8 Outcome 2: Pole Structures, Framing, Guys, and Anchors

Introduction:

In this section you will learn about pole structures, installing hardware, pole framing, transformer structures, wood pole characteristics, and guys and anchors. You will be presented with content and then given opportunities to test your understanding with short review exercises.

Topic: Pole Structures (1h)

Installing Hardware (25kV and Lower)

We have learned that the face or back of a pole is its strongest side. Therefore, we frame poles to always “face the strain”. All crossarms, timbers or spars which carry conductor are fastened to the back side of the pole (pole top equipment.)

Pole Framing

There are some general rules which should be followed when poles are framed.

Poles

• Proper class of pole and size of bolts in accordance with CSM
• Poles should not be gained (only done by the manufacturer.)
• Overhead guy poles should be 5 feet shorter than the pole it supports.

Bolts and Hardware

• Bolt holes should be 1/16 inch larger than the bolt being used. Example: 5/8 inch bolts use a 11/16 inch drill bit. ¾ inch bolts use a 13/16 inch drill bit.
• All hardware must be galvanized.
• The strongest part of a bolt is the unthreaded (bolt head) portion, so a bolt is positioned with the most strain on the bolt head.
• Bolts which are not under tension require double coil washers.
• Anti-split bolts are used on deflections where a pole may split.

Framing Practices

• A minimum number of holes should be drilled.
• Always frame the pole to leave room for climbing.
• Danger signs are used on all poles where equipment is accessible from ground level (switch handles, cable guards, ground wires, etc.)
• Ground wires are framed to the opposite side of the pole from cut-outs (prevents second point of contact accidents.)
• Crossarms are square to the pole.
• On three phase rural construction, the first two crossarms must face the deadend.
• Guy wire must be a minimum of 5/16 inch galvanized steel.
• Bail clamps must be used on ACSR or aluminum.
• Bonding must be done on hardware separated by less than 4 inches and on hardware within 6 inches of ground wires.

Three Reasons to Bond

• Prevent communication interference
• Safety to powerline technician (allows currents to flow around workers.)
• Fire prevention (if the potential between two objects is large enough, tracking can cause fires). For example, a gulf-port structure having all hardware at phase level or higher must be bonded to the ground wire.

Transformer Structures

When framing transformer structure, some general rules should be followed:

Grounding

• Ground wires to arrestors are kept short and snug (a blown arrestor can break and dangle on a pole.)
• Ground wires must be covered with molding (protects workers and the public.)
• Primary and secondary bushings may need to be grounded in some circumstances. This can be done by using one ground wire for both, referred to as a “common neutral.”
• Ground wires on the opposite side of a cut-out.
• On systems with a system neutral, only one path to ground is needed.
• On systems with no system neutral, two paths to ground are needed. Ground wires are put on opposite sides of the pole so if damage occurs, there is always another path to ground.
• Copper risers are preferred.

Apparatus

• Lightning arrestors are used on all transformers (some exceptions will occur on 3 phase banks).
• Cut-outs are located 90 degrees from the H1 bushing
• Minimum size of pole used:
  • 13.7 m (45 feet) in urban
  • 12.2m (40 feet) in rural
• Transformer poles are never raked.
• Voltage and phase rotation checks are always completed before a customer is connected. Serious damage can occur if voltage is too high, or the rotation is backwards.

Review Questions: Pole Structures (30m)

Answer Key

1. 1/16, 2. F, 3. A, 4. F, 5. C, 6. D, 7. T, 8. B, 9. Prevent communication interference, safety to powerline technician, fire prevention. 10. 4, 6, 11. C, 12. T, 13. F, 14. Rural 40’, urban 45’, 15. B, 16. Copper, 17. F, 18. Voltage, phase rotation.