Waterproofing AC motor conduit box in hazardous area

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Ram1991

New User
Location
Ky
Occupation
I&EC engineer
I have a question regarding sealing the conduit box entries for motors in Class 1 Div 1 and Class 1 Div 2 areas. We had a motor fail due to water intrusion in the conduit box were the 3 phase leads would hook up. The motor is located outdoor and is exposed to rain/snow. The conduit box cover mates up to the conduit box with a metal to metal surface. When we pulled the cover off of our motor that surface had a decent amount of corrosion like water had been slowing getting in for quite some time.
Is there an industry best practice to mitigate this issue?
 
Generally explosion proof junction boxes are not waterproof. This is because the whole idea of an explosion proof junction box is to allow the heat from a flame that gets ignited inside the junction box to Cool enough before it gets to the outside that it won't ignite anything on the outside. The flanges allow the flame to cool as it exits the box.
 
petersonra said:
Generally explosion proof junction boxes are not waterproof. This is because the whole idea of an explosion proof junction box is to allow the heat from a flame that gets ignited inside the junction box to Cool enough before it gets to the outside that it won't ignite anything on the outside. The flanges allow the flame to cool as it exits the box.
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Yes, if you want an explosionproof box for wet locations, you have to make sure it is rated fro that. Some that are, have an O ring type gasket in a grove to make it water tight. I assume the rubber gives enough when there is an explosion within the box.

However if the box is required to be explosionproof I would not make any field modifications to make it watertight, not even putting silicone on the outside as suggested in post #2.
 
I've had equipment that because of heating and cooling cycles I couldn't keep the water out. I just made up a little tin roof to shed the sealing area from rain and snow. When it rains or snows it cools the equipment and creates a Vacuum inside pulling water in
 
n top to prevent water from running in equipment, rated or not this isn't a good thing. Covers are good. I make covers for outdoor in use covers, that stuff is junk and never does work right.
 
In my experience water entry into wet location enclosures is almost always because the raceway system has not be arranged to drain and the conduit enters the enclosure at a location other than the bottom.
 
don_resqcapt19 said:
In my experience water entry into wet location enclosures is almost always because the raceway system has not be arranged to drain and the conduit enters the enclosure at a location other than the bottom.
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Yeah in non hazardous locations I've been known to drill a couple small holes in the bottom. Solves the vacuum problem and if any water gets in, it can drip out
 
ptonsparky said:
Pretty sure that question came up in one of our IAEI meetings and the swipe of silicone was a solution at one time.
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A thin swipe on the outside top really wouldn't change the pressure wave escaping much. The tensile strength of silicone is really low
 
petersonra said:
But how would you prove to the inspector that you didn't put something on the face of the flanges if he can see it on the outside.
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I've actually never seen an inspector while doing industrial maintenance. Yeah sure in a new installation, but never replacing a motor, controls, or anything like that.
 
Joethemechanic said:
I've actually never seen an inspector while doing industrial maintenance. Yeah sure in a new installation, but never replacing a motor, controls, or anything like that.
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Maintenance never required inspection here.
Joethemechanic said:
I've actually never seen an inspector while doing industrial maintenance. Yeah sure in a new installation, but never replacing a motor, controls, or anything like that.
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We never use conduit for AC motors. We use usually four wire stranded armoured and usually waterproof. These are closed cage induction motors.
 
My personal experience mirrors Don's in Post #7. Conduits breath and water can condense in overhead raceways. Providing an effective drain before the motor terminal box is usually a good idea in any installation, classified or not.

Motors in Division 2 generally are installed per Section 501.125(B)(3); i.e., they are General Purpose and not listed. Division 1 motors are usually Section 501.125(A)(1). I also agree with Don's assessment in Post #4. Explosionproof motors are listed and field modifications without NRTL recertification is a violation.

With both Division 1 and 2, heaters are available. There are additional restrictions though.
 
ptonsparky said:
Pretty sure that question came up in one of our IAEI meetings and the swipe of silicone was a solution at one time.
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Killark makes a compound for sealing explosion proof boxes outside. cat. # LUBG-6. Silicone should never be used. There are even instructions on their website as how to apply it. Coat the surfaces and (I use a putty Knife), to obtain a microfilm on the surface. This prevents corrosion on the polished surfaces and on equipment used, never allows moisture inside. Also, when opening an explosion proof cover, FOLLOW the instructions. They should be opened from the bottom with something like a small putty knife to lift the surface apart. And in the instructions, you are allowed to only tap the prying tool in so far as not to damage the sealing surfaces. I have seen enclosures pried open from the top and the damaged area allows contaminants to gain access to the interior of the enclosure.
Ram1991 said:
I have a question regarding sealing the conduit box entries for motors in Class 1 Div 1 and Class 1 Div 2 areas. We had a motor fail due to water intrusion in the conduit box were the 3 phase leads would hook up. The motor is located outdoor and is exposed to rain/snow. The conduit box cover mates up to the conduit box with a metal to metal surface. When we pulled the cover off of our motor that surface had a decent amount of corrosion like water had been slowing getting in for quite some time.
Is there an industry best practice to mitigate this issue?
Click to expand...
Killark makes a compound for sealing explosion proof boxes outside. cat. # LUBG-6. Silicone should never be used. There are even instructions on their website as how to apply it. Coat the surfaces and (I use a putty Knife), to obtain a microfilm on the surface. This prevents corrosion on the polished surfaces and on equipment used, never allows moisture inside. Also, when opening an explosion proof cover, FOLLOW the instructions. They should be opened from the bottom with something like a small putty knife to lift the surface apart. And in the instructions, you are allowed to only tap the prying tool in so far as not to damage the sealing surfaces. I have seen enclosures pried open from the top and the damaged area allows contaminants to gain access to the interior of the enclosure.
 
David,

Welcome to the Forum. Please update your profile to include your occupation. Thanks.
 
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