Working Space around transformers

[steve66]

Does the working space in Article 110.26 apply to transformers? Would a 480V panelboard across the isle from a 480 to 208 transformer require 4' between them? Also, do the working space requirements apply to the sides of the transformer? If not, how much space would required on the sides to run conduit in and pull wire (aren't transformers usually fed with a LB into to side?) I am laying out an electrical room, but I'm not an electrician, and I'm not sure how the connections to transformers are usually made.

Finally, can the transformer be backed right up aginst a wall, or does it need breathing room behind it?

 

[ron]

Re: Working Space around transformers

6" all around for ventilation. Generally only front access needed for xfmr.

 

[bennie]

Re: Working Space around transformers

The only working space required is 110.26. The dimensions in Table 110.26(A)(1), do not apply.

For clearance of a ventilated dry transformer, refer to manufacturers specs. Generally, space on the sides and back is not required. The enclosure should not touch the walls. Vibration noise can be commuted to the structure.

 

[ron]

Re: Working Space around transformers

bennie,
Why doesn't the Table 110.26(A)(1) apply?

 

[dcsva@aol.com]

Re: Working Space around transformers

Bennie,
Why does the table not apply?

 

[bennie]

Re: Working Space around transformers

Because a transformer does not require working while energized.

 

[dcsva@aol.com]

Re: Working Space around transformers

Bennie, I know that you have a whole lot more experience than me.
But in my opinion, a "Floor Mount" transformer is "Likely to require examination" while energized and thus the table would apply.

[ July 25, 2003, 03:38 PM: Message edited by: dcsva@aol.com ]

 

[jim dungar]

Re: Working Space around transformers

Almost all ventilated dry-type "floor" mount transformers require rear air flow spacing. In some cases it is as little as three inches, however you can never go wrong with 6" of space.

 

[gregoryelectricinc]

Re: Working Space around transformers

I would consider a tranformer "likely to require examination while energized" also.

 

[charlie b]

Re: Working Space around transformers

Originally posted by dcsva@aol.com:But in my opinion, a "Floor Mount" transformer is "Likely to require examination" while energized and thus the table would apply.

The key word here is ?likely.? And that word is very very subject to individual interpretation. I suspect that the only interpretation that matters comes from the AHJ. My own opinion on the topic is the same as Bennie?s: a transformer should not require live work. But as a Design Engineer, I always lay out a room to allow the 110.26 clearance in at least one direction from a transformer. Whether or not the device will ever be worked upon while energized, someone is going to have to work on it sooner or later. If that someone is to be denied sufficient room to maneuver, it will not be with my blessing.

 

[dcsva@aol.com]

Re: Working Space around transformers

Charlie b,
I agree from the design engineer stand point. But, I have examined transformers while hot.
That word "Likely" is very open to interpretation.

[ July 25, 2003, 03:59 PM: Message edited by: dcsva@aol.com ]

 

[bennie]

Re: Working Space around transformers

Please give me a valid situation where you must examine a transformer, without shutting it down?

If it is smoking...Shut it down.

If it is dancing all over...Shut it down.

If the paint is turning brown...Shut it down.

If sparks are flying...Shut it down.

There is no logical reason to remove the front cover while the power is on.

 

[iwire]

Re: Working Space around transformers

Thermal imaging, my coworkers who do that for the company will shut it down when removing the cover and turn it back on to take readings.

 

[bennie]

Re: Working Space around transformers

The key phrase is "likely to require'.

The word "require" is to demand as necessary.

Likely to "demand as necessary" working while energized. I don't think so.

 

[bennie]

Re: Working Space around transformers

Thermal imaging does not require physical contact. One foot clearance will permit it to be done.

Sola transformer company has transformers with only two cover screws, for the purpose of removal in constricted areas.

[ July 25, 2003, 04:15 PM: Message edited by: bennie ]

 

[steve66]

Re: Working Space around transformers

Thanks for all the feedback. I've got enough space, so I'll leave 4' in front of the transformer, and 6" around it.

 

[iwire]

Re: Working Space around transformers

Sure they can squeeze in there between a live parts and whatever, but why should they have to?

When in doubt I would talk to the local guy to see what he wants.

In an electric room we always leave the clearance, but I will be honest that in some ceilings we end up with less space, not logical, just how it goes.

 

[bennie]

Re: Working Space around transformers

A ventilated dry type transformer is cooled by the "chimney effect". The sides and back are completely enclosed. There is no need for side and rear clearance.

Also many of the new transformers do not require a vibration isolator pad, on the floor. The pads actually make them louder.

 

[brian john]

Re: Working Space around transformers

Iwire:

One thing that never ceases to amaze me is how little room Architechts/enginers give contractors for electric rooms, both main and distribution electric rooms. I realize the cost constraints; these individuals contend with, but sometime it looks like the 10lbs of stuff in the 5 lb box. Sometimes wonder how the contractor's meet the space requirements of the NEC, much less any future expansion.

We also do IR scanning and in every quote (for jobs where we pull covers) we have a statement regarding transformer covers, will only be removed these covers if our tech feels it is safe (not the exact wording but you get the idea).

 

[gregoryelectricinc]

Re: Working Space around transformers

Bennie. I remember a service call several years ago that went like this: 1)Employee reprted being shocked while vacuuming. 2) I arrived onsite and investigated possible causes, I found that the recept. used for vacuuming had a broken faceplate. I turned off the circuit and replaced the receptacle. While changing out the recept. I was jolted pretty good by the neutral wire. This was a pigtailed outlet box so this didn't add up to anything good for me. I opened the electrical panel and took voltage readings, found 120 volts Neutral to ground. Next I opened up the transformer (wile energized), to look at connections there since I found nothing wrong w/ wiring in the panel. I did this in an energized state because this was a large retail store full of customers and to de-energize was not a very good option. In the trans,. I found the bonding jumper from XO to frame of trans. missing. The bldg. steel GEC was connected to the frame of the trans. instead of directly to XO. Now that I'd located the problem and had the needed materials onhand to repair this dangerous situation, I had the manager clear the store (for security purposes they said :~) and shut down the trans and made repairs. The reason the store employee was getting shocked while vacuuming..... turns out she was touching the metal "shelf" standards on exterior walls. These are screwed into the metal framing members which are attached to, you guessed it, building steel.