Neutral Ground Bond

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shannonave

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Melbourne, FL
I am not an electrician but my job is inspection of Lightning Protection systems including earthing. I always look to see if there is a N-G bond and especially to ensure that there is one one. I find tha tthe meter base provides for a N-G bond. When this is done, I "assume" this is the only one allowed - but - then the earth and neutral should be seperately extended to the disconenct from the meter base and onto the distribution panel. If there is no meter base, the N-G bond should be in the disconnect.
 
shannonave said:
...I "assume" this is the only one allowed - but - then the earth and neutral should be seperately extended to the disconenct from the meter base and onto the distribution panel. If there is no meter base, the N-G bond should be in the disconnect.
Click to expand...

No, the grounded conductor (usually a neutral), if it exists, is always required to be bonded to the service-disconnect enclosure. An exception exists to also allow the additional connection in the meter base.

The grounding electrode conductor can be connected at any point from the service point to the disconnect.

Welcome to the forum.
 
And as you probably know the electrical power grounding electrode system needs to be bonded to the LP system, but cannot rely on it for the required grounding electrode(s).
 
Neutral Ground bond -

Neutral Ground bond -

Thank you Volta - however,
If there is a N-G bond in the meter base, then another at the main disconnect, (service entrance), do we not have two N-G bonds, particulary if the utility earth at the meter base is not extended to the MD and bonded to the "site" earth. Then the Neutral certainly has two sperate and distinct earths bonded to the neutral. All the work I am doing is outdoor traffic cabinets and the like. The meter can and MD can be on the cabinet or across the street. The issue of "touch voltages" at the metal poles at the various corners of the intersection is a pedestrian safety issue if FULL bonding is not implimented. For this reason I "believe" that the utility earth at the meter can "must" be brought forward to the MD and connected to the site earth and on throughout the system. Your comments please.
 
Qualifications

Qualifications

Bryan,
My job is to investigate a site that has sustained Lightning related damage and identify why and what the fix is. The areas of concern are the surge protectors (TVSS) on the AC, DC communications, data, video and other circuits. Then I measure the earth resistance (<25 ohms), and ensure there is a zero resistance bond to all components on a site (cabinets, tower, poles etc). The last is to check the N-G bond. Some sites I visit do not have a bond at all which puts the AC TVSS at risk when AC is floating relative to site earth. As to qualifications: I have an engineering & communications degree from the UK. I have been involved in lightning research for 10 years and extensively involved in TVSS devices for over 13 years. I have done investigations throughout the USA and abroad mainly focussed on cellular, wireless and traffic sites - not building structures. Because of their towers or remoteness, they are very vulnerable to lightning damage.
 
I can see some cross cultural terminology - Hopefully it won't lead to too much confusion...

Earth has been removed from our dictionary... :D So to speak.... "Earthing" isn't in our lexicon...

Welcome to the forum none-the-less but you may want to refer to some of this in our common terminology. "Grounding" and conversely "Bonding"

Take a peek here too...

http://forums.mikeholt.com/showpost.php?p=656116&postcount=37

Anyway the codes here 'require' certain connections, and 'allow' certain connections in the respect to the connection between the neutral (Grounded conductor) and 'grounding' conductors.

The NEC "requires" the bond between the Grounded and Grounding conductors in the main disconnecting means... The Main Bonding Jumper. (MBJ)

However - (and IMO contrary to intent of single point grounding) "allows" certain enclosures to be "Grounded" by the grounded service conductor - e.g. meter enclosures. In a political sense conductors prior to the main disconnect are under two sets of rules as well - the utility providing power - who may also require that the connection be made there, and the NEC which allows it to be made there.

Bottom line is you will "always required to have a MBJ in the main disconnect" and you may have a similar connection in the meter enclosure, and possibly be required to have that connection as well, acting as both a grounding and bonding means for that enclosure.

I'm sure someone will have a better way to put that - or correct me...
 
Shannon, welcome to the forum! :)

To put it simply, there is only one grounded conductor from the utility supply to the main/service disconnect. The meter is looked at as "a lump in the service cable." It's bond is basically ignored.

There is never a separate grounding conductor on the line side of the main disconnect. If a metallic raceway is used, it's parallel pathway with the neutral is also accepted and ignored as inevitable.

From the disconnect enclosure on, the grounded conductor is never bonded again, is fully insulated, and treated as any other circuit conductor (except for OCP), and never used for grounding.
 
You are right, confusion lies in the terminology and for this reason I want to ensure that I clearly understand. For example.
If I have a utility service 120/240 split single phase at the meter can, the N is bonded to a utility installed Grounding wire. Then 4 wires are connected to the MD L1, L2, N & G. At the MD there is probably a bond between the N & G again. Then 4 wires go to the point of use. At the point of use the green ground wire can / is also connected to any site ground system / wires. At all times after the meter can, N & G are two seperate and continuous wires throughout the system - correct ?
 
shannonave said:
You are right, confusion lies in the terminology and for this reason I want to ensure that I clearly understand. For example.
If I have a utility service 120/240 split single phase at the meter can, the N is bonded to a utility installed Grounding wire.
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Yes, the utility's connection to the earth, their Grounding Electrode Conductor (GEC).
Then 4 wires are connected to the MD L1, L2, N & G.
Click to expand...
The utility would only supply three conductors: L1, L2, and N (the Grounded Conductor).
At the MD there is probably a bond between the N & G again. Then 4 wires go to the point of use.
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Yes, that is where the Grounded Conductor and the Equipment Grounding Conductor (EGC) separate, never to bond again, with very rare exceptions.
At the point of use the green ground wire can / is also connected to any site ground system / wires.
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Your 'point-of-use' is "outlet" in the NEC: "A point on the wiring system at which current is taken to supply utilization equipment". If by 'ground system / wires' you mean GECs, or 'earth connections', then yes and no. It is allowed to 'reground' an EGC, but with limitations.
At all times after the meter can, N & G are two seperate and continuous wires throughout the system - correct ?
Click to expand...
Not if the meter can is on the line side of the Service Disconnect. The Grounded Conductor is required to be bonded to the enclosure of the Service Disconnect. It is allowed to be bonded one additional time to the enclosure of the meter base per 250.142(B)Exception No. 2
 
shannonave said:
If I have a utility service 120/240 split single phase at the meter can, the N is bonded to a utility installed Grounding wire. Then 4 wires are connected to the MD L1, L2, N & G.
Click to expand...
Negative. There are not separate neutral and ground conductors. One wire does double duty.

