stacked or suspended transformers

[anbm]

Are there any restrictions from NEC that we need to watch out when suspended or stack transformers? (Inside and not inside elec. room, 480V Pri - 208/120V sec, 75kVA or less xfmr)

 

[infinity]

I know of no restrictions and have done this in the past when space was at a premium. Just be mindful of the spacing issues around the transformer as outlined in 450.9. Above a hung ceiling your limited to a maximum size of 50 Kva.

450.9 Ventilation.
The ventilation shall be adequate to dispose of the transformer full-load losses without creating a temperature rise that is in excess of the transformer rating.
FPN No. 1: See ANSI/IEEE C57.12.00-1993, General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers, and ANSI/IEEE C57.12.01-1989, General Requirements for Dry-Type Distribution and Power Transformers.
FPN No. 2: Additional losses may occur in some transformers where nonsinusoidal currents are present, resulting in increased heat in the transformer above its rating. See ANSI/IEEE C57.110-1993, Recommended Practice for Establishing Transformer Capability When Supplying Nonsinusoidal Load Currents, where transformers are utilized with nonlinear loads.
Transformers with ventilating openings shall be installed so that the ventilating openings are not blocked by walls or other obstructions. The required clearances shall be clearly marked on the transformer.

 

[jwr570]

You may cook the top transformer, if there is not ventilation in the room. All the heat from the bottom transfromer will go up. I have done it in an small electric room with air conditioning.

 

[BJ Conner]

Seismic Areas

Seismic Areas

The UBC and the IBC have sections that will tell you what Seismic zone your in.
I couldn't get away with suspending 75 KVA trasnformers with all thread. Our choice was put them on the floor ( manufactures seismic ratings are based on floor installation ) or hire a structural engineer to design a seismically rated hanger structure.

 

[hillbilly1]

Keep in mind the structural load limitations of what you are hanging it from too.

 

[ohmhead]

Our company has been ordering from Square d transformer racks factory made it saves time and labor and its engineered for you .

 

[hurk27]

Keep in mind the structural load limitations of what you are hanging it from too.

That brings to mind a fiasco of an electrical contractor who was installing a new substation and buss work to MDP's located through out a plant I worked for back in the 70's (yes the same fiber plant mention in another thread)

Anyways, they were up on scissor lifts installing a 150 kva 480 to 208/120 transformer on a rack they suspended from perlings on the roof, the used 3/8" beam clamps and 3/8" all-thread, instead of instead of using the equipment in the drawings, they slid the transformer off the fork lift on to the rack and it held for just long enough for the fork lift to lower its forks and drive away, the beam clamps slowly opened and down it came, bouncing off a girder and right into the scissor lift knocking it over into a 4ka 480 volt buss duct, lucky it also stopped the men working in the lift from falling, but sparks went flying, and the whole plant went dead, production came to a halt for 4 days while they repaired the damage, the buss and the scissor lift was damaged and had to be replaced with another rental unit, transformer was toast. after looking at the engineering specs we saw that they were supposed to be using case harden 1/2" all-thread, and a special bolt on clamp to the main beams the perlings went to, these clamps had a small beam that ran between the main building beams that the all thread was to hang from, this cheating cost this contractor dearly, and could have got a couple of guys killed.

Our plant engineer could not believe they even tried to use soft malleable beam clamps for that heavy of a transformer