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Author Topic: Tbolt ground & The Sky is Falling! Oh My!  (Read 4952 times)
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WV Hoopie
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« on: July 28, 2010, 11:04:34 PM »

Rather than hijacking ke7trp thread, I'll raise a question here. First, I have no problems with the NEC in theory. A current copy was always within reach before I retired. But in practice relating to our homes with local electrical inspectors, with local twists of the code; I have second thoughts.

In my line of work; before a facility was built several inches of soil was removed. Some cases the soil was hauled away, not to be used on site. A grid of large gage copper wire was placed near & under equipment areas, iron work, compressors, pumps, motors and the like. Same gauge wire was cad welded and leads were placed where they were to be connected later.

Then the forms for concrete work, etc., were built and the site back filled with a dry mixture of sand, small gravel, and concrete. After back filling the area was compacted before concrete was poured, steel beams erected, and equipment installation.

My part in all this was as a member of a constrution & start-up team for hydrogen plants. Later after the facility was up and running the electrical engineering group would give me a heads up that a piece of test gear was on its way to my door step. That piece of gear was usually a AEMC 3711 or one of its cousins.

I had the pleasure of spending about three days going around facilities and testing ground resistance of all those leads. Copies of the grounding plot was made at Kinko's. On these copies I would date and record the reading as left. It wasn't real common but some of the cadwelds were broken off of the steel beams or during work on equipment some fasteners would become loose. Any thing out of normal had to be repaired! Broken cadwelds would end up on a work list to be repaired by a contractor.

There is a very improtant reason the ground resistance of all earth/safety grounds be the same! I've had work done by an electrical contractor here in Oregon, inspected by the local electrical inspector, ground rods installed. But never did anyone check to see if the safety ground at the main panel was connected to anything or test to see of the ground resistance was the same as the two that were required by the inspector!

If I understand the safety grounding and resistance issue; if the resistance isn't the same, current will travel through more than one circuit and with the current divided, the correct breaker might not trip.

My house is over fourty years old. Who wants to wager money on the integrity of the safety ground at the main panel?

Let the discussion begin.

Craig,



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w3jn
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« Reply #1 on: July 28, 2010, 11:13:16 PM »

Simple ohms law - in any current carrying circuit, if there's resistance between two elements, there's a voltage potential.  The NEC doesn't want anyone to be able to touch two metallic elements in a structure and get a shock, which could be the case if all grounds don't go back to the same point.   If there's a fault - for example, a hot wire whose insulation is skinned and faults to a conduit, the fault must be cleared by a breaker - which won't happen if the conduit's not grounded, or grounded to a different point from the service entrance.
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FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
n2bc
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« Reply #2 on: July 29, 2010, 08:26:54 AM »

Craig, excellent point.

My main experience came some years ago when I wanted to add a branch circuit to my entrance panel - appx 30 years old.  The local DIY outfit didn't carry the breakers.  A visit to an electrical supply could get me the needed breaker but at 5X the cost of other 'common' makes.

Why?  Seems the manufacturer was sued out of existance in the home market because some of their breakers failed to trip.  http://www.inspectapedia.com/fpe/fpepanel.htm

I ended up replacing the entire panel and in the process upgrading the entrance ground to current code - required by the utility in order to get my meter plugged back in.

So, how do you know your 40 year old house is OK?   LOOK or get it inspected by a competent electrician.    My original panel was full of potentially deadly breakers.

LOOKING was the point of my post regarding multiple BAs 'fixed' by multiple people.  If you don't LOOK you simply won't know if the stuff is safe.   

73, Bill  N2BC
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WV Hoopie
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« Reply #3 on: July 29, 2010, 10:11:19 AM »

Hi Bill,

Looking seems to be something we do at work, PM's at home don't happen. I like to compare boatanchors with clothes dryers. There must be millions of clothes dryers wired with a 3 wire plug. Heck I haven't lived in a home with a 4 wire recepticle for a clothes dryer. If there has been a recall for those old 3 wire dryers, someone has missed the one in my home. My clothes dryer has more hours running than the Johnson Desk/500 will ever have.

But due to the fact we as amateur radio operators  often litter the earth's surface with 8 foot ground rods, we just add another layer of complexity. Just sticking to the electrical safety ground subject, if the ground resistance isn't checked, we have wasted a lot of money purchasing copper wire and rods.

Here in Orygun the local electrical inspector required two 8 foot 5/8 dia ground rods for my radio shack, not because of the radios, but because the building had telephone and tv cable service. Neither the inspector or the contractor check ground resistance of the new rods or the one at the service entrance of the main panel. In my industry, this is how to build a better death trap.

Craig,
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WA1GFZ
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« Reply #4 on: July 29, 2010, 10:23:50 AM »

I am lucky to work with one of the smartest lightning guys on the planet.
Training day one. 1. Lightning is all about ohms law
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WV Hoopie
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« Reply #5 on: July 29, 2010, 10:53:51 AM »

Just to clarify, in case; Yes a four wire system is safer in theory and on paper. Chances are, for those who only have one ground rod connected to their electrical service, that fourth wire is a plus. I have little faith in a clamp style connection buried underground that has been there for years and never checked.

Notice, I've tried to stick to the electrical safety ground. RF and lightning are two different subjects and need to be treated in another maner.

Craig,
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W2VW
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« Reply #6 on: July 29, 2010, 11:38:31 AM »

Hi Frank,

       A certain contractor at a certain facility is trying to go cheap by installing 2" copper STRAP instead of the usual 4". I'd like to put a stop to this.

Whatsa?

 
I am lucky to work with one of the smartest lightning guys on the planet.
Training day one. 1. Lightning is all about ohms law
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