are transformers allowed in return air plenums?

[Dang old king]

Hollow: empty space ,void
50kva transformers and smaller are allowed in such areas.
Why 50kva limitation? Because the buildup of heat in such an unventilated area on higher rated transformers may cause them to fail and burn up.
Plenum: A compartment or duct to which one or more air ducts are connected and forms part of the air distribution system.
Although these areas may appear similar, they are two distinctively different portions of a building. A hollow space will not communicate to an environmental air passageway and likewise.
Electrical Equipment in Plenum?s: Must be of fire-resistant construction and of the ?Low Smoke Producing Type.
It is my contention that above grid return air plenums are a hollow space, but should not be considered as such, as they do indeed contain something:
Environmental air, The Article in 450 does not apply to transformers in environmental air, otherwise we would allow transformers to be installed in metal ducted plenums which are void and empty as defined by the term hollow. All equipment installed in return air above grid plenums must be rated for this purpose, not just electrical equipment.
Stalcup address it http://books.google.com/books?id=OkwGeMAXJa8C&pg=SA8-PA3&lpg=SA8-PA3&dq=transformers+installed+in+hollow+space&source=bl&ots=VGF24WbJ0T&sig=IoUrdqThUEkFw09h5QPHYlK5Vgk&hl=en#v=onepage&q=transformers%20installed%20in%20hollow%20space&f=false
Mike Holt address it http://forums.mikeholt.com/archive/index.php/t-120884.html?

The accessibility requirements prescribed in 450-13 are just that a matter of accessibility. If the hollow space communicates with and environmental air passageway, that hollow space now becomes an approved form of duct work as prescribed in the 03 International Mechanical Code. Which also address the installation of electrical equipment in environmental air return plenums in article 602.2.1.1 and then again in article 602.2.1.4 Article 300.22 applies to electrical equipment installed in environmental air plenums. The code writers intent in article 450.13 was to limit the size of a transformer based on its ability to dissipate the unwanted heat associated with transformers in concealed non ventilated space?s. Not to allow the installation of a piece of equipment in return air plenums. Although 300.22(C)2 address such applications and requirements.
U/L and the President of IAEI has made information available to me ?Transformers are not tested for the plenum rating as the body of the code already address their approved installation in a hollow space up to 50kva? .
Herein lies the problem.
I think he,the head state inspector & my supervisor's are wrong with aligning them selves with this line of thinking.
Am I wrong?
Should we be allowing transformers in environmental air plenums knowing that such equipment has not or ever been tested for such an installation?

 

[iwire]

Should we be allowing transformers in environmental air plenums knowing that such equipment has not or ever been tested for such an installation?

We cannot install any transformers in a plenum, 300.22(B) prohibits that.

We can install a transformer in 'other space used for environmental air' and the only requirement is that the equipment be a a metal enclosure or be listed for plenums.

I have yet to see a transformer that was not in a metal enclosure.

300.22 Wiring in Ducts, Plenums, and Other Air-
Handling Spaces.

(C) Other Space Used for Environmental Air. This section
applies to space used for environmental air-handling
purposes other than ducts and plenums as specified in
300.22(A) and (B). It does not include habitable rooms or
areas of buildings, the prime purpose of which is not air
handling.

Exception: This section shall not apply to the joist or stud
spaces of dwelling units where the wiring passes through
such spaces perpendicular to the long dimension of such
spaces.


(2) Equipment. Electrical equipment with a metal enclosure,
or with a nonmetallic enclosure listed for the use and
having adequate fire-resistant and low-smoke-producing
characteristics, and associated wiring material suitable for
the ambient temperature shall be permitted to be installed
in such other space unless prohibited elsewhere in this
Code.

Exception: Integral fan systems shall be permitted where
specifically identified for such use.

 

[Npstewart]

Transformers are not allowed in the air plenum, most of the transformers like optimus prime are like 50 feet tall! How go they possibly all fit in there???

 

[Dang old king]

So we cant put them in a metal duct that conveys environmental air.
But we can put them in an above grid cieling that performs the same function?
Is that correct?

