An analysis of the implications of a magnetic field threshold limit value on utility work practices

This article examines the implications of a 10 gauss (G) occupational threshold limit value (TLV) on the work practices of a utility that must maintain and repair 500 and 230 kV transmission lines. Three work practices are compared: bare-handed work with live lines (the current practice at the example utility), use of hot sticks, and de-energizing lines prior to work. Bare-handed work with live lines leads to occasional exceedances of the 10 G TLV. Use of hot sticks and de-energizing lines eliminate these exceedances, but they do so at a price. Both practices increase the job duration and, as a result, may increase occupational injury risks. The annual costs for the current live-line, bare-handed practice is approximately $175,000. Use of hot sticks increases this annual cost of maintenance and repair by 30 to 55%. De-energizing lines can increase annual costs by $4 million to $14 million, due to the need for adding additional electricity generation during the planned outages. De-energizing lines also increases the risk to service reliability slightly.