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Old 06-26-2012, 08:44 PM   #1
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Neutral with/without ground on residential service


Hello all,

I am looking for a clear answer as to why on some panelboards the neutral wires are tied in with the ground bar/wires and then on other panels the ground and neutral both have separate bars and are terminated separately in the panelboard.

Thanks for any and all help!

Marcus

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Old 06-26-2012, 08:51 PM   #2
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Neutral with/without ground on residential service


In the main panel or disconnect the neutral is bonded to the panel box and there for the equipment grounding. This is the ONLY place under modern codes.

Older codes allowed some remote structure sub-panels, and some ranges and dryers to also have a neutral/ground bond.

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Old 06-26-2012, 10:40 PM   #3
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Neutral with/without ground on residential service


If grounds and neutrals were bonded together everywhere else (i.e. in sub panels of the same system), you would be creating bridges or alternative paths for the current. The normal current flowing "back home" in the neutral could "deviate" through the ground conductors at those remotely tied points, causing potential shock hazard in your grounded/bonded infrastructure (i.e. metal boxes, metal frames, metal conduit, equipment, anything grounded, etc...).

Ground and neutral is bonded together only at the main panel because that is also only where your system is physically grounded to earth. Any deviant current will flow to earth (and not back to shock you) because there it is physically closest to earth. Electricity follows the path of least resistance.

Last edited by sixspeed; 06-26-2012 at 10:43 PM.
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Old 06-27-2012, 12:19 AM   #4
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Neutral with/without ground on residential service


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Originally Posted by sixspeed View Post
If grounds and neutrals were bonded together everywhere else (i.e. in sub panels of the same system), you would be creating bridges or alternative paths for the current. The normal current flowing "back home" in the neutral could "deviate" through the ground conductors at those remotely tied points, causing potential shock hazard in your grounded/bonded infrastructure (i.e. metal boxes, metal frames, metal conduit, equipment, anything grounded, etc...).
That's mostly true. The biggest issue is that if there are multiple neutral-ground bonds and the neutral path is compromised, then the grounded metal parts will become energized if the grounding path is also compromised.

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Ground and neutral is bonded together only at the main panel because that is also only where your system is physically grounded to earth. Any deviant current will flow to earth (and not back to shock you) because there it is physically closest to earth. Electricity follows the path of least resistance.
Definitely not. Earth grounding plays NO ROLE in protection from shock due to ground faults. That's what bonding is for. The neutral-ground bond is what makes a circuit breaker trip if a hot wire comes in contact with a grounded metal part. Current flows through the fault, along the equipment grounding path back tot he panel, and to the service neutral through the neutral-ground bond. Since all these parts are solidly connected together, it's a direct short-circuit and the breaker trips quickly.

Electricity does not seek the earth whatsoever. It returns to its source, which in the case of utility power is: the utility's neutral connection. The utility's neutral also happens to be rather well connected to the earth, but for unrelated reasons. A grounding rod will never pass enough current to trip a circuit breaker. You can connect a hot wire directly to a grounding rod and it will draw only a few amps (google it - the experiment has been done repeatedly). The grounding rod serves only to stabilize the system voltage with respect to the earth, and to help protect against some types of damage from nearby lightning strikes. If the neutral and ground are not bonded at the service equipment, the grounding system is worse than useless - it's a danger, because a single ground fault anywhere on the system will electrify all grounded metal on the system, including the ground rod, without tripping a breaker.

And FWIW, electricity follows all paths in inverse proportion to their resistance, not just the path of least resistance. So if multiple neutral-ground bonds exist on a system, the grounding path will always carry some portion of the load current even if the neutral path is perfectly intact.

Last edited by mpoulton; 06-27-2012 at 12:23 AM.
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Old 06-27-2012, 07:31 AM   #5
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Neutral with/without ground on residential service


Ok good explanation. Thanks.

Now, if the neutral path were severed between the utility and the N-G bond in the main panel, where does the current go and which short-circuit protection device first trips? (the main panel main breaker, the branch breaker, something at the utility...?)
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Old 06-27-2012, 04:19 PM   #6
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Neutral with/without ground on residential service


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Ok good explanation. Thanks.

Now, if the neutral path were severed between the utility and the N-G bond in the main panel, where does the current go and which short-circuit protection device first trips? (the main panel main breaker, the branch breaker, something at the utility...?)
No breaker trips, and it's a REALLY big problem. If there are any metallic paths back to the utility, the load will travel through them. This is often water or gas piping, cable TV shielding, or other things not intended to handle large amounts of current. If there are no paths, then the neutral/grounding system will float at a voltage determined by the distribution of load on each leg of the service. This means that 120V loads can see up to 240V across them. Things tend to get destroyed. Some current will flow back to the utility through the earth via the grounding rod and other buried metal, but not enough to stabilize the voltage and prevent major problems.

Pretty much only a downed power line will get a utility crew out faster than a call for a loose neutral.
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Old 06-27-2012, 04:40 PM   #7
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Neutral with/without ground on residential service


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Originally Posted by sixspeed View Post
Ok good explanation. Thanks.

