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General guidelines only are presented here. A discussion of some of the applications peculiar to specific situations is presented later.
1. Verify the line is truly de-energized:
[OSHA 1910.269]
Before applying any protective jumpers, the status of the line must be determined. Several techniques are available. A common field technique is “fuzzing” or “buzzing” the line by holding a wrench mounted on an insulated
“hot stick” or the metal head of a Universal
Tool near the conductor. The theory is that if the line is energized it will induce a voltage in the wrench or metal head and corona discharges will cause an audible sound.
“Fuzzing” is not a recommended technique.
The detection of any audible sound is very subjective and is dependent upon wind conditions, line voltage level, nearby noise levels, etc. It is reported to be more reliable on transmission lines because of their higher voltages, but the use of a detector designed for the purpose increases the level of safety.
Chance offers several models of the Multi-
Range Voltage Detector and Phasing Tools that can be employed to significantly increase the reliability of this determination. See Section 8 for a discussion of these devices.
Protective equipment can be installed once the line has been de-energized and the absence of voltage has been verified.
2. Clean the connections:
All of the connections should be made to a cleaned surface. Either a wire brush or serrated jaw clamp can be used on distribution voltage level conductors. On high voltage transmission towers only the wire brush is recommended. Use of the serrated jaw clamp may leave sharp edges on the soft aluminum conductor that could result in increased corona discharge.
For tower connections it may be necessary to clean away paint, rust or corrosion before making the connection. Fault current passing through a layer of paint that separates the clamp from the tower steel will cause it to heat and soften, melt or burn away. A flat face clamp could lose its grip and come off the tower, breaking a connection and possibly losing the protective parallel path. It may be desirable to tie the clamp to the tower steel to prevent it from coming off and to avoid the loss of protection from these hazards. Locate each clamp to maximize worker safety. The added resistance of a corroded connection may increase that of the parallel path as to jeopardize worker safety.
3. Order of installation of personal protective jumpers:
[OSHA 1910.269]
Install the personal protective jumpers using an insulated Grip-All clampstick. Begin by connecting a ground end clamp to an appropriate Earth connection. This may be a driven ground rod, a tower leg or grillage, etc. It is important that a pole down wire not be used for this connection. The small size of a pole down wire could cause it to fuse and melt during the flow of fault current, resulting in the loss of the connection for the Earth return path.
For wooden poles, the line end clamp should then be installed onto a conductive pole band attached around the pole as close as possible
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below the location of the worker’s feet. The pole band provides a conductive connection point for use with multiple clamps and a convenient parking location for clamps during installation. Additional protective jumpers are then installed from the pole band to the neutral and then to each conductor, beginning with the closest one and ending with the farthest one. The worker must remain clear of the conductors during the installation of this safety equipment and not approach within the minimum approach distance.
resistance is still too high, it may be necessary to use a larger cable size to obtain the necessary reduction in resistance.
Each connection should be situated so as not to interfere with the work being done. Finally, minimize the cable slack because shorter cables have lower resistance and reduce possible mechanical whipping action during a fault that could strike and injure a worker.
This is especially true as fault currents approach 40,000 to 50,000 Ampere levels.
A pole band would not be used on a steel transmission tower. The worker’s parallel protective jumper would connect from the tower to the conductor, still below the worker’s feet. While the tower is itself a connection to the Earth, depending upon the tower’s age, the amount of corrosion or paint present may or may not represent a suitable current path.
A part of the personal protective jumper assembly should consist of clamps with cable of sufficient length to reach from the elevated worksite to the Earth below and be installed as described above.
Procedures may be altered to fit different working conditions (for example, in substations or working from a bucket truck). More information is provided in following sections detailing these situations.
Try to minimize the maximum number of jumpers in series that can be in parallel with the worker. There will be three series jumpers in parallel with the worker if hand contact is made to the furthermost distant phase (see
Figure 9-6 of Section 9). Figure 9-7 reduces the maximum number of parallel jumpers to two by thoughtful placement. This may or may not present a problem, depending upon their total resistances. The process of calculating the maximum resistance with the worker (in Section 9) should be reviewed. If the center phase can be safely connected first, the maximum number of jumpers in parallel with the worker will be reduced to two. If the
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