Exposed conductor - how to guard it

[njose424]

Safety newb here trying to improve safety in general industry for my employer.

The general rule of thumb here is that if you break the plane of a panel containing 480VAC exposed conductors, you need to have appropriate shock hazard ppe (arc flash is irrelevant to this scenario - please ignore). I'm trying to dig a little deeper here....

An exposed conductor doesn't give me enough to go off of for applying that practically. I noticed that inside control panels a lot of the wire contacts where they land in a device, attached with a screw, and the screws are recessed so that you can't access with a finger tip. Is this considered guarded? Exampe from google search below.

Now let's say that I can reach a conductor with my finger tip, it's accessible to inadvertent contact and therefore "exposed". The next thing is to (without going into great detail)
1. ensure people are qualified and stay outside the restricted approach boundary for that conductive part/voltage,
2. qualified people with PPE inside the restricted approach boundary for that conductive part/voltage, or
3. guard the exposed conductor to prevent finger access

My question for number 3 is then, to what degree should it be finger safe? I'm seeing a UL507 articulated UL test finger accessibility probe as a potential means to test. Is this just a gut check to see if i can get a finger to it? are there any relevant standards that detail a conductor that is guarded vs unguarded?

Current scenario is that I have a qualified worker accessing a control panel with 480 into it. there is a small shield missing from a small transformer that has exposed screws where the 480 wires land and where the 120 volt wires land that leave the transformer.

The individual is entering the cabinet so they can test a sensor - unplug an ethernet cord from one drive to the other and then look at a display on the outside to see if it's measuring accurately. Wondering if they should be wearing PPE w/n 12" of the conductor or simply fabricate a little plexiglass shield to cover the conductors, or maybe they don't need any of that outside of 12".

Thoughts?

 

[TwoBlocked]

One possibility is to temporarily install an electrically insulated blanket over the danger, like maybe with magnets:

https://www.salisburyonline.com/category/351/insulated-blankets/blankets-class-0

 

[jim dungar]

Wondering if they should be wearing PPE w/n 12" of the conductor...

Why 12"?
Isn't the 480V clearance just a few inches?

Any plastic used for insulation purposes would need to have a Listed voltage rating.

However putting a simple piece of electrical tape over the exposed terminals should be sufficient, until it falls off.

 

[infinity]

Now let's say that I can reach a conductor with my finger tip

Can you touch the bare part of the conductor or just the insulated conductor itself. Looking at the photo is there any energized part that can touched by a finger?

 

[TwoBlocked]

I think the OP questions are in general what can or should be done.

Been through many such discussions at manufacturing plants. It boils down to who is likely to be observing what the electrician is doing and what they are likely to do about it.

 

[BillyMac59]

The panel meets safety requirements when the door is closed and locked. A label on the door should inform of the voltages within and the potential for arc flash. At a minimum, the qualified person entering the panel should be protected from shock using rated gloves, fused test leads, safety glasses etc.
Safety should be part of the design process. Finger safe fuse holders, terminal blocks with recessed terminals, etc. Clear plastic (Lexan) barriers with pre-drilled holes to allow meter terminal access are common.
The safest thing is to turn the panel off. Absence of voltage modules are often used. Graceport units comes to mind. Properly installed and maintained, these meet the requirement to confirm zero voltage present without the need of metering terminals after donning all applicable arc flash gear.