How to identify IMC vs Stainless vs galvanized RMC?

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Ravenvalor

Ravenvalor

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Piedmont region of NC
Hello,

I am replacing 8 explosion proof lights in an oil changing pit at a truck stop lube center. I need to replace 8 - 2” pieces of 3/4” rigid with 18” pieces to make the new lights fit. Would someone give me some suggestions on how to determine what type of rigid I am dealing with, IMC, Stainless, or Galvanized?

Thanks for the awesome help.
 
Stainless steels are non-magnetic, or only weakly magnetic.

IMC and rigid are made of the same material with the same coating, so you're going to need to either find some labeling/marking or measure the wall thickness.
 
Examples of rigid metallic raceways are: Electrical metallic tubing (EMT): Lightweight and easy to install. Intermediate metallic conduit (IMC):
Has a thicker, galvanized wall, making it suitable for outdoor applications. Galvanized rigid conduit (GRC), which is thickest and offers the most protection.

Intermediate Metal Conduit (IMC) is galvanized steel raceway. Used to protect and route conductors and cables, this IMC conduit can also be used as an equipment grounding conductor when installed with fittings and couplings in accordance with the NEC.

Galvanized Rigid Steel Conduit (GRC, RMC) is the heaviest weight and thickest wall of electrical conduits.

I believe you meant Aluminum and not Stainless Steel.

Rigid aluminum conduit is also known as rigid metal conduit, or RMC. It has threads as well as thick walls, with sections connected by screws. Thanks to its thickness, RMC is not only very strong and durable, it also does a great job of protecting cables from impacts and other types of damage.

Using any search engine Define (type) conduit; and you will find about the same.
 
Ravenvalor said:
Hello,

I am replacing 8 explosion proof lights in an oil changing pit at a truck stop lube center. I need to replace 8 - 2” pieces of 3/4” rigid with 18” pieces to make the new lights fit. Would someone give me some suggestions on how to determine what type of rigid I am dealing with, IMC, Stainless, or Galvanized?

Thanks for the awesome help.
Click to expand...
It doesn’t matter. Within the context of your question RMC and IMC are the only rigid raceways permitted in Division 1[Section 501.10(A)(1)(a)]. Both must be threaded in this particular application and, in the same trade sizes, they have the same OD; i.e., they both “fit” the same.

Stainless RMC and IMC do have some dissimilar metal issues [See Sections 342.14 & 344.14] but, unless the luminaires are stainless themselves, I’d use galvanized and not look back.
 
I gave it the magnet test and it’s RMC. Thank you for the help. This is a huge relief. 😀

Wondering, do I have to use a thread lubricant if the pipe screws into the fitting easily?

Thanks again
 
Ravenvalor said:
I gave it the magnet test and it’s RMC. Thank you for the help. This is a huge relief. 😀

Wondering, do I have to use a thread lubricant if the pipe screws into the fitting easily?

Thanks again
Click to expand...
The basic rules for threading are in Section 500.8(E). Neither sealant nor lubricant is mandated; however, if you use them, ensure the ground fault path through the threaded connections is not interrupted or compromised. The threaded connections are also part of the flame path.
 
Let me be the first to say this is outside my expertise...

I thought explosion proof and thread sealants were mutually exclusive?
 
If you use a thread coating make sure it is identified for the use. Something like Crouse-Hinds STL8 lubricant which is listed for hazardous locations. Or you have to clean the threads and spray a conductive zinc paint, let dry and then install.
 
This galvanized RMC along with the lights inside this pit are routinely washed down with I suppose to be a pressure washer. I would prefer not to use a sealer or lubricant but am concerned about water making it’s way down the threads.
 
Ravenvalor said:
This galvanized RMC along with the lights inside this pit are routinely washed down with I suppose to be a pressure washer. I would prefer not to use a sealer or lubricant but am concerned about water making it’s way down the threads.
Click to expand...

Any water ingress via threads will likely be much less than the result of normal condensation inside the pipe.
 
tthh said:
Let me be the first to say this is outside my expertise...

I thought explosion proof and thread sealants were mutually exclusive?
Click to expand...
General rules is you don't use thread sealers in explosion proof applications. When the system is asked to contain an explosion the pressure is relieved through the threads. Sealers can inhibit this. The idea is once the gases pass through the threads they have been cooled to a temperature that is low enough it won't ignite any vapors on the outside.

Same goes for enclosures with somewhat wide flat machined flanges between say enclosure and cover. You don't want any gasket or similar sealing component on those, they designed to relieve pressure in explosions yet have enough width to cool the escaping gas to a safe temperature before it reaches the outside environment.
 
With respect to classified locations, NEC, Articles 500 to 516 neither requires nor prohibits sealants or lubricants beyond what is already required in the relevant Chapter 3 wiring methods for the materials/equipment involved.

In classified locations, if a lubricant/sealant is used on threads, it must be conductive in order to meet the continuous grounding/bonding requirements of the classified location; for example Section 501.30. This is even if the raceway is not the primary grounding/bonding conductor. This is to prevent stray or circulating currents from becoming ignition sources.

To preserve the flame path relief route, the manufacturer’s instructions must be followed. It usually is not required for raceways except as an anti-corrosion measure.
 
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