Electrical code question

[Robert Green]

Disagree. Teaching people to plug high amperage appliances into the SAME outlet is just wrong. They'll tend to generalize and think EVERY outlet can handle 30 or 40A loads. What does your average Joe Homeowner know about Edison circuits? Nada, zip, bupkiss.

Because it's SO simple to add an extra box and circuit when you're doing the work, it seems like very false economy to save a little money (maybe - you've read my comments on wire costs and sales) and create an outlet that encourages people to overload *all* outlets because "the one in the kitchen never blows a breaker." Joe Homeowner is hardly likely to know that just those outlets in the kitchen can handle multiple high-amp loads plugged into them.

If running large loads out of one duplex outlet is the main reason for using Edison circuits (and it's a weak one IMHO) I counter by saying you can do exactly the same thing with a discrete feed from two breakers at the panel with no shared neutral. Same effect.

Then you can pull 40A from one duplex outlet if that's what floats your boat. Doing it with two discrete circuits and no shared neutral means you can use single pole (and MUCH cheaper) GFCIs using the downstream options or GFCI breakers in the circuit panel.

I'm still not convinced Edison circuits are saving anyone any money or makes them safer in any way. Mostly what I've heard is "gee, you can run one less conductor" as if that's really a substantial savings in wiring or labor costs. It's not if you're going to run a new cable anyway.

Explain to me again how you can GFCI protect an Edison circuit with two one pole GFCIs? The current in a shared neutral fluctuates with the load on both phases. Only a dual pole GFCI can monitor both hots simultaneously as I understand it. From what I've read at least some people who have tried to install two single pole GFCIs on an Edison circuit have been plagued by nuisance trips. Others have had success, apparently, by separating the shared neutral into two discrete wires before connection to the GFCIs. But that's no longer a true Edison circuit.

There may be a proper way to do it, but it seems inordinately "klugy" to try to force two single pole GFCIs to do something they weren't designed to do. It seems a long way to go for very little reward. Just run two circuits instead of an Edison circuit and you can use the much cheaper single pole GFCIs and you can use them in the pass-through mode to protect all downstream outlets.

I'm not the only one who isn't sanguine about MWCs:

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--------------------- Destruction of Equipment. Never remove the grounded (neutral) conductor from the grounded terminal bar in the panelboard if the phase conductors are energized. The grounded (neutral) conductor you remove could be part of a multiwire branch circuit, so this could result in destruction of electrical equipment. More important, even if the return conductor is not part of a multiwire circuit, removing a conductor from the grounded terminal bar when the circuit is energized could result in injury due to shock or arcing.

A typical 3-wire circuit is actually two otherwise-separate parallel circuits with a common conductor. If the grounded (neutral) conductor is accidentally opened, the circuit changes from two separate parallel 120 V circuits to one 240 V series circuit. This can result in fires and the total destruction of electrical equipment.

For example: A single-phase, 3-wire, 120/240 V circuit supplies a 1,275 W,

120 V hair dryer and a 600 W, 120V television. If the grounded (neutral) conductor is interrupted, it will cause the 120 V television to operate at 163 V and consume 1,110 W of power (instead of 600 W) for only a few seconds before it burns up. Figure

Step 1. Determine the resistance of each appliance, R = E2/P.

a.. Hair dryer rated 1275 watts at 120 volts. b.. R = E2/P, R = 1202/1275 = 11.3 ohms c.. Television rated 600 watts at 120 volts. d.. R = E2/P, R = 1202/600 = 24 ohms Step 2. Determine the circuit resistance: RT = R1 + R2

a.. RT = 11.3 ohms + 24 ohms = RT = 35.3 ohms Step 3. Determine the current of the circuit: IT = ES/RT

a.. IT = 240 V/35.3 ohms = 6.8 A Step 4. Determine the voltage for each appliance: E = IT x Rx

a.. Hair dryer: 6.8 A x 11.3 ohms = 76.84 volts b.. Television: 6.8 A x 24 ohms = 163.2 volts The 120 V rated TV in the split second before it burns up or explodes is operating at 163.2 volts.

