Am I Missing Something

[Michael Larson]

Originally Posted by agallatin

In the case of arching wouldn't there be an increase in current or load , causing a tripped breaker ?

Depends on the load. See post 10

[William Warner]

A good reference source and explanation for clients regarding the hazard of bundled neutrals and bundled grounding with grounded conductors under the same buss lug...

http://static.schneider-electric.us/...0100DB0705.pdf
This issue seems difficult for many inspectors (and some electrical contractors) to grasp, but the PDF is great at explaining the reasons why it is prohibited.

[Michael Larson]

Thanks Bill.

The connection of a neutral and equipment-grounding conductor in the
same termination creates a similar issue. One of the objectives of the
particular arrangement of bonding jumpers, neutrals and equipment
grounds is to allow circuit isolation while keeping the equipment grounding
conductor still connected to the grounding electrode (see UL 869A -
Reference Standard for Service Equipment). When the neutral is
disconnected, the objective is to still have the equipment ground solidly
connected to the grounding electrode. If both the neutral and grounded
conductor is under the same terminal, this cannot be accomplished.

[mnahrgang]

Originally Posted by mlarson

Thanks Bill.

Okay, Thanks Bill and Thanks Mike. I'm not being a smart *** here, but I'm going to ask the same question I did in post 6 just a little differently, because we are NOT doing code compliancy inspections.

So what, and what's the big deal? What's the harm, and what's the risk?

[Jim Port]

Originally Posted by mnahrgang

So what, and what's the big deal? What's the harm, and what's the risk?

When the neutral is
disconnected, the objective is to still have the equipment ground solidly
connected to the grounding electrode. If both the neutral and grounded
conductor is under the same terminal, this cannot be accomplished.

You don't think the chance of a serious shock hazard is a safety concern?

[Brian E. Kelly]

Originally Posted by Jim Port

You don't think the chance of a serious shock hazard is a safety concern?

Newer panels tell you in the instructions not to install them together as well.

[mnahrgang]

Originally Posted by Jim Port

You don't think the chance of a serious shock hazard is a safety concern?

If the neutral was being disconnected in the panel, the breaker would be off. So regardless of where the ground wire is lugged, or if it is lugged at all the risk of shock would not be from this, but from touching something else in the panel. If there is a shock risk it would be because the breaker/circuit is still live, not because of the location of the ground.

So again I ask, what's the big the deal of having them under the same lug? I've yet to hear a compelling reason why (above that it's not allowed) for it being any big deal...

[mnahrgang]

Originally Posted by bkelly2

Newer panels tell you in the instructions not to install them together as well.

Okay, newer panels say don't. Okay, NEC says not allowed. Still no answer as to why besides a smart *** "don't you think a shock is a risk".

I'm not arguing that it is allowed today. It clearly isn't under code. My question is, why not?

Why on a 30 year panel that was installed this way correctly under the codes at that time, would anyone call this out as a defect? There has to be a reason beyond "it's not allowed".

If it is a shock risk, there needs to be an explanation as to what circumstances a shock would happen, and why it would be important to call out.

[Jim Port]

It was not installed correctly in the 30 year old panel either. The requirement was listed in the UL standard which is not as easy to access as the NEC. It was a violation of 110.3 before. Now it is specifically spelled out in the NEC to avoid the chance of someone not knowing. I don't have access to a 30 year old panel label, but it might have been stated there and no one bothered to read it.

[Robert Meier]

Here's a pretty good explanation that was part of the required substantiation to put this directly into the 2002 NEC. This code change came from a representative of Square D. The CMP decided to make this a new code section and called it 408.21 in the 2002 NEC.

