Effective Coefficient of Friction

The effective coefficient of friction for a multiple cable pull is a function of the basic coefficient of friction K_Q and the weight correction factor W_c.

This increase in friction (K) is caused by an increase in the weight correction factor (W_c). The W_c accounts for the wedging action between the cables and the conduit. The following equation calculates the effective coefficient of friction:

K = K_Q W_c

Where:

K = Effective coefficient of friction (dimensionless)

K_Q = Basic coefficient of friction (dimensionless)

W_c = Weight correction factor (dimensionless)

Research data indicates that at a sidewall bearing pressure (SWBP) of approximately 150 Ib/ft or more, the effective coefficient of friction is significantly reduced. In effect, this means that when the cable is pulled around bends, initially use the higher coefficient of friction to calculate the SWBP. When the SWBP is greater than or equal to 150 Ib/ft, use the lower coefficient of friction.

Table: Basic Coefficients of Friction - K_Q

Type of Conduit

Cable Outer Covering Material

Bends where SWBP is < 150 lb/ft and Straight Pulls

Bends where SWBP exceeds 150 lb/ft

Single Cable Pull

Multiple Cable Pull

PVC

XLP, 600V
concentric wires
PE jacket
PVC jacket
Neoprene

.40
.40
.40
.50
.90

.60
.40
.45
.60
1.50

.15
.20
.15
.30
.15

Steel

XLP, 600V
concentric wires
PE jacket
PVC jacket
Neoprene

.60
.50
.50
.65
1.05

.65
.50
.50
.65
1.75

.25
.30
.25
.30
.25

Bitumenized Fiber

XLP, 600V
concentric wires
PE jacket
PVC jacket
Neoprene

.30
.40
.25
.40
.40

.65
.40
.60
.45
.55

--
--
--
--
--

Terra-Cotta or Transite

XLP, 600V
concentric wires
PE jacket
PVC jacket
Neoprene

.70
--
.70
.70
1.00

.70
--
.70
.70
1.80

--
--
--
--
--

Fiberglass

XLP, 600V
PE jacket
PVC jacket
Neoprene

.23
.25
.39
.53

.23
.25
.39
.53

.15
.15
.30
.15

PE

XLP, 600V
concentric wires
PE jacket
PVC jacket
Neoprene
CN

.45
.20
.25
.30
.65
.20

.55
.20
.85
.45
.65
--

.15
.20
.15
.30
.15
--

Type of Conduit	Cable Outer Covering Material	Bends where SWBP is < 150 lb/ft and Straight Pulls		Bends where SWBP exceeds 150 lb/ft
Type of Conduit	Cable Outer Covering Material	Single Cable Pull	Multiple Cable Pull	Bends where SWBP exceeds 150 lb/ft
PVC	XLP, 600V concentric wires PE jacket PVC jacket Neoprene	.40 .40 .40 .50 .90	.60 .40 .45 .60 1.50	.15 .20 .15 .30 .15
Steel	XLP, 600V concentric wires PE jacket PVC jacket Neoprene	.60 .50 .50 .65 1.05	.65 .50 .50 .65 1.75	.25 .30 .25 .30 .25
Bitumenized Fiber	XLP, 600V concentric wires PE jacket PVC jacket Neoprene	.30 .40 .25 .40 .40	.65 .40 .60 .45 .55	-- -- -- -- --
Terra-Cotta or Transite	XLP, 600V concentric wires PE jacket PVC jacket Neoprene	.70 -- .70 .70 1.00	.70 -- .70 .70 1.80	-- -- -- -- --
Fiberglass	XLP, 600V PE jacket PVC jacket Neoprene	.23 .25 .39 .53	.23 .25 .39 .53	.15 .15 .30 .15
PE	XLP, 600V concentric wires PE jacket PVC jacket Neoprene CN	.45 .20 .25 .30 .65 .20	.55 .20 .85 .45 .65 --	.15 .20 .15 .30 .15 --