5
\$\begingroup\$

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?

\$\endgroup\$
2
  • \$\begingroup\$ 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. \$\endgroup\$
    – zwol
    Oct 30, 2017 at 13:13
  • \$\begingroup\$ @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. \$\endgroup\$
    – The_Vintage_Collector
    Oct 30, 2017 at 13:16

3 Answers 3

Reset to default
13
\$\begingroup\$

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.

\$\endgroup\$
8
  • 2
    \$\begingroup\$ Thanks for the reply. So, its like two 110V lines and one neutral? \$\endgroup\$
    – The_Vintage_Collector
    Oct 29, 2017 at 20:16
  • 7
    \$\begingroup\$ @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. \$\endgroup\$
    – Trevor_G
    Oct 29, 2017 at 20:31
  • 2
    \$\begingroup\$ @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. \$\endgroup\$
    – The_Vintage_Collector
    Oct 29, 2017 at 20:40
  • \$\begingroup\$ @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. \$\endgroup\$
    – Harper - Reinstate Monica
    Oct 29, 2017 at 21:10
  • 2
    \$\begingroup\$ @RahulSalin Two 110V lines is exactly what it is. Regular 110V sockets are just one of those lines. \$\endgroup\$
    – Agent_L
    Oct 30, 2017 at 13:33
12
\$\begingroup\$

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...

\$\endgroup\$
2
  • 5
    \$\begingroup\$ 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. \$\endgroup\$
    – slebetman
    Oct 30, 2017 at 9:38
  • \$\begingroup\$ +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... \$\endgroup\$
    – Harper - Reinstate Monica
    Oct 30, 2017 at 16:53
7
\$\begingroup\$

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.

\$\endgroup\$
9
  • 6
    \$\begingroup\$ 132kVA? You sure about this? \$\endgroup\$
    – Vladimir Cravero
    Oct 29, 2017 at 20:59
  • 5
    \$\begingroup\$ If it's really rated for 50 and 60 Hz, then it should be fine, treat both mains-side terminals as hot/deadly (which you should do regardless, even for neutrals. Neutrals break, and when they do, other loads lift the neutral to near line voltage.) \$\endgroup\$
    – Harper - Reinstate Monica
    Oct 29, 2017 at 21:08
  • \$\begingroup\$ @Vladimir Cravero Oops! Sorry I meant 132VA \$\endgroup\$
    – The_Vintage_Collector
    Oct 29, 2017 at 21:12
  • 1
    \$\begingroup\$ 132 kVA sounds like the sort of drill Elon Musk is using for his tunnels ;) \$\endgroup\$
    – MSalters
    Oct 30, 2017 at 10:55
  • \$\begingroup\$ @MSalters My mini home substation transformer. :D Cheapest power at just $0.01. \$\endgroup\$
    – The_Vintage_Collector
    Oct 30, 2017 at 13:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.