The scope of this guide is to describe the effects and impacts of high temperature operation on conductors@ connectors@ and conductor hardware. The guide will identify operating metrics which constitute elevated temperature operation based on present industry practices and its effects on overhead line components@ and it will suggest potential mitigation options to manage or avoid identified adverse impacts. Purpose The purpose of this guide is to provide general recommendations for consideration when evaluating existing overhead transmission lines or designing new overhead transmission lines which will be operated at high temperatures. Although this guide is intended for overhead transmission lines@ most of the discussion will also be applicable to distribution lines. Recently within the industry a number of new and novel conductors have been designed using non-traditional materials specifically designed for hightemperature operation. The collection of new and novel conductors is identified in the industry as high temperature low sag (HTLS) conductors. These new conductors are typically formulated with either standard aluminum strands@ fully annealed aluminum or aluminum alloys which resist annealing at 200 ??or greater@ exotic core materials which result in minimal sag changes with increasing conductor temperature@ and extremely robust connectors. While the general concepts and cautions presented in this guide are appropriate for broad considerations when designing with the HTLS conductors@ this guide does not specifically address the HTLS conductors as they are supported with other documents. Rather@ this guide is limited to conventional conductors and connectors typically formulated with cold worked aluminum or copper with reinforcement achieved using steel galvanized or steel aluminum clad core strands. One notable exception is steel supported aluminum conductors (SSAC) developed in the late 1970s (Reynolds Metal) utilizing a galvanized steel core or aluminum-clad steel core and fully annealed aluminum strands. Modern versions of the SSAC conductor are referenced as aluminum conductors steel supported (ACSS) and typically carry a steel core of either misch metal or aluminum-clad steel core and fully annealed aluminum strands. The trend in most utilities today is to increase the capacity of their transmission lines wherever practical. It has become increasingly difficult to build new lines because of increased costs to obtain rights-of-way@ public intervention@ and state licensing requirements. These obstacles have significantly increased the cost and lead times required to place new lines into service. The lost revenue opportunities from power purchase/sale agreements with other systems because of limited transmission facilities can be substantial. Therefore@ utilities are attempting to find as much capacity as is practical from the addition of new highcapacity lines or modifying existing lines for operation at higher temperatures than the existing facilities. In the past@ utilities have typically been conservative in rating their lines due to the uncertainties in parameters which influence conductor temperature. Today@ with a better understanding of actual ambient conditions and improvements in monitoring instruments and sophisticated analysis tools@ utilities are rating lines at higher temperatures with the same or higher level of confidence than in the past. Many utilities have been increasing their transmission line's maximum conductor operating temperature as a way of increasing line capacity. Often higher operating temperatures are needed for only a few hours during the year. General concerns with increasing a conductor's maximum operating temperature relate to accelerating the aging process of conductors@ connectors@ and conductor hardware while maintaining adequate ground clearance for safe line operation. Operating at a higher conductor temperature is acceptable if the associated negative effects are adequately understood@ considered@ and mitigated in the design or analysis of a line. Some effects of high-temperature operation to consider are: ?? Increase in conductor sag resulting in reduced clearances ?? Reduction of life and integrity of connectors ?? Acceleration of component aging with higher operating temperatures ?? Loss of strength in the conductors and connectors ?? Increase in resistive losses ?? Potential damage to equipment attached to conductors (e.g.@ wave traps) Note that the magnitude of any of these possible effects is dependent on the type of conductor. This guide is limited to discussing the effects of high-temperature operation on bare overhead transmission conductors@ connectors@ and conductor hardware. These effects are discussed to identify their impacts on safety@ reliability@ and economy. A few methods to mitigate some of these negative effects of hightemperature operation are also d