# Greenhouse motor relay wiring.



## Kao Chen (Dec 14, 2010)

2005 NEC. Commercial Greenhouse 'U' occupancy. The ventilation fans have relays that require 24 volt wiring. All 120/240 volt conductors must be rated for wet location by insulation or approved type of conduit.

I can not find a listing for class 1 conductors indicating whether the 24 volt wiring must be in conduit or whether the insulation can be placed in wet locations. This is separate from physical protection. All help would be appreciated. Please site code references.

Thanks


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## north star (Dec 14, 2010)

** * * ** 

Are you saying that the location is a " Class 1 ", or that the conductor type

is a " Class 1 "?

Trying to locate an applicable article for you...    



** * * **


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## raider1 (Dec 14, 2010)

> I can not find a listing for class 1 conductors indicating whether the 24 volt wiring must be in conduit or whether the insulation can be placed in wet locations. This is separate from physical protection. All help would be appreciated. Please site code references.


First off Class 1 remote control and signaling circuits are wired using Chapter 3 wiring methods. Class 2 and 3 circuits can be wired using a Class 2 or 3 cable and are not required to meet the requirements of Chapter 3 unless specifically reference in Article 725.

There is nothing specific in Part III of Article 725 that requires Class 2 or 3 cables to be listed for a wet location but common sense would dictate that it would be a good idea.

Chris


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## north star (Dec 15, 2010)

** * * **

From doing some reading on other forums, it seems that a common concensus

is to have the wiring installed in a pvc coated emt type conduit, because of the

higher temperatures & corrosive environment of the greenhouse.  " IF " pvc

coated emt conduit is not used, then Schedule 80 pvc could be used, only it

would need to be supported more to prevent sagging.

I'm guessing that the relays you mentioned are inside the motor enclosure

[ sealed ] ?



Sorry,  presently I can not provide you with a particular code section.   I

will keep looking though!

** * * **


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## Kao Chen (Dec 15, 2010)

Class 1 conductors

The greenhouse is not a hazardous class location. Actually I would specifiy it as per Article 547 Agricultural Buildings. The conductors will be Class 1. Are any Class 1 conductors rated for wet locations by the insulation itself or should they be placed in a wet rated conduit? This is my first greenhouse and I never hesitate to ask those with more experience.


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## north star (Dec 15, 2010)

** * * **

In my reading on this type of environment, other more experienced electricians

all said that the greenhouse enviromment was a corrosive one.......Because of

that, they "suggested" that all wiring be installed in an approved, durable

raceway and that all conductors, fittings, etc. be sealed.

From the 2008 NEC:

*"Article 547.5©(3) - **Corrosive Atmosphere. *Where wet dust, excessive


moisture, corrosive gases or vapors, or other corrosive conditions may be

present, equipment enclosures, boxes, conduit bodies, and fittings shall have

corrosion resistance properties suitable for the conditions.

FPN No. 1: See Table 110.20 for appropriate enclosure type designations.

FPN No. 2: Aluminum and magnetic ferrous materials may corrode in

agricultural environments."
​*"Article 505.18 - Conductors and **Conductor Insulation.*


*(B) Conductor Insulation. *

Where condensed vapors or liquids may collect on, or come in contact with, the

insulation on conductors, such insulation shall be of a type identified for use under

such conditions, or the insulation shall be protected by a sheath of lead or by other

approved means.

*505.19 Uninsulated Exposed Parts. *

There shall be no uninsulated exposed parts, such as electrical conductors, buses,

terminals, or components that operate at more than 30 volts ( 15 volts in wet

locations )........These parts shall additionally be protected by type of protection

ia, ib, or nA that is suitable for the location."
​** * * **
​


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## raider1 (Dec 15, 2010)

Kao Chen said:
			
		

> The greenhouse is not a hazardous class location. Actually I would specifiy it as per Article 547 Agricultural Buildings. The conductors will be Class 1. Are any Class 1 conductors rated for wet locations by the insulation itself or should they be placed in a wet rated conduit? This is my first greenhouse and I never hesitate to ask those with more experience.


For the greenhouse to fall under Article 547 it must meet either 547.1(A) or (B). I don't see a standard greenhouse falling under either section so IMHO Article 547 does not apply.

What do you mean that the conductors are Class 1? Is the 24 volt circuit supplied by a t=low voltage transformer? If that is the case you would either have a Class 2 or 3 circuit and not a Class 1.

Again if this is a Class 1 circuit then you would use any Chapter 3 wiring method. Such as EMT, PVC etc...

I would classify this area as a wet location and use a wiring method that is suitable for use in a wet location.



			
				north star said:
			
		

> ** * * **In my reading on this type of environment, other more experienced electricians
> 
> all said that the greenhouse enviromment was a corrosive one.......Because of
> 
> ...


Article 505 is for Class 1 Zone 0, 1, and 2 locations and would not apply to a greenhouse.

Chris


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## north star (Dec 15, 2010)

** * * **

Chris, I will respectfully have to disagree with you here.....I believe that

with the amount of heat and moisture rich atmosphere present in a

typical greenhouse, that Article 547.1(B)(4) would apply!.......Those two

components [ heat & moisture ] will combine to rust [ corrosion ] the

various metal components in an accelerated manner, unless adequately

sealed/protected.

BTW, Mr. Chen I am no greenhouse expert either!.......Not by any stretch

of the imagination. 

** * * **


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## raider1 (Dec 15, 2010)

Kao Chen said:
			
		

> The greenhouse is not a hazardous class location. Actually I would specifiy it as per Article 547 Agricultural Buildings. The conductors will be Class 1. Are any Class 1 conductors rated for wet locations by the insulation itself or should they be placed in a wet rated conduit? This is my first greenhouse and I never hesitate to ask those with more experience.





			
				north star said:
			
		

> ** * * **In my reading on this type of environment, other more experienced electricians
> 
> all said that the greenhouse environment was a corrosive one.......Because of
> 
> ...





			
				north star said:
			
		

> ** * * **Chris, I will respectfully have to disagree with you here.....I believe that
> 
> with the amount of heat and moisture rich atmosphere present in a
> 
> ...


I don't see a greenhouse as any more of a corrosive area than a car wash or wash down area of a food processing plant, neither or which I would call an agricultural building.

110.11 already has provisions for requiring the wiring methods and equipment to be suitable for the environment in which they will be used so I see no need to try to call a greenhouse an agricultural building so you can require a wiring method that is suitable for a wet location.

Chris


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