Junction box mounted directly on digester tank? Box rating?

What rating does a junction box need to have if it's going to be mounted directly on the side of a digester anaerobic tank? Inside the junction box, there will be no arcing or sparking devices and 2” conduit will enter and exit the box. @rbalex
 

tom baker

First Chief Moderator
Staff member
It does make a difference on what circuits are in the box, power/lighting or intrinsically safe?
What type of conduit?
You should consider purchasing a copy of NFPA 820:
NFPA 820 Standard For Fire Protection In Wastewater Treatment And Collection Facilities, 2020 Edition
"This standard shall establish minimum requirements for protection against fire and explosion hazards in wastewater treatment plants and associated collection systems, including the hazard classification of specific locations and processes."
 
It does make a difference on what circuits are in the box, power/lighting or intrinsically safe?
What type of conduit?
You should consider purchasing a copy of NFPA 820:
NFPA 820 Standard For Fire Protection In Wastewater Treatment And Collection Facilities, 2020 Edition
"This standard shall establish minimum requirements for protection against fire and explosion hazards in wastewater treatment plants and associated collection systems, including the hazard classification of specific locations and processes."
Type of conduit: 2" pvc coated conduit with seals.
Circuits: Power for field equipment.


Does this application require the enclosure to be explosion-proof/type 10?
 

kwired

Electron manager
Location
NE Nebraska
I'd say if no arcing parts inside it doesn't have to be "explosion proof" but still needs to be rated C1D1 since it will be installed in C1D1 location, should not need seals near the box either.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Type of conduit: 2" pvc coated conduit with seals.
Circuits: Power for field equipment.


Does this application require the enclosure to be explosion-proof/type 10?
With respect to your diagram and this additional description, the equipment and wiring methods must be consistent with Section 501.10(A), especially Section 501.10(A)(3.) This ultimately means the box must be explosionproof unless it meets one of the other recognized protection techniques listed as suitable for Class I. Division 1 in Section 500.7. To be honest, unless is Intrinsically Safe or Purged/Pressurized, then Explosionproof is your most likely choice. That said. it will need to be sealed per Section 501.15(A)(1)(2).

BTW, sealing nonexplosionproof enclosures is generally useless in hazardous locations.
 
With respect to your diagram and this additional description, the equipment and wiring methods must be consistent with Section 501.10(A), especially Section 501.10(A)(3.) This ultimately means the box must be explosionproof unless it meets one of the other recognized protection techniques listed as suitable for Class I. Division 1 in Section 500.7. To be honest, unless is Intrinsically Safe or Purged/Pressurized, then Explosionproof is your most likely choice. That said. it will need to be sealed per Section 501.15(A)(1)(2).

BTW, sealing nonexplosionproof enclosures is generally useless in hazardous locations.
Just looking for some clarification...

So, if the circuits downstream have intrinsically safe barriers on them, does the junction box in the classified area require an explosion-proof enclosure?
 

tom baker

First Chief Moderator
Staff member
Is this then, an Article 504 application? If so do you have a control drawing per 504.10 (A)? If IS you can use a general purpose enclosure, I would suggest non metallic, such as fiberglass, if not exposed to the sun, or maybe SS 316. I've worked in WWTP and the gas is very corrosive. Also look at 504.70 Sealing, and one of the few places a specific color is required, 504.80 C
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Just looking for some clarification...

So, if the circuits downstream have intrinsically safe barriers on them, does the junction box in the classified area require an explosion-proof enclosure?
Downstream barriers do not create an intrinsically safe condition inside the box.
 

Bwas

Member
Location
Florida
Depends on a lot of things. Is the digester outside or enclosed? What type of roof does it have? What is is nearby that might contribute to the classification of the area? Most of the digesters i have seen are big tanks, outside and kind of by themselves. It most cases it seems like collection of gasses outside the tank would be unlikely. It is worth keeping in mind that a classification on top of the tank can roll over other side of the tank and extend down the outer wall to grade level.
 
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