Ground Rod Resistance

this is the Lyman channel hi I'm Travis Christensen with Northwest Lyman College the installation of ground rods is most important when installing personal protective grounds on a three wire system such as an ungrounded wire Delta system or transmission lines with an inadequate or no shield wire since electricity favors the path of least resistance to ground it's important to make sure that your ground rods resistance is as low as possible that way if the line becomes energized most electricity will go through the ground rod instead of through your body now that we know we need low resistance in the ground rod how do we achieve it well let's go do some tests and find out here we have a series of ground rods driven at different depths in the ground and using this ground rod resistance tester I'm going to measure each rods resistance our first ground rod is only driven one and a half feet deep and has a ground resistance of 750 ohms our second ground rod is three feet deep and has a ground resistance at 440 ohms and our last ground rod is driven seven feet deep and is reading 123 ohms as you can see the deeper the ground rod is driven the less resistance it has think of it like a sprinkler system spewing water for many different holes or paths but penetrating the earth deeper the ground rod provides more paths for the flow of electrons resulting in less resistance by doubling the rods depth you can reduce the resistance by 40% but what if you can't drive the ground rod as deep as you'd like your next option is the parallel multiple ground rods together I paralleled the one and a half foot and three foot ground rods and got a resistance of 255 ohms which is less than either of them individually if this technique is used it's important that you create spacing around the ground rods because as current is discharged into the earth it's displaced the same distance around the ground rod as its depth so if I install two ground rods four feet deep they need to be placed eight feet apart to avoid overlapping their areas of discharge if I install them any closer together the resistance will not be lowered resistance is also affected by the type of soil the ground rod is driven into I drove a ground rod three feet in the sandy soil and got a resistance of 750 ohms which is more than the ground rod driven three feet in the dirt they had a resistance of 440 ohms I also tested the resistance in swampy soil at the same depth and got a resistance of 122 ohms so of the three soils tested the swampy soil had the best grounding source there's no standard level of ground resistance in effect for personal protective grounding however finding the lowest ground resistance when installing your ground rods will provide the highest level protection for you and your crew for northwest lamin college i'm travis christensen work safe out there

Channel: Northwest Lineman College's Lineman Channel

Views: 107,273

Rating: 4.8391962 out of 5

Keywords:

Id: G2OtgeDkTLs

Length: 2min 47sec (167 seconds)

Published: Tue Apr 22 2014

Reddit Comments

[u/Kilocycles]

It's probably a really important note, that when using ground rods must be of 8-feet in length, and must be also driven to a minimum length of 8-feet. They also must be spaced no closer than 6-feet apart, but ideally no further than 16-feet apart.

 

Edit to add: The video does not provide applicable information for our hobby with regards to ground electrodes that folks use (this is only for protection for the linemen crews, any electrical inspector or engineer familiar with NEC would say "NO" to this in a heart beat if it were for home/commercial use), but it does show the effects of electrode length vs. installed depth vs. effects from rods placed next to each other. That part itself, is relevant.

This is all covered in National Electrical Code.

[u/somebodyelse22]

Technical critiques notwithstanding, I found it very informative and useful. Thank you OP.

[u/harlows_monkeys]

It would have been interesting to include a horizontal ground rod (30" deep, 8 feet long), which the NEC allows as an alternative to a vertical ground rod.

[u/[deleted]]

I'm probably good with my 9 ground rods. :)

(Radio room/antenna entrance is on the far side of the house from the main electrical ground, so additional rods and #4 wire were required.)