 

[iwire]

So we cant put them in a metal duct that conveys environmental air.
But we can put them in an above grid ceiling that performs the same function?

Is that correct?

That is exactly correct if they have metal enclosures or are listed for use in plenums.

 

[shepelec]

But I wouldn't say a transformer has a "low smoke producing charateristic".

I've seen a lot of smoke come out of one them things.

 

[infinity]

So we cant put them in a metal duct that conveys environmental air.
But we can put them in an above grid cieling that performs the same function?
Is that correct?

Up to 50 Kva.

 

[Dang old king]

I agree with you on the listing. I have been a Master electrician for 27years and an Inspector for almost 1/2 that time. I have never seen a 50kva transformer or smaller listed for use in a "Plenum"
The president of IAEI(The director of U/L Mr.Mellow) Has mad a statement in regard to this issue.
"The fact that the body of the code address' the installation of a transformer 50kva or less in a hollow spaces,negates the requirement for a test or listing of transformers,in fact transformers are not tested to that criteria". What would you say to that? & is a plenum considered a hollow space? as outlined in the body of the code.

 

[Dang old king]

But I wouldn't say a transformer has a "low smoke producing charateristic".

I've seen a lot of smoke come out of one them things.

This is my exact concern. When they fail they produce tons of smoke. By no means does this meet the Mechanical code in relation to the 25/50 smoke flame density spread.

 

[iwire]

But I wouldn't say a transformer has a "low smoke producing charateristic".

If it has a metal enclosure it is not required to have a low-smoke-producing
characteristics,

I've seen a lot of smoke come out of one them things.

As Rob points out the size is limited.

My personal opinion is that unless it can be shown the existing rules are causing a documented hazard that the rules should not be changed.

 

[raider1]

The president of IAEI(The director of U/L Mr.Mellow) Has mad a statement in regard to this issue.
"The fact that the body of the code address' the installation of a transformer 50kva or less in a hollow spaces,negates the requirement for a test or listing of transformers,in fact transformers are not tested to that criteria". What would you say to that? & is a plenum considered a hollow space? as outlined in the body of the code.

What would I say to that?

I would say that according to Mr Mellow, UL has determined that since transformers 50 Kva or less are permitted to be installed in hollow spaces (Including above ceiling spaces used for enviromental air) according to the NEC there is no need for them to test and list transformers for the purpose.

The space above a suspended ceiling is a hollow space regardless of wheter or not it is used to convey enviromental air. Therefore 450.13(B) permits transformers 50 Kva or less and 600 volts or less to be installed there.

Chris

 

[Strife]

Plenum is a lot more than hollow space. It's a space where the air returns from the ac (basically an AC system without return duct). So that air gets back in the air handler and gets pumped right back into the rooms. Not sure how many have seen how much smoke couple grams of PVC can generate. It's a LOT. And it's NASTY, it's so stingy it cuts your breath, literally knocks you out. Just a whiff. Seriously.
I left a heat box unattended for (let's say more than I should have), when I got to it to pull the pvc out (the whole 3 feet of it) there was enough smoke to knock out an elephant.

I agree with you on the listing. I have been a Master electrician for 27years and an Inspector for almost 1/2 that time. I have never seen a 50kva transformer or smaller listed for use in a "Plenum"
The president of IAEI(The director of U/L Mr.Mellow) Has mad a statement in regard to this issue.
"The fact that the body of the code address' the installation of a transformer 50kva or less in a hollow spaces,negates the requirement for a test or listing of transformers,in fact transformers are not tested to that criteria". What would you say to that? & is a plenum considered a hollow space? as outlined in the body of the code.

 

[infinity]

Plenum is a lot more than hollow space. It's a space where the air returns from the ac (basically an AC system without return duct). So that air gets back in the air handler and gets pumped right back into the rooms. Not sure how many have seen how much smoke couple grams of PVC can generate. It's a LOT. And it's NASTY, it's so stingy it cuts your breath, literally knocks you out. Just a whiff. Seriously.
I left a heat box unattended for (let's say more than I should have), when I got to it to pull the pvc out (the whole 3 feet of it) there was enough smoke to knock out an elephant.

