We had a consulting firm do an analysis of the arc flash risks throughout the plant. Most of the warning labels have flash protection boundaries of a 1/2 foot or less. Most have a hazard rating of 0 or 1.

If I have to open a 4ftx6ft machine control cabinet that has the 480V main feeds on the left side, does the 1/2 foot boundry include the entire cabinet, or just 6 inches from the high voltage components?

Most of the cabinet is PLC, IO racks and assorted 24V devices. Are they all in the flash protection boundary? Or if the boundary is just 6 inches from the 480V hardware, would a Lexan box greater than 6 inches from the hot stuff assure that you couldn't get within the FPB?

Good question. My opinion is that if the panel is energized, you must wear the PPE according to the label even if you are working on the 24 volt devices. The 24 volt device may be controlling a 480 volt motor contactor which could cause an arc flash.

With a 6" AFB, this is probably a CAT #0 cabinet. Long sleeve cotton shirt, jeans, eye and ear protection should be a minimum for working near energized parts 50 volts or above.

You have to be careful about splitting hairs in terms of policy. If the PLC side is seperated into its own metal enclosure, then you don't have to obey the AFB frrom the 480 enclosure. If it is one big enclosure, 480 on the left side and 24VDC on the right side, then you are kind of splitting hairs and potentially diminishing your program awareness. A person could easily side step a couple of feet while performing service on the PLC side.

IMO the motor starting kicking in or out does not come into play. If its in its own enclosure then it doesn't fit into the high energy switching category which is more for switchgear. If its in the same cabinet, then just having voltage present is sufficient to obey the AFB.

The boundary is measured from the live parts of the respective voltage.

A 480 volt cabinet should have a category 2 for any live work.

No PPE Exists

I have another question . This came up in a labeling discussion . A 13,800 breaker was determined >40 cal and marked "Danger no PPE exists" on the outside door. The cabinet is not Arc Resistant but it new enough that it can be racked with the door closed. (Siemens vac. breaker )
The plant people were using the table method and racking it with the door closed using Level 2 protection.
Can they still do that or did the study discover a real danger ( door open or closed )?
Should 2 labels be installed , One on the door and another one on the breaker ? Thanks

They must be using the old tables, all breaker racking is now HRC 4 doors open or closed. Most plants with this problem have gone to remote racking.

Here are some videos http://www.youtube.com/user/CBSArcSafe

Interesting that those videos don't show the set-up and break-down of the remote racker. Wouldn't a higher level of PPE be required for that?

BTW, hello Laszlo.