502.15 Sealing

[Howard Harris]

In a Class II, Division 1 location, I can install two rigid conduits, vertically down, one conduit to a 120V device, one conduit to a 4-20ma device, liquidtight from each conduit to each device, with no sealoffs, just ductseal the end of each liquidtight in each device enclosure. Is this correct per NEC? Or does this mean to use sealoffs and seal with ductseal instead of Chico? Please explain.

 

[Smart $]

In a Class II, Division 1 location, I can install two rigid conduits, vertically down, one conduit to a 120V device, one conduit to a 4-20ma device, liquidtight from each conduit to each device, with no sealoffs, just ductseal the end of each liquidtight in each device enclosure. Is this correct per NEC? Or does this mean to use sealoffs and seal with ductseal instead of Chico? Please explain.

I see 502.15 as being quite conflicting in and of itself. Subpart (1) says a permanent and effective seal... but the FPN says electrical sealing putty is a method of sealing. Since when is duct seal permanent? Then (2) through (4) utilize gravity as the "seal". Perhaps someone with a handbook can shed a little more light here...

Anyway, have you already established that sealing is required? A lot depends on where the other end of the conduits go...

 

[rbalex]

A significant difference between Class I and Class II is the way ignitions are handled for enclosures ?common? to the Classification.

For Class I ignitible material will enter the enclosure whether it is sealed or not. If the volatiles are ignited (and they will be) an ensuing explosion is contained within the enclosure. The seals themselves must be explosionproof.

For Class II the basic methodology is to prevent an internal ignition by inhibiting the ingress of ignitible material into the enclosure. Note the four methods outlined in 502.15 are with respect to ??an enclosure required to be dust-ignitionproof and one that is not.? All four methods have been proven to be effective in preventing the ingress of volatiles into the dust-ignitionproof enclosure.

The OP description of the installation is incomplete at the moment with respect to defining the terminus of the raceways.