Working Space Clearance Purpose

[Redskinsdb21]

What is purpose of working space requirements in NEC? Is it basically a safety zone provided when working on a panel when doors are open (energized)?

What about in case of working on either primary side or secondary side of a Xfmr? Is it required on each side for same reasons?

THanks for any input!

 

[Gr8blu]

"Working Space" requirements are there for two reasons.

First - to provide enough space for the worker to actually access the equipment (without undue contortions, in a safe manner).
Second - to provide sufficient arc distance between an exposed live conductor (e.g., the door is open) and the nearest ground plane or another conductor, when measured in a straight line.

Space requirements exist for frontal (where access occurs), overhead (above the equipment), rear (behind equipment) and side (to next equipment). In the case of transformers and some other equipment (like motors), there may also be a limitation to allow proper external coolant circulation. The requirements (actual distance) can vary depending on which direction we're looking at and whether the nearest surface is grounded or another live conductor.

Converting energy to motion for more than half a century

 

[crshears]

Adding to gr8blu's post: the Utility Work Protection Code and other documentation as used by Hydro One and numerous other utilities specifies that working clearance shall provide sufficient distance "for both planned and unplanned movement of personnel, tools and equipment," in other words not to rely on a worker's ability to avoid unthinkingly extending something conductive to within the limits of approach of energized equipment.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[resqcapt19]

What about in case of working on either primary side or secondary side of a Xfmr? Is it required on each side for same reasons?

This is always a question on the electrical code forums and some AHJs do not require 110.26(A)work space because they believe it is not likely that the energized parts of the transformer will be examined or worked on while energized.
However this is a bit flawed as you have to verify that the transformer is actually de-energized before working on it and the very act of that verification is "examining". Examination is one of the things that triggers the application of the 110.26(A), or 110.34(A) work spaces.

110.26(A) Working Space.
Working space for equipment operating at 1000 volts, nominal, or less to ground and likely to require examination, adjustment, servicing, or maintenance while energized shall comply with the dimensions of 110.26(A)(1), (A)(2), (A)(3), and (A)(4) or as required or permitted elsewhere in this Code.

It is my opinion that unless there is a built-in listed voltage verification system, the transformer requires working space.

 

[jraef]

Yes, but what about trapeze mounted transformers? (Clearance above?) Or vaults? (Below?).

In my experience, transformer clearances are one of the most often overlooked issues. I’m not saying it’s right, I’m just pointing out that people tend to shove transformers as an afterthought into spots that they probably shouldn’t, then inspectors often let it slide.




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