Water-proofing electrical fittings into flameproof instruments

[BurnabyBeej]

Hi all,

We're having a heck of a time with some of the Class I Division 2 Group D installations that we have done in the last couple of years. We are now finding that water ingress is causing premature instrument failures in many of the very expensive instruments that we have installed in the field.

My assumption was that the 7 running threads connection into the flameproof enclosure would be enough to stop water from being pulled in through capillary action but that appears to be false. There are 3/4" NPT threaded holes in the side of some instruments where 3/4" to 1/2" listed reducers are fitted and then a 1/2" rigid nipple connects the instrument to the poured EYS seal. If it were a 1/2" NPT hole, I would use a sealing ring and a locknut to waterproof the connection, but in this case there is an exposed 3/4" thread on the reducer.

Generally, how do you mitigate this problem and still maintain good electrical continuity?

As well, should we be putting some duct seal in the end of the pipe where it enters the instrument to stop humid air from entering?

Thanks in advance for any suggestions.

Cheers,

Beej

 

[Dsg319]

Hi all,

We're having a heck of a time with some of the Class I Division 2 Group D installations that we have done in the last couple of years. We are now finding that water ingress is causing premature instrument failures in many of the very expensive instruments that we have installed in the field.

My assumption was that the 7 running threads connection into the flameproof enclosure would be enough to stop water from being pulled in through capillary action but that appears to be false. There are 3/4" NPT threaded holes in the side of some instruments where 3/4" to 1/2" listed reducers are fitted and then a 1/2" rigid nipple connects the instrument to the poured EYS seal. If it were a 1/2" NPT hole, I would use a sealing ring and a locknut to waterproof the connection, but in this case there is an exposed 3/4" thread on the reducer.

Generally, how do you mitigate this problem and still maintain good electrical continuity?

As well, should we be putting some duct seal in the end of the pipe where it enters the instrument to stop humid air from entering?

Thanks in advance for any suggestions.

Cheers,

Beej

Can you use drain seals in the vertical position? We always put STL8 on threads and entries, paste it on good and it might help keep water from entering through the threads.

 

[BurnabyBeej]

Thanks for your quick reply. We had very little room to change the orientation of the sealing fittings because of the way that the process piping, support beams, and other instruments were mounted. I will definitely use drain seals in the future if I can get our mechanical guys to leave me room in future designs.

We are ordering STL8 right away for retrofitting in the field and for our initial builds. I really appreciate the help.

 

[Dsg319]

Thanks for your quick reply. We had very little room to change the orientation of the sealing fittings because of the way that the process piping, support beams, and other instruments were mounted. I will definitely use drain seals in the future if I can get our mechanical guys to leave me room in future designs.

We are ordering STL8 right away for retrofitting in the field and for our initial builds. I really appreciate the help.

I’m sure others will chime in with some other good ideas here soon.

 

[don_resqcapt19]

Are the reducers you are using listed for use in a classified area? They are not all so listed and the ones that are not often have fewer threads and may not provide a seal.

I would suggest the use of a 3/4" electrical street el at the instrument with the female threads pointing down and transition to the 1/2" nipple and seal at that point.

 

[petersonra]

These things are not supposed to have water tightness. If they were watertight they would not let the flame propagate through the threads and cool the flame while it went from the inside to the outside of the enclosure.

 

[MTW]

I would suggest sealing the wires inside the conduit where they enter the instrument. As noted above, sealing the conduit threads is prohibited, as that is the required flame pressure vent in the event of an internal explosion.

A picture of the situation could yield better suggestions.

 

[BurnabyBeej]

Are the reducers you are using listed for use in a classified area? They are not all so listed and the ones that are not often have fewer threads and may not provide a seal.

I would suggest the use of a 3/4" electrical street el at the instrument with the female threads pointing down and transition to the 1/2" nipple and seal at that point.
View attachment 2559190

Yes, we are using the listed Crouse Hinds reducers. I always have to shelve the reducers that the instrument manufacturers send with their instruments as they are usually not listed parts. The use of an el is definitely what we try to do. As I mentioned, I have to have a stern talk with our electrical designers to ensure that they are keeping the wiring in mind in future projects.

 

[don_resqcapt19]

These things are not supposed to have water tightness. If they were watertight they would not let the flame propagate through the threads and cool the flame while it went from the inside to the outside of the enclosure.

They must have water tightness if they are installed in a wet location. A threaded connection that will not permit water to enter will still be able to provide the required cooling flame path.

 

[BurnabyBeej]

These things are not supposed to have water tightness. If they were watertight they would not let the flame propagate through the threads and cool the flame while it went from the inside to the outside of the enclosure.

I would suggest sealing the wires inside the conduit where they enter the instrument. As noted above, sealing the conduit threads is prohibited, as that is the required flame pressure vent in the event of an internal explosion.

A picture of the situation could yield better suggestions.

I've asked our commissioning people to send me some pictures from the site but I'm not holding my breath. :^) I'll see what I have from our FAT.

 

[BurnabyBeej]

 

[don_resqcapt19]

View attachment 2559199

If that type of installation is leaking, something was not installed correctly...like the cover bolts, and/or the threaded fittings not being tightened.
Or maybe very large temperature swings resulting in condensation. I would not expect that assembly to let water in via the conduit entry.

As a side not, the UL Product Standards don't permit the cord grip to be used with a threaded fitting....however all of my installations of this type used LFMC and those fittings are not to be used like that either, but we always did and did not have any issues.

It appears that installation would be a Division 2 installation under the NEC. For that application, I specify sealed contacts for the valve limit switches so we don't have to use a seal. That also means the enclosure does not have to be explosionproof permitting both the equipment costs and installation costs to go down. Standard solenoids are suitable for use in Division 2 areas under the NEC, in most cases.

 

[BurnabyBeej]

Hi Don,

That's what we've been scratching our heads about.

You are correct. This is a Class I Division 2 Group D (Methane) application in open air. We'll have to look into your suggestion about the sealed valve limit switches but I don't think these come in a configuration that isn't explosion-proof. We're lucky to get anything within about a 20 week lead time these days.

We are using standard solenoids in any case where the process conditions and pipe sizes can accommodate them.

Thanks for your input.

 

[don_resqcapt19]

Hi Don,

That's what we've been scratching our heads about.

You are correct. This is a Class I Division 2 Group D (Methane) application in open air. We'll have to look into your suggestion about the sealed valve limit switches but I don't think these come in a configuration that isn't explosion-proof. We're lucky to get anything within about a 20 week lead time these days.

We are using standard solenoids in any case where the process conditions and pipe sizes can accommodate them.

Thanks for your input.

The valve position switch/ solenoid assembly we used with auto valves were Westlock. It was installed by the valve supplier on the valve and then shipped to the piping contractor for installation. The solenoid was directly attached to the position switch enclosure and the solenoid and limit switches wired to a terminal block in the enclosure. The enclosure is available in nonmetallic, metallic and explosion proof. We used the metallic version.

It would look something like this, but we typically used the standard green Asco solenoid for Division 2. Not sure what type of position switches this one had, but we would specify the hermetically sealed, magnet operated, reed switches to avoid needing a seal fitting.