A post by JLasater, 71543.1, has several replies that have me confused regarding the requirement to use pigtails on the neutral of multi-branch circuits. This is important enough I thought a separate thread was appropriate.
I did a Google search on NEC 300.13(B) and found conflicting interpretations regarding the requirement to pigtail the neutral.
Specifically, I am looking at the situation where you are using receptacles with back wired connections with screw clamps (not back-stab connections that does not use screw pressure) or wrapped screw connections.
Two Receptacle Example:
1. Hot lead from the breaker, black wire, to brass screw side of receptacle
2. Neutral lead from the panel, white wire, silver screw side of receptacle
3. Ground lead from the panel, green or bare wire, 3-way mechanical splice – ground lead, pigtail, and ground wire to second receptacle. The pigtail wire to green/ground screw on receptacle. Boxes are non-conducive plastic.
4. Hot lead from a second back-wire hole or brass screw, black wire, to second receptacle’s hot side.
5. Neutral lead from a second back-wire hole or silver screw, white wire, to second receptacle’s neutral side.
6. Ground from first receptacle box splice, green or bare wire, direct to ground/green screw on second receptacle.
OK, removing the first receptacle/device in this example would not create a down-stream safety problem as the hot and neutral conductors would be disconnected/terminated and the ground connection to the second device would be intact.
Perhaps that is the reason that duplex receptacles have two screws and four back-wire holes per side with only one ground screw that is difficult to wire more than one conductor to.
I like this method of wiring, as it makes the box far less crowed, which I see as a bigger safety and reliability problem. I have seen a lot of wirenut connections with high resistance from corrosion near the coast. Granted, this method creates dead devices downstream of a failed receptacle. I see that as a good thing. That may be an inconvenience for uninformed homeowners, but having a failing device in a circuit is a fire hazard. Making more devices dead makes it harder for your average soccer-mom to ignore.
Edited 3/31/2006 10:31 am by CJD
Replies
In a multiwire branch, two circuits share the same neutral. If you allow removal of a fixture to disconnect the neutral, it is possible to end up with fixtures in series across 220V.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
Edited 3/31/2006 10:34 am ET by philarenewal
I don’t get it. Perhaps I should have specified in my example that they are 120 VAC single phase circuits on grounded duplex receptacles. How could you have 240 VAC with one hot and one neutral that have been disconnected? Downstream is zero volts with nothing but a ground (bare/green) wire connected to the panel. Is there a fault condition that I am missing?
I think Bill already answered your question.
The NEC section you reference applies only to multiwire branch circuits. That means circuits using BOTH busses in the panel with a shared neutral.
Doing it this way can save some wire. One home run neutral. One home run ground. Two home run feeds.
If you are talking about a single branch circuit, the section does not apply.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
One more point...they make wire nuts that will not corrode and are good for damp locations. More cost but they do work.
The requirement for pigtail neutrals is ONLY for multi-wire circuits.
To make it clear a multi-wire circuit has two hots (one from each leg) and shared neutral so that you have 240 between the 2 hot legs and 120 from either hot to the neutral.
For example if if you have the black and hot looped through the first receptacle, then at the 2nd the red and neutral, and the 3rd the black and neutral.
Now the neutral on the first receptacle is removed it interrupts the neutral going to the 2nd and 3rd receptacles.
Now plug a heat into the 2nd receptacle and a lamp in the 3rd one.
Since the neutral is not connected to back to the panel then you have the heater in series with the lamp across 240 volts. And the lamp will guickly burn out or explode.
One a non-multi-wire circuit and the same thing happens the receptacles downstream are just dead.
Here is a link that shows the differences.
http://www.ecmweb.com/mag/electric_code_qa_5/index.html
I saw that link. I saw others that indicate that it is the ground circuit that can't be interrupted by a device removal, not the neutral. I don't have a copy of the latest NEC code so I am looking for an accurate interpretation.
The other thing I don't understand is if only one neutral can be wired to a 3-wire 120VAC single phase duplex receptacle, why are there two back-wire, or for that matter back-stab, holes for each hot and neutral on each of the two reciprocal sockets? Granted, a duplex receptacle can have the tab broken off to make independent circuits out of each receptacle socket, but there are still 2x too many holes.
The last thing that eludes me is why would it be OK with the NEC to spice in the receptacle for the hot and not the neutral? I understand wanting a third wire ground that will not be broken by a device removal.
