T110.26

[Isaiah]

They’ve installed a 480V MCC directly across from a lineup of 480V VFD’s. The MCC is a live front but I’m not sure about the VFDs...does this constitute a live from to live front scenario (condition 3) or is it live front to grounded surface (condition 2)?


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[tortuga]

What do you mean by live front?

 

[kwired]

Not certain on live front either, wouldn't be pretty uncommon to not have dead covers on each unit in a typical MCC of 600V and less, and likely even on many over 600 volts.

If VFD's are in metal enclosures, they will almost always be grounded surfaces. Some smaller drives however are housed in non metallic enclosures though the back wall is often an aluminum heat sink.

 

[tortuga]

Live front makes me think of this photo don posted of his home service awhile back:
https://forums.mikeholt.com/threads/confused-about-the-term-exposed-live-part.2561258/#post-2672636

 

[Isaiah]

Not certain on live front either, wouldn't be pretty uncommon to not have dead covers on each unit in a typical MCC of 600V and less, and likely even on many over 600 volts.

If VFD's are in metal enclosures, they will almost always be grounded surfaces. Some smaller drives however are housed in non metallic enclosures though the back wall is often an aluminum heat sink.

Live front meaning the front of the panelboard, switchgear, switchboard or MCC. The measurement is taken from the closed door or bucket, not the devices within the equipment
I also believe the VFDs represent a grounded surface.


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[kwired]

Live front meaning the front of the panelboard, switchgear, switchboard or MCC. The measurement is taken from the closed door or bucket, not the devices within the equipment
I also believe the VFDs represent a grounded surface.


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OK. That is where you are supposed to measure from for 110.26 clearances.

"Live front" throwing some of us off, as it generally would be something like tortuga posted a link to. Most all modern equipment is "dead front" equipment as long as doors and access panels are in place. Anything that isn't dead front is probably still within some other barrier to keep non qualified away from it.

 

[tortuga]

If the two 480V systems across from eachother are related and if they could require examination of live parts while energized then i say its condition 3.

 

[Isaiah]

If the two 480V systems across from eachother are related and if they could require examination of live parts while energized then i say its condition 3.

I tend to agree - but it doesn’t list VFDs. It only applies to switchboards switchgear MCCs and Panelboards


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[don_resqcapt19]

I tend to agree - but it doesn’t list VFDs. It only applies to switchboards switchgear MCCs and Panelboards


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The only part of 110.26 that lists specific equipment is 110.26(E) for dedicated equipment. This question is about work space in 110.26(A) and applies to all electrical equipment.

 

[Isaiah]

The only part of 110.26 that lists specific equipment is 110.26(E) for dedicated equipment. This question is about work space in 110.26(A) and applies to all electrical equipment.

After careful review of 110.26, I have concluded you are correct. Thanks for the feedback!


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[kwired]

After careful review of 110.26, I have concluded you are correct. Thanks for the feedback!


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and if you want to review art 100 carefully, equipment is a pretty general term though it is in art 100. If you want to take it literally it includes things like couplings in raceways as well, but a key phrase in 110.26 is "likely to require examination, adjustment, servicing or maintenance while energized". But even that seems to be subjective. Isn't taking a voltage or current reading examination or servicing, you can perform that task in a junction box or other locations that often does not have 110.26 clearance nor does most AHJ's require said clearance for much of anything beyond switchboards, panelboards, MCC's and similar items.