Need help with main panel board buss bar

[Steve McIntire]

Need help with main panel board buss bar. how far back in the code books or any other listing is it a defect to double tap grounded conductors at the buss bar? I have found NEC 408.41 which appears to be 2005 code and NEC 408.21 from 2002 Code. I have always assumed this went back to the 60's. I am doing research on a house built in 1990 with numerous double taps. Prior to 2002 was it mostly dependent on manufactures or is there something else?

[Steve McIntire]

I found this reference on a separate post, does anyone have a copy of this?
Underwriters Laboratories Standard 67 for panel-boards

[Mike Whitt]

The rule for one grounded (neutral) conductor per terminal was inducted into the 2002 code cycle.

Although UL standard 67 had information concerning the use of one terminal per conductor there was no verbiage in the NEC to enforce this standard.
What was used to judge the installation of conductors under a terminal screw was 110.3(B) prior to the adoption of the rule into 408 during the 2002 code cycle process.
I am not sure when Standard 67 was accepted as part of UL listing but I am thinking it was in the latter part of the 90s.

The words found in 110.3(B) has been unchanged from its induction to the 1971 code cycle;
(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

On the label attached to the inside of all panels is a guide that states the allowable conductors per terminal for the terminal bars. Most will allow more than one conductor of the same size per screw and is why it is still legal to install two or more equipment grounding conductors per screw.

I will not tell you how to make a Home Inspection but I will tell you that if I am the electrician that is called to check out the double neutral under one screw and I see no sign of damage to the conductors and the panel was installed before the adoption of the 2002 code cycle I will tell the person that called me that I don’t see a problem with the installation.

In my professional opinion this poses a lot less danger than other things that are done in service equipment. The use of one terminal for more than one screw will pose a danger only if the conductors are of a different size or in the event that one of the conductors needs to be removed.

What I do see as a grave danger in electrical panels is the use of the enclosure as a return path for the grounded (neutral) conductor. In the picture below you will see two terminal bars. The one on the right is for equipment grounding conductors ONLY due to the fact that there is no main bonding jumper that ties the two terminal bars together as outlined in 250.24(B).



To use the terminal bar on the right for terminations of the grounded (neutral) conductors now makes the enclosure part of the return path of the circuit or it just made the panel enclosure part of a 120 volt circuit.

Looking at the panel in this post it is clear to see that the panel enclosure is now part of the 120 volt circuits and poses a much greater danger than the double conductor circled.

Edited to correct "now" in the last sentence. I did have a "t" instead of a "w" which was a tyop

[Paul W. Abernathy]

Let us not forget however that Panelboards must be installed by the manufacturers intent via 110.3(B) and I have first hand knowledge from Eaton and other manufactures that they never listed their panels for the intent to doubled up a "grounded" conductor.

While the 2002 NEC bought the issue to light, it has always been a bad practice in my mind and I have never done it. The issue with UL 67 actually dates back to the 70's and so does the installation intent of the manufacturer to not allow any double tapping of a "grounded" conductor.

Just figured I would chime in....

[Paul W. Abernathy]

lol....could be wrong on the UL date........however!..lol

[Mike Whitt]

Sorry Paul but this is what I have found so far;

Complete information regarding the provision of markings and instructions for these panelboards is
contained in the Standard for Panelboards, UL 67 (eleventh edition, dated December 8, 1993).
References to the

National Electrical Code ® (NEC) are to the 2002 edition, with parenthetical references
to the 1993 edition.

This came from here

Edited to add;

In order to get a copy of Standard 67 it must be purchased from UL

[Paul W. Abernathy]

Thanks Mike....heck if I could remember the UL stuff..

My conversations with Eaton and their engineers has always been that they have never allowed it.......their stance is FINALLY the NEC got some "GONADS" and put it in the NEC in 2002.....I said to them...ahhh...no comment..lol

[Mike Whitt]

It has been my stance for a long time that there is not that much danger in the doubling-up of the neutrals in an electrical panel as far as the function of the circuits as long as the conductors were the same size. It has nothing to do with the heating or arcing of the conductors and poses absolutely no danger to the function of the system.

The danger lies in the need to remove one conductor while the other circuit is still energized.
Below is the text that was included with the change in the Analysis of Changes 2002 published by the IAEI.



