Thread: Grounds and Neutrals under common lug

I see ground wires and neutral wires under common terminals on the bus bar ALL the time. Does anyone no when the separtion requirement was implemented? Does this condition pose a threat to anyone except possibly someone who is working on the system or trying to isolate a cicuit. In addition, I have always wondered why it is an issue. They (the grounds and neutrals) all terminate on the same busbar anyway. How does the separtion of the two wires isolate a circuit? The bus bar is metal and can carry current. I need help on this subject.

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Greg, first read the threads at the bottom of this page. Follow any similar strings , and if your'e feeling adventurous go to the forums and look for similar strings. There's a good start. If you wait a week Mr. Peck might avail you of more info than you can handle.

Originally Posted by Greg Jenkins

I see ground wires and neutral wires under common terminals on the bus bar ALL the time. Does anyone no when the separtion requirement was implemented? Does this condition pose a threat to anyone except possibly someone who is working on the system or trying to isolate a cicuit. In addition, I have always wondered why it is an issue. They (the grounds and neutrals) all terminate on the same busbar anyway. How does the separtion of the two wires isolate a circuit? The bus bar is metal and can carry current. I need help on this subject.

A very simple explanation:

Once they leave the service equipment then they are to be on separate bus bars and each should be under it's own lug. The neutral should be floating or isolated from the panel and the grounds should be bonded to the panel.

The bus bars are usually insulated from the panel with a piece of non-conducting material, it could be plastic, heavy paper/cardboard, etc. This is why with a large number of panels a grounding bus bar kit needs to be added or a bonding strap of screw needs to be connected to the panel/bus.

Most home inspectors are never taught that the neutral is desigend to carry current all of the time (it is a "live" wire). Why it is not taught, I don't have a clue, but this is one of the main reasons that they need to be isolated from the grounds. Having an energized ground is not always a healthy condition.

Originally Posted by Scott Patterson

A very simple explanation:

I believe Greg is referring to the all too common practice of a ground and neutral under the same screw terminal.

It is now codified in the NEC but my understanding is that it has always been required to have separate a terminal for each neutral as part of UL67 for panel boards.

Originally Posted by Michael Larson

I believe Greg is referring to the all too common practice of a ground and neutral under the same screw terminal.

It is now codified in the NEC but my understanding is that it has always been required to have separate a terminal for each neutral as part of UL67 for panel boards.

Well the reason that they need to be under their own lug screw is so that a proper contact is made between the screw, wire and bus bar.

Originally Posted by Scott Patterson

Well the reason that they need to be under their own lug screw is so that a proper contact is made between the screw, wire and bus bar.

While that is certainly true, the screw terminals are often rated for two conductors of the same size under a single screw as in ground conductors just not more than one neutral.

Well explained, Scott

I am referring to the grounds and neutrals under a common screw in the main panel board where the main service disconnect is in the same panel and where grounded conductors and equipment grounds ARE Permitted on the same bus bar. No remote panels. No seperate service equipment disconnect.

Redundancy. That is the issue. When assessing mechanical and structural systems, it becomes apparent that redundancy is designed into these systems. For safety, to prevent overload, to reduce the chances of complete failure or collapse.

Let's say you want to replace a kitchen outlet. You don't know what you are doing, so instead of opening the OCPD, you just unscrew the terminal holding the neutral and ground for the circuit you want to work on. The neon tester says the circuit is dead, but is it?

Requiring the neutral and grounding conductors to have separate terminations reduces the chances of this type of issue. Note that if the buss is rated, two neutrals or two grounding conductors may share a terminal screw. The safety concern is best served when each conductor terminates at a separate screw.

Good Video from Mike Holt on this very issue.

408.21 Grounded Conductor Terminations
Intent: This new section should ensure that grounded (neutral) conductors terminate within the panelboard to an individual terminal. This has been a UL requirement (UL Std. 67 – Panelboard Standard) for some time, and the addition to the NEC is intended to bring this information to the installers. Technically, this is covered by 110.3(B), which requires all equipment to be installed in accordance with the manufacturer's installation instructions and markings, but nobody knew it existed. UL Std. 67 (Panelboard Standard) permits up to three 10 AWG equipment grounding conductors to terminate on a single terminal, if the terminal is marked for this purpose. Figure 408-3

The intent of this requirement is to ensure that the grounded (neutral) conductor of a multiwire branch circuit is not momentarily disconnected, which could result in the destruction of electrical equipment and fires from overvoltage.

I found two additional videos on Mike Holt's web site that are very helpful.
Here's the link. The videos are under the heading "section 408 switchboards and panelboards".
Mike Holt

Greg,

In the olden days (prior to the 2002 NEC), it was permissable to put multiple current carrying conductors (hot or neutral) under the same terminal, IF OKd by the manufacturer. As far as I know, this was never OKd by the manufacturer. The problem was the wording in the NEC and on the label in the panel. This label usually gives permission to secure more than one grounding conductor under a single screw to the terminal bar. This was often misinterpreted by electricians as well as inspectors to mean it was OK to to double tap neutrals as well.

Not sure if it was ever OK to double neutrals or combine neutrals and grounds.

Originally Posted by Gunnar Alquist

The problem was the wording in the NEC and on the label in the panel. This label usually gives permission to secure more than one grounding conductor under a single screw to the terminal bar. This was often misinterpreted by electricians as well as inspectors to mean it was OK to ...

... do the same with the groundED conductor.

The problem was that of wording and mis-understanding, which as been undergoing changes for the last few code cycles, including in the 2008 code.

The problem has always been "groundING" conductors versus "groundED" conductors.

A "groundING" conductor is the equipment groundING conductor, while a "groundED" conductor is the neutral, the "groundED" conductor which is "groundED" at the service equipment to the "groundING" conductor and the "groundING" electrode conductor.

That was, and still is, cause for much confusion among many electricians and inspectors.

The "groundED" conductor is a current carrying conductor and needs to be treated as such as it carries current, which causes heat, which in turn causes expansion and contraction issues. The terminals must 'only have' one "groundED" conductor in each terminal, even though that same terminal may be approved and rated for 2 "groundING" conductors.

The "groundING" conductor is not a current carrying conductor (at least, it is not "intended" to carry current), thus, as it is seldom, if ever, carrying current, you are allowed to do some things with it which are not allowed with a current carrying conductor, such as multiple tapping at terminals when the terminals are approved for such.

For 2008 standards (2005 NEC or newer), can someone share with me the code reference to separate neutral and ground wires on their own bars? This should be how it is done and I always call this out as a safety issue, however I have a pissy contractor saying it is O.K.

I just want to give him a paragraph with specific code reference on this.

Thanks for your help.

From the 2008 NEC. (underlining is mine)
- 250.24 Grounding Service-Supplied Alternating-Current Systems.
- - (A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
(5) Load-Side Grounding Connections. A grounded conductor shall not be connected to normally non–current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article. (Jerry's note: This tells you *where NOT to* connect it.)
- - - FPN: See 250.30(A) for separately derived systems, 250.32 for connections at separate buildings or structures, and 250.142 for use of the grounded circuit conductor for grounding equipment.
- - (B) Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28. (Jerry's note: This tells you *where to* connect it.)
- - - Exception No. 1: Where more than one service disconnecting means is located in an assembly listed for use as service equipment, an unspliced main bonding jumper shall bond the grounded conductor(s) to the assembly enclosure.
- - - Exception No. 2: Impedance grounded neutral systems shall be permitted to be connected as provided in 250.36 and 250.186.