Transformer support

[dvcraven052256]

I have attached a photo of a Unistrut support rack that will support a transformer for owner provided equipment. Is this a code violation to mount a transformer over another floor mounted transformer?

I am thinking no if proper ventilation is provided for.

Thank you
Dan Craven

 

[infinity]

No violation although some thought should be given to providing enough air space for proper cooling. You strut system looks fine with the 4 rods you don't even need the wall attachment. I would raise it up a bit because someone might get all nervous and jerky about the air flow.

Another thought regarding the spacing. I've never seen a transformer enclosure that go so hot that you couldn't touch it with your hand so the amount of heat generated by the floor mount should not significantly impact the hanging transformer.

 

[roger]

I agree with Rob, I would want a little more space between lower and upper.

Here are some we did a while back.

 

[dvcraven052256]

Thanks so much. You all always come through with good comments.

 

[Deltaforce]

I am thinking no if proper ventilation is provided for.

Check manufacturer instructions also

 

[Strathead]

I on the other hand think you have plenty of space between them. We usually weld steel racks, but rarely put more space than that between them. Stacking transformers is virtually a must in a hospital where you often have 3 or more transformers per electric room

 

[jim dungar]

Think how much space is below a transformer when it is mounted on the floor, often just 3" or so. Heat is not primarily disappated through the top of the transformer, the top front and rear vents create a chimney effect for venting.

I believe most manufacturers provide more guidance on front and rear clearances then vertical ones.

 

[infinity]

Here's few others:

 

[Deltaforce]

Sorry but white paper Eaton not stacking transformers

https://www.eaton.com/content/dam/eaton/products/low-voltage-power-distribution-controls-systems/transformer/transformer-dry-type-install-best-practices-white-paper-WP009003EN.pdf

 

[don_resqcapt19]

We did one stacked assembly per the engineers design, and the upper transformer failed in less than a year, likely from excessive heat.

 

[jim dungar]

Sorry but white paper Eaton not stacking...

It does not say stacking is prohibited. It says ventilation may be an issue and should typically be avoided. You notice they fail to give any verticle clearance restrictions.
Most of the issues revolve around the total ventilation, ambient temp and airflow, of the room the transformers are mounted in. Stacking transformers often occurs when trying to put 10lbs into a five pound bag, so additional air flow is likely needed.

I have seen sloping dividers installed between stacked transformers to redirect the heated air from the lower unit as well as to prevent/reduce the lower transformer from being used as a shelf.

 

[dvcraven052256]

Last question relative to my transformer install.

I have attached a sketch how I interpret the NEC 2017 for transformer primary and secondary protection scheme. Comments are appreciated.

 

[LarryFine]

I've never seen a transformer enclosure that go so hot that you couldn't touch it with your hand . . .

I have.

 

[augie47]

Last question relative to my transformer install.

I have attached a sketch how I interpret the NEC 2017 for transformer primary and secondary protection scheme. Comments are appreciated.

I believe your primary protection exceeds the 250% max allowed by 450.3B

 

[dvcraven052256]

Is the 25' max look appropriate?

 

[augie47]

Is the 25' max look appropriate?

There is no specific distance on the primary conductors.
The appropriate 240.21(C) transformer secondary conductor rules would apply. Likely the 25 ft secondary rule could be used based on 240.21(C)(3) but you would need to confirm all the stipulations were met.