As can be seen by Proposal 9-27 the danger lies in the removal on one of the grounded conductors while the other conductor is still energized.

[Steve McIntire]

It does not seem like there is anyway to backup the defect statement, unless it is listed on the panel or an installation after 1993.

[jtedesco1]

Originally Posted by smcintire

It does not seem like there is anyway to backup the defect statement, unless it is listed on the panel or an installation after 1993.

Theory backs up the problem:

[Mike Whitt]

Originally Posted by smcintire

It does not seem like there is anyway to backup the defect statement, unless it is listed on the panel or an installation after 1993.

I would say that there is no way to back up a statement of defect unless the installation was made after the adoption of the 2002 NEC in the area of the installation.
There is no verbiage in the National Electrical Code that an electrical inspector could turn a job down for prior to the adoption to the 2002 NEC for more than one neutral under one screw.
I understand that there is and was Standard 67 published by UL but it was not adopted into the NEC until 2002. Even with this standard being written all the electrical contractor would use and electrical inspector could enforce was 110.3(B) which clearly stated; (B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
If these instructions did not come with the piece of equipment or there was language in the NEC then the standard was not enforceable.

As I said earlier and as is stated in the Analysis of Change by the IAEI it is not a defect in the installation but a safety issue when removing one of the conductors.

If the terminal is approved for more than one conductor and all conductors are the same size and are tightened properly there is no danger to the operation of the installation.

When time will allow you to do so look around your house at the different appliances that will have multiwire connections under one screw, a couple that comes to my mind right now are the air handler and air conditioner that heats and cools the house.
In these units there are several high draw conductors that will land under one screw without a problem.

This should be enough to let anyone know that if done properly the danger is not with the operation of the system but with the servicing of the equipment. This is the same as the rule found in 300.13(B) “Device Removal. In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity.”

The sole purpose of not having more than one neutral for one screw is the probability of opening an energized circuit when removing one of the other conductors.
I personally think that the danger of more than one neutral for one screw in a panel has been overblown until the true intent has been lost.

[Mike Whitt]

Originally Posted by jtedesco1

Theory backs up the problem:

Joe I don’t understand how a multiwire circuit can back up more than one neutral under one screw.
Would you care to elaborate on you post a little?

[jtedesco1]

Originally Posted by Mike Whitt

Joe I don’t understand how a multiwire circuit can back up more than one neutral under one screw.
Would you care to elaborate on you post a little?

Read the report again Mike, read the analysis in the report.

Analysis: The shock was caused by an open neutral (grounded) conductor that was carrying a load. Although hazards caused by open neutrals in a multi-wire branch circuit (also known as an Edison circuit) are well known to electricians, this incident did not involve such a circuit. An improper circuit modification was performed sometime in the past that resulted in power being supplied to a device by a panel other than the one on which work was being performed, which had been locked out and zero energy verified. That would not have been a problem except that the modification left the neutral conductor for the circuit in the existing panel that was being relocated. Since a voltage check of the neutral conductor (that caused the shock) with any of the ungrounded conductors in the panel being relocated would not indicate a live circuit, there was little that could have been done to prevent this. There was no reason to suspect anything that would have suggested testing all neutral conductors to ground, which might have been the case had it been known that an improper modification had been performed. This incident should serve as a reminder of the hazards of open neutral conductors. A voltage check of an open neutral to ground would be advisable if a multi-wire branch circuit is suspected, or if working in a panel or enclosure (e.g., auxiliary wire way) where multiple sources of power may be present.

[jtedesco1]

NECH COMMENTARY for 300.13(B):

Grounded conductors (neutrals) of multiwire branch circuits supplying receptacles, lampholders, or other such devices are not permitted to depend on terminal connections for continuity between devices. For such installations (3- or 4-wire circuits), a splice is made and a jumper is connected to the terminal, unless the neutral is looped; that is, a receptacle or lampholder could be replaced without interrupting the continuity of energized downstream line-to-neutral loads (see commentary to 300.14). Opening the neutral could cause unbalanced voltages, and a considerably higher voltage would be impressed on one part of a multiwire branch circuit, especially if the downstream line-to-neutral loads were appreciably unbalanced. This requirement does not apply to individual 2-wire circuits or other circuits that do not contain a grounded (neutral) conductor.

[jtedesco1]

More information:

Hazards with Neutral Conductors