location they must be encased assuming they are considered to be in a Class I, Division 1 location.

Second, if the boundary is considered to be where the raceway emerges from grade, there’s no option consistent with 501.15 (A)(4) to permit a conduit body between the seal and the boundary.

The problem is your selection of the boundary. NFPA 820 is fine as the basis; however, the wall of the “room or space” should be selected as the boundary and the boundary seals should be within the “room or space” with no other “… union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 1 location.”

I appreciate your desire not to break seals. Assuming the motor is fed using Section 501.140 techniques, typically the motor junction box will not need a separate seal and any need to replace the motor can be accommodated without breaking a seal since all conductor terminations would be in the motor terminal box.

If the instrumentation is IS, the seals (including the boundary seals) are not required to be explosionproof. See Section 504.70. Using IS brings Sections 504.50 and 504.60 into play, be very careful with the associated grounding and bonding, especially with PVC raceways.

With what I said above, the PVC can be installed without encasement because it isn’t in a Division 1 location, since the Division 1 location stopped at the wall, and no seals are required above grade at all.

 

[zapit480v]

I see what your saying and appreciate your elaboration on the matter.

You are correct about the IS conduits sealing requirments nor is an XP fitting of any kind required for IS wiring per 504, but out of consistency and to create no confusion for the installing contractor I treat the conduits for IS and non-IS the same in an outdoor submersible pump station application to mitigate transmission of explosive gases from the CI,D1 area to the non hazardous area thru the conduit system.

With flygt submersible pumps, wedco submersible pumps, among other submersibles the motor/sensor cable(s) are potted (or sealed at the motor termination box as noted by mcnut) into the motor terminal compartment of the motor and are not removable for the most part (unless replaced by a factory field tech), if a pump is replaced a new cable comes with the pump and must be routed thru the existing conduit system. Same with floats and transducers, the failed instrument can not be disconnected from their cables for replacement with a new instrument, the instrument along with its cable will be replaced.

As for the boundry and seal requirement ?the sealing fitting is permitted within 10' of either side of the boundry with no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 1 location. There in lies the gray ambiguous area, the XP JB ahead of the seal leaving the CI,D1 area, but as mcnut noted the pump cable is sealed at the pump motor. I'm satisfied with the final determination of the AHJ to let the design intent stand as is with the XP JB installed in the installation for splicing cables only serviced by qualified :slaphead: personell and the conduit seals have been provided to minimize the amount of explosive gas or vapor within the CI,D1 portion of the conduit from being communicated to the conduit beyond the seal and into the general purpose 4X control panel.




Thanks for the comments

Rich D.

 

[rbalex]

The bottom line is you have a noncompliant installation and without a documented Section 90.4 (second paragraph) waiver from the AHJ you will have no defense if a problem should ever arise. Inconvenience of repair is not a justification, qualified workers or not. In fact, a qualified worker would know to pour a new seal, if necessary. A waiver can’t assure that equivalent safety objectives have been achieved either. If sewer gas enters the raceway then you still have a gas delivery path to an unclassified location through the threads of the GUAC. Eliminating as many gas delivery paths as possible is the reason for the boundary seal restrictions of 501.4(A)(4). Since Articles 514 an 515 don't apply you haven't justified the lack of PVC raceway encasement.

Note: To be honest, if the source were Division 2, I wouldn't care too much and I've made Code Proposals to that effect; nevertheless, the basic boundary rules are pretty much the same for Division 2 except the seals aren't required to be explosionproof. Again to be honest, I don't believe they are usually necessary at all for Division 2; however, as it stands now, they are still required to minimize the passage of gasses. See 501.15(B)(2).​

Sealing at the motor only addresses Section 501.15(D)(1). There is nothing ambiguous about what is permitted between raceway seal and the boundary in 501.15(A)(4); i.e., nothing except listed explosionproof reducers at the seal itself. In this case, the GUAC in the raceway is noncompliant.

The most likely reason you have had no problem is the past is your good fortune that methane is the primary sewer gas and it disperses very quickly above grade. But there is no documented basis the would permit it as the reason for ignoring 501.14(A)(4).

