Lightning Damage to Concrete Encased Electrodes

[Pierre C Belarge]

Yes Don but the caveat here is POLE FOUNDATIONS because the amount of concrete is so small in comparison to say a slab on grade building the extra cost of double tied are justified for the extra protection it offers.

When you get into regular sized buildings due to the scale of and number of interconnections there is no real benefit IMO to double tie or spot weld. It has been my experience with a foundation as small as say a average size home, just using single tie method can result impedance as low as 1 ohm.

But as I get older and wiser, I am less convinced that such low impedance is of any real benefit. In fact I can make a good argument having such a low impedance can actually cause some problems like high GEC return current as experienced in the ole days of a metallic water pipe system.

:grin:

The impedance you are speaking of here is of relative small area, such as the area around the cell tower site, etc... am I correct?

Water pipes can/do travel for great distances and actually connect different buildings together.

I am not trying to be argumentative, I am trying to understand how this all works.
Say for instance I take several cell sites and they are somewhat close together. Would they have the same conductance through the earth between them as say a number of buildings sharing the same metal waterpipe system?

 

[hornetd]

The impedance you are speaking of here is of relative small area, such as the area around the cell tower site, etc... am I correct?

Water pipes can/do travel for great distances and actually connect different buildings together.

I am not trying to be argumentative, I am trying to understand how this all works.
Say for instance I take several cell sites and they are somewhat close together. Would they have the same conductance through the earth between them as say a number of buildings sharing the same metal waterpipe system?

I would think that the obvious answer is no. One of the reasons that the code specifically forbids using the earth as an Equipment Grounding Conductor is that the earth itself is a very poor conductor. It is only it's huge cross section relative to the direction of current flow that makes it behave as a good place to dissipate destructive current flows. If you measure the impedance of the water piping against the sum of the impedance of the two Grounding Electrode Systems I would be very surprised if the water piping impedance wasn't lower. Cell sites are not likely to be as close together as adjacent homes in any non rural setting.
--
Tom Horne

 

[don_resqcapt19]

...that the earth itself is a very poor conductor. It is only it's huge cross section relative to the direction of current flow that makes it behave as a good place to dissipate destructive current flows. --
Tom Horne

Actually the earth itself is a very good conductor because of its huge cross setional area. It is the connection to earth that causes the problem.

 

[K8MHZ]

Actually the earth itself is a very good conductor because of its huge cross setional area. It is the connection to earth that causes the problem.

While 'the earth' may be a good conductor, 'earth' or soil, sand, gravel, etc., is not, necessarily.

Our area has a very high sand content and making a good earth connection is very, very difficult. Tests have shown that a single 8 foot ground rod has 1300 ohms resistance 'to earth' in my area.

It's not unusual to see 6 or 7 volts between old metal water pipe from the city to the rest of the system (two ground rods, plus the POCO's ground, which is usually one rod at the base of the pole the tranny is on). Sometimes you can actually see a spark when you connect the conductors together.