User's Manual

6 Fluke Corporation Concerned about arc-flash and electric shock?

An important point here is that the flash

protection boundary and the rules govern-

ing access within it take precedence over the

shock hazard boundaries. So, for example, if

the flash protection boundary is greater than the

limited approach boundary then no unqualified

person can be permitted in the limited approach

area and even qualified workers must wear

appropriate arc-resistant PPE here.

You can determine the flash protection bound-

ary for an electrical system using the calculating

methods contained in NFPA 70E and IEEE Std

1584. The equations are based on the voltage

level, fault level and the trip time of the protec-

tive device.

The conditional flash protection boundary

is 48 inches for low voltage (<600 V) systems

where the total fault exposure is less than 100k

amperes-seconds (fault current in amperes mul-

tiplied by the upstream device clearing time in

seconds). On such a system, a qualified person

who works closer than 48 inches from the live

components must wear PPE for arc-flash protec-

tion including flame-resistant (FR) clothing. Of

course, further PPE may be necessary for pro-

tection against electric shock according to the

location of the shock protection boundaries.

Please refer to IEEE 1584 for comprehensive

calculation methods for a wide range of electri-

cal systems; the procedures describe calculation

methods for equipment with voltages in the

range: 208 V to 15 kV.

Choosing the right PPE

As an option to incident energy analysis to

assist in the choice of appropriate personal

protection equipment for arc flash hazards, NFPA

70E defines five hazard risk categories (HRCs):

0, 1, 2, 3, and 4.

Figure 3. The Flash protection boundary takes precedence over the

shock hazard boundaries.

Hazard/Risk