Design references for secondary racks

[tft2001]

I am in the process of designing the support system for the attachment of a Hubbell secondary rack unit. The ANSI document pertaining to the design of secondary racks indicates that for a deadend condition, the maximum load per insulator is 3,000 pounds. The particularly rack that our client is having installed consists of 4 insulators. The main wire feeds will have the necessary intermediate hangers for supporting the wires (spaced approximately 12 on center).

Based on the layout of the wire feeds and intermediate supports, the total maximum load of 12,000 pounds seems very excessive. Does anyone have any design guides, resources, etc. That pertains to the design of supports for this type of secondary rack installation?

 

[jghrist]

What is the rack mounted on? A guyed pole? Do you really have 3,000 lbs tension in each secondary conductor? Seems pretty high. Do you need to pull the conductor that tight for clearance?

Rural Utility Service (RUS) at

http://www.usda.gov/rus/electric/bulletins.htm

has guides for pole and guy loading.

 

[tft2001]

The support system is to be either steel pipe (or tube) that is framed within an existing building. More specifically, a vertical pipe of tube will be positioned below existing steel trusses, the rack is to be connected to this vertical member and strut braces are to be framed up into roof purlins.

 

[waross]

If the conductors are strongly fastened to the rack then you may experience deadend conditions in the event of a broken conductor.
For intermediate supports you may want to consider the weight of the conductors plus ice loading, wind loading and the force needed to pull the conductors through the rack in the event of a deadend condition resulting from a broken conductor. You may not have much ice or wind in the building but don't forget the possibility of vehicles. Use suitable safety factors. I haven't done this type of design for over thirty years and even if I could remember my guides they may not be applicable now.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tft2001]

Thanks to all.