The thermal capacity of power equipment has been traditionally based o
n simultaneous occurrence of worst case weather conditions and peak lo
adings. A dynamic thermal rating method has been developed where the t
hermal capacity of power equipment is based on actual realtime weather
conditions and circuit loadings. This normally results in higher ther
mal ratings which may allow the power utility to postpone replacement
of underground cables and substation equipment or reconstruction of ov
erhead lines. It may also allow immediate increased access to low cost
power sources. This paper describes the technical philosophy and fiel
d data collection plan necessary to apply the EPRI Dynamic Thermal Cir
cuit Rating Methods to overhead lines within the PECO Energy transmiss
ion area. It also briefly describes field test management for a power
transformer and an underground cable in the same transmission system.