Step 5. Determine the power consumed by each appliance: P = E2/R

a.. Hair Dryer: P = 76.82/11.3 = 522 watts b.. Television: P = 163.22/24 = 1100 watts The 600 W, 120 V rated TV will operate at 163 volts and consume 1110 watts. You can kiss this TV goodbye!

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All to save (perhaps) a few bucks on cable costs. Not worth it.

[Robert Green]

No truer words were ever spoken. It seems to me that the MWC *reduces* the available outlet count and encourages people to use "cheaters" like six-way plug-in adapters to get more outlets. They can be pretty dangerous if the hots are connected in the adapter. I've used some. The older ones did tie the neutrals together but the newer ones don't. The cheapest of them had press-fit connectors between the outlets and the internal bus bar of the adapter. When one of the connections came loose, it arced and melted the adapter.

[Robert Green]

He could be right if we're talking split receptacles. They might be "disallowed" if the circuits were not fed with a tied breaker. The expectation is that if you kill power to an outlet that both upper and lower halves will be dead. In the split wire receptacle it requires a tied breaker.

But again, why would you want to feed an upper and lower duplex receptacle from two different circuits when you could just add a second circuit and outlet? Has anyone ever lived at a place that had *enough* outlets? (Hyperbole alert)

[gfretwell]

You are arguing with the wrong guy. I am not the one who was promoting that ancient Canadian split receptacle rule on the countertop. . There is still no good reason why you couldn't bring a MW circuit into a 2 gang box, put 2 GFCIs in there and split put your counter top receptacles from there.

That is not what we were originally talking about tho. It was using a MW to feed the dishwasher and disposal.

To the point of the actual note you responded to, I was asking why Clare thinks you can't have 2 separate branch circuits in the same box.

[Robert Green]

But I suspect there wasn't any wannabe electrician 17 yr old rewiring the power company's pole-mounted transformers. I know that my house *had* been rewired by a 17 yr old, so I would (and did) worry way more that any Edison circuit I found wouldn't be wired correctly in my house, not on the poles outside. Turns out I was right to worry.

I would guess that any house over 50 years old has had some sort of very underqualified homeowner "electrician" do some sort of electrical work in the house. From what people have posted elsewhere, I don't think Edison circuits are well understood by weekend electricians. Anyone touching anything they don't understand can lead to trouble. I know that multiwire circuits are the way the whole power grid works. And I know that Edison circuits it have some advantages and specific uses. But I think it's clear that the original reason to use them, cost savings, is extinct, or nearly so.

That's because 12/3 is way more expensive than 12/2 almost everywhere I looked (and that's not even using sale prices). 12/3 is SO much more expensive (nearly twice as much at some sites) that there's no wire cost savings and very little labor savings. And even if you did manage to save $20 on wire, the dual pole (or multiple one pole) GFCIs you'll have to buy to get proper GFCI protection will eat up those meager savings in a NY second.

(-"

[trader_4]

I don't see how a multi-wire circuit reduces the outlet count. How many you can put on a circuit doesn't depend on the wiring method.

[Robert Green]

Whoops. My apologies.

Wouldn't their breakers have to be either dual pole or tied-handle to address the NEC's obvious concern with leaving something live that someone might reasonably expect to be dead? I believe lots of people expect that when they cut power to a breaker (using the plugged-in radio playing loudly method, for example) that the outlet it controls will be completely dead.

Feeding two discrete circuits from different breakers into one duplex outlet clearly re-creates that danger in a slightly different format.

[trader_4]

You could just as easily have multiple receptacles on an Edison circuit and plug appliances in and overload it. Overload protection is provided by the breaker, not how it's wired.

What a peculiar mess.