"I saw that link. I saw others that indicate that it is the ground circuit that can't be interrupted by a device removal, not the neutral."Did say grounded circuit or GROUNED CONDUCTOR? Grounded conductor is the technical name for the neutral.The GROUND is called the equipment grounding conductor (EGC) from the panel to the load. "The other thing I don't understand is if only one neutral can be wired to a 3-wire 120VAC single phase duplex receptacle, why are there two back-wire, or for that matter back-stab, holes for each hot and neutral on each of the two reciprocal sockets?"What do you mean by 3 WIRE?If you mean ungrounded conductor, grounded conductor, and EGC (hot, neutral, and ground) there is no restriction on using the device for feedthrough. And I don't know if there is a specific restriction on EGC, but the design of the devices prohibit that option for the EGC.If by mean multiwire (two hots and neutral) while legal and allowed it is not that common and even where used it often splits off into 2 separate circuits at the first receptacle. Thus I don't see reason to restrict the option of using the device as for feedthrough because of those "rare" cases."The last thing that eludes me is why would it be OK with the NEC to spice in the receptacle for the hot and not the neutral?"As I mentioned this only applies to multiwire circuits and with multwire circuits you can get almost 240 volts across a load if the neutral is disruppted.Now I don' tknow how it read in the newest NEC."In MULTIWIRE branch circuits the continuity of the GROUNDED CONDUCTOR (neutral) shall not depend on device connections such as lampholders, receptacles, etc., where removal of such device would interrupt the continuity (of the neutral)."
Man, am I feeling thick here. I suspect that some of it is my misunderstanding NEC terminology. Let's see if I have this straight.
Condition: Residential, one 120 VAC single pole breaker, single phase, duplex receptacles with ground/3-prong (standard new construction stuff):
Hot, black wire, copper plated screw on receptacle, wire from breaker = ungrounded conductor
Neutral, white wire, chrome plated screw on receptacle, wire from neutral bus in breaker panel = grounded conductor
Ground, bare or green wire, wire from ground bus in breaker panel = EGC (equipment grounding conductor)
Sequence of wiring where Rn = a duplex receptacle
Breaker Panel -----> R1 -----> R2 -----> R3
Is this correct: Can I wire the neutral from the breaker panel's neutral bus directly to receptacle R1, then run another neutral wire through R1 to R2, and another neutral wire through R2 to R3 all without pigtails? Can this correctly be called a daisy-chain or series configuration?
However, if I wire from R1 to and R2 and R3 I must pigtail (Y configuration) like http://www.ecmweb.com/images/archive/0202ecmCQAFig6.gif Also True?
If correct so far, suppose I were to wire 3 receptacles in a Y configuration as described above but through the receptacles without pigtails. What is the danger if R1 is removed? Wouldn't that leave R2 and R3 completely open except for their ECG/ground? It seams to me that I would be looking at 3 hot and 3 neutral wires hanging out of the wall, one pair of which could be energized if the breaker were on.
Thanks for the patience.
"reaker Panel -----> R1 -----> R2 -----> R3Is this correct: Can I wire the neutral from the breaker panel's neutral bus directly to receptacle R1, then run another neutral wire through R1 to R2, and another neutral wire through R2 to R3 all without pigtails?"Yes, you can do it."Can this correctly be called a daisy-chain or series configuration?"Yes it is called daisy-chaining. Calling it "series" is another confusing area.Yes the DEVICES are in Series. That is removing move will disconnect the downstream desvices.The the LOADS are not connected in series. That you don't have to have something connected to each receptacle like SERIES Christmass tree lights.But you will commonly see it refered to as "series". But also expect to get complaints that it is not in series."However, if I wire from R1 to and R2 and R3 I must pigtail (Y configuration) like http://www.ecmweb.com/images/archive/0202ecmCQAFig6.gif Also True?"NO!You can still "wire through" the device. That picture is only about what color connectors (wirenuts) can be used and absolutely nothing to do with this discussion.I have no idea why the why that was drawn that way (pigtailed neutral, but feedthrough on the hots) other than the same drawning might have been used for another purpose.BTW, I don't believe that you can use both the terminals and the backwire connections at the same time. That is an only covered indirectly by the code as the code requires that materials be used in an approved method (either per UL standards are manufactures instructions).Uless I see UL standards for spec grade receptacles with backwire that allows both to be used I assume not. The reason being that the screw also applies pressure to the backwire clamping plates. Now I have not internals to see exactly how the pressure plate is connected to the screw.
If you do not have to pigtail neutrals in the Y configuration I described, when do you have to pigtail (assuming the receptacle can legally accept the required number of back-wired conductors)? What configuration is NEC 300.13(B) talking about?
I must admit, I have never heard electricians refer to Neutral grounded conductor or Ground as an EGC or equipment grounding conductor. The vast majority of my exposure to electricians dealing with the NEC has been in office and factory floor installations. Does anyone besides the NEC actually use this terminology?
I have frequently seen both back-wire holes clamped by one screw on spec grade receptacles. It "appears" to me that two wires in the clamp makes a better mechanical connection because the clamp is not skewed as it is with one wire.
Most of my power systems background is in shipboard applications where there is no Neutral. 120 VAC comes off a transformer and both sides are hot. As I recall, all 120VAC single phase breakers were double pole. This probably adds to my confusion factor.
