110.26 space about electrical equipment

[Tfret]

I work in a large factory that has hundreds of control panels to factory machinery on the factory floor. We are auditing our installations for the 3.5' clearance rule of table 110.26A1. The question has been brought up, does this clearance apply to power disconnect switches, operator interface panels, and junction boxes? I don't see it clearly spelled out in the book, but I can see where it would apply to the disconnects since that's a power feeding service with servicable fuses inside that must be accessed. Operator interfaces and junction boxes seldom contain over 110 volts but are sometimes entered while hot in order to trouble shoot machine problems. Are these areas also covered under this 3.5' rule?

 

[augie47]

You pretty much answered your own question The key wording "likely to require examination, adjustment, servicing or maintenance while energized"
There is often some debate on that wording... even here... but I think that's the key as you look at each piece of equipment.
Do note in 110.26 the distances vary with voltages and situations.

 

[wallypiper]

Most of the plants we work in are adopting arc flash rules that are making the distinction nearly obsolete if you you work by the rules. Most panels with 480 in them simply cannot be opened while energized by rule, even for troubleshooting. In some plant's it's allowed if you don appropriate arc flash PPE, but that makes troubleshooting extremely difficult in many cases. Poking around with a meter trying to figure out why a relay isn't energizing while wearing a face shield and heavy gloves is, in my opinion, more dangerous than doing it carefully and thoughtfully without the restrictive gear on. But that's another discussion.

The rules in many cases make it impossible, if you follow the rules, to "examine, adjust, service or maintain" anything inside the panel while it's energized. The variation in the implentation and enforcement of the rules is great at least partially due to variation in the hazard that is calculated for the panel. One customer has made Hoffman Sequestr disconnects a universal requirement for new panels in their plants. If you haven't seen one, it puts the main disconnect for a panel in a separate enclosure so that the line side feeder to the disconnect is not in the main enclosure, thus eliminating the arc flash hazard from the feeder which remains hot even though the disconnect is off. Interestingly, you CAN turn the main disconnect on while the control panel doors are open as long as the main disconnect door is closed, creating many arc flash hazards in the main enclosure. That customer is not particularly strict about not working in an energized panel at least during the time I'm on site while new equipment is being commissioned and lots of "hot" troubleshooting is traditionally done.

 

[George Stolz]

The rules in many cases make it impossible, if you follow the rules, to "examine, adjust, service or maintain" anything inside the panel while it's energized.

I look forward to the day when 110.26 has no meaning at all, because no equipment meets the criteria.

As for "careful troubleshooting without gear", I would be concerned in your environment about a transient blowing a meter in my hand and creating an arc blast through no fault of your own too. Better to be suited up than crispy.

 

[wallypiper]

Better to be suited up than crispy.

No doubt. But some possibilities seem so remote that allowing for them really seems overkill.
Most troubleshooting involves probing 120v or 24v control circuits. Anything is possible I suppose. It is occasionally necessary to probe 480v lines, if a motor hums but doesn't spin for example, and that obviously carries more risk than control voltage. Understanding the circuit you're testing helps a lot. I had a report from a customer that a VFD wouldn't accelerate to full speed. I asked them to make sure that all three phases had power at the input. They had an electrical contractor who was on site check and he said they did. Out of long distance ideas, I eventually traveled to the site and found that one of the input fuses was blown. I don't know where the contractor checked that led him to conclude that there was power on all three phases but he obviously didn't understand where power should be and should not be present. I put in a new set of fuses and the drive has operated normally ever since (several years).

I did that, by the way, while the motor continued to run via a bypass contactor. Our panels are specifically designed to allow that but it does mean working in an energized panel. But knowing which disconnect to open and which contactors should be and are on or off allows you to safely do this. But even though I know the circuit design, I check the input and output side of the fuses before removing them or installing new ones, since anything is possible.

A very infamous arc flash event in Atlanta, where I'm based, is always in the back of my mind. Here's a link: http://www.interfire.org/res_file/pdf/Tr-033.pdf

 

[Sandman1110]

Arc flash and arc blast have really become priority issues with organizations like OSHA. According to them, approximately 80% of electrically related accidents and fatalities involving "qualified" workers are caused by arc flash/blast. The National Safety Council reckons that work related electrical injuries can cost businesses up to $30 million in fines, litigation, medical costs, lost business, and equipment costs. Arc flash studies and safety are becoming more attractive for companies to implement to save money, lost time, and personnel, so it's going to become more and more prevalent as time goes on. and rightly so. Anyway, off the soapbox, I have gone by criteria, if it's operable or has some sort or sorts of components inside, clearances apply, if not and are just wire splices or wires in a J-box, clearances do not apply.