Drill holes in Class 1 Div 2 enclosure

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I have a question on a Class I Division 2 junction box. Here is the following back ground information. We are building a machine that has a NEMA 4X junction box with only terminals. It will be wired using RMC and devices on the machine will be 24 VDC and 4-20 mADC instruments. The customer would like to mount a stainless steel nameplate on this enclosure by drilling holes and mount it to the enclosure with stainless steel screws. I looked though Articles 500, 501 and other sources and can’t find if this is acceptable in a hazardous location. I do not see were stainless steel screws and holes is a listed or a approved method. The screws will penetrate the enclosure in a Class I Div. 2 area. What is your opinion?
 

Kobe85

Member
Location
New York
Since it's a NEMA 4X enclosure and only containing terminal blocks it's not an issue. We do it all the time.

it may surprise you, but NEMA 4X/IP66 rated screws do exist and if you don't use them with some sealant you may derate the 4X rating.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Since it's a NEMA 4X enclosure and only containing terminal blocks it's not an issue. We do it all the time.

it may surprise you, but NEMA 4X/IP66 rated screws do exist and if you don't use them with some sealant you may derate the 4X rating.

the screws won't help you any. The seal has to be made to the wall of the enclosure. the sealing screws have an O ring on them that would seal against the nameplate, so would do no good. The sealing washer can mount on the inside of the enclosure against the wall.

here is an example.

http://www.newark.com/apm-hexseal/7...+washer&categoryId=800000004262&categoryName=
 

MechEdetour

Member
Location
NY, USA
I think there is one other thing that needs to be highlighted here. Being that it is a Class I Div 2 location, and only terminal blocks are being used inside the enclosure (no arcing/sparking/etc devices) then a NEMA 4X enclosure is suitable. So in this case, penetrating the enclosure means you have to do it in a way not to compromise the ingress protection.

In the case where the enclosure would have a breaker or relays (arcing/sparking/etc) then the enclosure would need to be explosion-proof (there are other protection techniques too but for the sake of argument. . .). In that case, drilling and tapping into the enclosure can be a serious issue since then you'd be compromising not only the ingress, but the explosion-proof nature of the enclosure. Highly unlikely that a screw would fix that issue. It would really come down to manufacturer's instructions at that point to ensure its allowed.

This might all be obvious but when I originally read the post it seemed like the hesitation could've been due to the two cases above.
I can picture a situation where someone would say that drilling into enclosures in Class I Div 2 locations is a no no, when there are numerous cases where it wouldn't be as big an issue. . . like the one presented by the OP.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Perhaps a different approach to mounting the nameplate might solve this. 3M makes a line of double stick foam tapes called VHB (very high bond). This stuff will stick wet ice cubes together. No drilling necessary. Just make sure to get the nameplate on straight the first time. You only really get one shot at placement :)

http://www.mcmaster.com/#vhb-tape/=zli9f2


SceneryDriver
 

Fulthrotl

~Autocorrect is My Worst Enema.~
I can picture a situation where someone would say that drilling into enclosures in Class I Div 2 locations is a no no, when there are numerous cases where it wouldn't be as big an issue.

working in CL I div I a number of years ago, i was surprised to find
that drilling and tapping cast enclosures was acceptable in the
field, provided that the tapped hole passed with a go/nogo gauge.
five full threads of engagement, and all is well.

i'd a never considered it, but they had us mark the locations, and they
drilled three 2" holes, and tapped them, and nobody even blinked.

as to the name plate, i'd attach it with urethane, or VHB as mentioned above,
and call it a day.
 
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