Sealing Conduit Between Unclassified and Classified

[stripedbass]

We have a trailer that contains pumping equipment. Outside the trailer in the unclassified area is a control panel and breaker panel. From these boxes, there are several 1" EMT conduits that are piped to a trough under the trailer. There are no seals between the the boxes and the trough.

On the backside of the trough under the trailer are about eight rigid conduits. These conduits go up inside the trailer to the various motors, lights, etc. Again, there are no seals on the rigid conduit.

The inside of the trailer is rated Class I, DIV II. There are/will be seals located within 18" of the arcing devices/motors, etc. Shouldn't there be conduit seals in the rigid piping on the backside of the trough under the trailer in addition to the seals required at the motors, light switches, etc?

Also, inside the trailer are three XP lights mounted in the same conduit as the light switch. Do I have to provide conduit seals on either side of each light or can I have the seal that is "downstream" of the light switch double as the seal for the bank of lights?

thanks for the help

SB

 

[dpc]

In general, NEC Article 501 requires a seal when crossing from Class I, Div II to unclassified.

However... there are four exceptions to this requirement and it may be that Exception 2 and/or Exception 4 apply in your case.

I think this will require you to closely read the exceptions and see if they apply to your situation.

BTW, EMT cannot be used at all in classified areas, I don't believe.

 

[peebee]

You have not provided enough information to answer most of your questions.

Where is the boundary between Div 2 and general purpose areas? At the trailer wall? Why have the motors been provided with seals? (seals are not required on squirrel cage motors unless they have other integral arcing devices such as overloads). What you have identified as a motor seal may well be the required Div 2/GP seal. Is there any coupling between the Div 2/GP boundary and the motor seal?
Also, many Div 2 light switches have an integral seal - do yours?

Seals are not required at light fixtures in any XP area so far as I know. However, something that is often overlooked in Div 2 areas is that you MUST match the temperature rating (T-rating) of the fixture to the vapor in question. Otherwise, your fixture surface temperature may exceed the vapor ignition temperature, and you'd be out one trailer.

Do yourself a favor and read Articles 500 and 501. Crouse Hinds and Appleton also both issue nice publications which further explain the requirements.

 

[stripedbass]

The motors have internal over-temp protective devices. The boundry between unclassified and classified is the trailer floor. The motors are entirely within the DIV II area.

 

[peebee]

Seal anything that arcs. An integral seal is OK for that (LOTS of switches are integrally sealed or have hermetically sealed arc chambers). You do not need a separate seal.

Seal at all division boundaries (to Div 1 or GP). The seal can be on either side of the boundary. There can be up to 10 feet of conduit between the boundary and the seal so long as there are no other fittings or couplings between the boundary and the seal.

One seal can serve both purposes, ie, if you have a motor with overload within 10' of the boundary fed from some source outside the trailer, one seal may take care of both issues.

Assuming the entire outdoor area is general purpose (verify), the seals would have to go somewhere between the trailer electrical equipment and the trench. The seals could go inside or outside the trailer. If you have remote motor starters with overloads located in the GP area, you can pull the overloads out of the motors, replace them with blanks and skip the seals at the motors.

Hope this helps.

 

[stripedbass]

We're wiring the internal motor thermal overloads in series with the the starter coil. In addition, the 3-phase starter has an overload block on it. The motor is XP and is rated for Class I, DIV I, DIV II, etc. Do I still have to seal within 18" of the motor? There is a seal right under the trailer floor in the GP area about 4 feet from the motor.

The classified area is Class I, DIV II. I also understand that it is OK to use short lengths of flexible conduit in a DIV II area to connect from the motor to the rigid conduit stubbed up through the floor. If you can use flexible conduit, it makes no sense to have to use a seal unless the seal is right at the motor and the flexible conduit is connected to the seal.

thanks,

stripedbass

 

[peebee]

Yup, within 18" of the motor.

They could have made things a bit clearer in the code, but I suspect most inspectors would hold you to 501.5(A)(1), "only explosionproof unions, couplings, reducers, elbows, capped elbows, and conduit bodies similar to L, T, and Cross types . . . shall be permitted between the sealing fitting and the explosionproof enclosure."

Two questions for you: what Group are we talking about? Also, have you given any thought to ventillating the trailer, maybe with a couple big louvers, and calling the whole thing general purpose?

 

[Ares]

Use common sense.
The seals are requred to prevent passage of explosive gasses from the clasified area to the unclasified area.

Lets say you had a negative pressure (exhaust fan is on) in your unclasified area. It would ssack the gas trough the conduit to the feeding panel where spark could cause explosion. As long as you prevent that you are safe.

As additional precuation try to maintain your unclasified are under a positive pressure (no exhaust ON unless make-up air is running) to minimize the hazard.

 

[busbar]

Somewhat off topic, but the recently [4 editions?] NEC-adopted terminology of "Unclassified and Classified" can surely be inappropriate and confusing within a good number of facilities. It has long been established and frequently used under other “technical” contexts.