Explosionproof Boundary for Sewage Wetwell

[matt_verrando]

NFPA 820 defines the boundaries for Class I, Division 1 & 2 areas in and around a wet well of a sewage lift station. The Conduit that route into the wet well are open on the wet well side to allow the float switch and pump feed cables (SO Cords) to be routed inside the wet well. An explosionproof seal fitting is required in each of these conduit between the NEMA-3R control panel and the wet well. It is my interpretation that all conduit between the seal fitting and the wet well is explosion proof regardless of the conduits location relative to the NFPA 820 boundaries. Based on this, a junction box installed in the raceway between the seal fitting and the wet well needs to be rated Class I, Division 1, regardless of location to the wet well.

 

[BPoindexter]

Actually per Article 501 the seal fitting has to be the first fitting on either side of the boundary whether C1D1 to C1D2 or C1D2 to Unclassified. If the junction box is not located inside the C1D1 then it is not required to be explosion proof. If it is inside the C1D2 and is only used for a pullbox or terminations then it is not required to be explosionproof either. And it most certainly does not have to be explosionproof if is in an unclassified location.

 

[augie47]

Actually per Article 501 the seal fitting has to be the first fitting on either side of the boundary whether C1D1 to C1D2 or C1D2 to Unclassified. If the junction box is not located inside the C1D1 then it is not required to be explosion proof. If it is inside the C1D2 and is only used for a pullbox or terminations then it is not required to be explosionproof either. And it most certainly does not have to be explosionproof if is in an unclassified location.

I have a slightly different read. As noted in post 2: Actually per Article 501 the seal fitting has to be the first fitting on either side of the boundary whether C1D1 to C1D2 or C1D2 to Unclassified. IMO: IF your seal-off is between the pit (classified area) and the j box, no problem. If the seal-off is between the j box and the control panel, the j box would need to be explosion proof.
B Poindexter may be saying the same thing I am, or if not, we don't happen to agree.

 

[matt_verrando]

Actually per Article 501 the seal fitting has to be the first fitting on either side of the boundary whether C1D1 to C1D2 or C1D2 to Unclassified. If the junction box is not located inside the C1D1 then it is not required to be explosion proof. If it is inside the C1D2 and is only used for a pullbox or terminations then it is not required to be explosionproof either. And it most certainly does not have to be explosionproof if is in an unclassified location.

The conduit is directly open to the wet well (contains Methane a potentially explosive gas). While we call this pipe a conduit, it is actually a vent line with the seal fitting to prevent gas migrating into the control cabinet. Since the potentially explosive atmosphere is inside the raceway up to the seal fitting, my interpretation is that it is C1D1 all the way, regardless of the physical location relative to the wet well.

 

[GoldDigger]

The conduit is directly open to the wet well (contains Methane a potentially explosive gas). While we call this pipe a conduit, it is actually a vent line with the seal fitting to prevent gas migrating into the control cabinet. Since the potentially explosive atmosphere is inside the raceway up to the seal fitting, my interpretation is that it is C1D1 all the way, regardless of the physical location relative to the wet well.

If it is a vent line, you may not be allowed to run wiring in it.
If it is a conduit which incidentally happens to serve as a vent line, is the seal at the first fitting outside the boundary? If not, there may be no way to comply without rebuilding the line.

a junction box installed in the raceway between the seal fitting and the wet well

This point was made by BPoindexter and augie47 but you may have overlooked it. Can the classified area extend an unlimited distance physically beyond the physical boundary, inside the conduit and j-box? Making the seal correctly placed at the first fitting after the boundary?

 

[BPoindexter]

For Div 1 Boundary (501.15(A)(4):

"...Except for listed explosionproof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 1 location."

"Exception No. 2: For underground conduit installed in accordance with 300.5 where the boundary is below grade,the sealing fitting shall be permitted to be installed after the conduit emerges from below grade, but there shall be no union, coupling, box, or fitting, other than listed explosionproof reducers at the sealing fitting, in the conduit between the sealing fitting and the point at which the conduit emerges from below grade."

