Using a PCB in a Nema 4X enclosure in Class 1 Division 2 environment

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I am re-engineering an existing safety shower with electrical components on a mounting plate inside a Nema 4x junction box. The safety shower is classified for use in Class 1 Division 2 environments. I want to simplify the construction of the shower by converting the electrical components inside the junction box to a single pre-assemblied PCB. I have done a lot of research, however I cannot find any standards that specifically apply to Printed Circuit boards. Not even the components that I have looked at for the PCB mention Class 1 Div 2 classification.

Am I searching in vain? Can I only use a C1D2 enclosure, or do I need to be more creative in my interpretation of the NEC Codes for C1D2? The design is simple as the only components on the PCB will be 1 fuse, 1 DPDT Relay, 1 Solid State Flasher, 1 sliding switch and wire connections.
 

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don_resqcapt19

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The relay and the switch, as arc producing devices, trigger the requirement for an explosionproof enclosure.
 

petersonra

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I was on my tablet when I responded before so gave the short answer. This is a longer answer.

The box that you put such an assembly in does not require a CID2 rating. In fact, as far as I know there just is no such thing. A type 4X box is more than adequate.

The PCB that you have designed cannot be made to CID2 standards as it is so no matter what enclosure you put it in (unless it is an XP enclosure) it can never be suitable for a CID2 area.

With a little redesign it could meet CID2 standards and be manufactured by a UL 698 shop. The simple circuit you have could readily be redone by someone familiar with these standards and built as a UL 698 listed control panel. My guess is someone familiar with the standards could come up with a viable design in a few hours.

Your other option is to try and redesign it yourself and get UL to list it under whatever category they deem appropriate. My guess is that would be prohibitively expensive given the limited market for such a thing and the insane cost of that approach.

Personally, I do not see a PCB ever being an economically viable option for such a limited application, especially if it has to be suitable for a CID2 area.
 
Thanks for the insights. I know that it is possible to have a pcb inside a nema 4x enclosure in C1D2 environments because we are looking at an Emerson Rosemount wireless transmitter that is C1D2 and has a PCB inside a Nema rated enclosure. I was just not sure where to proceed from my initial design because I could not find a lot of info out there on PCBs and their application in Hazardous locations.
 

petersonra

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Thanks for the insights. I know that it is possible to have a pcb inside a nema 4x enclosure in C1D2 environments because we are looking at an Emerson Rosemount wireless transmitter that is C1D2 and has a PCB inside a Nema rated enclosure. I was just not sure where to proceed from my initial design because I could not find a lot of info out there on PCBs and their application in Hazardous locations.

UL can list a PCB for use in a CID2 area, but it has to meet all the requirements of whatever UL standards have to be met. It is a nontrivial task that requires considerable experience in such things to get a design that will meet their standards for whatever they say it has to be and pass the tests (you will have to make one or more prototypes for them to destroy as part of their testing process).

There are things that a person with experience in designing this kind of thing can do to make the process more affordable, but it is not a DIY type project.

OTOH, a UL698 shop can design and build you a very serviceable C1D2 listed industrial control panel, probably w/o a whole lot of NRE. In fact, if you knew what to do you could design it yourself and just have them build it, but chances are you don't know how to design to those standards so it will be more cost effective to just have them do it.
 

don_resqcapt19

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Thanks for the insights. I know that it is possible to have a pcb inside a nema 4x enclosure in C1D2 environments because we are looking at an Emerson Rosemount wireless transmitter that is C1D2 and has a PCB inside a Nema rated enclosure. I was just not sure where to proceed from my initial design because I could not find a lot of info out there on PCBs and their application in Hazardous locations.
That is correct, but the transmitter you are talking about does not have an open relay or switch contacts.

Your device has a slide switch and a relay. Those are arc producing devices, unless, as Bob suggested, you have hermetically sealed contacts. Sealed contact relays for Class I, Division 2 are commonly available. I am not sure if the same is true for the slide switch, but other types of switches are available with sealed contacts.
 
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Update

Okay, I have done a little more research on "hermetically sealed" relays and switches and I have 2 more questions.

1) Does the hermetically sealed relay have to be soldered directly to the PCB, or can it be a socketed relay where the socket is the part that is soldered to the PCB?

2) Would a toggle switch that is "IP67/68; NEMA 3, 3R, 4, 13" rated be considered as a C1D2 switch? Honeywell has a few toggle switches that they claim in their documentation to have a "completely sealed switching chamber"
 

petersonra

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Okay, I have done a little more research on "hermetically sealed" relays and switches and I have 2 more questions.

1) Does the hermetically sealed relay have to be soldered directly to the PCB, or can it be a socketed relay where the socket is the part that is soldered to the PCB?

2) Would a toggle switch that is "IP67/68; NEMA 3, 3R, 4, 13" rated be considered as a C1D2 switch? Honeywell has a few toggle switches that they claim in their documentation to have a "completely sealed switching chamber"

1) I don't think it matters any if you use a socket or not. That might be an issue to take up with UL when you go to get it listed. They may have some requirements that would apply. Having said that, I cannot recall ever seeing a socketed relay of any kind that was on a PCB listed for a CID2 area. But that may just be because very few people design PCBs with socketed relays anymore. Relays are not real common in CID2 listed equipment anyway.

2) You would need to review the UL listing requirements for the type of equipment that you would be having listed to see what UL will accept. My guess is they won't accept it as most of these type of switches are made to various MIL specs and are generally not UL recognized.
 
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