We build control rooms for customers. Our problem is that inside the room we are in an unclassified area and the 4/0 ground passes through the 1/4" steel plate floor to a ground pad on the skid which is in a Class 1 Div. 2 area. We have a seal which the 4/0 goes through. The seal is attached to the floor by a close nipple which screws into a Myers hub which is installed at the floor penetration. Recently we had the customer's inspector onsite and he flagged the seal because according to the NEC the seal should not have any couplings, fittings, etc., between the seal and the classified area. Does anyone have any insight on this subject?
Class 1 Div. 2 Seal offs
- Thread starter E Torres
- Start date
- Status
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Depending on the basis for classifying the control room, you are most likely covered under [2005] Section 501.15(B)(2) Exception No. 3. If you are NOT covered by the exception, I'd probably question the classification, not the sealing method.
- Location
- Illinois
- Occupation
- retired electrician
This does bring up an interesting question. Bulkhead entries to control rooms and or MCC are common in installations where the area outside of the control room or MCC is a classified area. A bulkhead hub is used and the seal is installed after the hub. The bulkhead itself is the boundry. This common installtion does not appear to be code compliant and I don't see a way to make it compliant.
Don
Don
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
don_resqcapt19 said:
What if the bulkhead fitting was fabricated with a male thread instead of a female thread? Then you could screw the seal directly to the ("conduit") male threads of the bulkhead fitting.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I?ve been mulling this one over quite some time Don. (Wish we had a "scratching head" icon)
In general, I believe whether it was intentionally designed that way or not, many of the installations you cited could probably still be covered by 501.15(B)(2) Exception No.3, if analyzed deeply enough. The actual maintained pressure required is very low. An air conditioner or just proper mechanical ventilation from a ?clean source? may be all that is needed.
The Exception permits omitting the seal altogether; so, if it does exist it could be though of as simply assisting in maintaining the enclosure pressure - especially since a Division 2 boundary seal is no longer required to be explosion proof.
But what about the cases where there is no mechanical ventilation at all? In those cases, depending on the system geometry, the internal volume of the enclosure may indeed be misclassified. It is simply another example that, as a ?source? of ignitable materials itself, a Division 2 location is fairly unlikely.
In general, I believe whether it was intentionally designed that way or not, many of the installations you cited could probably still be covered by 501.15(B)(2) Exception No.3, if analyzed deeply enough. The actual maintained pressure required is very low. An air conditioner or just proper mechanical ventilation from a ?clean source? may be all that is needed.
The Exception permits omitting the seal altogether; so, if it does exist it could be though of as simply assisting in maintaining the enclosure pressure - especially since a Division 2 boundary seal is no longer required to be explosion proof.
But what about the cases where there is no mechanical ventilation at all? In those cases, depending on the system geometry, the internal volume of the enclosure may indeed be misclassified. It is simply another example that, as a ?source? of ignitable materials itself, a Division 2 location is fairly unlikely.
- Status