Sidewall Bearing Pressure Max

[briezydai]

I am in process of updating a set of company standards for conduit and cable pulling. Currently our maximum sidewall bearing pressure is limited to 300 lbs/ft. However, the values in the AEIC CG5 are significantly higher (i.e. 1200 lbs/ft). So far I am unable to locate the source for the 300 value. Where does the 300 lbs/ft value come from? Why not use the higher values from CG5? Comments??
Thanks

 

[wareagle]

You are not limiter to 300 lbs. Side wall pressure is the
tension out of a bend expressed in pounds divides by the radius of the bend in ft. For 1 cable up to 3 singles cables
the max allowed tension out of the bend shall not exceed 300 times the radius of the bend in ft. The max tension for 2 thru 6 cables is 500 times the radius. It also depends on the type of cable or conductor.
Check this site for table 6 and the different max values of SWBP. Don't forget that when pulling cable thru a PVC bend that there is a limit in pounds due to the pulling rope "burning" thru the PVC.

 

[wareagle]

I for got the site. Sorry.

http://www.ecmweb.com/mag/electric_simple_calculations_cable/index.html

 

[briezydai]

Thank you for the website. It is very informative.
I actually answered my own question this morning. Apparently we have been using a three to one safety factor in our conduit/cable design, hence the 300.
Again thanks,

 

[cuky2000]

...So far I am unable to locate the source for the 300 value. Where does the 300 lbs/ft value come from? Probably that comes from published data for low voltage power and instrumentation cables particularly for those with rubber base insulation such as RHW.

Many progresses have been achieved increasing the strength of cable insulation. However still today there are many cable manufacturers that recommend lower sidewall pressure (SWP) values than the one published by AEIC.

As an additional reference, the report EL-3333-CCM from the Electric Power Research Institute (EPRI) published similar values from the AEIC standard. However, this report limit the SWP without jacket to values as low as 750 lb/ft for 3 cable pull and reduce to 1500 lb/ft when the jacket is not applied tightly to the cable core.

SUGGESTION: indicate in the spec the minimum SWP for different type of insulation materials and implement procedures to verify the compliance with the specified values during the purchasing process and prior the installation of the cable.