Picture yourself standing in the electrical room of your employer's facility. In front of you are two 600-volt switchgear lineups positioned side by side. The manufacturer, type, bus rating, available fault current, arc flash incident energy levels and just about anything else you can think of are all identical. All except one thing... one switchgear lineup has hinged doors and the other has bolted covers. If you wanted to take a peek inside the equipment (a peek that would expose energized electrical conductors) would the risk of causing an arc flash be the same for each?
As with any assessment of risk, it always seems to depend on who you ask.
Ask a carpenter...
A carpenter? Sure why not, they work with hinged doors all the time. In fact, I learned a pretty neat trick from a carpenter once about doors. If you ever need to remove a door (maybe to paint it), instead of removing every screw from the hinges you can simply take a hammer and chisel and "pop" the pin out that holds the two parts of the hinge together (I'm sure that some of you are saying "well duh!", but I digress).
Seriously, though... let's take the same example from above, make a few adjustments to put it in perspective, and look at it through the eyes of a carpenter. If you asked a carpenter if there was a greater risk of injury in opening a hinged door that led to a bedroom than removing the door from the hinges he would probably think you were crazy... how much risk can there be from opening a door?
And that is a valid point. Looking at the example above I have a hard time thinking that opening a hinged door is more dangerous than removing all the bolts of a cover, grabbing it with your hands and setting it out of the way?
But the experts don't agree
As far as I can tell the experts who wrote CSAZ462 and NFPA70E treat these tasks as equals when it comes to arc flash risk. Think of it this way...
Imagine when the carpenter opens the door (either by swinging it on its hinges or totally removing it from the doorway) there was a hungry lion waiting inside the bedroom.
Now would you say that the risk is the same?
One might argue that you could slam the hinged door shut very quickly thus saving you from the clutches of the hungry lion. Or argue that if the door was completely removed the lion would surely get you, but the point is that in either case, the risk is still too high for comfort.
What is the logic behind all this?
The logic is actually quite simple. It's boolean algebra.
One or zero.
If measured on a scale from one to one-hundred the experts would surely come out with different numbers for the two tasks. Removing bolted covers carries all kinds of additional risks such as dropping bolts or nuts into live electrical conductors or falling into the gear while trying maneuver the heavy panel cover. But it not measured on a scale of one to one-hundred, it's measured as either a one or a zero. Because the risk is at an unacceptable level for both of these tasks, in boolean algebra, they both score a one.
If there are exposed energized conductors that you could reach out and touch when you open a hinged panel or remove a bolted cover then you had better do something about it.
Just ask the carpenter when he is faced with the hungry lion. Does he really care if the door was simply opened or if it were completely removed? No. He's faced with a hungry lion and he is not taking any risk either way!
Mitigate the risk
Wear the proper arc flash and shock hazard PPE. This might come as a surprise to some of you, but wearing arc flash and shock hazard PPE, even while just taking a peek inside a cabinet is highly recommended and will ensure you stay safe.
I hope you found this article useful and if you did please share it using the social media buttons at the bottom of the post! Also if you would like some help with your electrical safety program, feel free to contact me anytime.