Dry contacts in a Class 1 Div 2 area

[mykeknauff]

I'm looking to place a particular instrument/monitoring system in a junction box in a Class 1 Div 2 area. The device has dry contacts and is not listed for use in class 1 division 2 environments. I'm thinking we may be able to use this anyway if we only use the device's 4-20mA output and leave the dry contacts disconnected. I see in the 2023 NEC section 501.105 (B)(2) that exception 2 allows for contacts in general purpose enclosures in non-incendive circuits. We would like to avoid putting these components in an explosion proof or purged enclosure. My interpretation is that leaving these contacts open circuited would make this section of the device a non-incendive circuit, however I don't have a lot of experience with classified areas so was hoping for a second opinion.

 

[petersonra]

if the dry contacts are not energized where would the energy to cause a spark come from?

However, I think you need to look closely at what the code allows you to put in a classified area.

By the way, it is very hard to help you with a problem when you are so vague about what you are doing. If you posted the model number of the instrument it might be that people here have some solution for you.

Its also possible the manufacturer has a solution already.

 

[rbalex]

I'm looking to place a particular instrument/monitoring system in a junction box in a Class 1 Div 2 area. The device has dry contacts and is not listed for use in class 1 division 2 environments. I'm thinking we may be able to use this anyway if we only use the device's 4-20mA output and leave the dry contacts disconnected. I see in the 2023 NEC section 501.105 (B)(2) that exception 2 allows for contacts in general purpose enclosures in non-incendive circuits. We would like to avoid putting these components in an explosion proof or purged enclosure. My interpretation is that leaving these contacts open circuited would make this section of the device a non-incendive circuit, however I don't have a lot of experience with classified areas so was hoping for a second opinion.

I would suggest reviewing Section 501.10(B)(3) very carefully. While the “dry contacts” would indeed constitute simple apparatus,` there is quite a bit more required of a Nonincendive field wiring system; for example - even if the simple apparatus isn’t required to be shown on the control drawing , the control drawing must still exist.

 

[mykeknauff]

if the dry contacts are not energized where would the energy to cause a spark come from?

However, I think you need to look closely at what the code allows you to put in a classified area.

By the way, it is very hard to help you with a problem when you are so vague about what you are doing. If you posted the model number of the instrument it might be that people here have some solution for you.

Its also possible the manufacturer has a solution already.

Apologies, I'm a newbie here, so wasn't sure how much detail to included. The device is a Bender isolation monitor (ISO685(W)-D/-S), it will have connection to 24V power, ground, an external platform being monitored for electrical isolation, and the 4-20mA output signal. The enclosure will be NEMA4X

 

[petersonra]

I don't think this device would be safe in a classified area regardless of whether the relay contacts are even used. It deliberately injects current into the earth connection. If that connection fails, there is a good chance of a spark due to that single failure.

 

[gadfly56]

I don't think this device would be safe in a classified area regardless of whether the relay contacts are even used. It deliberately injects current into the earth connection. If that connection fails, there is a good chance of a spark due to that single failure.

You could always put it inside a listed enclosure. For multiple $K dollars.

 

[petersonra]

You could always put it inside a listed enclosure. For multiple $K dollars.

How would that mitigate the hazard? The device is deliberately injecting current into the earth. It's not necessarily only hazardous at the instrument itself. Personally, I think the analysis of whether the hazard, if it exists, is mitigated is beyond my limited capacity to determine.