I’ve wired a fair bit but am no sparky and had someone question this practice: running 3 wire (2 ug conductor) cable, shared neutral (g conductor) to, say, a split receptacle. The claim is this delivers 220v[240] to _the box_ (not the device/ receptacle) which poses a higher risk to anyone accessing box, et al. I would agree, it seems that 2 110’s will give you a 220[240], but it’s a common practice in my area and not even frowned upon to the best of my knowledge. (The argument that anyone poking around in there should be well aware of the risks aside.) Your considered input, feedeback, etc. appreciated.
David
Edited 11/6/2007 9:47 pm ET by peedee
Edited 11/7/2007 9:52 am ET by peedee
Replies
I'm not sure exactly what the question is. "The claim is this delivers 220v to _the box_ (not the device/ receptacle) which poses a higher risk to anyone accessing box," the differnce between voltage delivered to the box and that delivered to the device escapes me. If you are comparing the use of 3 conductor cable "shared neutral" to running 2 two conductor cables to power 2 outlets on opposite phases, there are some who agree in that it is less confusing to someone coming along later, but the box has the same 220 v inside it. Either way, both are done frequently and there is no safety difference between them. If you can be any more specific on what difference you are asking about, maybe some of the electricians on the board can answer more intelligently than me.
Thanks, Rich. The concern, as was explained to me and I understand it, is that 2 120's with a shared neutral pose a greater risk that two 120s with individual neutrals (even though they're all bonded at the panel). I personally don't see the issue but am seeking to further understande the scenario (or establish if this individual is 'blowing smoke').
No it would not give you 220 in the box.
It would give you 240. If you measure 220 then call the power company or fix your defective wiring.
What you are talking about is a mutliwire circuit.
If both legs are on single device the it is spose to be feed by a 2 pole breaker.
If no single device has both legs on it then you can use 2 single pole breakers.
Until recently Canada required such split receptacles for kitchen countertop.
Another "problem" with then is that the neutrals need to be pigtailed and you can't use the receptacle to feed through the neutrals.
And you have split receptacles or even alternate receptacles be GFCI protected unless you use a 2 pole gFCI breakers.
A more reasonable way of doing this, for a kitchen, is to run the mutliple wire to the first box. Then split it into 2 separate circuits with the first device in each being a GFCI receptacle.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
It would give you 240. If you measure 220 then call the power company or fix your defective wiring.
It depends on how you measure it and how your local power is setup (i.e. wye or delta transformer).
The normal range for "220V" is 215VAC to 240VAC, per spec used by most utilities.
RMS measurements add further confusion - most meters that claim to measure RMS approximate the reading - a "true RMS" meter will give you different numbers.
If you want to learn more about this, Wikipedia actually has a pretty decent treatment of these issues at
http://en.wikipedia.org/wiki/Three-phase_electric_power
and
http://en.wikipedia.org/wiki/Split_phase
Edited 11/7/2007 3:53 pm ET by woodturner9
Do you mean putting the two hot legs on the top and bottom of a duplex receptacle with the tab broken off?
It is clearly more dangerous to someone working live in the box than if it were 120v, whether they know what they're doing or not......there is 240v exposed on the side of the receptacle and only about an eighth of an inch apart.
Or someone might turn off one circuit and mistakenly believe they have shut the whole thing off. I would put it on a 2-pole breaker to prevent that problem anyway.
But I don't like the practice and avoid it. It's a lazy and dangerous way to provide split-circuit power to a location. Then there is the question: doesn't the device need to be 240v rated (which I would answer "yes")?
Ed
Edited 11/7/2007 7:29 am ET by edlee
I don't want to take attention away from the primary post question, but I'm wondering where the line is drawn between 'lazy' and 'efficient'? I wouldn't do it (or anything for that matter) out of laziness, but I do always seek to do things most efficiently. In this case I thought this to be a more efficient manner of handling split-circuit power to a single location.
Thanks for your thoughts.
but I'm wondering where the line is drawn between 'lazy' and 'efficient'
That's an interesting question........I've think about that exact question sometimes when I have one of those employees who's always trying to figure out a way to do a task that involves less work than the way I instruct them. Sometimes they come up with something good!
But I swear some people would rather stand around and argue than work.
Ed