TM 10-3950-672-10
Boom Cage/Guards afford limited protection from the electrocution hazards. They are designed to cover only the boom-
nose/point, and a portion of the boom. Performance of boom cages/guards is limited by their physical lengths, insulating
characteristics, and the operating environment (e.g. dust, dirt, moisture, etc.).
Insulating links installed into the load-line afford limited protection for those handling the load. Links have limited lifting,
insulating, and other properties that affect their performance. Moisture, dust, dirt, oils, etc. can cause a link to conduct
electricity. Due to their capacity ratings, some links are not effective for large cranes and/or high voltages/currents.
The only protection afforded by a link is that which is obtained below the line electrically downstream, provided the link
has been kept clean and free of contamination and is periodically (right before use) tested for its dielectric integrity.
Proximity sensing devices are available in different types. Some use boom nose (localized) sensors and others use full
boom length sensors. No warning may be given for components, cables, loads, etc. located outside of the sensing area.
Much reliance is placed upon you, the operator, in selecting and properly setting the sensitivity of these devices.
Never rely solely on a device to protect you and your fellow workers from danger! Some variables which you must be
aware of with regard to proximity devices, are:
1. Proximity devices are supposed to detect the existence of electricity not it's quantity or magnitude.
2. Some proximity devices will detect only alternating current (AC) not direct current (DC).
3. Some devices detect radio frequency (RF) energy others do not.
4. Most proximity devices simply provide a signal (audible, visual, or both) for the operator the signal must not be
ignored.
5. Sometimes the sensing portion of the proximity devices becomes confused by complex or differing arrays of
power lines/sources.
Plan ahead and plainly mark a safe route before traveling under power lines. Erect rider poles on each side of the
crossing to assure sufficient clearance is maintained.
Overhead power lines tend to blow with the wind. Allow for this when determining safe operating distances.
DO NOT store material under power lines or close to electrical power sources.
DO NOT depend on grounding!
Grounding of a crane affords little or no protection from electrical hazards. The effectiveness of grounding is limited by
the size of the (wire) conductor used, the condition of the ground, the amount of the voltage and current present, etc.
Power source contacts have been known to cause serious arcing due to grounding.
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