Sub Panels: Is more better? or Cheaper?

[Steve Meliza]

You cannot bore a hole in a joist within 2" of the outer edges of the width and it cannot exceed 1/3 of the width of a joist. So a 2x6 joist being 5 1/2" wide would allow for a 1 1/2" hole exactly in the middle of the width. You can also notch the edge of a joist, but only in the outer 1/3 of the span and not deeper than 25% of the width of the joist. I'd say you probably can run your cable for option #2.

For some reason multiwire branch circuits are popular on SMC despite their shortcomings (cost and electrical hazards). Price out 12/3 and 10/3 and you'll find they are made of gold. Then compound the fact that you have multiple types and sizes of wire to run. What you really want to do is use a common size such as 12/2 everywhere than you can so that you can buy it in a large spool. Compare the price of 100' of 12/2 to 250' of 12/2 and you'll see what I mean. In my garage they would be even less practical in that all 120VAC circuits must be GFCI protected. If I ran 12/3 to all my outlets then every single outlet would have to be a GFCI outlet and that gets expensive in a hurry and discourages regular testing of the GFCI capability. Instead my two 120VAC general purpose outlet circuits are from GFCI breakers that cost me $35 each. Time to test GFCI? Walk over to the sub-panel and knock it out. But if you decide to run 12/3 or 10/3 because you feel it has advantages too good to pass up then so be it, it isn't wrong to do so.

[Chris Padilla]

One nice thing about X/3 wiring, including multiwire branch circuits, is that you can make the red a switched hot. Now in a shop this might not be a big deal but as I've renovated my house, I've replaced most of the branch wiring with X/3 so that I can have a switched hot anywhere I want it. VERY HANDY. Is it possible that running two x/2 is cheaper than running one X/3? I've never priced it out but I'll take a look next time I'm at the borg.

Multiwire branch circuits are acceptable by NEC, Steve, so what is so hazardous about them? Cost I won't argue with and GFCI is another good point but hazardous??

And as far as boring holes in studs closer than 2", isn't that what plate protectors are for? Also, this must only be true for load-bearing walls. What about non load-bearing walls and chewing up the studs? I recently gutted my master bathroom and let me tell you, the 2x6 plumbing wall in there had 2x4 studs and 2x6 studs chopped quite severely. I was shocked but I also realized it wasn't a load-bearing wall, either.

[Tom M King]

Use No-Ox, or some such anticorrosion coating on all aluminum wire junctions, and tighten the lug really tight. I keep a 1/4" breaker bar, short extension, and Allen sockets in the Electrical box to tighten all such lugs tight enough that the inspector can't come behind me and tighten them any more.

http://www.sanchem.com/electrical-co...lubricant.html

[Ole Anderson]

And leave a dedicated circuit for a future 3 hp 220 v dust collector, you may take the plunge sooner than later. I vote for running the fat cable to your shop and keep the #12 runs shorter. Less voltage drop that way. Plus the breakers will be close when you need them, no running to the garage. And you will likely have to upgrade your service drop from the pole.

[Rollie Meyers]

Use No-Ox, or some such anticorrosion coating on all aluminum wire junctions, and tighten the lug really tight. I keep a 1/4" breaker bar, short extension, and Allen sockets in the Electrical box to tighten all such lugs tight enough that the inspector can't come behind me and tighten them any more.

http://www.sanchem.com/electrical-co...lubricant.html

Code requires that they be torqued with proper tools to manuf. specs, & too tight is just as bad as too loose, & No-alox is not required unless manufacturers instructions require it's use, proper use of the anti-oxidant compound means working it in between the strands.

[Julie Moriarty]

FWIW, when I was a first year apprentice, a representative from the aluminum wire industry came to one of our classes to educate us on the wonders of aluminum wire. At the time, aluminum was just beginning to show up in our area and the rep wanted to get us on board with using their products. I saw aluminum wire being used on the jobsite for about the next 8-10 years or so but gradually it disappeared, even the larger stuff.

Most know the problem with smaller aluminum wire but many felt larger size wire was okay, as long as you did everything right. What we found over the years is the wire in the lugs tended to become loose and had to be re-tightened periodically or arcing would occur. Products like Noalox would reduce arcing problems but it did nothing to prevent the loosening effect that occurred with aluminum wire. I did a few jobs where we had to go back into the switchgear years later and re-tighten all the lugs. I was surprised how loose they had become. Also, while aluminum wire is lighter and cheaper, it doesn't like to make tight bends and if you score it, it can easily break where scored.

[Chris Padilla]

For fun, I took some pics of the prices of the various x/2 and x/3 and for 250' of it from the orange box, we had the following prices:

10/2 - 133.00
10/3 - 191.00
12/2 - 66.74
12/3 - 122.00
14/2 - 43.57
14/3 - 72.24

For #14, you are paying an extra 28.67 for that red wire over /2. For /2, each wire is 21.79 each (black and white only).
For #12, you are paying an extra 55.26 for that red wire over /2. For /2, each wire is 33.37 each (black and white only).
For #10, you are paying an extra 58.00 for that red wire over /2. For /2, each wire is 66.50 each (black and white only).

For #14, the red wire is 6.88 higher in /3 versus the black and white in /2.
For #12, the red wire is 21.89 higher in /3 versus the black and white in /2. Quite a jump from #14.
For #10, the red wire is 8.50 LOWER in /3 versus the black and white in /2.

Interesting stuff.

[Chris Padilla]

...and I think I'll check the breakers that have Al wire on them...make sure they aren't loose.

[Rod Sheridan]

Agree Julie, however annual maintenance along with an infra-red survey is basic maintenance for switchgear, prevents most failures...........Rod.

