Aluminum conduit in an explosion proof environment

[searlest]

Hello, I will be bidding a industrial paint booth installation soon and was wondering if aluminum conduit was expectable by the NEC and NFPA standards in the explosion proof areas ?

Secondly i want to be certain I understand what intrinsically safe grounding requirements are for the application can someone shed some light on this ?


Thanks in advance

 

[Smart $]

Hello, I will be bidding a industrial paint booth installation soon and was wondering if aluminum conduit was expectable by the NEC and NFPA standards in the explosion proof areas ?

Secondly i want to be certain I understand what intrinsically safe grounding requirements are for the application can someone shed some light on this ?


Thanks in advance

Aluminum conduit is not 'expected', but this is likely a Class I Division 1 hazardous location area, and 501.10(A) limits conduit type wiring methods to threaded RMC (which doesn't have to be steel) or steel IMC. Under the exception you can also use PVC or RTRC embedded in concrete.

I'm uncertain what you mean by intrinsically safe grounding requirements... but it appears from that statement you need a better understanding (or I do )...

http://www.omega.com/techref/intrinsic.html

 

[Gregg Harris]

Hello, I will be bidding a industrial paint booth installation soon and was wondering if aluminum conduit was expectable by the NEC and NFPA standards in the explosion proof areas ?

Secondly i want to be certain I understand what intrinsically safe grounding requirements are for the application can someone shed some light on this ?


Thanks in advance

Take a look at 500 and 504
No on the aluminium
Intrinsically Safe Circuit. A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions.

 

[Smart $]

...No on the aluminium...

No in what way? No as in not expected, or no as in not permitted.

My understanding is theaded aluminum RMC is a permitted wiring method in CID1 locations.

 

[kwired]

Take a look at 500 and 504
No on the aluminium
Intrinsically Safe Circuit. A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions.

Can you give a specific section that says no to the aluminum?

Subsection .10 in 501, 502 and 503 all just say rigid metal conduit.

344.2 defines rigid metal conduit.

344.2 Definition.

Rigid Metal Conduit (RMC). A threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings. RMC is generally made of steel (ferrous) with protective coatings or aluminum (nonferrous). Special use types are red brass and stainless steel.

Aluminum, brass and stainless steel are included in the definition, but type of metal used may not be limited to those mentioned either.

 

[Gregg Harris]

Can you give a specific section that says no to the aluminum?

Subsection .10 in 501, 502 and 503 all just say rigid metal conduit.

344.2 defines rigid metal conduit.

Aluminum, brass and stainless steel are included in the definition, but type of metal used may not be limited to those mentioned either.

(3) Aluminum RMC. Aluminum RMC shall be permitted to be installed where judged suitable for the environment. Rigid aluminum conduit encased in concrete or in direct contact with the earth shall be provided with approved supplementary corrosion protection.

I am going with the corrosive atmosphere and dissimilar metals

 

[Smart $]

....

I am going with the corrosive atmosphere and dissimilar metals

I don't see where a paint booth would be corrosive. Painting is typically for corrosion protection, even on aluminum.

How do you get dissimilar metals? A lot of XP equipment is made of aluminum. Aluminum's anodic index actually falls amid the range of various types of steel, so galvanic corrosion would be at a minimum compared to other metals.

 

[rbalex]

Aluminum RMC/IMC is suitable. Technically, any RMC/IMC is acceptable. See Sections 501.10(A)(1)(a). “Dissimilar metals” is not an enhanced issue. Aluminum/steel interfaces are specifically accepted. See Sections 342.14 and 344.15.

Grounding/ bonding and sealing requirements in intrinsically safe installations are outlined in Sections 504.50, 60 and 70. There's a little relief for sealing but virtually none for grounding /bonding if understood properly.

If this had been posted in the Hazardous (Classified) Locations forum, I’d have spotted it sooner.

 

[Gregg Harris]

I don't see where a paint booth would be corrosive. Painting is typically for corrosion protection, even on aluminum.

How do you get dissimilar metals? A lot of XP equipment is made of aluminum. Aluminum's anodic index actually falls amid the range of various types of steel, so galvanic corrosion would be at a minimum compared to other metals.

I stand corrected, I read it as "Indusrtial Paint process" and assumed corrosive atmosphere. I shall go take a nap now.

 

[Smart $]

Aluminum RMC/IMC is suitable. Technically, any RMC/IMC is acceptable. ...

Under 501.10(A), only steel IMC is permitted.

 

[rbalex]

Under 501.10(A), only steel IMC is permitted.

Well that's true; but then, IMC is always steel. See Section 342.2.

 

[Smart $]

Well that's true; but then, IMC is always steel. See Section 342.2.

I knew that... but the way your post was worded made it seem otherwise.

 

[weressl]

Hello, I will be bidding a industrial paint booth installation soon and was wondering if aluminum conduit was expectable by the NEC and NFPA standards in the explosion proof areas ?

Secondly i want to be certain I understand what intrinsically safe grounding requirements are for the application can someone shed some light on this ?


Thanks in advance

AFAIK there are no cast aluminum fittings that are approved for Class I, Div. 1 areas and Rigid Aluminum Conduit is not what is tested in combination with cast iron X-fittings. There is no problem using aluminum conduit with fittings in Div. 2 areas.

The phrase 'intrinsically safe grounding requirements for the application" is ambigous. Please clarify.

 

[weressl]

Aluminum RMC/IMC is suitable. Technically, any RMC/IMC is acceptable. See Sections 501.10(A)(1)(a). ?Dissimilar metals? is not an enhanced issue. Aluminum/steel interfaces are specifically accepted. See Sections 342.14 and 344.15.

Grounding/ bonding and sealing requirements in intrinsically safe installations are outlined in Sections 504.50, 60 and 70. There's a little relief for sealing but virtually none for grounding /bonding if understood properly.

If this had been posted in the Hazardous (Classified) Locations forum, I?d have spotted it sooner.

Bob, are you sure that Aluminum RMC/IMC was tested for explosion withstand? All I ever seen tested were RSC. If I recall correctly it was for several hundred feet long with couplings and filled with hydrogen/air and acetylene/air mixtures.

 

[rbalex]

Neither 501.10(A)(1)(a) nor 344.10(A)(3) place a restriction on aluminum RMC in Class I, Divison 1. Section 344.14 permits general aluminum/steel interfaces.

 

[augie47]

Only know what I read and info can be biased:

http://www.bpmmetals.com/pdf/suppliers/indalex/Indalex Rigid Aluminum Conduit.pdf

Explosion Proof
? Replaces Rigid Steel in Virtually All Locations
? Non-Sparking
? Aluminum Conduit Meets All National Electrical
Code ? Article 500 Hazardous Area Requirements
? No Toxic Fumes

 

[sgunsel]

I recommend you look at NFPA 33 Standard for Spray Application Using Flammable or Combustible Materials and NFPA 77 Recommended Practice on Static Electricity for more information on grounding/bonding requirements. As a practical matter most electricals, including lighting, at spray booths are normally relocated to non-classified areas - NFPA 33 has some examples on how to do this. The 2011 NEC is not in sync with the 2011 NFPA 33, regardless of what it says. The 2011 NFPA 33 reduced the Division 2 areas significantly - so it would be wise to check with the AHJ ahead of time to verify what will be acceptable.