Class I Div 2. Cable sealing Requirements when run through conduit

[Journeyman106]

The situation we are having on-site here is that our standards require for our contractors to run TC cable from cable tray through conduit to the device being served. The question I have is this. In accordance with 501.15 (E)(1) it requires that multi-conductor cables to have their ends sealed when entering a device that is required to be explosion proof. However a little further down it tells you to refer to 501.15 (D) for multiconductor cables running through a conduit and in 501.15 (D)(2) it states that if the cable is capable of transmitting a gas or vapor then you must strip the outter insulation and pour around the individual conductors, but the exception to this states that if the cable passes through a seal-off within 18" of the device then the cable can be treated as a single conductor as long as the end of the cable is sealed.

Well the problem we have here is that most of our installations are complete but the seals have not been poured as of yet. I am trying to determine if I need to make the contractors go back and strip off the outer insulation of the cable and then pour the seals, or if they make something that will allow them to use the exception and seal the end of the cable?

Personally I do not see how gas can travel through the core of the cable since the cable originates in a non-classifed area and then goes to the device which is in a rated enclosure. I do understand the need to seal the conduit to keep the gas from entering into the disconnects through the conduit, but I am not sure how it will enter the cable, unless the gas gets into the disconnect and then travels through the cable back to the non-classified area.

This is all becoming very confusing and I need some assitance. My personal interpretation of the NEC is that the cable must be sealed where it enters the enclosure or the insulation must be stripped back at the seal-off and then poured. But this would mean alot of re-work and time and expense.

Any help would be greatly appreciated.

 

[BPoindexter]

As you say you can strip the cables and pour around them, or you can pour the seal as if it is a single conductor and then seal the cable itself. Either way is acceptable. If it is already installed then might consider a gas blocking kit on the cables inside the enclosure.

And yes that is what they are protecting against is the transmission of the gas through the cable. If the room where disconnect is located is at a higher pressure than where the cable originated then it is possible (though how likely is debatable) that gas could be transmitted.

 

[Journeyman106]

Thank you for taking the time to reply. Do you have any suggestions for a gas blocking kit? I considered allowing the use of Crouse Hinds TSC epoxy, but Crouse Hinds will not support stand alone applications of the product they state it must be used in conjunction with a hub or cable seal fitting. I believe I am just going to have to make the contractors de-terminate the cable and strip it back and seal it accordingly.

 

[BPoindexter]

We always used a 3M kit. I will see if I can get a part number for you.

 

[weressl]

The situation we are having on-site here is that our standards require for our contractors to run TC cable from cable tray through conduit to the device being served. The question I have is this. In accordance with 501.15 (E)(1) it requires that multi-conductor cables to have their ends sealed when entering a device that is required to be explosion proof. However a little further down it tells you to refer to 501.15 (D) for multiconductor cables running through a conduit and in 501.15 (D)(2) it states that if the cable is capable of transmitting a gas or vapor then you must strip the outter insulation and pour around the individual conductors, but the exception to this states that if the cable passes through a seal-off within 18" of the device then the cable can be treated as a single conductor as long as the end of the cable is sealed.

Well the problem we have here is that most of our installations are complete but the seals have not been poured as of yet. I am trying to determine if I need to make the contractors go back and strip off the outer insulation of the cable and then pour the seals, or if they make something that will allow them to use the exception and seal the end of the cable?

Personally I do not see how gas can travel through the core of the cable since the cable originates in a non-classifed area and then goes to the device which is in a rated enclosure. I do understand the need to seal the conduit to keep the gas from entering into the disconnects through the conduit, but I am not sure how it will enter the cable, unless the gas gets into the disconnect and then travels through the cable back to the non-classified area.

This is all becoming very confusing and I need some assitance. My personal interpretation of the NEC is that the cable must be sealed where it enters the enclosure or the insulation must be stripped back at the seal-off and then poured. But this would mean alot of re-work and time and expense.

Any help would be greatly appreciated.

If the electrical device is required to be sealed, then you must install a seal. The purpose of the seal is to contain the explosion within the enclosure and in the case of multiconductor cable the containment would not be accomplished if the seal is poured only around the jacket. Even in the case of single conductors/conduit the installation instructions require that your spread the individual conductors apart to allow the sealing compound to flow into the spaces between the conductors.

As far as boundary seal of cables, it has been now widely accepted that multiconductor cables will not transmit the ignitable mixture when the cable length is a typical installation of 100' or more. Of course an abnormal pressure difference could still produce this effect. This could occur if this connection is to an inline direct connected instrument with a SINGLE isolating seal between the process material and instrument enclosure. See 501.17.

 

[BPoindexter]

As far as boundary seal of cables, it has been now widely accepted that multiconductor cables will not transmit the ignitable mixture when the cable length is a typical installation of 100' or more. Of course an abnormal pressure difference could still produce this effect. This could occur if this connection is to an inline direct connected instrument with a SINGLE isolating seal between the process material and instrument enclosure. See 501.17.

In the end it is up to the AHJ to make that call. The installation in question has seals that he intends to pour the question is to decide whether to strip the jacket back and then pour or pour and then cable seal the ends. As this involves rework he will need to decide which involves the least work. I would certainly check with the AHJ and see what their view on the installation is before I did any rework.