Now, if the neutral path were severed between the utility and the N-G bond in the main panel, where does the current go and which short-circuit protection device first trips? (the main panel main breaker, the branch breaker, something at the utility...?)
Nothing trips, your service becomes a 240v series circuit.

Same results, just a smaller scenario.
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Old 06-28-2012, 12:09 PM   #8
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Neutral with/without ground on residential service


I see. Service entrance wiring is like a MWBC from the utility, and comes with the inherent dangers of such.

If no breakers would trip in the event of a lost neutral between the utility and premise, I wonder if there exists a protective device that would sit ahead of a main panel (or load), that would constantly monitor and compare L1-N and L2-N voltages, and would trip open when the readings indicate a bad or open neutral.

Similarly, if such a device could be installed at the end-of-line of a MWBC, it could trip the breakers when it senses an open branch neutral by inducing shorts to ground... just thinking aloud here: an NFCI device.

Last edited by sixspeed; 06-28-2012 at 12:13 PM.
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Old 06-28-2012, 05:17 PM   #9
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Neutral with/without ground on residential service


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I see. Service entrance wiring is like a MWBC from the utility, and comes with the inherent dangers of such.

If no breakers would trip in the event of a lost neutral between the utility and premise, I wonder if there exists a protective device that would sit ahead of a main panel (or load), that would constantly monitor and compare L1-N and L2-N voltages, and would trip open when the readings indicate a bad or open neutral.
The power company has great insurance and will cover any of your losses should such an event take place. Of course, if it's on your end, you better have great insurance.

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Old 06-30-2012, 06:31 PM   #10
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Neutral with/without ground on residential service


Sorry for missing the great discussion. Really opened my eyes quite a bit. And it seems pretty simple. So regardless if there exists a separate ground bar in the panelboard or the neutral/ground branch circuit wires terminate at the same bar there must exist a n/g bond at the panel in some way? So I assume different panelboards may create that bond in different ways.
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Old 06-30-2012, 06:54 PM   #11
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Neutral with/without ground on residential service


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Originally Posted by Hexamexapex View Post
Sorry for missing the great discussion. Really opened my eyes quite a bit. And it seems pretty simple. So regardless if there exists a separate ground bar in the panelboard or the neutral/ground branch circuit wires terminate at the same bar there must exist a n/g bond at the panel in some way? So I assume different panelboards may create that bond in different ways.
The neutral-ground bond must occur at the service equipment, which is the first means of disconnect after the meter. So if the panel has a main breaker and is not a subpanel, the bond must be in that panel. If there is a disconnect ahead of the panel, the bond is there. If it's a subpanel, the bond is back at the main panel or disconnect. In many panels there is a single isolated bar that can be bonded to the chassis with a green screw, which is normally installed at the factory. Removing that screw isolates it and allows it to be used as a neutral bar, in whcih case a separate grounding bar must be installed that's bonded to the chassis.
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Old 06-30-2012, 08:31 PM   #12
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Neutral with/without ground on residential service


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The neutral-ground bond must occur at the service equipment, which is the first means of disconnect after the meter. So if the panel has a main breaker and is not a subpanel, the bond must be in that panel. If there is a disconnect ahead of the panel, the bond is there. If it's a subpanel, the bond is back at the main panel or disconnect. In many panels there is a single isolated bar that can be bonded to the chassis with a green screw, which is normally installed at the factory. Removing that screw isolates it and allows it to be used as a neutral bar, in whcih case a separate grounding bar must be installed that's bonded to the chassis.
Ok that makes sense. The n/g must be bonded on the supply side? So in the case of a separate grounding bar.........it can be bonded to the neutral bar through the chassis? Or would this type of arrangement only be used on main lug and subpanels?
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Old 07-01-2012, 10:06 AM   #13
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Neutral with/without ground on residential service


Another thought just popped up ........since the neutral and ground are bonded at the disconnect or main breaker this would mean the ground wires in each respective location are "live" or "hot" conductors right? Since the neutral wire is returning the current and the ground wires are bonded with the neutral? Or does the path of electricity follow the inverse portion of resistance as explained earlier by poulton?
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Old 07-01-2012, 02:19 PM   #14
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Neutral with/without ground on residential service


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The neutral-ground bond is what makes a circuit breaker trip if a hot wire comes in contact with a grounded metal part. Current flows through the fault, along the equipment grounding path back tot he panel, and to the service neutral through the neutral-ground bond. Since all these parts are solidly connected together, it's a direct short-circuit and the breaker trips quickly.

Electricity does not seek the earth whatsoever. It returns to its source, which in the case of utility power is: the utility's neutral connection. The utility's neutral also happens to be rather well connected to the earth, but for unrelated reasons.

And FWIW, electricity follows all paths in inverse proportion to their resistance, not just the path of least resistance. So if multiple neutral-ground bonds exist on a system, the grounding path will always carry some portion of the load current even if the neutral path is perfectly intact.
In the case of a panel with a disconnect ahead of it. How does the breaker trip in the panel if the N/G bond is back at the disconnect? Why doesn't the main breaker trip first. Fundamental question I know......

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