Double Taps Re-visited

[Victor DaGraca]

I know that the subject has been beaten to death, however, I don't recall this situation being discussed. I did try to look up past threads on the subject, but couldn't find any references.

Are double taps under neutral and ground lugs allowed?

[Paul Kondzich]

Not neutrals, and grounds according to specs on panel.

[Victor DaGraca]

Would that be on All panels?

[Richard Rushing]

Victor,

No. The neutrals are not supposed to be double or multi-tapped.

Double lugged grounded conductors:
Today’s requirements prohibit the installation of multiple grounded conductors into the same terminal for safety purposes. The NEC states the following;

408.21 "Each grounded conductor shall terminate within the panel-board in an individual terminal that is not also used for another conductor."

Now, was this always a requirement? No. However, the reason this requirement was implemented was for safety concerns (which most electrical requirements are). One of the concerns is that an unsuspecting contractor or individual may trip a breaker thinking that he has isolated a circuit in-order to work on a given item (possibly a ceiling fan or such). Well, if the grounded conductors are double tapped under the same buss screw, the contractor who “thinks” he has isolated that circuit may very well be surprised to find out otherwise. Basically, this is a safety concern.

Knowing what we know today, it is ill-advisable to continue to use outdated methodologies (due to safety concerns) when we now know better. If we know an item has the potential to cause a safety or overheating concern, it is our policy to always alert the client to make the necessary upgrades/ repairs.

__________________________________________________ _______
Below is a very good posting by James Pauley, Squre D Company:

Log from the NEC Code Panel, regarding the new clarifying language in the Code.
(Log #3287) 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 conductors 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 grounding 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 by 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 panel-board (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.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 11
VOTE ON PANEL ACTION:
AFFIRMATIVE: 11
______________________________________

[Victor DaGraca]

Thank you.

[Mike Gault]

Old thread bump - Jerry, is this still the reference for this common call out. My clients got this today from the local AHJ...

"After inspecting the panel at 2xxx River Bluff Ln. and reviewing the National Electrical Code. I found no code sections that restrict two neutrals in one lug.

Sean Kxxxx
Town of xxxx
Building Inspector"


??????????????????????????????????????????????

[Speedy Petey]

Old thread bump - Jerry, is this still the reference for this common call out. My clients got this today from the local AHJ...

"After inspecting the panel at 2xxx River Bluff Ln. and reviewing the National Electrical Code. I found no code sections that restrict two neutrals in one lug.

Sean Kxxxx
Town of xxxx
Building Inspector"


??????????????????????????????????????????????WOW! !! That was from an AHJ????

2008 NEC:

408.41 Grounded Conductor Terminations.
Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.

[Mike Gault]

Yeah, and I'm trying to figure out how to respond without being condescending (and it's quite difficult) to him.

[Mike Gault]

It's was also 408.11 at some point back, was it not? Home is about 4 years old...

[Speedy Petey]

Yeah, and I'm trying to figure out how to respond without being condescending (and it's quite difficult) to him.
I know what that can be like.

I know you guys don't like to do code, but just politely suggest to him that he read that code section. If he refuses it is out of your hands I would think.

[Speedy Petey]

I have:
2002 NEC - 408.21
2005 NEC - 408.41

[Mike Gault]

Thanks Petey... you rock.

And yes, I'll be polite, even in the email. :-)

[Speedy Petey]

Keep in mind, 384.21 never made it into the 1999 NEC, so prior to 2002 this was NOT an NEC code requirement, other than that of the manufacturer's listing and instructions.

[Jerry Peck]

Keep in mind, 384.21 never made it into the 1999 NEC, so prior to 2002 this was NOT an NEC code requirement, other than that of the manufacturer's listing and instructions.

Which means it was a violation of 110.3(B) in the NEC. :)

[Mike Gault]

Knew you'd be here Jerry... thanks

[Brent Crouse]

Well, if the grounded conductors are double tapped under the same buss screw, the contractor who “thinks” he has isolated that circuit may very well be surprised to find out otherwise. Basically, this is a safety concern.

Richard,

Trying to understand this. I'm not seeing how a double tapped ground is any less isolated than 2 grounds under their own lug (which would then be connected to the same buss).

[Jerry Peck]

Richard,

Trying to understand this. I'm not seeing how a double tapped ground is any less isolated than 2 grounds under their own lug (which would then be connected to the same buss).

Brent,

Go back and read the entire section, including the sentences before the one you are questioning.

This is an excellent example of why taking something out of context loses what is being said and allow you to think it is saying something else.

[Brent Crouse]

Nope, I'm still not seeing it. Is this implying that by having doubled tapped neutrals, it becomes more likely for current from the other circuit to "backflow" up the other neutral, and thus become a shock hazard to the "isolated" circuit?

[Mike Gault]

Back from my meeting at Town Hall with Sean.

They are allowing it via an exception in the 2003 IRC (enforced during the build in 2005) from section 3606.4 with the exact same exception verbiage from the 384.21 proposal language.

"Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connection of more than one conductor."

I lost (evidently)... even though I explained how others enforce it (other counties and municipalities) He will re address it at next Tuesdays Building officials meeting...

p.s. Home Buyer is having them separated immediately after closing.

p.p.s Sad thing is there was always room there to have done it correctly to start with...

