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Today my A/C compressor had given up its ghost and when I tried to disconnect it from the wall switch after turning OFF the wall circuit-breaker,I assumed like most 110V lines where only one line (Live-L) lights with neon tester.

When the circuit breaker was turned OFF the neon tester on A/C switch line turned OFF and I assumed the power was out. But while disconnecting I accidentally touched the other wire and I received a shock. On testing with neon tester I noticed the light was glowing for the other line also and I later discovered it had in fact two breakers(no handle tie) for the A/C circuit. When I checked on my normal 110V lines the neon test light glows only on one wire i.e., Live wire.

Even most of my google searches showed a 220V line with just L and N. So,doesn't the US 220V have a neutral?

The_Vintage_Collector
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  • I don't think the thing you turned off was a circuit breaker, I think it was just a regular switch. The actual circuit breaker for a USA-style 220V circuit, which should be hidden away in a "fuse box" somewhere, is required (by the electrical code) to disconnect both wires simultaneously. If it doesn't, get an electrician to replace it with one that does. – zwol Oct 30 '17 at 13:13
  • @zwol I did mention in next answer in a comment that I had turned off from the breaker but the electrician who repaired it as it was faulty for this A/C replaced with two separate breakers or the handle tie is missing for this particular one. Anyway I just turned OFF only one breaker. Lucky that I'm still alive. – The_Vintage_Collector Oct 30 '17 at 13:16

3 Answers3

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US residential (and most commercial) uses split-phase electricity, therefore both wires of a 220V outlet are live; the neutral is used to provide two 110V connections, each 180 degrees out of phase.

Ignacio Vazquez-Abrams
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    Thanks for the reply. So, its like two 110V lines and one neutral? – The_Vintage_Collector Oct 29 '17 at 20:16
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    @RahulSalin there really ought to be a double pole breaker on that line so when you flip it, or it pops, both sides should disconnect. You should not be able to turn off only one side. – Trevor_G Oct 29 '17 at 20:31
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    @Trevor Now I remember mate.For the other rooms its a double pole. It was a double pole breaker initially for this room too. But some while ago it went faulty and the idjit who replaced it went with individual ones as he did not have I think. That was many years ago. I better replace it now. – The_Vintage_Collector Oct 29 '17 at 20:40
  • @RahulSalin yes, most 2-pole breakers are twice the cost of singles, or about $9 unless you're into a weird panel like Pushmatic. Also they make handle-ties so you can assure common maintenance shut-off (common trip not guaranteed). I have seen nails used as handle ties, which is better than nothing at all. – Harper - Reinstate Monica Oct 29 '17 at 21:10
  • @Harper. I've three window A/C and one split unit. Currently two Window A/Cs circuit breaker is double pole breaker with handle ties but the other one doesn't have. I wasn't really aware about the two live wire setup either. – The_Vintage_Collector Oct 29 '17 at 21:20
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    @RahulSalin Two 110V lines is exactly what it is. Regular 110V sockets are just one of those lines. – Agent_L Oct 30 '17 at 13:33
  • Most commercial electricity in the US is three-phase "wye", with the phases 120° apart. The discriminating reader will note that 120 and 180 are not the same number, the result of which is that any two hot phases that are 120VAC from their common ground are in fact 208VAC from one another. This is close enough to "220" that it works fine. https://forum.allaboutcircuits.com/threads/what-is-the-actual-household-voltage-110-115-120-220-240.3320/ – Monty Harder Oct 30 '17 at 19:07
  • @MontyHarder I measured mine and its around 117V on the outlets near the electrical box to 115V in the outlets on first floor. I use voltage regulator for certain devices just to keep it smooth at 110V. – The_Vintage_Collector Oct 31 '17 at 05:29
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Here in the US we have a split phase, that's true. The "Neutral" is a center point of ONE phase of a transformer, so both ends are not "180 degrees out of phase", they are the same phase, just opposite ends. I know, it's semantics, but it's important to be correct.

If you have a device that needs 240V (220, 230, 240V is all nominally the same), the device generally will not care if that is derived as 1 phase and a neutral as you find elsewhere in the world, or 2 ends of the same phase as you find here, just so long as the voltage measured between the two lines reads 240V. But here in the US, if you are using 240V, you are REQUIRED to have over Current Protective Devices (OCPDs, i.e. fuses or a circuit breaker) on EACH of the ungrounded conductors. You can however CONTROL a 240V device by switching only one leg. Many people get this confused and think that they can use a single pole breaker to feed a 240V device, because they see a single pole switch controlling it. But that's an incorrect assumption. 2 poles of protection, regardless of how it's controlled.

If the device in question has no need for 120V inside of it, you do not need the Neutral conductor brought out to it. So your Bosch power tool is fine with just the 2 hot wires going to it, plus a safety ground (unless it is "double insulted, in which case it will have a 2 pin plug on it)).

GROUND however is not the same as Neutral, even though they are usually at the same potential. Neutral is considered a "Current Carrying Conductor" and must be insulated, Ground is a SAFETY conductor and must NOT carry any current unless these is an accident. You cannot use the Ground wire as a Neutral connection. People do it all the time, but every one of them is illegal...

JRaef
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    Same phase 120V when connected together will always give you 0V. Only if the second line is 180 degrees out of phase will it give you 240V. "Opposite ends" of same phase is separated by time, not voltage. If they are separated by volgate then they cannot be the same phase. – slebetman Oct 30 '17 at 09:38
  • +1 for Neutral Is Not Ground. (Hardest of all for EEs to understand due to routinely calling the current return GND). Not all uses of neutral as ground are illegal, however: dryers, stoves, and some inter-building subpanels are grandfathered to allow bootlegging of ground from neutral. Terrible idea with a body count... – Harper - Reinstate Monica Oct 30 '17 at 16:53
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Most of the world is supplied with 220-240V single-phase. Neutral (and ground) are on one end, and the other end is 220-240V.

In North America, houses are supplied with 240V split-phase. Neutral and ground are in the center, with 120V to either "hot" pole.

That means if you want 240V-only, in Europe only one of the two conductors is at a dangerous voltage, the other is near earth potential. In North America, both conductors have a dangerous voltage.

Harper - Reinstate Monica
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