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#71491 - 10/31/06 06:59 AM Dry type transformer locations  
poorboy  Offline
Member
Joined: Jun 2005
Posts: 124
Central Maine
What guidelines do engineers use to determine if a xfomer will be hung above the ceiling or floor mounted? Do any code issues dictate this? Small offices in retail stores or schools often end up with a floor mounted "heated table" (as I call them)and are very hot and noisy rooms as a result. The old answer (teach it the words) to the often asked question "How can I get that thing to stop humming?" is not well recieved.


Work Gear for Electricians and the Trades

#71492 - 10/31/06 10:22 AM Re: Dry type transformer locations  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
There are really no code references, thought NECA standards do describe preferred practices.

In the air or on the floor? How much can you lift?

The transformer itself need not be readily accessible; having to use a ladder is acceptable. The disconnect- that's a different matter.

The 'hum' is part physics, part design, part installation, and part age.

The electrical forces involved both make the transformer go 'thunk' when you power it up, and create internal vibration that get made into that 'hum.'

Many transformers are now designed with the internal parts 'floating' on cushioned mounts, as well as other components designed to reduce the hum that you hear.

When you instal the transformer, you can reduce the amount of hum that you hear by:
-Mounting on rubber foot pads;
-Making final cttachemnts through lengths of flex, rather than rigid pipe;
-Cushioning adjacent surfaces; and,
-Not installing in corners, or other places that will tend to focus, or amplify, the sound.


#71493 - 10/31/06 10:34 AM Re: Dry type transformer locations  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
Dry transformers larger than 45 kva cannot be mounted above a drop ceiling. Stay tuned for an actual code reference in about 6-10 minutes


#71494 - 10/31/06 10:46 AM Re: Dry type transformer locations  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Quite right, Mike! I got "up in the air" in my mind.. the guy did ask "above the ceiling!"

OOPS [Linked Image]


#71495 - 10/31/06 10:51 AM Re: Dry type transformer locations  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
Its 450.13 (B) and its 50 kva, my mistake not 45. My mind plays tricks with me sometimes. I don't install many 50 kva transformers, lots of 45 kva transformers and therefore I mentally moved the 50 to 45 kva.


#71496 - 11/01/06 07:58 AM Re: Dry type transformer locations  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,208
Chesapeake, VA
macmikeman, when you start talking close 50kVA, that's going to be dumping a significant heat load into the cavity and you have to start worrying about ventilation, too. A drop ceiling tends to trap hot air, so it's a little more difficult than just putting a few grilles in.

poorboy: to answer your question, as an engineer, there is very little difference between wall-mount, floor-mount or ceiling-mount. It depends on the size (if it's large, it's WAY easier to install on the ground), but moreso the cable routing and other practical reasons that factor more into the cost of the job than anything else. As transformers generate a lot of heat load, we usually like to place them in ventilated spaces vs air conditioned spaces so as to avoid the A/C costs.

And yes, everyone hates the hum- there are numerous reasons not to install transformers in office spaces. If the transformer was put there, it was probably just to shave a couple bucks.

[This message has been edited by SteveFehr (edited 11-01-2006).]


#71497 - 11/03/06 12:32 AM Re: Dry type transformer locations  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
The only time I specify to have a Transformer mounted on some shelf, or the dreaded "Suspended Above A Ceiling" is due to the Client's request.

For example, if the Forklift Operators have a really bad case of Tunnel Vision (they only see what's directly in front of them, within a 3 foot square window, which is no less than 6 feet above the floor), placing a Transformer on a wall mounted shelf - Which Has Been Designed Properly By A Structural Engineer, is done to eliminate frequent Transformer replacement.

The alternative would involve protecting the Transformer with an array of Bollards (and the Bollards having a very high testosterone level...D-Ohh...)

This would be something discussed during preliminary meetings.

Hanging Transformers above Ceilings would also be (to me) a Design Issue, mentioned to the Client during meetings, or by the Client during same meetings.

I tend to try and find better locations to place Transformers, where they might have issues - especially when it comes to hanging them above Ceilings, but sometimes things just don't workout that way and the Transformer needs to be "Floated" out of harms way.

Being that my Designs are the first half of a complete project (Design/Build), I know that sometime soon I will be hanging and hooking up that Transformer - so reluctance to place it anywhere but on the finished floor begins from that understanding!

Nevertheless, having this "Default Thought Process" of placing heavy Transformers on the floor would trickle over to any design ideal, if I ever do go out and design stuff for others to install.

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#71498 - 11/03/06 05:47 AM Re: Dry type transformer locations  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Most of our engineered jobs show us hanging transformers in electric rooms to save floor space or another way is having them stacked.

It's a lot of fun hanging a 1,200 Lb transformer. [Linked Image]

Most are in the 600 lb range.

The specs will usually show vibration isolators installed in the threaded rod supports with additional isolators under the feet of the transformers.

This weekend I will be in an electric room with so many ceiling hung transformers that the lighting is suspended from the bottom of the transfomers...I will try to get some pics.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#71499 - 11/03/06 11:21 PM Re: Dry type transformer locations  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Quote
This weekend I will be in an electric room with so many ceiling hung transformers that the lighting is suspended from the bottom of the transfomers...


I'd love to be in there during an earthquake...NOT!!!


Stupid should be painful.

#71500 - 11/04/06 12:27 AM Re: Dry type transformer locations  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
I was just going to get to that earthquake issue and I see Mxslick's post... Anyway to the best of my current knowledge, none of the many I have hung up in ceilings came down during the recent very discernable earthquake we had. I have done some in Kona too, by the way on the Big Island and it got jolted really good. I like using long struts suspended across the top of two structural beams with hanging rods down to the struts supporting my xfmrs. Beam Clamps just seem to me to be less secure.


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