As long as the breaker opens both hot legs you can feed line to line and line to neutral loads from a multiwire circuit. The NEC handbook has a picture of that combo receptacle in the section that defines this rule.
Save $200 for some thing else regardless if you have 2 phases in one box or two.
Art.
| snipped-for-privacy@aol.com (Greg) writes: | |>If you have both phases in the same box, why not save $200 and put in a 6-15r | | speaking of which, I have an interesting fixture. Duplex outlet, top is | standard 5-15R, bottom is 6-15R. The hot of the 5-15R is jumpered to one | of the hots of the 6-15R the same way the top and bottom of every 5-15R | duplex outlet is. Didn't know that was legal.
Shared neutral circuits are legal (need a 2 pole breaker to be safe), though they are frowned on (I won't allow them in my home unless they terminate in a single box.
Your combination 5-15R + 6-15R is not even a shared neutral, by itself. The neutral wire goes to the 5-15R only; the 6-15R doesn't connect to it at all. But if that circuit did run to another combination like it, but the next 5-15R tapped hot from the other side, then it would be a shared neutral (with respect to the two 5-15R's).
Oh. For some reason I thought you couldn't feed a 120V outlet off of a
240V circuit (with shared neutral 120V-only wiring explicitly exempted) as well as rules that 240V supposedly only going to a dedicated outlet, you can't have a string of 5 6-15Rs serving a couple of rooms.
There are a couple rules about "multiwire" circuits, basically that the neutral can't depend on a device and that if they terminate on a single yoke or serve a
240v load they must have a common trip breaker but other than that they are just circuits like the rest. In fact some could say there are less restrictions since most 240v circuits don't require GFCI protection. The major exception is a circuit feeding a skid pack for a spa.
By 'can't depend on a device' you mean you can't wire the neutral from a downstream load to the silver screw on a recepticle and connect the neutral from the panel to the other silver screw, correct? Same as the rules for the ground.
yup
I understood everything EXCEPT "terminate on a single yoke."
Also, if a GFCI is required/indicated they why would "they" permit eliminating it if you have a "multiwire"/shared neutral circuit. Doesn't make sense to me.
That is NECspeak for both sides of the multiwire circuit end up in the same receptacle (top/bottom)
It would still be required on the 120v outlets but 240v outlets are not generally required to be GFCI, wherever they are.
OK.
BTW: I have a northern VA high rise condo. The building wiring,of course, is 3 phase. Each unit gets two phases. One of the kitchen outlets was a "multi-wire" to a "single yoke." The unit was put in service back in 1977. There are NO doulble pole breakers in the CB box. SO: did the NEC change, or was the electrician lazy? (Just academic: one "side" now goes to the built-in microwave oven and the other side is to a duplex GFCI.)
I would LOVE to see a duplex 240 GFCI outlet with 240/120 feed. I understand that multi-wire outlets are standard in Canader, do THEY (The Canadians) have GFCIs that work with "multi-wire" shared neutral feed?
EMWTK BTW: Before the microwave was put into my condo, there were no GFCI's in the kitchen (or anywhere else, for that matter.)
| BTW: I have a northern VA high rise condo. The building wiring,of course, | is 3 phase. Each unit gets two phases. One of the kitchen outlets was a | "multi-wire" to a "single yoke." The unit was put in service back in 1977. | There are NO doulble pole breakers in the CB box. SO: did the NEC change, | or was the electrician lazy? (Just academic: one "side" now goes to the | built-in microwave oven and the other side is to a duplex GFCI.)
The NEC probably changed since 1977. I doubt the electrician was lazy, but the contractor could have been a cheapskate. Are the two sides really controlled/protected by separate single pole breakers? Are they really on separate phases?
| I would LOVE to see a duplex 240 GFCI outlet with 240/120 feed. I | understand that multi-wire outlets are standard in Canader, do THEY (The | Canadians) have GFCIs that work with "multi-wire" shared neutral feed?
I've never seen a GFCI receptacle for 240 volt, though there are many two-pole GFCI breakers for that.
