General Order 95

Appendix C

Conductor Sags

(e)     Sags for Supports at Different Elevations

The sag curves have been based on the supports being at the same elevation. The curve on chart 8 covers the correction of the sag to care for the difference of elevation of supports.

 

The use of this correction may best be illustrated by taking a concrete case:

 

Example

 

Assume - A span of 300 feet - Heavy Loading District.

 

A difference in level of supports of 5 feet.

 

Conductors No. 0 AWG copper, medium–hard–drawn, stranded bare.

 

The curve, on chart 4 , requires a sag of 5.30 feet.

 

The ratio of difference in level of supports divided by the sag is 5.0 divided by 5.30 which equals 0.94 and is the ratio marked h/S on curve, chart 8 . The multiplier C for this ratio is 0.58. Therefore the sag below the lower point of support is,

 

If the sag is to be measured from the higher support, the sag below the lower support may be obtained as above and the difference in elevation of supports added thereto, which gives the sag below the higher support as 3.07 + 5.00 which equals 8.07 feet. The difference of levels may be such that the resultant pull is upward at the lower support; that is, the lowest point in the span is at the support. To cover this condition, and also as an alternative method of solving cases like that just considered, use may be made of the following approximate rule which is sufficiently accurate for all ordinary situations “The apparent sag, or the vertical distance between a straight line joining supports and the tangent to the span, parallel thereto, equals the sag for a normal span of the same length.”