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Double-tapped neutrals = massive 'char-job'..


Rob Amaral
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I don't have a photo, but I saw a case where an electrician had double-wired two circuit neutrals (120V) under one screw. The homeowner was using that/those (we are not sure) circuit(s) for a treadmill and either an electric space heater or portable AC unit (we are not sure, but those are the possibilities).

The result was either an instantaneous 'high heat' situation (or long-term..) we don't know which.

That caused one of the two circuits to 'go dead'. I opened up the panel and found one of the two circuit neutrals completely burned-away (thus the dead circuit). Insulation on adjacent neutrals was burned away also.

It was a Homeline panel and the black plastic insulator behind the breakers/bus bar tabs was charred and melted severely. A few breakers above the area of high heat were barely held in place as a result.

Two wires under one screw can indeed be a big problem in some cases..

Even when they are neutrals.. (It was not a client's house---a friend of mine).

The result was total replacement of the entire panel due to the degree of heat damage.

FYI: The 'electrician' who did the initial double-tap work was 'the neighbor'. He's an electrical engineer (of course!) (Circuits were added during a 'finished basement' project).

File under 'double-wired circuits' and 'collection of circumstances that can lead to problems' and 'what electrical engineers don't know' :)

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Two wires under one screw can indeed be a big problem in some cases..

Mornin' Rob,

An electrician who participates on another forum recently stated that he sees more issues with singed/ burned neutrals when they are placed under their own terminal screw. I wonder if that's just because there are more panels wired "properly", so more of a chance for loose wires to cause an issue?

I rarely run across evidence of overheating at these double taps, so I'm curious........could you tell if there was a loose connection?

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Erby,

Good thing you took that panel cover off huh?

And some people have suggested that part (remove a panel cover) be removed from the SOP's; go figure.

Darren,

please try to be nice! You and I have had a day. Enjoy your weekend and don't bother private emailing me with details!

'course you know I'm jerking your chain?

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It looked way worse than that Erby, but that is the gist of it.. ramp that degree of problem ten-fold... the heat melted the copper conductor of one of the neutrals.. the heat then melted the black plastic insulation that the breakers clip onto.. The heat rose and damaged insulation of wiring above and the plastic.

The only other time I saw heat at a wire/terminal connection due to double-tapping was a doorbell circuit with another 120V circuit.. the connection got loose and burned (like Erby's photo).

Of course, in my own house, my electrician did not tighten a neutral on a transfer-switch panel job I had him do and it burned.. (We wave all the time now... he lives nearby and works nearby..) I checked it about 3 mos after he did the job.. "Never assume anything"..

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Sometimes the neutrals get burned when (example 14/3) cables are wired wrong in the panel. The error happens when both of the hots are run from the same bus. In this case, the neutral of said 14/3 cable has to carry the load from both circuits at the same time. This makes the neutral overheat.

If a 14/3 is wired correctly (having the hots split between both buses), the alternating current allows the neutral to handle the load of both with out overheating.

If I butchered this explanation, someone please clarify it.

BTW, two neutrals under one termination can cause a safety concern when it comes to servicing the electrical system. However, when installed that way with the panel cover closed and the system in service, it really doesn't cause a problem of overheating. Multiple neutrals under one terminal is an issue because it complicates the isolation of circuits during servicing.

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I disagree John. It's also more likely to come loose and generate heat even with the panel cover closed.

Many panels have instructions in them that allow multiple conductors under one ground/neutral terminal. If they're torqued properly, it isnt an issue. Again, outside of the panel instructions, the single neutral termination rule has to do with simplifying isolation of circuits during servicing or working on the electrical system.

See this file.

http://home.comcast.net/~marylandhomein ... rounds.pdf

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That document doesn't state that isolation is the only reason. It even states: "Also, the neutral assemblies are not evaluated with multiple neutral conductors in the same terminal".

Aside from that document, John's got a point on both counts. Just makes good sense.

Marc

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It's a prohibited practice: 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.

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.

Almost every panel board allows multiple grounds but only one neutral per terminal.

John's point concerning miswired MWBC's using space saver breakers is well taken- I've seen toast colored neutrals caused by either issue.

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I've never seen a residential electrician carry a torque driver. Anyone?

Now, I haven't seen every load panel ever made but the ones I have seen that actually have connection termination and torque information in the panel have never specified or implied 2 neutrals in a tap. Grounds, yes; Neutrals, no.

Multiple neutrals: With the exception for breakers designed for 2 conductor terminations, Why are circuit breaker double taps disallowed? The neutral in a circuit carries the same current that the "hot" conductor at the breaker. So why would it be permissible to "double tap" the neutral? Does not compute.

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I've never seen a residential electrician carry a torque driver. Anyone?

Hello Stu, I've never owned one, seen one or cared to even buy one.

Multiple neutrals: With the exception for breakers designed for 2 conductor terminations, Why are circuit breaker double taps disallowed?

Because the manufacturer didn't intend for it to be used for more than one conductor.

The neutral in a circuit carries the same current that the "hot" conductor at the breaker. So why would it be permissible to "double tap" the neutral? Does not compute.

It's not about the amperage, it's about what the manufacturer designed it for.

Marc

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Ye see, I thought that the no doubled neutral rule came up about 10-12 years ago. Of course any newer panel wired that way is against the rule. Now we all have seen older panels wired that way right?

There are panels out there that had doubled neutrals prior to the rule being established in conjunction with manufacturers labels allowing multiple conductors under one terminal screw. I've seen the labels that say up to 3 #14 or 2 #12 etc.

Maybe I missed the part about it only being allowable for grounds. If I can't find a picture on my own file, ( I got some buried deep somewhere), I'll snap a pic of the next one I see.

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I've never seen a residential electrician carry a torque driver. Anyone?

Several in my area do. I understand that in some parts of California, it's difficult or impossible for an electrical contractor to get his work approved unless he can show his torque screwdriver to the inspector.

. . . Multiple neutrals: With the exception for breakers designed for 2 conductor terminations, Why are circuit breaker double taps disallowed? The neutral in a circuit carries the same current that the "hot" conductor at the breaker. So why would it be permissible to "double tap" the neutral? Does not compute.

You're confusing the amount of current with the number of wires. They're completely and totally unrelated. At issue is the integrity of the connection, not the amount of current.

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Hi,

I would have sworn that Douglas Hansen has pointed out many times that the 'no more than one grounded conductor per terminal' rule has been around since the 1940's.

ONE TEAM - ONE FIGHT!!!

Mike

Not sure of the timeframe on this, but prior to being added to the NEC it was covered under the UL listing standard. It was added to the NEC so that it was more readily available to ensure compliance.

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As pointed out in the link from Michael Thomas, the code proposal for the 2002 cycle for individual terminals for neutrals cited a "long standing" provision in UL 67. I don't know exactly how far back it goes, though it was at least 1964, and possibly much before that year.

As for torque screwdrivers and torque wrenches, there are indeed several jurisdictions here that require the terminals to be torqued in the presence of the inspector. Loose terminals and connections are a major contributor to electrical fires, and you cannot get the proper torque by feel alone. At last year's NFPA conference, there was an excellent demonstration titled "Do you think you have a calibrated elbow?" Doing it by feel alone, most electricians will get the torque outside of the acceptable variance on almost 50% of their connectons. When I took the "test" my connections were over-torqued (just as bad in some cases as being under).

Douglas Hansen

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