[trader_4]

It's one less conductor, but two less wires, the other being the ground. Your point on increased cost of double pole GFCI breakers versus two single pole probably negating some or all of the cost savings is valid though. But that's only if you put the GFCI at the panel. You could use two GFCI receptacles at the end of the Edison circuit.

Good catch. If you do it as Clare suggested, it won't work. He's claiming you can put a GFCI outlet or outlets next to the panel and feed the Edison circuit from that. It won't work for the reasons you cite. It needs a single GFCI that can sum up the currents on the two hot legs and neutral and make sure it equals zero. Besides that, it just gets screwier. Now because of this curious Canadian penchant for split outlets with Edison circuits, you're supposed to mount more crap next to the panel too?

I disagree with your last sentence though. You could run an Edison circuit to where the receptacles are going, separate it into two runs serving two groups of receptacles. Put a GFCI receptacle on the first spot on each chain, then feed the others downstream. That will work and it's still an Edison circuit.

Per the above, an Edison circuit can be used with two GFCIs just like running two separate circuits and putting the two GFCIs where the Edison splits to serve two chains of receptacles.

Exact same thing exists with ovens, dryers, spas, any other 240V appliance that has 120V as part of it. You shouldn't be removing neutrals on any energized circuit, unless you know what you're doing.

It is an additional potential failure point where bad things could happen. That already exists with ovens, etc, but I think it's less likely that a neutral will come loose on ovens, etc than on a circuit that has a bunch of receptacles, daisy chained.

[Ralph Mowery]

I would not knock the 17 year old. If I was 17 again, I would trust my wiring more than a licensed electrician I know that is over 50 years old.

Seems like everyone makes a big deal out of wiring a house. As long as the breakers and wire size is correct and the connections are tight, there is not much to worry about. Just make sure it is done to code.

That done to code takes me back to the over 50 year old licensed electrician. I worked with him in a large plant. Most everyone laughed at himand the way he did things. Never did see why they did not let him go. Well, I do as the only requirement at the plant was to show up every day. That man would do outside work for people. Even when the electrical inspector told him to do something a certain way, he would do it some other way and complain about how the inspector was always turning his work down.

[gfretwell]

You will need to use the 2 pole or handle tie breaker under the current code but that is fairly recent.

[Robert Green]

Here's what I found:

National Electrical Code Citations for Multi Wire and Split Wire Devices 1.. The 2008 National Electrical Code, 210.4(B) Multiwire Branch Circuits, now requires that effective 1 January 2008,information about conductors of multiwire branch circuits originating from the same panelboard or distribution equipment has been relocated to 210.4(A). Now 210.4(B) addresses disconnecting means for simultaneously disconnecting all ungrounded conductors of all multiwire branch circuits. Simultaneously disconnecting all conductors of multiwire branch circuits is now expanded to all multiwire branch circuits, not just those that supply more than one device mounted on the same yoke or mounting strap. -- Minnesota Electrical Association. 2.. NEC Paragraph 210-4 addresses multiwire branch circuits.

3.. NEC 210-4-b makes clear that split receptacles must be protected by a simultaneous disconnect to all ungrounded (hot) conductors (i.e. use a double-pole breaker with a common trip tie installed). NEC Paragraph 210-4 addresses multiwire branch circuits. 4.. Split-receptacle means each half of a duplex receptacle is wired to a different "polarity" or phase and the single grounded conductor (neutral) is used). NEC Paragraph 210-4 addresses multiwire branch circuits.

[gfretwell]

Nothing particularly onerous in any of that and those changes have eliminated virtually all of the issues are hung up on.

You can argue about whether two 12-2 wg is cheaper than one 12-3 and whether the boxes need to be upsized but the improved voltage drop efficiency is undeniable and goes on forever. I2R =$ and a few bucks on the front end disappears pretty quickly in the out years. If you are at the other end of the house from the panel, a multiwire circuit starts looking pretty attractive, assuming you are not putting a sub panel down there ... essentially a big multiwire circuit.

