I am installing a 30 Foot Round Straight Steel Light Pole, 5 Inch Diameter that I am purchasing from LightMart. I live in the outside of Las Vegas, NV near the mountains where sometimes its very windy, gusts around 50mph. I am installing just one light on top of the pole. I was researching what dept do I have to go and how wide. I've read that for width I would have to go 3 times the pole size 5" so 15" inches wide and for dept about 4ft to 5ft. To use a lot of rebar and a good strength concrete. What do you guys recommend?
5” cover around the steel pole is not enough.
Most electrical contractors have augurs in the 12”, 18”, 24” diameter. I’d go with the 24” diameter for four reasons: 1) it will give you 9 1/2” cover (if the pole ends up EXACTLY in the middle...doubtful), 2) the 24” width will help resist overturning, if it’s windy like you say, and 3) the rebar needs to be 3” from the outside edge and this leaves you plenty of room between the rebar and pole, and 4) the weight of the concrete base will help overturning.
For depth, I’d go 4’ in the sandy soil where you’re located. At 24” diameter and 4’ deep, that gives you about 630 lbs of concrete resisting overturning.
A light and bar at the top of the pole will have about 8” x 12” =96 sq. In. / 144 = .66 sq. ft. X 30’ pole = 20 ft. lbs. (not counting the pole). Wind equals about 25 psf x 20 = 500 lbs.
Therefore, the concrete footing has more resistance than the wind on the light at the top of a 30’ pole...and the pole will break before it rotates.
The standard for mounting a pole is 2' plus 1' for every increment of 10' of pole. That would mean your minimum depth would be 5' deep. That does not take into account the pole and fixtures EPA rating (which is a wind rating). I am guessing in your area the wind rating is somewhere around 70 to 80 mph. Most pole standard bases in commercial and retail parking areas are a minimum 6' deep and they are usually 8' deep. As far as a concrete pole pier this usually has to be worked out by a structural engineer familiar to you area. He specifies the pier circumference and the size of the rebar needed.
Here's an example for a 30' pole and fixture: You probably don't need to raise the pier 3' above ground level, that's to prevent cars from running over it. Also you can see the hand written grounding note. You would need to install a ground rod and attach it to the metal pole with a #6 solid copper conductor.