 

[zapit480v]

Again I understand all you are saying, thats why I posed the question and have always questioned it myself. I have seen other installation not installed or designed by myself and they have used only a stainless or poly JB in the place where I provide the XP GUAC. Since this specific AHJ questioned it I did hours of research. I have found several federal government specs, county specs and local specs along with inspector inspection check sheets throughout the US that explicitely want the seal between the XP JB (some only call out a stainless or poly JB with din mount terminals for the conductors) and control panel above grade where the below grade conduit emerges. This is what perplexed me, everywhere I looked it told me to do what I have been doing and in some instances even less strigent (ie, stainless of poly JB), but when going to the code it is not defined as such just as you say. I will talk to the AHJ and get a waiver as you say since this is a deviation from the NEC.

Having worked in chemical plants for a good share of my working life I do understand the purpose of and the installation of seals in both CLI,DIV1 & CLI,DIV2 areas along with CLII & CLIII. For CL1,DIV2, just because you could only have the potential for explosive gases or vapors in the event of a catastophic failure or under maintenance or process (changing inline valves, pumps, flow tubes in explosive material handling piping systems, open hatches on mixing tanks for measuring in chemicals, etc) routines does not mean you couldn't have an undetected leak at a flange gasket, hatch gasket or anywhere else in the system undetected long enough to introduce an explosive mix into a non-hazardous area through a conduit system in a undetected concentration that could ignite with even a small spark, heat from a transformer, etc.. I personally would never use anything other than a standard hazardous seal-off in any CLI area.

Again Thank You and I appreciate the input,

Rich D.

 

[hardworkingstiff]

Well you guys are much more educated than I, but I thought I remember a thread a couple of years ago about this where one option was to stop the conduit under the control panel down low so it's still in the classified location and then let the cord continue to the bottom of the control panel (which is mounted above the classified location). Since the conduit never left the classified location the conduit seals were not required and the air gap between the conduit and enclosure took care of needing any kind of sealing at the enclosure (since the wiring method was cord instead of individual conductors.

I don't know if I remember the details correctly, but I thought it was agreed that this was an option. (Did I remember it correctly?)

 

[kwired]

The problem is your selection of the boundary. NFPA 820 is fine as the basis; however, the wall of the ?room or space? should be selected as the boundary and the boundary seals should be within the ?room or space? with no other ?? union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 1 location.?

That paragraph is all the inspector should have needed for an explanation of the violation.

The seal must be the first item (either side, IIRC) of boundary - only exception is a reducing fitting if seal fitting is not same size as raceway.

 

[texie]

This is an interesting situation to me as I have faced this as well. While I concur that using a jbox above ground with a seal off between it and the control panel is not compliant, it has been my experience that this is common practice with many waste water utilities. As others have noted, a simple task of changing out a float switch can be a real pain without having the jbox. Seems like there must be some kind of solution to this.

 

[zapit480v]

hardworkingstiff:
What you mention is a perfectly acceptable means, but should be incorporated only if the Lift Station enclosure is in a controlled area (ie, fenced from the public) and or with heavy mesh guarding around the cables. Problem with this practice if cables are not guarded or protected by some means is most lift stations are next to public sidewalks, public roads, in the yards of private property owners, in public parks, etc. For public safety (curious kids especially), vandals and to protect idiots from themselves the pump cables should be protected in a conduit. I have tried to get municipalities to allow using this practice and guarding the cables with a heavy stainless steel mesh guard shaped around the cables and connected to equipment pad and bottom of enclosure with flanges welded to the top and bottom of the guard. They all seem to frown upon it because it is more work for them, especially in northern midwest climates with snow and ice where I am. They generally always want conduit, with a JB above grade and a seal-off prior to entering the control enclosure. Right or wrong seems to be what they all want and until now this was the first AHJ that questioned it. As stated when I explained to the AHJ the maintenance issue and potential future danger of a seal-off not being replaced if a pump is replaced he said "sounds like a great idea and using the XP JB will contain an explosion in the event one ever were to occur".

I do understand the NEC does not allow this. Right or wrong I see it done this way almost 100% of the time, sometimes even with a fiberglass or stainless JB, and those material would never contain an explosion, nor would I ever allow them in one of my designs.

 

[zapit480v]

That paragraph is all the inspector should have needed for an explanation of the violation.

The seal must be the first item (either side, IIRC) of boundary - only exception is a reducing fitting if seal fitting is not same size as raceway.

and it must be an XP rated reducer with more than 5 threads (the long reducers, not the short ones).