The new AFCI requirement for bedrooms will be interesting. Square-D refuses to manufacture 2-pole AFCI breakers, but Cutler-Hammer already makes them.
| BTW: Before the microwave was put into my condo, there were no GFCI's in | the kitchen (or anywhere else, for that matter.)
BTW: you can derive 3-phase power from 2 phases of 3-phase using a couple of 120 volt to 120 volt transformers. The answer is:
210-4(b) does not show up in my 75 NEC but it is in my 90 NEC (not as a new change) so I guess that was something that showed up before the 87 code cycle.
The 75 code required them in the bathroom but not in the kitchen. BTW it is very possible that your AHJ was still on a much older code in 77. These things are not automatic and some jurisdictions can be several code cycles behind
The AFCI requirement is only for 15 and 20a 120v outlets. I suppose that could still be a multiwire but with all the problems they are having with AFCIs I doubt anyone would cut that corner and kick that bucket of snakes.
BTW it was Cutler Hammer who came up with the AFCIs and lobbied CMP2 to get this into the code. Everyone else is in catch up mode.
Pretty sure. It's been 2 tenants since I looked at things. But I believe I measured the higher voltage between the two "hots" of the outlet. There are NO double pole breakers in the CB box in the unit. The cooking and the clothes dryer are both GAS operated and the air conditioning is from a central water chiller so there just are any "natural" 240/208 loads.
Well aware of that. Quite a few busineses here use "dog leg"
120/240/240/240 for three phase service with two transformers in an open delta.
Until I put it in myself, even the BATHROOM didn't have a GFCI. The unit was supposed to have been completed in '74/'75 but the building collapsed (I kid you not) and they didn't "top" out until around '76.
Could be. But while I still own the unit, I'm not going to ask if it's up to code!
On 25 May 2004 20:54:58 GMT Greg wrote: |>The new AFCI requirement for bedrooms will be interesting. Square-D |>refuses to manufacture 2-pole AFCI breakers, but Cutler-Hammer already |>makes them. | | The AFCI requirement is only for 15 and 20a 120v outlets. I suppose that could | still be a multiwire but with all the problems they are having with AFCIs I | doubt anyone would cut that corner and kick that bucket of snakes.
I personally have no trouble with a shared neutral circuit provided that it is protected by a common trip breaker (required by code, anyway) and terminates at a single load point (one box, or very close boxes that are obviously tied together, or a dedicated load). The only place I might expect that in a bedroom, though, is a combination 5-20R/6-20R outlet I would be putting in for A/C use.
There is talk of eventually expanding AFCI requirements beyond the bedroom. That might also include requiring them on higher voltage circuits as well. That could force them to make a 3-phase version, too. And 3-phase GFCIs are only in equipment protection (30ma) not people protection (2ma) versions.
Personally, I think that they should do the higher voltage requirement soon (but it is not in the 2005 draft). Why would a 240 volt A/C outlet in a bedroom be any less of a risk? I've personally seen one burn up (though it was definitely wired in violation of today's code, and probably of 1960's code as well, since it was exposed in the closet and hanging in the air). OTOH, A/C compressors might also cause false trips on AFCI. I have yet to test things.
FYI: I don't like central A/C or central heat. So don't suggest that to me.
| Until I put it in myself, even the BATHROOM didn't have a GFCI. The unit | was supposed to have been completed in '74/'75 but the building collapsed (I | kid you not) and they didn't "top" out until around '76.
I have _twice_ seen an _entire_ multi-home development, where sticks are up and some or most of the walls are up, collapse in a "once or twice a year" level of storm severity. One was separate 2-story homes (all 15 in the development collapsed in the same storm), and the other was 3 multi-unit
3-level condo buildings where the top 2 levels crunched the bottom level.My wife had a block wall blow over the other day. The cells were not poured yet tho.
Unfortunately my email program is not setup to keep old messages, therefore I pick it up from here, even thou this tread went different way:
We talked about the effects of induction due to the fact that the magnetic flux does not cancel when wires from multicircuit are going through different openings in the metal plates. I promised a little experiment, you can find more info at:
Interesting. I wonder what it looks like with 2 wires running in adjacent holes in the same plate or box. The mitigation in the NEC is to cut a slot between the holes. I wonder how hot the web gets if you don't.
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