IEEE Std 525 Maximum allowable pulling tension

The maximum allowable pulling tension is the minimum value of Tmax from the applicable following guidelines, unless otherwise indicated by the cable manufacturer. The maximum tension on an individual conductor should not exceed

T(cond) = K× A

where

T(cond) is the maximum allowable pulling tension on individual conductor, in newtons (pounds)
A is the cross-sectional area of each conductor in square millimeters (mm2) (kcmil)
K equals 70 N/mm2 (8 lb/kcmil) for annealed copper and hard aluminum
K equals 52.5 N/mm2 (6 lb/kcmil) for 3/4 hard aluminum

When pulling together two or three conductors of equal size, the pulling tension should not exceed twice themaximum tension of an individual conductor, i.e.,

T(max)  =2  × T(cond)

When pulling more than three conductors of equal size together, the pulling tension should not exceed 60% of the maximum tension of an individual conductor, times the number of conductors ("N"), i.e.,

T(max)= 0.6 × N ×  T(cond)

When pulling using a pulling eye, the maximum tension for a single-conductor cable should not exceed 22.2 kN (5000 lb), and the maximum tension for two or more conductors should not exceed 26.7 kN (6000 lb). The cable manufacturer should be consulted when tensions exceeding these limits are expected. When pulling by basket grip over a nonleaded jacketed cable, the pulling tension should not exceed 4.45 kN (1000 lb). When using a basket-weave type pulling grip applied over a lead-sheathed cable, the force should not exceed 6.67 kN (1500 lb) as determined by the following formula:


T (max) = K(m) x  pi x t ( D – t )

t is the lead sheath thickness, in millimeters (inches)
D is the OD of lead sheath, in millimeters (inches)
K(m) is the maximum allowable pulling stress in MPa (10.34 MPa to 1.38 MPa [1500 to 200 psi] depending on the lead alloy)

1. Pulling Tension When Using Conductors
When pulling a cable using the conductors, the maximum allowable pulling tension (\T_{max}\) is calculated as:

T_{max} = S \cdot N

Where:

• S: Allowable stress in the conductor (lbs or N), typically 0.008 times the Ultimate Tensile Strength (UTS) for copper or aluminum.
• N: Total number of conductors.

Example:
- For a 3-conductor copper cable with UTS of 40,000 lbs per conductor:
S = 0.008 \cdot 40,000 = 320 \, lbs/conductor
T_{max} = 320 \cdot 3 = 960 \, lbs

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2. Pulling Tension When Using a Pulling Eye or Grip
When pulling a cable using a pulling eye or grip (not the conductors), the maximum pulling tension is limited to:

T_{max, pulling eye} = \text{Manufacturer's Specified Pulling Tension}

Notes:
- This value depends on the cable's construction, including insulation type, shielding, and jacket materials.
- Always consult the cable manufacturer's specifications for this limit.

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3. Sidewall Pressure
Sidewall pressure is the force exerted on the cable at bends. It must be calculated to ensure it remains below the maximum allowable value. The formula is:

P_s = \frac{T}{R}

Where:

• T: Tension at the bend (lbs or N)
• R: Radius of the bend (ft or m)

Typical Allowable Sidewall Pressure:
- For medium-voltage cables: 500 lbs/ft (varies with cable type).

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4. Recommendations from IEEE Std 525
To ensure safe cable installation:

• Use Lubrication: Approved cable lubricants reduce pulling tension.
• Bend Radius: Maintain a bending radius that meets or exceeds the manufacturer's specifications.
• Tension Monitoring: Use tension-limiting equipment to avoid exceeding allowable tension.
• Optimize Pulling Path: Minimize bends and obstructions in conduits or trays.
• Calculate Total Tension: Ensure pulling tension over the entire path remains below the maximum limits.

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5. Summary
The maximum allowable pulling tension ensures the mechanical integrity of cables during installation. IEEE Std 525 provides key formulas and considerations to guide safe practices:

• Pulling Tension Using Conductors: Follow the formula T_{max} = S \cdot N.
• Pulling Eye or Grip Tension: Always adhere to the manufacturer's specified limits.
• Sidewall Pressure: Monitor and control the force at bends to prevent damage.

Proper planning, tools, and adherence to standards ensure a safe and successful cable installation process.

References: IEEE Std 525, manufacturer specifications, and cable engineering guidelines.