Connect with us

Problems caused by reversed AC polarity

Discussion in 'Misc Electronics' started by Chris, Apr 9, 2004.

Scroll to continue with content
  1. Chris

    Chris Guest

    I am renting in an apartment where the electricity is pretty bad.
    I have tested the outlets and found that many of them have open ground and
    reversed polarity.

    Can anyone tell me if this will be destructive to my equipment?
    The types of things I use are TV's Computers, Uninterruptible power
    supplies, DC transformers (IE: 110v to 9v) solid state and tube guitar amps.

    Thanks in advance,

    Chris
     
  2. Bjoern Rost

    Bjoern Rost Guest

    open as in 'not connected to ground'? That is indeed very dangerous and can
    break your equipment and also lead to accidents.
    We're talking about AC, right? I don't think there is much polarity to
    reverse, there. Please explain this.
    TV should work well without ground, lamps, radios and that kind of stuff
    too. But Computers, UPS and most transformers should not be used when not
    connected to GND

    Bjoern
     
  3. MikeM

    MikeM Guest

    If you have an open ground, how do you tell that the "polarity" is
    reversed?

    In the US, the 120V line is distributed on two wires, called "Line"
    (Black wire), "Neutral" (White wire), with an optional "Ground"
    (Green/Bare wire).

    On newer style outlets, the ground is the round fat pin.
    The Neutral slot is located clockwise from the ground pin.
    It is usually slightly wider (or T shaped). The Line slot is
    located counterclockwise from the ground pin.

    In the main circuit distribution panel, the Neutral line
    is supposed to be connected to the same "earth ground" as the
    the ground pins on the outlets.

    In other words, all of the white wires from the respective
    outlets come together to a common (insulated from the panel)
    screw-terminal bus inside the panel. All of the green/bare
    wires from the respective outlets come together to a bare
    screw-terminal (connected directly to the panel box). There
    is a "jumper" which ties the ground bus to the neutral bus
    in the panel...

    There are lots of old houses with outlets which only have two
    identical slots. The outlet is not "polarized", so you have
    no knowledge of which slot is which.

    In these old houses, there where only two wires inside the wall
    box (Line and Neutral). The third wire (ground) doesn't exist.
    What happens over time is the two slot outlet gets replaced
    with a new outlet, so the ground pin is left unconnected.
    If the installer knew the color code, they may have connected
    the Line to correct pin; or not!

    MikeM
     
  4. Guest

    | Chris wrote:
    |
    |> I have tested the outlets and found that many of them have open ground
    |
    | open as in 'not connected to ground'? That is indeed very dangerous and can
    | break your equipment and also lead to accidents.
    |
    |> and
    |> reversed polarity.
    |
    | We're talking about AC, right? I don't think there is much polarity to
    | reverse, there. Please explain this.

    Back before there was a grounding wire, outlets were polarized so that
    only a specific prong would be connected to the neutral (grounded) side.
    That prong could then be attached to the chassis frame of the equipment
    to protect from the possibility a broken wire could make the chassic hot
    (e.g. it would then short out and blow a fuse first). It was a cheap
    form of ground protection. It didn't work all that well. But many
    things still are connected that way using 2 prong plugs because so many
    ungrounded outlets are still around.

    If the polarity is wired to the outlet backwards, this is a very serious
    safety hazard.

    If I could go back in time a re-design the electrical distribution system
    based on the safety hazards we know today, I would eliminate the neutral
    wire and require a grounding wire. Transformer secondaries would still
    be grounded via the central connection (where the neutral would come from
    if it were used, whether one phase or three phase), but all loads would
    be connected to two hot wires at a standard hot-to-hot voltage (three phase
    loads would be connected to all 3 hot wires in delta configuration), and a
    grounding wire would always be required as a NON-current carrying wire.
    One phase and three phase systems would then be put on the same standard
    hot-to-hot voltage (three phase would thus have a slightly higher voltage
    relative to ground), which I would take liberty to increase so that today's
    heavy demands would not result in such high currents.

    The legacy of the neutral wire, is, IMHO, part of the hazard still present
    in today's power systems. It isn't really needed; only a true grounding
    wire is needed.


    |> Can anyone tell me if this will be destructive to my equipment?
    |> The types of things I use are TV's Computers, Uninterruptible power
    |> supplies, DC transformers (IE: 110v to 9v) solid state and tube guitar
    |> amps.
    |
    | TV should work well without ground, lamps, radios and that kind of stuff
    | too. But Computers, UPS and most transformers should not be used when not
    | connected to GND

    The issue is really whether there is a connected, or connectable, metal
    chassis that could become energized by the hot wire. Computers, UPSes,
    and transformers can function just fine with ungrounded and/or reversed
    outlets, unless they have built in protection that detects the problem
    and shuts off (which would be a good thing). People do tend to touch a
    computer more often than a TV (thanks to remote controls, now), so the
    shock hazard on a computer is greater.