Almost all modern buildings that would that would have a transformer above the hung ceiling would also have return air duct detectors which would shutdown the fans if a transformer went up in smoke.

 

[Dang old king]

I appreciate all the response to this topic. It certainly appears to be one of confusion.and should be clarified. This forum has stated that the transformer must be listed for the location was touched and concluded on not so long ago.And now it has changed.. go figure electricians are a fickle bunch.
The discussion of metal enclosure& hollow space,are not exactly clear..Metal enclosure: Yes indeed transformers are in metal enclosures but they have vent opening to dissipate heat so much so that the combined measurement of the opening equals one of the transformers 6 sides. In essence you have a 5 sided cube. I don't think that's what the code writers were talking about when they spoke of metal enclosures..Its not completely enclosed that's pretty simple
Hollow Space..lets break down that little gem..why should we only allow up to a 50kva in a hollow space.. the way a lot of people see it,is because there is no air movement and transformers larger than 50 kva have a history of performing poorly in unventilated areas such as a hollow space. I think the code writers intent here is pretty obvious as well.
Is an above grid return air plenum hollow? Not so much in most cases those areas are used as plumbing, communication and ventilation chases those three items themselves disallow the definition of Hollow.I'm being a bit persnickety.
The code does not allow transformers. in metal ducted plenums but they are the most accurate definition of "Hollow" there is.
So why cant we put a transformer larger than 50kva in a hollow space that is used to convey conditioned air..heck we've accounted for the heat problem with ventilation..(condition air to be exact) as prescribed in the NEC..450.9
So where does this leave the code official? In a quandary..lol
We are obligated as building officials and qualified people to protect the public from this thing we call electricity.The only thing we can stand behind is code in our effort to provide said protection.
I would rather error on the side of caution and protect a building and it's occupants from possible exposure to the noxious fumes and vapors that are emitted by burning transformers than to vicariously approve them in such spaces.
Thanks again for all the input.Cheers
DOK

 

[Sierrasparky]

I have been in Mechanical rooms that are plenums the have enough area that you could place 20 of those size transformers. Boy the noise and the constant hurricane wind inside.

 

[patriot]

I wonder what building codes in your area would say about this one? I came across this years ago. It seems to me(from what I can remmember from 15 years or so back) that the G.C had to wrap a dry wall box around it and duct the box out of the ceiling. I recall this becuase I remmember the G.C. had to tear the first box out and redo it because it did not meet electrical clearances.

 

[iwire]

It certainly appears to be one of confusion.and should be clarified.

I see no confusion at all.

This forum has stated that the transformer must be listed for the location was touched and concluded on not so long ago.

There is no specific listing for installation in a hollow space and none is required.

That is like saying a transformer would have to be specifically listed for installation in a boiler room or specifically listed for installation in a office building.

The discussion of metal enclosure& hollow space,are not exactly clear..Metal enclosure: Yes indeed transformers are in metal enclosures but they have vent opening to dissipate heat so much so that the combined measurement of the opening equals one of the transformers 6 sides.

Irrelevant, the code does not require that the enclosure be 'air tight' only that it be metal ... and it is.

In essence you have a 5 sided cube. I don't think that's what the code writers were talking about when they spoke of metal enclosures..Its not completely enclosed that's pretty simple

You are reaching, you are stretching things to get the result you feel is needed.

Hollow Space..lets break down that little gem..why should we only allow up to a 50kva in a hollow space.. the way a lot of people see it,is because there is no air movement and transformers larger than 50 kva have a history of performing poorly in unventilated areas such as a hollow space. I think the code writers intent here is pretty obvious as well.

I have no idea what you are trying to say here.

The code does not allow transformers. in metal ducted plenums but they are the most accurate definition of "Hollow" there is.