9- 113 - (384-21 (New) ): Accept
SUBMITTER: James T. Pauley, Square D Co.
RECOMMENDATION: Add a new 384-21 to read as follows:
384-21. Grounded Conductor Terminations. Each grounded
conductor shall terminate within the panelboard in an individual
terminal that is not also used for another conductor.
Exception: Grounded conductors of circuits with parallel
parallel shall be permitted to terminate in a single terminal if the
terminal is identified for connection of more than one
conductor.
SUBSTANTIATION: This revision is needed to coordinate the
installation requirements with a long standing product standard
requirement. Clause 12.3.10 of UL 67 (Panelboards) states “An
individual terminal shall be provided for the connection of each
branch-circuit neutral conductor.” The requirement has been
enforced in the past by a close review of the manufacturers
markings and by NEC 110-3(b). However, since it is a rule that
specifically effects how the installer can make connections, it is
important that it be in the NEC.
Even with the manufacturers markings, inspectors still indicate
that they see a number of panelboards installed with two (or
more) branch circuit neutrals under one terminal or they see an
equipment grounding conductor and neutral under the same
terminal.
There is very good rationale for the requirement in the product
standards. Doubling up on the neutrals creates a significant
problem when the circuit needs to be isolated. In order to
isolate the circuit, the branch breaker is turned off and the
neutral is disconnected by removing it from the terminal. If the
terminal is shared with another circuit, the connection on the
other (still energized) circuit will be loosened as well. This can
wreak havoc, particularly if the neutral is part of a 120/240V
multi-wire branch circuit. Also, the neutral assemblies are not
evaluated with doubled-up neutrals in the terminals.
The connection of a neutral and equipment grounding
conductor creates a similar issue. One of the objectives of the
particular arrangement of bonding jumpers, neutrals and
equipment grounds is to allow circuit isolation while keeping the
equipment grounding conductor still connected to the grounding
electrode (see UL 896A - Reference standard for Service
Equipment). When the neutral is disconnected, the objective is
to still have the equipment ground solidly connected to the
grounding electrode. If both the neutral and grounded
conductor are under the same terminal, this cannot be
accomplished.
This addition to the NEC does not change any product or
permitted wiring arrangement from what it is today. It will
however, it will help installers to avoid wiring the panel in
violation of 110-3(b) and then have to contend with a red-tag
from the inspector.
The code language is proposed in a fashion to allow consistent
enforcement of the provision the the AHJ. Although the UL
wording is adequate for the product standard, it is important that
the NEC language is as clear an unambiguous as possible. This is
the reason for specifically noting that the terminal cannot be used
for another conductor. Furthermore, the code requirement has
been worded to make sure that both branch circuit and feeder
neutrals are covered since it is not uncommon to have feeder
breakers as well as branch breakers in the panelboard (the issue
for the neutral is the same regardless of branch or feeder). Also,
the term “grounded conductor” is used to be consistent with the
code terminology and to recognize that not all grounded
conductors are neutrals.
An exception has been proposed to avoid any confusion relative
to parallel circuit arrangements. In these instances, multiple
neutrals could be in a single terminal if the terminal has been
identified as acceptable for multiple conductors.
PANEL ACTION: Accept.
In the proposed exception, change the second instance of the
word “parallel” to “conductors”.
PANEL STATEMENT: The correction of the typographical error
meets the intent of the submitter.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 11
VOTE ON PANEL ACTION:
AFFIRMATIVE: 11
___________________

[mnahrgang]

Thanks Bob for taking the time to post this...

Originally Posted by Robert Meier

Here's a pretty good explanation that was part of the required substantiation to put this directly into the 2002 NEC. This code change came from a representative of Square D. The CMP decided to make this a new code section and called it 408.21 in the 2002 NEC.

This is the relivant info.

One of the objectives of the
particular arrangement of bonding jumpers, neutrals and equipment
grounds is to allow circuit isolation while keeping the equipment grounding
conductor still connected to the grounding electrode (see UL 869A -
Reference Standard for Service Equipment). When the neutral is disconnected, the objective is to still have the equipment ground solidly connected to the grounding electrode. If both the neutral and grounded conductor is under the same terminal, this cannot be accomplished.

But we still come back to the question of why, and so what? If the neutral and ground for the circuit are under the same lug and the power it turned off there is no need for maintaining the equipment ground because there is no current.

Soooo... it's not allowed by NEC because the equipment manufacturers say they should be under the same lug.

That's not really a good explanation.

So let me ask again in a different way... Why does the manufacturer of the panel wish that the ground be connected if the neutral is disconnected? After all, if you are disconnecting the neutral, the power would be off anyway.

I know why you can't have neutrals sharing luggs that's obvious because they are different circuits.

The question is why not a ground and neutral that are in the same circuit. As far as I can tell it wouldn't make any difference one way or the other...

PS... I'm not trying to be a jerk, or be argumentative. I am just trying to understand what the reason behind the rule, not just the rule itself.

[Robert Meier]

Originally Posted by mnahrgang

Thanks Bob for taking the time to post this...



This is the relivant info.

But we still come back to the question of why, and so what? If the neutral and ground for the circuit are under the same lug and the power it turned off there is no need for maintaining the equipment ground because there is no current.

Soooo... it's not allowed by NEC because the equipment manufacturers say they should be under the same lug.

That's not really a good explanation.

So let me ask again in a different way... Why does the manufacturer of the panel wish that the ground be connected if the neutral is disconnected? After all, if you are disconnecting the neutral, the power would be off anyway.

I know why you can't have neutrals sharing luggs that's obvious because they are different circuits.

The question is why not a ground and neutral that are in the same circuit. As far as I can tell it wouldn't make any difference one way or the other...

PS... I'm not trying to be a jerk, or be argumentative. I am just trying to understand what the reason behind the rule, not just the rule itself.

The answer is there really is no answer if the lug is listed for more than one conductor and the condcutors are within the size range of the lug. You're correct that no one has provided any real substantiation for this rule.

[William Warner]

I think in this instance it simply boils back down to a "double tap" scenario and the associated hazard "potential" (similar to the hazard of a double tapped breaker)... as well as the intent of simply maintaining equipment ground at all times.

[Jim Port]

It is quite possible that if the device failed someone could pull it out to troubleshoot the problem. The power is not off so there is a very good chance of a shock hazard with no path back to the panel to clear the fault.

There is also the diferent coefficient of expansion from a current carrying conductor vs a non-current carrying conductor.

[agallatin]

Originally Posted by mlarson

Depends on the load. See post 10

Thanks Michael . I got it . I always thought that arching was an increase in current . Now I now better .