minimum working space

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unionman

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In the 2008 handbook it states minimum working clearances are not required if the equipment is such that it is not likely to require examination, adjustment,servicing,or maintenance while energized. Could anyone elaborate on this subject?
 
I haven't seen it, but that's always been my take on things like AC disconnects. Do we work them hot? Yes, usually. Do we have to? Nope there's a breaker to turn off the power to them.
 
110.26 clearly states that working clearance is required for equipment that is likely to require work while it is energized. It is no great leap of logic to state that if live work is unlikely, then working clearance is not required. This is nothing new. Naturally, it is wide open to interpretation as to what is meant by "likely."
 
charlie b said:
110.26 clearly states that working clearance is required for equipment that is likely to require work while it is energized. It is no great leap of logic to state that if live work is unlikely, then working clearance is not required. This is nothing new. Naturally, it is wide open to interpretation as to what is meant by "likely."

Gets even more interesting when OSHA chimes in

1910.333(a)(1) "Deenergized parts." Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations. Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs.

If I were to use this as a guideline , there is almost nothing that requires me to work live as a mostly residential guy
 
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Experience has shown that, for most types of electrical equipment, there will likely be a time when the cover will be off, or the door will be open, while it is energized. This applies to CB panels, distribution boards, M-V switchgear, dry-type transformers, disconnect switches, terminal boxes, junction boxes, VFD's, UPS's, PFC's, ........

This is especially the case when a problem of some sort has been discovered, after the equipment has gone into operation. Covers start coming off of lots of equipment, trying to isolate the problem. Covers are also often removed, and doors opened, on energized equipment to perform infrared testing - which is often included in start-up specs and preventive maintenance procedures.

Since a designer, engineer, or installer usually has little or no control over an installation after a project is completed, it is safer to design and install with the understanding that the equipment will LIKELY undergo "examination, adjustment, servicing, or maintenance while energized", at some point in its life. Thus, adequate working space about the equipment should be provided in accordance with the NEC.
 
rwilsond,

I disagree with you regarding the dry type transformers. These are static devices that do not typically require service or adjustment while energized.
 
In my designs for electric room floor plans, I typically do not allow for the 110.26 working clearance for dry-type transformers. I just make sure a person can walk around them, and that there is some room for natural ventilation.
 
Agreed, it is unlikely that a dry-type transformer would "require service or adjustment while energized". But it IS likely that it would be "EXAMINED" while energized.

As one example (of many) is the attached photo of a lighting transformer. It experienced overheating (on one winding) soon after it was put into operation. The electrician removed the cover to it, as well as the covers of the upstream distribution board and the downstream panelboard, while all were still energized, so that voltage and current readings could be taken throughout to better understand the problem (and to maintain illumination in that part of the facility). This transformer was also "examined" - while energized - by many people that had an interest in it for one reason or another. Fortunately, the design required that the installation be provided with 42 inches in front of it (i.e., more than just enough space to squeeze by it, and the 6 inches of ventillation space required by the manufacturer).
 
Clearance For Disconnect

Clearance For Disconnect

After Reading Many Responses It Seems Clear That This A Gray Area At Best. Leaving It Up To The Inspector To Decide After The Fact. Time For The Nec Boys To Clear It Up So We Can All Be In Agreement
 
M. D. said:
Gets even more interesting when OSHA chimes in


If I were to use this as a guideline , there is almost nothing that requires me to work live as a mostly residential guy

Troubleshooting is live work and OSHA does permit that type of live work assuming the correct PPE.
 
don_resqcapt19 said:
Troubleshooting is live work and OSHA does permit that type of live work assuming the correct PPE.

not always live ,..in fact not even all that often...
 
leaving it up to the inspector can cause its own set of problems. We recently had an inspector who wants to measure from the end of the knob on a bucket switch (3" out from what I would call "the enclosure"), to a trough on the other side of the room ( 2" in front of the panels on that side - we could not envision the trough ever needing servicing while energized (all fused wire). So we failed by 5". Its not his fault, but its just another lesson in how the code can mean different things to different people.
 
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