For Div 1 Boundary (501.15(A)(4) contains the same language for Div 2 with a couple of additional exceptions which do not apply in this case.

So Augie47 if you are saying that you can indeed install a j-box between the boundary and the seal we would be in disagreement.

 

[augie47]

For Div 1 Boundary (501.15(A)(4):

"...Except for listed explosionproof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 1 location."

"Exception No. 2: For underground conduit installed in accordance with 300.5 where the boundary is below grade,the sealing fitting shall be permitted to be installed after the conduit emerges from below grade, but there shall be no union, coupling, box, or fitting, other than listed explosionproof reducers at the sealing fitting, in the conduit between the sealing fitting and the point at which the conduit emerges from below grade."

For Div 1 Boundary (501.15(A)(4) contains the same language for Div 2 with a couple of additional exceptions which do not apply in this case.

So Augie47 if you are saying that you can indeed install a j-box between the boundary and the seal we would be in disagreement.

I'm saying that IF any j box is installed between the boundary and the seal, it would need to be an explosion-proof box. Do we agree ?

 

[rbalex]

One of the more-or-less unique qualities that waste water facilities and off-shore drilling rigs share is that most of the Division 1 locations occur as much from lack of adequate ventilation as constant or frequent ?sources.? The volatiles tend to collect in the location. The principal volatile in waste water facilities, methane, disperses very quickly when subject to good ventilation.

Another similarity is that the classified envelope is created by solid boundaries rather than arbitrary radii from the sources. In the OP case, the boundary is the wet well ?room.? For what it?s worth, Section 501.15 (A)(4) makes no distinction between a Division 1/Division 2 boundary and a Division 1/Unclassified boundary.

In the OP case the boundary is ?solid.? A boundary seal may be either side of the boundary but ?Except for listed explosionproof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 1 location.? In the link, see my commentary at Post 13.

So, if the seal is in the wet well, the wiring method to the boundary must be per 501.10(A). A coupling, fully embedded in the wall, would be an acceptable transition to an Unclassified location. Beyond the boundary any wiring method suitable for the location (Division 2 or Unclassified) is acceptable.

Here it gets a bit tricky. Where the seal is in the Division 2 or unclassified location. Again, referring to Section 501.15 (A)(4): ?The sealing fitting shall be permitted on either side of the boundary of such location within 3.05 m (10 ft) of the boundary and shall be designed and installed so as to minimize the amount of gas or vapor within the Division 1 portion of the conduit from being communicated to the conduit beyond the seal.? In other words, the boundary is effectively the wall?s thickness; but, in this case, between the seal and the wet well, all wiring needs to be suitable for Division 1.

I do find it interesting that a ?vent? has been sealed ? how does it perform its vent function?

 

[rbalex]

I'm saying that IF any j box is installed between the boundary and the seal, it would need to be an explosion-proof box. Do we agree ?

Afraid not Gus; only reducers at the seal can be between the seal and the boundary.

 

[augie47]

Afraid not Gus; only reducers at the seal can be between the seal and the boundary.

No problem. Learning every day, especially when you are involved
Makes sense when I read more carefully.
Just seemed odd that I can have an XP box inside the boundary, but not outside..... but I see it now that you made me open my eyes.

Thanks, as always

 

[GoldDigger]

Just seemed odd that I can have an XP box inside the boundary, but not outside..... but I see it now that you made me open my eyes.

You can have it inside the boundary, but not between the boundary and the seal if the seal is inside. If the seal is outside, you can have it, but you don't need it.
Also, the way the sealed pipe can also be a vent is that there is a tee on the well side of the seal (inside or outside the well) going to an empty open pipe, the other end of which is outside the well somewhere. Methane gas will rise, given half a chance, having a density roughly .6 of air.
Curiously, that could lead to the methane concentration at the seal always being a lot lower than anywhere else in the whole system. :happyyes:

My earlier comment suggested the problem resulted partially from trying to save money by running wires through the vent, and thereby requiring the seal to be on the far side of said tee.