450.22

[charlie b]

Consider a pad-mounted, outdoor, dry-type transformer in excess of 112.5 KVA. The site plan shows a fuel oil tank and a gas tank (I don?t know if ?gas? is gasoline or propane or something else) a few feet away. 450.22 tells me I only need to keep the transformer 12 inches away from combustible materials. But does that only refer to a combustible surface of the exterior wall of a nearby building? I don?t know if there is another relevant code section. I would not call this ?classified area,? under the 500-series articles, particularly since it is outdoors. Can we not postulate a short circuit failure within the transformer that could create an ignition source for a nearby fuel oil tank? Is there some other code that would mandate a minimum separation?

 

[G._S._Ohm]

450.22 tells me I only need to keep the transformer 12 inches away from combustible materials.
Can we not postulate a short circuit failure within the transformer that could create an ignition source for a nearby fuel oil tank? Is there some other code that would mandate a minimum separation?

FWIW, based on what you've posted I think one valid conclusion would be that 12" is enough separation for a transformer in the face of almost any reasonably foreseeable transformer failure mode. This would be based on experiment or calculation or both and may include a safety factor.
The 12" may have been a longer distance if practical considerations or incident history weren't taken into account, but I don't have any information as to what went into this 12".

 

[jim dungar]

Is there some other code that would mandate a minimum separation?

I would never locate a oil-filled transformer simply using the NEC.
I do not have the reference with me, but I can 'picture' a Factory Mutual publication that addresses clearances as well as oil containment issues.

I know you are dealing with a dry type transfromer, I just wanted to point out that I use other sources like FM when I am involving non-electrical issues, like clearances and structure types.

 

[Dennis Alwon]

Charlie, I believe that the req. in 450 is for combustible surfaces. The section does state combustible materials of buildings.

450.22 Dry-Type Transformers Installed Outdoors.
Dry-type transformers installed outdoors shall have a weatherproof enclosure.
Transformers exceeding 112? kVA shall not be located within 300 mm (12 in.) of combustible materials of buildings unless the transformer has Class 155 insulation systems or higher and is completely enclosed except for ventilating openings.

 

[Rockyd]

Does Section 514 do anything for you?

Just because your outside doesn't solve the whole picture. Working oil facilities, we have a lot of outdoor work, and a lot of it is classified spaces. They are built on a lot of worse case scenarios, such as in valves in overhead piping have a classified space at 45 degrees downward from each valve configuration. I would think that an engineer who works for API (American Petroleum Institute) and is an expert in the field, to classify areas may be the call. Plus they would be a big liability relief...

 

[hurk27]

You might want to look at 515.3 and table of the same?

 

[charlie b]

I should clarify that, as I understand the situation (not my project, I am just advising) the fuel oil and "gas" tanks are intended to serve as day tanks for a standby generator, a fire pump, or equipment of similar type. This equipment is part of a rennovation of a small office/training building. This is neither a fuel dispensing facility nor a bulk storage facility, so I don't think 514 or 515 are players. Thanks for the suggestions, however.

 

[hurk27]

Well if there is nothing in the code that keeps a distance between a transformer and a fuel tank, I would resort back to the possible liability issues, we have all heard the statement "That should never have been allowed" after the fact when things go terribly wrong, and we must keep in mind that even if something is not in the code, we could be found liable just on a statement that we should have known better?

We have all seen the recently posted photo's of what can happen with a transformer when things go wrong, but could it in effect cause a rupture to the tank, thats the part I don't know how to address?