Grounding concept.

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cripple

Senior Member
Location
Santa Fe, New Mexico
I have some questions about Mikes :confused: grounding concept.
Maybe I should tell you my concept of grounding and you can pick it apart.
1. The 1897 Electrical Code grounding requirements were to control static electric, and for lightning protection.
2. Utility ground to increase reliability of their distribution systems.
3. Utility prefer multiple grounding point, because of their increase grounding points it will insurance against the entire loss of the return path back to the source.
4. The purpose of utility grounding is to provide practical methods of grounding for the safeguarding of employees and the public from injury that may be caused by electrical potential on electric supply or communications facilities, by being able to ensure that the return path is not broken, so as to operate the overcurrent protection devise.
5. NEC grounding is to help prevent accidents to persons and damage by fire to property in case of lightning, breakdown between primary and secondary windings of the transformers, or accidental contact between high-voltage wire and low-voltage wires. If some point on low-voltage circuit if grounded:
1.Lightning striking the wires will be conducted into the ground
2.Breakdown of the transformer insulation between primary and secondary coils will reveal itself through blowing of the primary transformer fuses if one wire of the primary circuit comes in contact with one of the secondary wires.
6. Keeping in mind that the utility does ground their system and the ground (earth) is used as parallel path back to its sources. If the secondary side of the transformer is not grounded, and a crossover does occur the primary 7621 volts, (on a four wire 13.2KV destitution system) would be impressed on the secondary system. The insulation of the secondary system only 600 volts, numerous insulation breakdowns would occur, which would cause considerable damage to equipment installed on a grounded surface (earth), and there would be an extreme damager to human life when coming in contact with any part the secondary system.
7. I do agree that lightning does not protect electrical or electronic equipment from lightning voltage transients induced onto the circuit conductors.
8. I do feel that bonding of source and all noncurrent carrying metal parts is to ensure a low impedance path back to the source to operate the overcurrent protection device.
I hope I have been able to explain my concept, so that you tell me where I want wrong.
 
B

bphgravity

Senior Member
Location
Florida
Re: Grounding concept.

The problem is that actual grounding benefits is not provable, whereas bonding benefits can be.

Take 250.4(A)(1), "limit voltage imposed lighning" - no proof or evidence this is true, "line surges, or unintentional contact with higher-voltage lines" - please exaplain how? and of course "stabilize the voltage to earth during normal operation" - who cares.

The fact is that grounding, no matter what the benefits may be on the utility side, is really not all that important on the premises wiring system side. There is way too much focus and energy wasted on trying to figure out the function of grounding on today's electrical systems.

Bonding on the other hand is just about the single most important aspect of any electrical system. This is the function that will save lives and property during fault events.
 
C

cripple

Senior Member
Location
Santa Fe, New Mexico
Re: Grounding concept.

Take 250.4(A)(1), "limit voltage imposed lightning" - no proof or evidence this is true, "line surges, or unintentional contact with higher-voltage lines" - please explain how? and of course "stabilize the voltage to earth during normal operation" - who cares.

To better understand the intent of the rule you would need to look at what was trying to be accomplished.
In the 1947 National Electrical Code Handbook sixth edition on page 269 section 1902 the following is stated on the Purpose of System Ground:
Interior wiring systems are grounded for the purpose of limiting the voltage upon the system which might otherwise occur through exposure to lightning, or through exposure in any other manner to voltage higher than that for the system is designed: or to limit the maximum potential to grounding due to normal voltage.

An interior wiring system is considered as being ?exposed? to voltage higher than that for which the system is designed if it is supplied through a step-down transformer, because there is possibility that the insulation between the primary and secondary windings of the transformer may break down. The possibility of cross between the primary and secondary means constitutes another such exposure.

This is what meant by the statement number five in my posting.
 
B

bphgravity

Senior Member
Location
Florida
Re: Grounding concept.

That still doesn't explain how grounding the service equipment and service neutral actually limits those occurances? :confused:
 
charlie

charlie

Senior Member
Location
Indianapolis
Re: Grounding concept.

Bryan, grounding does nothing worthwhile for low voltage stuff (systems under 1 kV) in clearing a fault. However, it does wonders for medium voltage stuff and higher (systems that are greater than 1 kV). We are prohibited from using the earth as a return but it is permitted to use the earth to help clear a fault. In fact, we depend on the earth to open our cutouts when our lines come down in a storm if the phase wire missed the system neutral.

Lightning is also looking for the earth and will sometimes use our system for that path. :D
 
P

pierre

Senior Member
Location
Westchester County, New York
Re: Grounding concept.

"Lightning is also looking for the earth and will sometimes use our system for that path."

This statement is not entirely true - as lightning is not always looking for earth - such as cloud to cloud lightning.
 
charlie

charlie

Senior Member
Location
Indianapolis
Re: Grounding concept.

I agree Pierre, it depends on where the charges are located. Does the stroke go from the clouds to the earth or the earth to the clouds in a normal strike? :D
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
Re: Grounding concept.

Does the stroke go from the clouds to the earth or the earth to the clouds in a normal strike?
Click to expand...
That would depend upon the polarity of the charge.
Most lightning is of the negative flavor in which the lightning is a cloud to ground event and has many branches which divides the current in all branches that make contact with Earth. This type does less damage.
In a positive charge the lightning it leaves one point on Earth and strike many points on the clouds in this case since it only has one point of attachment on Earth, all the current is focused upon one point and can cause catastrophic damage. We use to call positive charged lightning "super lightning" as when it strikes LOOK OUT!!!! I have seen the damage a positive strike causes. But they are rare.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Re: Grounding concept.

wonder what happens when "super lightning" hits "super neutral" from an earlier thread?

[ August 25, 2005, 08:31 AM: Message edited by: augie47 ]
 
Dnkldorf

Dnkldorf

Senior Member
Re: Grounding concept.

Hurk, Can you provide any info on the ground to cloud lightning strike?

Streamers may leave a point, or points from the earth, and provide a path for lightning to strike, but I have yet to read anything from anyone, that proves lightning originates from the earth and travels to the clouds.

There are cloud to earth strikes, and cloud to cloud strikes, and I have heard this theory from alot of people, but can't find any info pertaining to it.

A return charge, heads to the clouds, but actual lightning originating from the ground has been an elusive subject of mine.

This link provides some basics about lightning.

http://skydiary.com/kids/lightning.html


Dnk..
 
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