California Electrical Code Seismic Supports for cable tray and conduit systems

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
As far as I know ‘seismic’ is purely a structural function. Has anyone out there installed cable tray or conduit in CA where seismic calcs and supports were required?


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junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
in years past, designed and installed a lot of trays,equipment, and cables in Minuteman silos, seismic loads trivial (by factors > many 100s) compared to nuclear blast shock specifications.

No conduits across anything that can move, everything stationary in welded sch 40 joints. Boxes all cast or drawn steel, welded mounting or with rock bolts. Where movement (e.g shock mounted equipment racks) heavy duty cables with shock loop to allow movement.
Example - 45 kVA delta-wye transformer in die forged aluminum housing, vacuum potted into housing, , forging mounted to wall with 12ea 2" dia rock bolts grouted into the silo liner, etc.
 

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
Yes, assembled with threads fully engaged, then circumferential weld at all joints. Stainless steel unions did not need welding at the interfaces, but does anyone use unions on RMC in normal electrician practice.

Some field expedients at remote sites we would apply galvacon or other high zinc powder loaded paint to the couplings before mating rather than needing to weld them.
In addition to structural strength, filling threads with conductive compound or welding required for EMP shielding. Something like TFE tape a definite No-no for EMP shielding.
 

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
extensive grounding system

lol,
big 80 ft deep silo 12 ft diameter, solid steel liner. Near Grand Forks, ground water so loaded with fertilizer that conductivity near that of sea water. Every electrical ground tied to that liner.
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
As far as I know ‘seismic’ is purely a structural function. Has anyone out there installed cable tray or conduit in CA where seismic calcs and supports were required?


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the seismic design is an issue in CA, it depends on how heavy the cable tray is and how far from the ceiling it hangs down.
 

Todd0x1

Senior Member
Location
CA
in years past, designed and installed a lot of trays,equipment, and cables in Minuteman silos, seismic loads trivial (by factors > many 100s) compared to nuclear blast shock specifications.

No conduits across anything that can move, everything stationary in welded sch 40 joints. Boxes all cast or drawn steel, welded mounting or with rock bolts. Where movement (e.g shock mounted equipment racks) heavy duty cables with shock loop to allow movement.
Example - 45 kVA delta-wye transformer in die forged aluminum housing, vacuum potted into housing, , forging mounted to wall with 12ea 2" dia rock bolts grouted into the silo liner, etc.

Ok that's cool! I have always been fascinated by the ICBM silos, hope to visit the minuteman historic site in SD.
 

grich

Senior Member
Location
MP89.5, Mason City Subdivision
Occupation
Broadcast Engineer
in years past, designed and installed a lot of trays,equipment, and cables in Minuteman silos, seismic loads trivial (by factors > many 100s) compared to nuclear blast shock specifications.

No conduits across anything that can move, everything stationary in welded sch 40 joints. Boxes all cast or drawn steel, welded mounting or with rock bolts. Where movement (e.g shock mounted equipment racks) heavy duty cables with shock loop to allow movement.
Example - 45 kVA delta-wye transformer in die forged aluminum housing, vacuum potted into housing, , forging mounted to wall with 12ea 2" dia rock bolts grouted into the silo liner, etc.
You'll see a lot of those techniques in photos of the old Long Lines underground facilities...shock mounted everything, flex transitions, etc.
 

Todd0x1

Senior Member
Location
CA
You'll see a lot of those techniques in photos of the old Long Lines underground facilities...shock mounted everything, flex transitions, etc.
Ooh another one of my favorites. There were a few for sale maybe 15 or 20 years ago that still had all the equipment in them.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Getting back to the OP, it would be great to get an example if anyone has one. E.g. if you've done an installation that was seismically engineered, provide the details on the cable tray, loading, distance from the structural ceiling, and the supports required. Then compare that to the supports that would be standard practice in a region of low seismicity.

Cheers, Wayne
 
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