Series or parallel

Atroxx

I'm not talking about the screw terminals, I'm talking about that little 1/8" or so tab between them. You'd have a hard time convincing me that the resistance through that little piece is lower than the resistance in a proper, tightly twisted wire nut connection.

If you had some 12g wire and every 10 feet it thinned down to 18g for 1/8" or so, would you use it as is? Do you think it would be safe and up to code like that? If not, then what's the difference between that and running your circuit through a cheap receptacle?

Red Squirrel

I always run in parallel if you run in series you need to have something plugged in each one for them to work and the voltage will be low. Old style Christmas light nightmares all over again.

Speedy Petey

If it were you you should go back and read post #2.
Series and parallel are NOT the correct terms to describe what this thread is about and will only serve to confuse DIY'ers.

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Speedy Petey

This is one of the funniest things I have read in a while.

What would you call a "fair" margin? Ten cents a year?

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Yoyizit

The resistance of this link is higher than #14 [I guess] but it is a very short distance so the overall added resistance is not that high.

As to temp. rise, this probably depends on the conduction of the heavier busbars around it.

Pass 10A through the link by using a hair dryer as a load. Measure the voltage drop across it without touching the connections that are putting the current in.
If 1/8" of #14 copper is ~30 uΩ and gives a ~300 uV drop, this should give even less.
Having an opamp with a DC gain of x100 would come in handy for this measurement.

But then, a pigtail of #14 copper 6" long is ~1.3 milliohm.

Or if you know the dimensions of the tab,
R = ρL/A
Where
ρ is the static resistivity (measured in ohm-metres, Ω m);
R is the electrical resistance of a uniform specimen of the material (measured in ohms, Ω);
L is the length of the piece of material (measured in metres, m);
A is the cross-sectional area of the specimen (measured in square metres, m²).

ρ for copper is 20 nanoohm-meter.

We definitely be having fun now. . .

InPhase277

For the $0.39 receptacle that I just measured the tab dimensions of, according to the values above, I get 2.374 x 10^-5 ohms. Because there is two tabs per receptacle, we can double that to about 4.75 x 10^-5 ohms.

Someone can check my math. I've drawn a pic of the tab. The specific transition from the tab to the screw back plate is not shown except by the "legs" on the bottom. But these legs have no length, as they immediately become part of the back plate.

Attached Images

 

Atroxx

Well, I guess it's all theory anyhow, but you guys are all talking about one single receptacle. If Momma's in the living room vacuuming the floor, and daughter Judy is in her bedroom drying her hair with a floor heater plugged into the same receptacle while at the same time Dad is out in the garage running a table saw, and all 3 of those receptacles happen to be on the same circuit for whatever reason then that's a helluva lot of juice going through the first plug on that circuit. Yes, I know it's unlikely that all those plugs would be on the same circuit, but it is possible.

Personally, I'd rather trust my wire than a 39 cent disposable receptacle.

Speedy Petey

It is also possible (read: likely) that as soon as two of those are turned on the breaker will trip.

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InPhase277

It's really all in how you look at it. I personally like to pigtail the connections myself, but I don't always do it. Let's think about the nature of the connections. Sure, the tab is a small piece of metal, but it is solid from one back plate to the next. There is no joint mechanical joint in it. When you tighten a wire under the screw, contact is made with bolted pressure, on two sides of the wire.

With a twisted splice, you more or less are relying spring tension of the wire itself to maintain contact. Actual surface area of contact is pretty small. Twisting a wire nut on helps add some contact surface area through the spring.

Under analysis, it seems that the receptacle is a better "conductor" than the made splice. But at any rate, I have seen both of them fail. And that is usually due to poor installation. Besides, we weren't talking initially about what the more trustworthy connection is. You stated that there would be a significant savings on energy costs by using a pigtail. When we really get down into the meat and potatoes of it, which I like to do, it doesn't seem that's the case. If we loaded a circuit to 20 A from the last receptacle on a chain of 11, the amount of power dissipated through all twenty tabs would be, if my numbers are correct, 1.9 watts. If that was allowed to run continuously 24 hours a day for an entire year, it would amount to 16.6 kWh. What's that, $2.50-$3.00?

Yoyizit

I move that we adjourn this Design Review meeting.

Atroxx

It's also possible (read: likely) that when your average idiot out there blows a lot of fuses, instead of trying to figure out why it won't hold, they just go out and buy a bigger one. The last fuse box I worked on had a minimum of 30a fuses in every single slot. If the above mentioned scenario happens every night, and they get tired of blowing fuses so they go buy a 50a and throw it in there, then the receptacles becomes the weak link in the chain and a potential fire hazard. Even under normal conditions, it's very plausible to be pulling 20a through a receptacle designed to handle only 15a without having any breaker trouble whatsoever.

You seem to be right Inphase, it isn't a significant amount of money, but for whatever the reason, I stand by my position that the pigtail method is, in most if not all cases, the superior connection method for two reasons. If the plug fails, it doesn't kill power to the whole circuit, and the receptacle isn't designed to handle as much power as can theoretically be going through it.

What are the advantages of passing through the screw terminals? It's a faster install(which saves the electrician money via labor time I guess). It can be argued that when done properly it can be a more secure connection than a twist method, although personally if I had an electrician in my house and he told me that he didn't trust his own twist connection to hold, I would probably ask him to leave right then. It also saves space in the box, which would probably be one of the only reasons I would choose not to use pigtails.

Speedy Petey

1) For the amount of times I have seen a receptacle fail I don't think this is a valid argument. The majority of the time it is dues to a poor connection, NOT the fact that the screws themselves were used.
More an installer error than a material failure.

2) Completely incorrect. The receptacle is most certainly designed to carry the full current of the circuit it is installed on.

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Speedy Petey

You could put a "what if" situation on so many scenarios in a home it's not funny. Besides, there are other weaker links out there than the tabs on a receptacle.
Also, a 30A is the largest fuse you could possibly install, so the over dramatic scare tactic 50A fuse example holds no water.

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Speedy Petey

Both ideas are correct.

Saves time, saves box space and convenience.

PROPERLY done, pigtailing and screw terminals are equally safe and effective.

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joed

Wire nuts count towards box fill in Canada. I use the screw terminals if there are enough of them.

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