[Jerry Peck]

(red and underlining is mine for highlighting)

One of the concerns is that an unsuspecting contractor or individual may trip a breaker thinking that he has isolated a circuit in-order to work on a given item (possibly a ceiling fan or such). Well, if the grounded conductors are double tapped under the same buss screw, the contractor who “thinks” he has isolated that circuit may very well be surprised to find out otherwise. Basically, this is a safety concern.



Nope, I'm still not seeing it. Is this implying that by having doubled tapped neutrals, it becomes more likely for current from the other circuit to "backflow" up the other neutral, and thus become a shock hazard to the "isolated" circuit?

.Yes.

[Jerry Peck]

Back from my meeting at Town Hall with Sean.

They are allowing it via an exception in the 2003 IRC (enforced during the build in 2005) from section 3606.4 with the exact same exception verbiage from the 384.21 proposal language.

"Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connection of more than one conductor."

I lost (evidently)... even though I explained how others enforce it (other counties and municipalities) He will re address it at next Tuesdays Building officials meeting...

Mike,

Take this section from the 2003 IRC with you and meet with him again. I'm betting he changes his mind.
(red text is mine)
- E3306.6 Conductors in parallel. Circuit conductors that are electrically joined at each end to form a single conductor shall be limited to sizes No. 1/0 and larger. Conductors in parallel shall be of the same length, same conductor material, same circular mil area and same insulation type. Conductors in parallel shall be terminated in the same manner. Where run in separate raceways or cables, the raceway or cables shall have the same physical characteristics.

Ask him: 1) are those conductors 1/0 and larger?; 2) are those conductors of the same length?

"Conductors in parallel" has a completely different meaning that what he applied.

[James Foy]

Victor,

...
Now, was this always a requirement? No. However, the reason this requirement was implemented was for safety concerns (which most electrical requirements are). One of the concerns is that an unsuspecting contractor or individual may trip a breaker thinking that he has isolated a circuit in-order to work on a given item (possibly a ceiling fan or such). Well, if the grounded conductors are double tapped under the same buss screw, the contractor who “thinks” he has isolated that circuit may very well be surprised to find out otherwise. Basically, this is a safety concern.
...
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.

______________________________________
Thanks for the reference. Always enforced it, but hadn't thought about the back current flowing around via a untripped breaker. Now I know why.

[Ken Amelin]

I'm missing something here.

Quite ofter we see wire nuts used to connect both ground and neutral connections in multiple branch circuits, in Service equipment panels and in J-boxes throughout the home. Many of these are not the same circuit, but a common connection of multiple neutrals and grounds that are daisy chained within these wire nut connections.

Why is it not OK at the service equipment panel terminal bar, but OK within the branch circuit wiring???

[Jim Port]

Grounding conductors from multiple circuits should be connected together. Neutrals from different circuits should not be connected unless you are dealing with a multiwire branch circuit. To do so otherwise could potentially overload the neutral.

It is not ok in the panel since there is a code prohibition against it.

[Corn Walker]

While I agree that it is prohibited in code, the 'why' described here is unfortunately wrong.

Double-tapped neutrals place two neutral conductors in the same terminal on a bus bar. Single-tapped neutrals separate those two neutral conductors on the bus bar by... a conductor! That means when those single-tapped or double-tapped neutrals are in the bus bar, there is NO difference between them in terms of conductivity. Therefore simply tripping the breaker does NOT isolate the circuit. You can only isolate circuits by disconnecting ALL conductors from shared busses. A standard breaker only disconnects 1 of the 3+ conductors.

The difference, and potential danger, is when the neutrals are double-tapped and somehow become isolated from the neutral bus bar. In that case, the current flow travels from the hot wire, through the load, along the neutral wire, jumps to the other neutral wire, and up to the supposedly disconnected load. This is the only scenario in which a double-tapped neutral might be more problematic (from a shock hazard point of view) than single-tapped - assuming the equipment supports both.

Therefore the logical remedy would be to only allow double-tapped neutrals if the equipment manufacturer states the terminal is designed to support such an installation. This also addresses the potential arcing problems and such when installed according to manufacturer directions. The NEC takes it one step further than this minimum safety requirements and disallows double-tapped neutrals altogether.

[Tom Rees]

I like this explanation:

http://ecatalog.squared.com/techlib/docdetail.cfm?oid=09008926803d7d0a (http://ecatalog.squared.com/techlib/docdetail.cfm?oid=09008926803d7d0a)

[Mike Gault]

Mike,

Take this section from the 2003 IRC with you and meet with him again. I'm betting he changes his mind.
(red text is mine)
- E3306.6 Conductors in parallel. Circuit conductors that are electrically joined at each end to form a single conductor shall be limited to sizes No. 1/0 and larger. Conductors in parallel shall be of the same length, same conductor material, same circular mil area and same insulation type. Conductors in parallel shall be terminated in the same manner. Where run in separate raceways or cables, the raceway or cables shall have the same physical characteristics.

Ask him: 1) are those conductors 1/0 and larger?; 2) are those conductors of the same length?

"Conductors in parallel" has a completely different meaning that what he applied.


I give him this and let you know the outcome of Tuesdays meeting...

Thanks...