Electrical code question

Page 2 of 4  

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.
--
Bobby G.



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, May 24, 2015 at 5:44:00 PM UTC-4, Robert Green wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 24 May 2015 06:59:58 -0400, "Robert Green"

It makes it virtually impossible to overload a circuit when each half of a duplex receptacle is on a separate circuit. You can plug a toaster and a coffemaker into one "outlet" with no danger of overloading it - and only have one wire required to be pulled for each "outlet" - giving you, in effect, a 30 amp circuit.
What I have seen done for dual GFCI (And even single gfci) protection is to run from the panel to a box with a gfci outlet, and feed-through from there to the house circuit. The GFCI protector is on the panel board with the electrical service panel, but is not IN the panel (for cases where a gfci or dual gfci is either not available or rediculously over-priced)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote in message
<stuff snipped in line>

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:
https://www.mikeholt.com/mojonewsarchive/ET-HTML/HTML/UnderstandingDangersMultiwireBranchCircuits~20020218.htm
---------------------------------------------------------------------------- --------------------- 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!
---------------------------------------------------------------------------- ---------------------
All to save (perhaps) a few bucks on cable costs. Not worth it.
--
Bobby G.



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, May 24, 2015 at 5:13:54 PM UTC-4, Robert Green wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, May 24, 2015 at 2:15:15 PM UTC-4, snipped-for-privacy@snyder.on.ca wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

the

it

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 25 May 2015 22:24:50 -0400, "Robert Green"

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<stuff snipped>

Circuits,

of

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.
--
Bobby G.


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tuesday, May 26, 2015 at 5:29:31 PM UTC-4, Robert Green wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
`On Tue, 26 May 2015 14:48:09 -0700 (PDT), trader_4

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 26 May 2015 17:07:08 -0400, "Robert Green"

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How is that different than loosing the line neutral (which, statistically is much more likely) Then EVERY circuit in the panel will have extra high voltage on the lower load side, and low voltage on the heavily loaded side/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Saturday, May 23, 2015 at 7:04:47 PM UTC-4, snipped-for-privacy@snyder.on.ca wrote:

I guess the argument can be made that the less points of potential failure like that, the better. And if it's the service netural that goes open, it's probably less likely that you'd have a big imbalance because for a whole house, there would be many loads on each leg, tending to average things out. So, I think the possibility that you'd see close to 240V appear on one leg would be a lot less.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 05/23/2015 07:04 PM, snipped-for-privacy@snyder.on.ca wrote:

Losing the neutral in *my* entrance panel is extremely unlikely. I actually check my panel and meter pan connection every 5 years. Of course the poco neutral is tagged to ground at my panel as well.
> Then EVERY circuit in the panel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I have lost the power company's neutral TWICE in the past year and a half. Once it just broke in the middle of the span from the pole to the house, and once it broke right at the pole mounted transformer. the first time I had no damage, the second time (when I was not even at home with anything on but maybe a couple security lights) I had a couple of blown GFCI outlets - and I mean BLOWN. Fire! Luckily the wallboard was not flammable, but there were scorch marks, even on the kitchen cabinets. Utility paid off quickly, but it didn't amount to much (maybe I should have put in for a new TV?)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 05/24/2015 11:45 AM, taxed and spent wrote:

Since you lose poco neutral so frequently, consider having a proper ground rod system installed.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I do, but that will not end the problems created with a lost neutral.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How will that help? Do you really think the ground ROD does anything? The only time the ground electrode will actually help with an open utility neutral is if it is a metal water pipe, connected to metal utility water pipe systems. Even a Ufer, the best of all ground electrodes, is not going to sink much neutral current in most places.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, May 24, 2015 at 12:22:30 PM UTC-4, snipped-for-privacy@aol.com wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.