[Robert Green]

Well, you didn't see this kid's work, notching joists at exactly the wrong place, bringing a neutral from a different circuit into his bedroom because all he had access to was a switch leg and no outlets. He had finished the basement himself with no insulation or vapor barrier using spike nails that caused massive damage to the very soft blue cinder block. He also apparently used scraps of whatever junkheap wire he could find to make his kluged connections. I had to rip much of it out and start over again. He also put 20A breakers on old, 15A cloth covered wire because the 15A breaker that was there "tripped too often."

Are you *still* sure I should trust this guy? (-:

That's not going to encourage your best quality workers to stick around.

The world is full of nitwits, some of them even hold licenses. (-: I am going to have to relocate a message I saw posted in one of the electrical forms by someone who makes even you nitwit look competent. He was wrong about the basics but quoted scientists and legit (though woefully misapplied) theories to back his claims.

Wiring a home has become a little more complicated with the advent of GFCIs and AFCIs.

For me it was a question of what I needed to upgrade protection to the latest NEC. I found that AFCI double pole breakers for MWC were non-existent at the time, although now there are a few manufacturers making them.

Eventually every breaker in a panel will protect against arc faults, ground faults, overloads and short-circuits because that's where it makes the most sense to protect branch circuits.

I use GFCI's on the first outlet in circuits that I installed and used the line connections to protect downstream but that turns out to make trouble shooting more troublesome. Did the breaker blow? Check the panel. Did the GFCI trip? Look behind the desk (actually I made damn sure all the GFCIs were accessible easily, if not visually).

Then I had a devil of a time trying to work AFCIs into the mix and ended up protecting only two outlets (space heater and A/C) with a discrete outlet-format AFCI for each because the panel mounted AFCI's were, like 2 pole GFCI, incredibly expensive compared to their outlet-format counterparts.

[TimR]

That has always seemed highly likely to be true to me, but I've not heard anyone agree.

A Ufer will always get you a favorable resistance measurement, but I've always had some skepticism about whether that translated into current sunk.

[gfretwell]

\When I was working in the computer biz, one of the things we did was lightning mitigation and analyzing grounding electrodes was a big part of it. One of the first things you find is there is no such thing as "ground". I have found up to 35 volts difference between building ground electrode systems that were less than 50 feet apart and that was using a low impedance meter. They had what seemed to be very robust electrodes so the difference was in what earth potential was. This is generally caused by current imposed on these electrodes. There are a number of things that can cause this, not the least of which is a compromised neutral. Another problem is the voltage drop in the PoCo neutral conductors themselves. I took my clamp on down the street looking at current in the ground wire on the poles and got some surprising results. There was over 2 amps on some of them. I had close to an amp on my grounding electrode conductor with my main breaker turned OFF. (I had a similar number on the PoCo neutral) I was providing the grounding for the grid. Granted I have a better ground electrode system than most since it integrates several thousand square feet of concrete slab, 5 ground rods, many feet of buried copper wire and an inground concrete pool.

[Robert Green]

I suspect you meant to say "you are hung up on." Even so, I am not "hung up" on anything. The most popular reason I've seen given for using MWC is that it saves money on wire. But when investigated real-world costs, that turns out to be untrue. With the recent code changes requiring GFCI breakers, the economy reason no longer exists. It's more expensive to wire a MWC because of the extremely high cost of the now required double pole breaker compared to two single pole units.

You still sound hesitant to admit that's a fact. Is the cost issue in dispute or do you concede that 2P GFCI breakers are WAY more expensive. Five to ten times by my estimate. The "saving money by using less wire" reasoning is now extinct except for fairly unusual circumstances.

Have you found prices that actually make it a reasonable argument because I have not, especially when you look at sale prices. Whatever you save by using the more difficult to work with (thicker and stiffer) 12/3 is eaten up by the special 2P breaker required.

Now I will also agree you can use discrete GFCIs in a MWC if you're into cluster-fu& engineering, but the proper way to protect MWCs is with devices in the panel especially designed for the task.

