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haze10 (Electrical) (OP)
22 Sep 11 14:13
All UL listed Explosion Proof Motors have factory seals for the wires leaving the motor housing and entering the motor conduit box.

For a Class I, Div 1, Group D enviroment installation a UL listed motor for the area, is it necessary to also install conduit seals (ie Crouse Hinds EYS fittings) at the motor conduit box?

I believe it is not necessary because inside the box is only wire splices, not arcing contacts or hot components.

However, NEC 501.15(A)(1)(2) says seals are required for trade size 2" or larger and the enclosure contains terminals, splices, or taps.

Are you putting seals on all EX motor conduit boxes, only those 2" or larger, or never on any regardless of size.
Helpful Member!  rbalex (Electrical)
22 Sep 11 14:46
Whether someone is doing it or not is irrelevant. In Class I, Division 1, seals are required on all enclosure entries 2" and larger where there are terminals, splices, or taps. You already cited the correct Section.
haze10 (Electrical) (OP)
22 Sep 11 19:34
Yes, you are correct.  I meant to say does anyone know of any exception in another section of the code.

The code is not always practical even though it attempts to be.
The code says that in my 12x12 wireway I need to derate the 31st conductor.  What if they are all number 14 awg?   Do we all go back and rework existing wiring in the wireway when we add the 31st conductor?
DRWeig (Electrical)
22 Sep 11 21:11
No other exceptions in Div 1.  Gotta seal it.

Good on ya,

Goober Dave
rbalex (Electrical)
22 Sep 11 21:11
There is no exception to this particular requirement. If you were installing to IEC there would be; however NEC Article 505 isn't actually IEC. In fact, it has essentially the same requirement as Article 501 in Section 505.16(B).

Most people would consider 30-#14 in a 12x12 wireway impractical - and not too likely a design choice either. But, if you did make such a choice, then yes you would have to derate if you added the 31st conductor.  
DRWeig (Electrical)
22 Sep 11 21:30
As for the code not being practical, it's written to prevent fire, explosion, electrocution, etc...  

The reason you need a seal when leaving the terminal box is thus:  If a termination gets hot or loose (arcing) while a combustible mixture is in the box, the explosion's pressure will vent down the conduit (since the entry from the motor is sealed).  The more distance it goes, the higher the pressure-piling effect will be -- possibly (probably) enough to blow the conduit apart at the next seal or enclosure -- resulting in the explosive mixture outside the electrical system being ignited.  Hence, the need to seal near the termination box.

Good on ya,

Goober Dave

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