I still run into this from time to time and now I’m second guessing. If you are gathering data on a switchboard fed from the 480 volt secondary of a 1500 kVA utility owned transformer, what PPE do you wear?

There is a pretty good likelihood that the utility fuses would take a long time to operate which would result in an incident energy well above 40 cal/cm2. It is not possible to ask the utility to de-energize, all we want to do is open the enclosure and take a look. What is everyone doing with this? Thanks!

What I usually try to do is to get all the utility information prior to gathering any information on site. From the utility I request the txf protective device, riser cable info, txf info. I will then make a reasonable, based on NEC, assumption on secondary conductors and usually have an idea of length. This gives a reasonable approximation of what the afh is at the switchboard/switchgear. I also look at the 2 second cutoff if it is appropriate to use.
If it is still Extreme Danger, this is where the risk assessment of the hazard of the work you are trying to accomplish could come into use. Or you can make some assumptions on the bkrs based on the switchboard. In some cases, I have waited until there was a complete shutdown, including utility opening the fuses.

JoeB, you are correct that most utility fed panels are a high AFHC. When I collect data for the utility feed I am the most nervous due to the probable rating. In nearly all cases, to get the utility to shut off the power is very difficult and sometimes costly.
To determine the PPE to wear for the utility connection is no different than any other place in the system. You can actually find places in the system that are worse than the utility connection.

It is virtually impossible to find a higher incident energy than on the customer side of the service point, which is usually the 480V service equipment when supplied by a utility owned transformer. Keep in mind the incident energy at the service equipment is not reduced by a main service disconnect unless the equipment is true compartmentalized switchgear. This is one slide is from a presentation I did for an IAEI State Chapter meeting. It is very conservative and has some very good support data.

Due to liability concerns, I indicated "work-de-energized" above 40 cal/sq. DOES THE DATA BELOW SURPRISE ANYONE?


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