At the MD there is probably a bond between the N & G again. Then 4 wires go to the point of use.
Click to expand...
The neutral isn't "bonded again." It's more accurate to say that the EGC system originates at the main disco enclosure, the electrode conductor(s) bond there, and the neutral being required to be insulated and isolated also starts there.

At all times after the meter can, N & G are two seperate and continuous wires throughout the system - correct ?
Click to expand...
No, it's at all times after the main disco. Nothing changes in the meter enclosure; it's usually bonded to the neutral.

Otherwise, it's just a "lump in the service conductors."
 
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LarryFine said:
Shannon, welcome to the forum! :)

To put it simply, there is only one grounded conductor from the utility supply to the main/service disconnect. The meter is looked at as "a lump in the service cable." It's bond is basically ignored.

There is never a separate grounding conductor on the line side of the main disconnect. If a metallic raceway is used, it's parallel pathway with the neutral is also accepted and ignored as inevitable.

From the disconnect enclosure on, the grounded conductor is never bonded again, is fully insulated, and treated as any other circuit conductor (except for OCP), and never used for grounding.
Click to expand...




Except under 05' in a detached structure with 3 wire, but 08' squashed that
 
Current flow on the ground wire

Current flow on the ground wire

I realize that my use of terminology is not quite NEC jargon. I understand that "bonding" is required by article 250 primarily as a "safety" issue. My concern is related to a traffic intersection where the cabinet ground, mastarms (traffic poles) and pedestrian push button pole grounds are all cross connected to the cabinet ground and the utility ground. Such a ground array provides equi-potential grounding that is a key to mitigating the risk of damage from a direct or nearby lightning strike. This is caused by an elevated earth potential wanting to equalize between poles and cabinets flashing over to use the signal circuits to equlaize. When the array is <5 ohms resistance and often lower than the utility ground <25 ohms, there is a considerable current flow in the array ground system that can "electrify" the cabinet & poles connected to it, via the safety "bonding". In this case the bonding "could" create a hazard to a pedestian known as "touch voltages". I am not really sure if this is truly a hazard or just a theory out in the left field.
I would welcome your views and advice.
 
shannonave said:
I realize that my use of terminology is not quite NEC jargon. I understand that "bonding" is required by article 250 primarily as a "safety" issue. My concern is related to a traffic intersection where the cabinet ground, mastarms (traffic poles) and pedestrian push button pole grounds are all cross connected to the cabinet ground and the utility ground. Such a ground array provides equi-potential grounding that is a key to mitigating the risk of damage from a direct or nearby lightning strike. This is caused by an elevated earth potential wanting to equalize between poles and cabinets flashing over to use the signal circuits to equlaize. When the array is <5 ohms resistance and often lower than the utility ground <25 ohms, there is a considerable current flow in the array ground system that can "electrify" the cabinet & poles connected to it, via the safety "bonding". In this case the bonding "could" create a hazard to a pedestian known as "touch voltages". I am not really sure if this is truly a hazard or just a theory out in the left field.
I would welcome your views and advice.
Click to expand...

If you are still talking about the neutral ("Grounded Circuit Conductor") and connection to "Equipment Grounding Conductors" (EGC) and connection of the two?

It may seem contradictory to what you therorize happening with lightning.... But connection of a circuit conductor to grounding conductors creates a touch potential all the time the circuit is energized to varying degree depending on load and distance... Which is why they are seperated - never to meet again after the Main Bonding Jumper (MBJ). Think of that in the same way you do lightning effects...

Now back to lightning itself - Another reason to keep the circuit conductors isolated from exterior supplimental electrodes and other grounding is to keep those types of high energy faults from being part of fault path... What you don't want is for devices, switches, controls or the load to become part of a fault path. As the would if bonds were to be made in seperate stuctures (poles ect) with loads and devices on the circuits feeding to it. Draw a schematic of a typical install and follow the fault paths to the multiple electrodes at each structure....

As for the Main, and the utility grounded conductor - think of it as a larger grounding array - it is grounded (earthed) with an electrode at every service. (And has no loads or devices in any paths between each making it a relitively safe and sizable path of travel to other electrodes.) Locally our utility does not even put an electrode at pole mounted transformers very often. The grounded conductor - is grounded with an electrode at every service on the transormer - making a sizable electrode array for them. And the most likely fault path for lightning to structures and buildings... :roll: (Hopefully thats where all the fault paths end...)

And I could see in your case, where having all of these tall seperate stuctures with electrodes and inter-connected circuits 'could' create a path to 'jump to' - to widely disapate a possible but unlikely lightning strike. But you would not want a circuit conductor for that - you would want an Equipment Grounding Conductor (EGC) to serve as the equipotential bonding conductor for that. As an Engineer - you could spec that to be what ever size you felt justified the need.... :roll:
 
Here's two images I think explain what you're thinging about - but with lighting as a fault. In that case you would want an EGC, or electrode bonding conductor (but not both) to just the electrodes most likely to handle that type of fault.




GroundBondPoster001.jpg


touch.gif
 
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