[Steve Meliza]

Multiwire branch circuits are acceptable by NEC, Steve, so what is so hazardous about them? Cost I won't argue with and GFCI is another good point but hazardous??

Most of the electrocution and fire hazards are resolved by using a double pull breaker as now required by the NEC, but we all know why DIY homeowner's have a bad reputation; they're not always known to follow code or get a permit and inspection. How many "clever" homeowners would save a buck by replacing a defective double pull breaker with two single pulls or clear up some room by replacing it with a 1" tandem? There used to be a website with lots of pretty drawings and clear explanations how a fault in a piece of equipment could result in an over-voltage condition on the other side of the circuit, but I'm having trouble locating it, but what I did find was a real life example of what can happen when the neutral comes loose: http://mattgreensmith.wordpress.com/...rical-problem/ Note that in this story and in the comment at the end neither had a double pull breaker.

The MWBC doesn't really save much money, especially if you have to use GFCI. It requires that you use a double pull breaker spanning both phases which may or may not happen depending on the installer and if a good inspection is performed. If your neutral comes loose in operation kiss your equipment electrical goodbye. If a load shorts out then all or part of the 240VAC appears across the other leg. About the only true advantage is the ability to have 120VAC and 240VAC available from one run of wiring, but I've never found myself needing such an arrangement as my 240VAC equipment are few in number and get a home run dedicated circuit.

In summary, the MWBC is not safe unless installed and maintained properly while the traditional branch circuit with dedicated neutral can be abused pretty badly before becoming unsafe. A good design fails into a safe mode, not a dangerous one.

And as far as boring holes in studs closer than 2", isn't that what plate protectors are for? Also, this must only be true for load-bearing walls. What about non load-bearing walls and chewing up the studs? I recently gutted my master bathroom and let me tell you, the 2x6 plumbing wall in there had 2x4 studs and 2x6 studs chopped quite severely. I was shocked but I also realized it wasn't a load-bearing wall, either.

The question and answer were specifically relating to ceiling joists, not walls. The issue is joist strength, not protection from nails. Load bearing or not, I'd never assume that what a plumber (or DIY homeowner) did to a stud was prudent or to code.

[Rod Sheridan]

Steve, the multi-wire branch circuit is used to supply every residential customer in Canada and the USA, as you're aware.

It must be a terrible safety hazaard.

I presume you're also against 3 phase 4 wire circuits as well?

The MWB circuit is safe, and is a great way to power your shop from one circuit................Regards, Rod.

[Julie Moriarty]

Most of the electrocution and fire hazards are resolved by using a double pull breaker...

In the three and a half decades I worked as an electrician, practically all the circuitry I worked on was multi-wire branch circuits fed from single pole breakers. Not once did I ever get a shock from feedback through the dead leg of of a MWBC nor did I ever hear any of my fellow electricians claim they did either.

As for MWBC being the source of a fire, I can only say I've never heard any fire inspector make that claim, and in my position, I had to deal with many fire inspectors. The primary concern fire inspectors had was making sure the fire safety protections were in place and installed properly. Nor did I personally see or hear of any instance where there may be a fire hazard due to the application of MWBC.

This is not to say the code changes requiring MWBC to be fed from two-pole breakers were unwarranted, only that if there are claims being made stating most of the electrocution and fire hazards are resolved through the application of the new code, those claims may be a bit exaggerated.

[Steve Meliza]

Like I said before, there is nothing wrong about choosing to use a multiwire branch circuit if the advantages outweigh the disadvantages for the woodworker wiring up their home workshop. We are rarely discussing 3 phase or commercial settings where MWBC are common and never worked on by the same guy that flipped the burger you had for lunch. All I did was inform of the risks to the DIY homeowner that are widely recognized outside of SMC.

Perform a search for "multiwire branch circuit" on your favorite Internet search tool then filter out those hits which are simply explaining what it is. I get the following results on the first page:
"improper multi wire branch circuits are a common yet easily overlooked defect in ... "
"Understanding the Dangers of Multiwire Branch Circuits. By Mike Holt"
"The savings from multiwire branch circuits can come at a high cost."
"Beware; the Multiwire Branch Circuit"

Move on deeper into the search results and confusion abounds about the ability to add AFCI and GFCI protection to multiwire branch circuits.

Keep moving on and look for a credible advocate of MWBC's in a residential application (other than here at SMC). I'll wait.

For fun switch your search string to "advantages of multiwire branch circuits". In the first page of results I found not one of them listed any advantages of MWBC without also describing the hazards, and one of the most common cited is fire - "A misfed multiwire branch circuit will silently heat the neutral until it either burns clear inside an enclosure or ignites flammable building material resulting in property loss or worse."

I repeat, use a multiwire branch circuit if you want to.

[Chris Padilla]

Steve,

Electricity in general is dangerous if things are done incorrectly. Perhaps MWBC are "more" prone to being wired improperly or handled improperly? I did the search and found a link describing how IF THE NEUTRAL was disconnected and how long would a TV with 240 V across it burn up? I guess I can see that. Perhaps someone is working on a receptacle on a MWB and removes it temporarily or something. If that receptacle wasn't wired pigtailed, I guess that neutral could be disconnected. I can see in 3-phase that if the wrong neutral is picked to add a circuit too and if the circuit isn't fully shut down that an over-voltage condition can exist.

But again, if things are done wrong, then sure, things could go awry quickly. An open/disconnected neutral is an extremely dangerous condition and I can see how it would be more so in a MWBC. I can see how things in MWBC can go awry more easily than in other situations.

[Steve Meliza]

Perhaps someone is working on a receptacle on a MWB and removes it temporarily or something. If that receptacle wasn't wired pigtailed, I guess that neutral could be disconnected.

I once had a good friend proudly announce that she had replaced several receptacles in the house without having to shut the breaker off.