This topic seems to have many different opinions.

When labeling plug in bus duct, we apply/recommend that the arc flash labels be placed:

• At the ends only
• At specific intervals
• At each bus plug
• We do not use bus duct
• Something else

Bus Duct Protection

How many labels and how often is not something that we recommend too strongly. It is usually a matter of how each particular facility wants to manage things (and train).

The big mistake that we see is the labeling of each plug with calculation that depends on the response of the fuse/device contained in the plug being labeled. Such a label should be placed on the downstream equipment/disconnect.

The bus duct should be labeled on the basis of the upstream device that protects the duct. Is is recommended that the most distant end of the duct, with minimum available fault current be compared with the near end (least impedance) and the maximum available fault current. The entire duct should be labeled according to the worst-case energy between the two.

I am curious of what the "Something else" answer was.

Something else = label at one end only.

We place an arc flash label on each bus tap box (or if no tap box then at the service). This label shows the highest IE on that bus.

Also, since the buses may be long, the tap box not always easily accessible and the standard AF label cannot be read from the ground, we place an additional label listing just the AFB, IE and PPE Level in large print on the tap box so that you don't have to actually maneuver a lift into the area just to read the label when the work is actually being done further down bus.

Is there really a need to place an Arc Flash label on a bus duct? Is there work that needs to be done on an energized duct? My company’s typical approach has been to ignore bus duct in arc flash calculations as it is not a switching device, and it would not be open when energized.

For feeder duct, I would say no. The question was meant for plug in bus duct but it was not clear. I edited the original question to include "plug in".