Conduit drains

[cornbread]

I recieved the following note on the use of conduit drains.

The NEC states that conduit systems shall be provided with an "approved means" to prevent accumulation of condensation and permit drainage of such liquid (Ref. Article 501 Class 1 Locations, Par. 501.15 Sealing and Drainage, (F) Drainage, (1) Control Equipment). In addition, the NEC Handbook provides an example of breather-drain fitting for this purpose. Based on this, I feel that drain fittings are required on conduits.

However,

The NEC also states that cable tray systems shall be permitted to have "mechanically discontinuous segments" between cable tray runs and equipment. The code permits wiring across the discontinuous segment up to 6 feet in length with proper support and guarding from physical damage. (Ref. Article 392 Cable Trays, Par. 392.6 Installation, (A) Complete System.)

Discussion/Interpretation:
The above articles actually address two types of wiring systems (ie; conduit and cable tray). In the plant, we can have 3 types of wiring systems; (1) a totally conduit system, (2) a totally cable tray system, and (3) a combination of conduit and cable tray. In totally conduit systems, standard individual building wire (ie: TW, THW, etc.) may be used. In cable tray systems, tray rated cable (ie: PLTC, TC, etc.) must be used. In a combination conduit and cable tray system, again, tray rated cable (ie: PLTC, TC, etc.) must be used.

In the case where totally conduit systems are installed with standard building wire, an approved drain or breather-drain fitting must be used. Standard building wire (ie, TW, THW, etc) is not rated or constructed for protection against physical damage, so the conduit system must protect it. Yes, even at the fitting.

In the case where tray rated cable is used in cable tray or combination conduit and cable tray systems, the code allows for mechanically discontinuous segments as long as 6 ft. Since tray rated cable has an additional jacket for physical protection, the wiring is protected over the discontinuous segment (3/4" hole). Based on this, I feel that any conduit systems using tray rated cable are in still in compliance without a drain fitting

I would appreciate your opinions.

 

[steve66]

I dont agree. I'm not sure tray cable provides protection against moisture or liquids.

I also think you are missing the intent - that you don't want an accumulation of flammable gasses or liquids to remain in a conduit system forever - regardless of the wiring type.

That said, I'm wondering why you think there is a "probability" that liquid or condensed vapor will be trapped inside your conduit system? If that probability doesn't exist, you still don't need the conduit drains.

Steve

 

[KentAT]

I recieved the following note on the use of conduit drains.

The NEC states that conduit systems shall be provided with an "approved means" to prevent accumulation of condensation and permit drainage of such liquid (Ref. Article 501 Class 1 Locations, Par. 501.15 Sealing and Drainage, (F) Drainage, (1) Control Equipment). In addition, the NEC Handbook provides an example of breather-drain fitting for this purpose. Based on this, I feel that drain fittings are required on conduits.

First, this reference is specifically for Hazardous Locations, not for ALL conduit systems. Are your installations in hazardous locations? The note you received might be stretching the idea to ALL conduits. I don't have my handbook in front of me, but I believe the photo shows a breather/drain on an enclosure or as part of a conduit seal.


Secondly, the full text reads "Where there is a probability that liquid or other condensed vapor may be trapped within enclosures for control equipment or at any point in the raceway system, approved means shall be provided to prevent accumulation or to permit periodic draining of such liquid or condensed vapor. " If the probability does not exist, I feel you don't need the drains.

Based on this, I feel that any conduit systems using tray rated cable are in still in compliance without a drain fitting

Again, are you referring to ALL conduit or cable tray systems in your plant, including those in non-hazardous locations?

It appears as though your point is that as long as tray rated cable is used in ANY conduit system, then drains are not required. I do not agree.


The moisture drain issue is not just about the cable type. For example, if an outdoor conduit system has a seal installed just above grade, there's a chance the seal will accumulate water and freeze in the winter, cracking the body of the seal (I'm in PA). No wire insulation type will prevent that.

IMO, although it would be a stretch to require drains in most indoor conduit seal applications, some boundary seals (like in a basement area) where the conduit is tied into either underground conduits or exposed outdoor conduits with the probability of conducting water into the seal would be best served with a drain.

Kent

 

[cornbread]

"the intent is to leave off the drain fitting at the end of a "tee" fitting on the bottom of a vertical conduit run that is part of a cable tray raceway. The installation is outdoors and/or in a wash down area indoors. Water/condensation accumulates in conduits but drain fittings often plug due to oil, metal shavings, dust, etc. in the conduit. If NEC permits 6ft of mechanically discontinuous segments in a cable tray system (ie; tray rated cable that is exposed), is an open ended "tee" fitting that is carrying tray rated cable an acceptable installation method to allow water/condensation to drain off?