Pad Mount Transformer

[W@ttson]

Hello All,


I wanted to see if there is anywhere else in the NEC that dictates the space requirements around a big green oil filled pad mount transformer.

110.32 says that the work space should be 36" wide and a depth as outlined in 110.34(A). From this I gather that no clearance is required to the left, right, and back of a pad mounted transformer, at least as per the NEC. Is there anywhere else in the NEC that requires some sort of clearance to the back and sides of pad mounted transformers?

Bonus question:
When are medium voltage transformers such as these:
https://www.hammondpowersolutions.c...ient-medium-voltage-distribution-transformer/

Used instead of big green pad mount transformers? Is it usually because of a utility requirement, or the requirement that the transformer be lockable and isolated from unqualified personnel.

Thanks for any input.

 

[kwired]

Hello All,


I wanted to see if there is anywhere else in the NEC that dictates the space requirements around a big green oil filled pad mount transformer.

110.32 says that the work space should be 36" wide and a depth as outlined in 110.34(A). From this I gather that no clearance is required to the left, right, and back of a pad mounted transformer, at least as per the NEC. Is there anywhere else in the NEC that requires some sort of clearance to the back and sides of pad mounted transformers?

Bonus question:
When are medium voltage transformers such as these:
https://www.hammondpowersolutions.c...ient-medium-voltage-distribution-transformer/

Used instead of big green pad mount transformers? Is it usually because of a utility requirement, or the requirement that the transformer be lockable and isolated from unqualified personnel.

Thanks for any input.

Transformer instructions might have clearance requirements. Depending on design some may have different requirements than others - this be true for liquid filled as well as dry transformers.

2400 and 4160 are at low end of medium voltages. I don't claim to know all about transformer design, but am guessing they are right about on the line of whether it makes more economic sense to build these as dry transformers or oil filled. Most low voltage transformers are dry transformers.

 

[Julius Right]

NEC it is actually NFPA 70 that means they are other NFPA standard stating the distances.
For instance for power station NFPA 850/2010 - 5.1.4 Outdoor Oil-Insulated Transformers
On the other hand, in my opinion, Green Power Transformer liquid it could be considered less flammable liquid [350oC instead of 150 for usually mineral oil].
https://www.gegridsolutions.com/pro...PTR-L3-Green_Transformers-0299-2016_07-EN.pdf
NEC 2017 450.23 Less-Flammable Liquid-Insulated Transformers. or
NFPA 850/2013 5.1.4.7 Outdoor transformers insulated with a less flammable
liquid should be separated from each other and from adjacent
structures that are critical to power generation by firewalls or
spatial separation based on consideration of the factors in
5.1.4.2 and 5.1.4.

 

[JoeStillman]

An outdoor oil-filled transformer will have separate compartments for the primary and secondary. They also come with a lot more options, like primary load-break elbows and bayonet fuses. They provide better isolation from live parts because there are no air vents - just oil-filled steel fins.

If it's a utility co. transformer, the utility will have rules about the clearances. Here in PECO land, the rules they use are requirements of their insurance co. They have a lot to say about distances from windows, doors and combustible construction.

 

[MrJLH]

When you refer to space, do you mean keeping unqualified person away?

 

[paulengr]

FM Global requires 25 feet between transformers if they are mineral oil filled. It drops to zero if they are less flammable fluid. Obviously access matters and although I haven't seen a requirement space between cooling fins is obviously required so it can actually cool.

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