Floor Mounted XFRMRS

[iwire]

But what about it having to be readily accesible for inspection...no ladders etc.?

It does not have to be, please see what I have highlighted.

450.13 Accessibility. All transformers and transformer vaults shall be readily accessible to qualified personnel for inspection and maintenance or shall meet the requirements of 450.13(A) or 450.13(B).

(A) Open Installations. Dry-type transformers 600 volts, nominal, or less, located in the open on walls, columns, or structures, shall not be required to be readily accessible.

(B) Hollow Space Installations. Dry-type transformers 600 volts, nominal, or less and not exceeding 50 kVA shall be permitted in hollow spaces of buildings not permanently closed in by structure, provided they meet the ventilation requirements of 450.9 and separation from combustible ma-terials requirements of 450.21(A). Transformers so installed shall not be required to be readily accessible.

Notice it is readily accessible OR the others, IMO hanging from the ceiling is an open installation.

 

[Haji]

The only issue as they get larger is the weight

Not only that. During a fault, the transformer can send down hot discharges and you wouldn't like to be below it. A catcher plate is needed for such installations.

 

[kingpb]

Better be careful stacking them as the heat from the one below will cause the temp to rise in the one above it.

Just say'in.

 

[iwire]

Not only that. During a fault, the transformer can send down hot discharges and you wouldn't like to be below it. A catcher plate is needed for such installations.

It might be a nice idea but it is not a requirement.

 

[GoldDigger]

It does not have to be, please see what I have highlighted.

on walls, columns, or structures,

Notice it is readily accessible OR the others, IMO hanging from the ceiling is an open installation.

Hanging from the ceiling is definitely open. My concern is that it is not mounted on a wall or floor or column, and if you count the ceiling as a structure it is still mounted under it not on it.

If the language said "attached to" instead of "mounted on" I would not have any objection.

 

[iwire]

Hanging from the ceiling is definitely open. My concern is that it is not mounted on a wall or floor or column, and if you count the ceiling as a structure it is still mounted under it not on it.

If the language said "attached to" instead of "mounted on" I would not have any objection.

Or structures.

A unistrut trapeze is a structure.

 

[GoldDigger]

Or structures.

A unistrut trapeze is a structure.

An interesting idea. Is is then a separate structure from the rest of the building? Does it need its own GEC and ground electrode? Of course it is not a detached structure.

I would be interested in seeing the reasoning of the CMPs working with this section over the years.

PS: I seem to recall a thread here about accessibility requirements for cable-trapeze-hung transformers floating just above floor level, but I am having a problem finding it.

 

[infinity]

I see nothing wrong with hanging or stacking.

 

[iwire]

I see nothing wrong with hanging or stacking.

And neither do inspectors in MA, RI and CT.

I think we hang more from the deck than sit on the floor. No owners want to give up usable floor space for a transformer.

 

[GoldDigger]

I see nothing wrong with hanging or stacking.

I don't either, mechanically or electrically. I just do not see that it necessarily complies with the conditions for exemption under 450.13(A).

When we see arguments that a disconnect behind a screw-fastened panel is not readily accessible, I find that transformer location to be a stretch too.

If it were mounted on a wall, even at the same height, you could get at it via an extension ladder. When it hangs from the middle of the ceiling, you need to bring in a lift or scaffolding. The first case is an arguably reasonable relaxation of the readily accessible rule. The second is enough different quantitatively to approach a qualitative difference.

I am wondering just how an inspector would check the rating of the transformer after installation, for example.
We have an electrician's take on the subject. Would any inspectors care to weigh in?

 

[kwired]

I don't either, mechanically or electrically. I just do not see that it necessarily complies with the conditions for exemption under 450.13(A).

When we see arguments that a disconnect behind a screw-fastened panel is not readily accessible, I find that transformer location to be a stretch too.

If it were mounted on a wall, even at the same height, you could get at it via an extension ladder. When it hangs from the middle of the ceiling, you need to bring in a lift or scaffolding. The first case is an arguably reasonable relaxation of the readily accessible rule. The second is enough different quantitatively to approach a qualitative difference.

I am wondering just how an inspector would check the rating of the transformer after installation, for example.
We have an electrician's take on the subject. Would any inspectors care to weigh in?

How does an inspector check for anything on other equipment that is not readily accessible? When items are required to be readily accessible it is not to make the inspectors job easier, it is generally because the item normally needs to be accessed in some way during normal use. Once a dry type transformer is installed, how often does it ever need any access? Luminaires often need fairly frequent lamp or ballast changes, but very few are really readily accessible.

 

[kingpb]

All else aside code wise, I hope a structural engineer has provided input on hanging and stacking. That is a lot of weight, lbs/sqft and the infrastructure needs to be able to handle the weight, as well as the unistrut parts and pieces.