ser vs seu?

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yelwdog

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can someone tell me exactly why i need to seperate grounded and grounding conductors after the main disconnect?
 
infinity

infinity

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Because if they're connected on both ends they are in parallel and the EGC, which under normal conditions shouldn't carry current, will.

Welcome to the forum. :)
 
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yelwdog

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ser vs seu

ser vs seu

thanks for the help. ive worked in the field doing mostly res for about 6 yrs now. i know how things are to be done but sometimes i forget the why. lately ive been digging into grounding vs bonding just because i had questions on the two. it seems i dont fully understand some items and i hope this forum will help.
 
jumper

jumper

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Here is a picture showing what the others stated

1113844669_2.jpg
 
mcclary's electrical

mcclary's electrical

Senior Member
Location
VA
yelwdog said:
thanks for the help. ive worked in the field doing mostly res for about 6 yrs now. i know how things are to be done but sometimes i forget the why. lately ive been digging into grounding vs bonding just because i had questions on the two. it seems i dont fully understand some items and i hope this forum will help.
Click to expand...



Welcome to the forum,



and thanks Derek. Good graphic
 
Dennis Alwon

Dennis Alwon

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Yes, objectionable current yet the NEC allows emt or metal conduit between the meter and the first panel along with a neutral conductor. Is that not parallel and objectionable when it is all bonded together? I never understood that.
 
LEO2854

LEO2854

Esteemed Member
Location
Ma
yelwdog said:
thanks for the help. ive worked in the field doing mostly res for about 6 yrs now. i know how things are to be done but sometimes i forget the why. lately ive been digging into grounding vs bonding just because i had questions on the two. it seems i dont fully understand some items and i hope this forum will help.
Click to expand...

you have come to the right place you will learn a lot .I have in just a few weeks.
Derck How did you post that graf???
 
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yelwdog

Member
thanks for that illustration it helps to clear things up. the only issue i still have (trying not to be too much of a dub here) is what difference does it make that this occurs on the load side of the main disconnect? the grounded and egc are still tied together at the service.:confused: i get the parallel current issue......................i think
 
infinity

infinity

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yelwdog said:
thanks for that illustration it helps to clear things up. the only issue i still have (trying not to be too much of a dub here) is what difference does it make that this occurs on the load side of the main disconnect? the grounded and egc are still tied together at the service.:confused: i get the parallel current issue......................i think
Click to expand...

The parallel issue would only occur if they're connected on both ends not just at the service.
 
reddy kw

reddy kw

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Mudville, upstate New York.
yelwdog said:
thanks for that illustration it helps to clear things up. the only issue i still have (trying not to be too much of a dub here) is what difference does it make that this occurs on the load side of the main disconnect? the grounded and egc are still tied together at the service.:confused: i get the parallel current issue......................i think
Click to expand...

Electricity follows path of LEAST resistance.
Have one low resistance grounding point with shortest possible distance to earth (greater length=more resitance). Fault currents get routed safely to ground rod or electrode, away from human contact. Ground loops (which parallel path would create) double the distance current must travel.

High-amp faults travelling on surface of metal enclosures or conduits can and will jump to shorter (less resistive) path to ground, I.E.: person touching metal, standing on concrete basement floor in bare feet...

To prevent this, make ground path resistance low as possible, seperate grounds from neutrals at all points (EXCEPT where service entrance conductors connect to service equipment).
We bond neutral to grounding electrode conductor once (at service entrance), to give fault current in neutral a safe way out of system, to earth.
 
jumper

jumper

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reddy kw said:
Electricity follows path of LEAST resistance.
Click to expand...

Not so sure about that,

From here:

http://forums.mikeholt.com/showthread.php?t=95495

"Electricity does not seek the path of least resistance to the earth. It seeks all available paths back to it?s source, in proportion to their resistance. The reason that a person gets shocked when touching an ungrounded conductor and the earth is because the neutral of the system is repeatedly connected to earth in a grounded electrical system. The earth becomes part of a return path to the transformer ? it?s part of one route back to the source; the earth is not the destination for the electricity."



Have one low resistance grounding point with shortest possible distance to earth (greater length=more resitance). Fault currents get routed safely to ground rod or electrode, away from human contact. Ground loops (which parallel path would create) double the distance current must travel.
Click to expand...

"Driving a ground rod to ?ground? any electrical equipment does not provide the low-resistance path required to trip breakers. Driving a ground rod, or using a Ufer, or a metal water pipe is not a substitute for an EGC. A ground rod with 25 ohms to earth will allow almost five amps to escape the system into the earth when directly energized from a 120V source. Five amps will never trip a 15A or 20A breaker, and in the meantime everything bonded to this ground rod will be energized to 120V."
 
infinity

infinity

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Staff member
Location
New Jersey
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Journeyman Electrician
reddy kw said:
Electricity follows path of LEAST resistance.
Have one low resistance grounding point with shortest possible distance to earth (greater length=more resitance). Fault currents get routed safely to ground rod or electrode, away from human contact. Ground loops (which parallel path would create) double the distance current must travel.

High-amp faults travelling on surface of metal enclosures or conduits can and will jump to shorter (less resistive) path to ground, I.E.: person touching metal, standing on concrete basement floor in bare feet...

To prevent this, make ground path resistance low as possible, seperate grounds from neutrals at all points (EXCEPT where service entrance conductors connect to service equipment).
We bond neutral to grounding electrode conductor once (at service entrance), to give fault current in neutral a safe way out of system, to earth.
Click to expand...


As Derek said current follows all paths regardless of resistance. If it didn't then two different resistive loads could not operate on the same circuit.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
jumper said:
"The reason that a person gets shocked when touching an ungrounded conductor and the earth is because the neutral of the system is repeatedly connected to earth in a grounded electrical system. The earth becomes part of a return path to the transformer ? it?s part of one route back to the source; the earth is not the destination for the electricity."
Click to expand...
It also helps to mention that the shocking current is in addition to the circuit's existing current.
 
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