"I must admit, I have never heard electricians refer to Neutral grounded conductor or Ground as an EGC or equipment grounding conductor. The vast majority of my exposure to electricians dealing with the NEC has been in office and factory floor installations. Does anyone besides the NEC actually use this terminology?"My background is in electroncis, so I want the black wire to be grounded.I see a few of the electricans that post her grounded and EGC from time to time. Without doing a survey my guess is that the use of EGC is fairly common, but grounded conductor is less so.In general though neutral and ground are used. But in certain circumstances, such as this thread, one needs to be clear about which is whihc and tht oftern requires going through a stage of more confusion first.But if you look at the electrican and code forums you will see grounded conductor and egc used very often. But of course they are debating the finer points of the codes."If you do not have to pigtail neutrals in the Y configuration I described, when do you have to pigtail (assuming the receptacle can legally accept the required number of back-wired conductors)? What configuration is NEC 300.13(B) talking about?"That is only for multiwire circuits. That is where you have two hots, each on a different leg, sharing a neutral. Thus there is 120 volts from either hot to the neutral and 240 hot to hot.One place where they are sometimes used is for the 2 kitchen small applicance circuits. Then either spliting them off into two separate circuits or 12/3(w/g) and alternating receptacles on each hot. But that does get into "issues" with GFCI's that can be solved, but best not added to this confusion.As to why the multiwire circuit can be a problem with a disconnected neutral go back to my earlier posts in the thread.
It appears that "multiwire circuits" is where I got off in the weeds. I tend to be more concerned over wiring for easy understanding and troubleshooting so I have never used multiwire circuits. It usually does not take long for drawings to be lost and cryptic labels on breakers to become unreadable. I would rather have the wiring layout be the homeowner or electrician's first guess.
I can't think of any applications where I specify or install a 240 VAC circuit where one double-pole breaker does not feed a single consumer, whether it is terminated at a receptacle or junction box. The cost of a little extra wire is not worth it if you have the panel space to make it so.
Many thanks for your assistance.
PMFJIWhat is likely to cause overheating of a neutral, as in the attached pic.Multiwire circuits won the same buss sharing a neutral seems like one possibility - any others?
Fighting Ignorance since 1967
It's taking way longer than we thought
It went overcurrent and the breaker is FUBAR. Is that an FPE panel? ;-)
Shared neutral would not cause overheated neutral because each phase draws 180 degrees apart from the other. As current draw on one goes up, on the other it's going down and so on at 60Hz.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
"Shared neutral would not cause overheated neutral because each phase draws 180 degrees apart from the other. "ONLY if it is wired properly. That was Bob's question. What other than a miswired multiwire could cause this.BTW, I found one in my house.Tracing another problem I needed to ID all of circuit. Got down to about 6 that I could not ID and then shut them all off and tried them one by one.Found TWO breakers that that would power the HVAC.I have two systems side-by-side. It was wired with multiwire and someone installed a single disconnect switch and the furance and tied the two hots together and moved one of the hots on th epanel so that they where on the same leg.
It went overcurrent and the breaker is FUBAR. Is that an FPE panel? ;-)FPE? It wasn't a Federal Pacific Stab-lok.FWIW, I look at maybe 4-6 FedPac Stab-loks a month and have not seen any greater degree of problems in them than in any other box.
Fighting Ignorance since 1967
It's taking way longer than we thought
>>FPE? It wasn't a Federal Pacific Stab-lok.
>>FWIW, I look at maybe 4-6 FedPac Stab-loks a month and have not seen any greater degree of problems in them than in any other box.
I'm sure you know that the "folklore" (seems pretty solid info, but you never know) is that FPE double pole breakers were made defectively and don't trip on overcurrent.
That's what I meant. Overcurrent and the breaker didn't protect the circuit.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
My first thoughts is there is a bad connection to the neutral bus. It looks like there might some corrosion just where the wire goes into the bus. And I see corrosion (rust) on two nearby scews. Might havbe been aided by water in the box.Other reasons are a mis wired multi-wire circuit.An overloaded circuit and bad breaker.An overload circuit that has been "fixed" by changing the breaker to a 20 or 30 amp.
One more thing to add to your list, though less likely than what you have already:
If someone through incompetence cross connects the hots of two different circuits on the same leg, you can get more than the allowed current in one of the neutrals without tripping either breaker.
-- J.S.
You really can never tell. Once a spot in a wire starts to heat it will heat faster than elsewhere, and a slightly bad termination will cause the end of a wire to heat faster than the rest. So one part of a wire can overheat with no (obvious) damage elsewhere.Certainly a shared neutral in a single-phase multi-circuit situation can overheat, if the hots are fused to their rated currents. This can happen accidentally if individual breakers feeding a multiphase circuit are swapped around without care. This is one reason why it's unwise to use individual breakers, even though code seems to allow this.It is possible to have an overcurrent situation on the neutral of a "proper" 3-phase circuit when exposed to certain reactive loads. "Switching" computer power supplies are one of the worst offenders (though recent power supply designs reduce this potential considerably).
If ignorance is bliss why aren't more people
happy?