And in how many installations is voltage drop a serious enough problem to warrant using MWCs? Huge, million dollar houses where the cost of some extra wire is chump change, I'd venture. In my case, the only device that would have any problems with voltage drop is the CAC - and it IS normally wired with MWC's primarily because 240 volts are needed to run the compressor, not because some Canadian code-meister thinks it's a good idea to deliver 30 or 40A to a single 110V outlet.

A subpanel is the *right* way to deal with super-long wiring runs. Running multiple Edison circuits not so much. Besides, homeowner electricians usually don't go futzing around in sub-panels but they will pull an outlet in a heartbeat. And most of them won't know jack about why there's 240V coming into a 110V outlet box. That danger is reduced by the new code, but not eliminated.

How many times have we seen problems like low voltage being an issue in normal residential work? Far less than we've seen complaints about backstabs coming loose or wires under connection screws breaking because they were nicked when stripped, IMHO. Those conditions create the potential for a broken neutral which is a far, far worse thing in a MWC than it is in a normal two-wire one.

In my reading I've learned that there are people lobbying the NEC folks to outlaw MWCs in residential work. Apparently this is a "Apple or IBM" issue for many people. My major concern is that it's no longer cheaper because of protection device costs although it's still "sold" that way. I agree with you that anyone with a voltage drop issue can benefit from a MWC but then again, they can also benefit by using bigger gauge wire.

That said, I doubt voltage drop in kitchens is a big issue. Those are resistive loads that are thermostatically controlled. Unlike some motors that could burn out at too low a voltage, the electric skillet and toaster can probably tolerate a respectable voltage drop without serious issue. So I wonder, like you seem to, why the F they're required in Canadian

*kitchens*? The case could be made that it will result in substantially fewer breaker trips, but so would multiple outlets on normal circuits.

[trader_4]

What exactly is a cluster F*** about using a regular double pole breaker in the panel and then two GFCIs on the first two receptacles that need GFCI protection? From there you can feed downstream outlets just like with any other GFCIs. Just because you don't understand it, doesn't make it a CF.

[gfretwell]

Why would I need a 2 pole GFCI breaker when I can use 2 GFCI devices at the far end? They have also loosened the rules on AFCIs and allow the device type under some circumstances. I expect the restrictions to be completely gone in 2017.

You are still ignoring the voltage drop issue and in a world with ever increasing energy costs, it may be a bigger issue than wire. Even so a roll of 12-3 is less than twice the cost of 12-2, particularly at a real electrical supply house that does not have promotional prices on

12-2

I just looked at HD and 12-2 is $68, 12-3 is $117. The difference will be less at a real supply house I also pointed out you only need a 2 pole standard breaker (or a handle tie kit). The GFCI can be at the far end.

Why? Most people think it is better to have the GFCI near the load so you can more easily identify and reset it.

Perhaps you should put the numbers in a V/D calculator, even at a modest 50-60 feet and plot it out over 50 years (the typical design number for electrical installations)

The NEC is not an instructional manual for unqualified people. If the concept of a MWC baffles harry homeowner, he should leave the covers on.

CMP 2 and CMP 5 will laugh that out of the building. NFPA does not cater to the unqualified. The new emphasis seems to be more toward energy conservation than making the world safe for DIY guys. In fact I am not sure I have ever seen that even get to the proposal stage.

The voltage drop issue is I2R losses. If you are out at 60 feet, not that far, even in a pretty small house, with 2 circuits pulling 10a each, the combined voltage drop in the neutrals is 2.3v. In a MWC that is zero. That is 23 watts wasted. (>1% of the power used)

There are even people promoting going up a size on all branch circuits to save energy and they come up with the same kind of calculations.

[gfretwell]

Bobby keeps ignoring the fact that a dollar handle tie will comply. There are still AHJs who will accept linking the breaker handles with a piece of 12 ga wire but they are getting less common