clearance behind ordinary dry type transformers

Status
Not open for further replies.
mshields

mshields

Senior Member
Location
Boston, MA
I'm looking to put a dry transformer in a shallow space. Shallow in the front and to the sides owing to work clearance of other equipment (i.e. not because there isn't ample space in front of those faces. But the rear of the unit will be up against a wall, and I'm trying to find out what the minimum space requirement is.

Let me back up. This would be a 15 to 45kVA, 480delta to 208Y/120V 150 deg rise, ordinary dry type transformer with Al or Copper windings.

Whatever the answer is, I would that it is defined by not the vendor but the standard it's built too. Then again, maybe you can build it different ways within the parameters of the standard and have different requirements. I don't know.

Square D says 3 inches (music to my ears). MGM says 6 inches or at least their rep does - I've asked him to check.

What do you think?

Thanks,

Mike
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I have a copy of UL 5085 for dry type transformers, here's the only thing I see:
6.4 Mounting
6.4.1 A transformer shall be provided with a secure mounting means. It shall be constructed so that there
will be a spacing through air of not less than 6.4 mm (0.25 in) between the supporting surface and the
enclosure when the device is mounted on a plane surface.
Click to expand...

But it has everything to do with their convection air flow and heat rise testing to UL standards. So if Sq. D tested theirs at 3" to a wall and passed the heat rise test, it's good. If MGM tested at 6" and passed, it has to be 6". They MIGHT have passed at 3" but didn't test to that distance, or they may have tested at 3", 4" and 5" but failed, so 6" was the minimum where it passed. You may never know.

I never did heat rise testing on transformers, but I did on drives. We always tested with the back right up against a wall, no clearance at all. Usually there is SOME small gap, in which case so much the better; we just tested to the worst case scenario. But we also had to test vertical clearances to obstructions, and that's where we often had to test multiple times to get a real value. So when we said "Minimum 4" of clear space above", we had tested it at 3-1/2" and failed the heat rise test... That's usually how it ends up.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
To look at it exactly the same thing from a different perspective:

The UL standard quoted by jraef refers to the construction of the transformer and its mounting brackets. It has nothing to do with how you yourself mount it relative to the wall(s).
But the thermal performance requirements for spacing distance will not be found in any standard, since it depends on how the manufacturer builds and tests a particular product.
So you will not find an general rule that applies to all transformers. Instead you have to obtain and follow the manufacturer's installation instructions.

If you are trying to design an installation without knowing yet exactly what transformer will be used, you would have to look at a variety of products and design for the worst case among them. :)
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
We use mostly Eaton transformers and from the few nameplates that I've looked at the minimum distance from the vented sides is 6".
 
steve66

steve66

Senior Member
Location
Illinois
Occupation
Engineer
It seems like the manufacturers are very bad at providing this info. on cut sheets and such.

It might be listed on shop drawings, but I can't usually find it in the standard catalogs and cutsheets or on the typical dimensional drawings.
 
I

Ingenieur

Senior Member
Location
Earth
this says 6"
but you need to look at instructions for the specific unit

http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/ilp24836591h.pdf

https://docs.natlswgr.com/docs/W1000053.pdf[FONT=Arial,Bold][FONT=Arial,Bold]
VENTILATION[/FONT][/FONT][FONT=Arial,Bold][FONT=Arial,Bold][/FONT][/FONT]For adequate cooling the unit should be installed at least six
inches (152 mm) and preferably a foot (305 mm) or more away
from walls and other obstructions which might prevent free
circulation of air through and around the unit. Mechanical
clearances should be taken into consideration in installing the
transformer. Sufficient room should be allowed for removal of
panels for cleaning and, with reverse arrangement of units, for
changing of taps.
 
J

jrohe

Senior Member
Location
Omaha, NE
Occupation
Professional Engineer
mshields said:
I'm looking to put a dry transformer in a shallow space. Shallow in the front and to the sides owing to work clearance of other equipment (i.e. not because there isn't ample space in front of those faces. But the rear of the unit will be up against a wall, and I'm trying to find out what the minimum space requirement is.

Let me back up. This would be a 15 to 45kVA, 480delta to 208Y/120V 150 deg rise, ordinary dry type transformer with Al or Copper windings.

Whatever the answer is, I would that it is defined by not the vendor but the standard it's built too. Then again, maybe you can build it different ways within the parameters of the standard and have different requirements. I don't know.

Square D says 3 inches (music to my ears). MGM says 6 inches or at least their rep does - I've asked him to check.

What do you think?

Thanks,

Mike
Click to expand...

The new Square D EX-series transformers only require 1/2" of clearance on the back and sides.

http://download.schneider-electric....File_Id=4283003987&p_File_Name=7400CT1501.pdf
 
steve66

steve66

Senior Member
Location
Illinois
Occupation
Engineer
GoldDigger said:
I love that there is an RU label on the guts of the transformer so you if you are a manufacturer/fabricator you can throw away the enclosure and just mount the guts in your own configuration.
Click to expand...

Yea, they probably charge extra if you just want the guts without the enclosure :)

Like buying a panel just to get one breaker.....
 
Status
Not open for further replies.
Top