ECN Forum Forums General Topics of the Trade General Discussion Area #6 G-rod, #4 Ufer

What is the difference between resistance and impedance? Where do we have to be concerned with impedance? What is reluctance?

Impedance is the total opposition to the flow of current in an AC circuit. A DC circuit is only opposed by the resistance of a circuit (wire and and other device in the ckt) an AC circuit is opposed by the resistance of the wire, coupled with the capacitive reactance (two wires, carrying current = capacitance) and the inductive reactance of the ckt (such as the pipe the wires are in, bx skin, bldg. steel, etc.). you need to be concerned with it in all ckts, and design that way. Reluctance is alas an OLD electronics term I probably should not have used, the proper more up to date term is reactance. Sorry, geezerism strikes on occasion

This (Impedence/Resistance) sounds like a good topic for the Theory area. Anyone care to start sonething there?

Bill

Along this same thread - Creighton Schwann wrote a good article for EC Mag. "Things Are Not What They Seem"...discusses grounded, bonded, grounding conductors - their function and sizing them properly. This article is available online at ecmag.com in the back issues section of the web sites. It is pretty well written and helps clarify these 3 conductors.

Thanks for the link, Dana.

Make that:

Things Are Not Always What They Seem

W. Creighton Schwan

and you'll have a little less trouble searching for it than I did.

Whats a ufer?

George I can't believe a master electrician doesn't know what a ufer is!!

It's rebar used as a grounding electrode - 20' long, run along the lower part of your foundation footing (at least 2" above ground level)....don't have my notes with me but I believe the guy who actually tested and started this system was named Ufer -thus the name ufer for this system.

nothing like the internet! "during WWII, a retired vice president of UL, Herbert G. Ufer developed it for the US Army.....a cheap earthing system that consistently outperforms typical ground rod installation....developed it for grounding bomb storage sheds.....rebar is in the concrete foundation which is more conductive than all but the best soil...tests confirmed stability...many of his findings are detailed in IEEE Transactions paper #63-1505....so ....the way to install a Ufer is use a piece of 20' rebar, bend it up on the end (the above ground connection), tie wrap the encased portion of the bar to the other rebar grid-work and you have a Ufer that is far superior to most other grounding systems.

Hat's off to ol' Herb, a Ufer beats a municipal H20 line amyday!
http://www.scott-inc.com/html/ufer.htm