So why cant we put a transformer larger than 50kva in a hollow space that is used to convey conditioned air..heck we've accounted for the heat problem with ventilation..(condition air to be exact) as prescribed in the NEC..450.9
So where does this leave the code official? In a quandary..lol

It does not leave you in any quandary whatsoever, you apply the code as written and if you do not agree with how it is written you try to have it changed.

We are obligated as building officials and qualified people to protect the public from this thing we call electricity.The only thing we can stand behind is code in our effort to provide said protection.

You are also as much obligated to enforce the adopted code not your own ideas about what is righ or wrong.

I would rather error on the side of caution and protect a building and it's occupants from possible exposure to the noxious fumes and vapors that are emitted by burning transformers than to vicariously approve them in such spaces.

It is not up to you to decide, it is your obligation to enforce the rules as written and if I install a 480 to 208Y/120 45 kva transformer in a suspended ceiling used for environmental air you have no choice under the NEC but to accept it.


Cheers.

 

[patriot]

I appreciate all the response to this topic. It certainly appears to be one of confusion.and should be clarified. This forum has stated that the transformer must be listed for the location was touched and concluded on not so long ago.And now it has changed.. go figure electricians are a fickle bunch.
The discussion of metal enclosure& hollow space,are not exactly clear..Metal enclosure: Yes indeed transformers are in metal enclosures but they have vent opening to dissipate heat so much so that the combined measurement of the opening equals one of the transformers 6 sides. In essence you have a 5 sided cube. I don't think that's what the code writers were talking about when they spoke of metal enclosures..Its not completely enclosed that's pretty simple
Hollow Space..lets break down that little gem..why should we only allow up to a 50kva in a hollow space.. the way a lot of people see it,is because there is no air movement and transformers larger than 50 kva have a history of performing poorly in unventilated areas such as a hollow space. I think the code writers intent here is pretty obvious as well.
Is an above grid return air plenum hollow? Not so much in most cases those areas are used as plumbing, communication and ventilation chases those three items themselves disallow the definition of Hollow.I'm being a bit persnickety.
The code does not allow transformers. in metal ducted plenums but they are the most accurate definition of "Hollow" there is.
So why cant we put a transformer larger than 50kva in a hollow space that is used to convey conditioned air..heck we've accounted for the heat problem with ventilation..(condition air to be exact) as prescribed in the NEC..450.9
So where does this leave the code official? In a quandary..lol
We are obligated as building officials and qualified people to protect the public from this thing we call electricity.The only thing we can stand behind is code in our effort to provide said protection.
I would rather error on the side of caution and protect a building and it's occupants from possible exposure to the noxious fumes and vapors that are emitted by burning transformers than to vicariously approve them in such spaces.
Thanks again for all the input.Cheers
DOK

I'm going to take an uneducated guess on why the code does not allow any transformers over 50kVA to be installed in a plenum rated ceiling. I think its not so much that the heat put off by the transfomer will affect the transformer, but since the plenum rated space is the return air for the HVAC system,seems like the heat that a transfomer (expecially a large transformer or transformers) that would be put off would be hard on that system.

 

[Dang old king]

You are also as much obligated to enforce the adopted code not your own ideas about what is righ or wrong.

I don't think its a matter of adoption as more, one of interpretation.
I as a multi- trade inspector understand what the difference between a plenum and a hollow space.
I don't think I have turned the code to fit the current situation. I think it's been minimized in body and needs to be firmly addressed by definition.
I think it simplistic to believe that hollow space and an above grid environmental air way are one in the same,other than appearance. There is a responsibility to be as restrictive as the code allows when considering this application towards construction.
Thanks again to all who commented,

 

[jeremysterling]

I'm going to take an uneducated guess on why the code does not allow any transformers over 50kVA to be installed in a plenum rated ceiling. I think its not so much that the heat put off by the transfomer will affect the transformer, but since the plenum rated space is the return air for the HVAC system,seems like the heat that a transfomer (expecially a large transformer or transformers) that would be put off would be hard on that system.

With that logic you would have to put the XFMR outside or on the roof ( both are great locations by the way but not nearly as good as above a suspended ceiling).