    Equipment that has unintended connection between neutral and ground could
    be damaged by reversed polarity due to current now flowing at that point.
     
  5. Myron Samila

    Myron Samila Guest

    Fuses are always on the "hot" side of a typical 110-120VAC North American device, CSA
    mandates this. So, if the device being plugged into a reversed hot-neutral outlet has a
    fault, the device's fuse will not protect it as CSA requires it to, nor does the power
    switch in fact switch off the "live(hot)", you'd be switching the neutral.

    NOT a good thing.

    If a unit is designed to be grounded, it MUST be grounded. CSA requires any equipment
    with a metal chassis to pass specific dielectric strength tests so to test the chassis
    from becoming "live", and if it does, it must be able to blow the fuse, hence polarized
    Neutral spades on 2 lead plugs.
     
  6. Myron Samila

    Myron Samila Guest


    It is quite easy to test which wire is hot or not, use a volt pen, available at any "Home
    Depot". Bring it near the wire in question, and if voltage is present, it will either
    beep or light up (depending on the model, some do both), the neutral wire will not do
    this. No physical connection is required to the wire, just hold it up near it. It is
    inductive.

    You mention that ground is optional in the US? hehe, it certainly isn't in Canada. I
    believe you mean that older homes may or may not have ground running up to conventional
    outlets.

    And the T shaped style U-ground receptacles are designed for 15A/20A nothing else. They
    accept a standard 15A 120V U-ground, and a 20A 120V U-ground which is designated by one
    blade on a horizontal plane.

    BTW: if you observe a standard 120V 15A plug, the zinc plated screw is Neutral, the brass
    screw is Hot.

    The biggest problem with reversed hot/neutral wiring in a home is if you "think" you've
    switched off power to lets say a lamp fixture, and you are servicing it, you "hope" that
    you've switched off the hot, if it were reversed, you'll be working on a live circuit.


    Another poster suggested that he would have designed 120VAC to be made uo of two hots (60V
    lets say each leg), the problem with that is, you would need to switch both lines at a
    switch, complicating everything, (3-way switches for example), fusing would have to be
    doubled (as in 220VAC single phase), so simply put, a hot/neutral setup isn't such a bad
    thing. Same with HV (Canadian industrial is 347/600VAC 3 phase), you can supply an entire
    row of HV 347 flourescent lamps with one hot, but if you had to do it with two hots, this
    would complicate matters, unbalanced loads, etc....

    The whole moral of the story, a properly wired outlet is important.
     
  7. Bob Myers

    Bob Myers Guest

    Not really "polarity" as such, but at least in the U.S. home
    outlets are generally "polarized" in that they distinguish between
    the "hot" or "line" side of the pair and the "neutral." The "line"
    is the side that's actually providing the power, and yes, it
    swings both positive and negative with respect to the local
    ground - which is where the "neutral" side is connected.
    Assuming that there's no significant potential between the
    neutral and the ground (which is the case unless the neutral
    line is carrying enough current to create that potential over
    however far it is back to "ground"), you can't get a shock
    from the neutral side - only the "line."

    This makes absolutely no difference to the operation of the
    equipment in question, IF everything is normal - but it
    has some pretty significant implications in terms of potential
    (no pun intended) safety problems.

    Bob M.
     
  8. Yukio

    Yukio Guest

    Are we looking at a floating Neutral on the Power Panel ? It happens most
    frequently with Aluminum Wiring, occasionally with an old all copper wiring
    too. Cure is a half turn on the appropriate screw. Is 200+ AC volts harmful
    to your equipment. This can happen with a bad Neutral connection !, even
    though it is nominally 110 Volts, It is 110 volts between one side of the
    line and Neutral , but in the case of a poor neutral , that Neutral buss
    could easily be close to 90 Volts AC of the opposite phase under a heavy
    load, symtoms include badly flickering lights, short lamp life, electrical
    interference to AM radios. What are you using for " ground" in testing ??
    A small potential ~ 1 or 2 Volts ac is normal between a GOOD ground and the
    neutral Buss. Is this an ancient New York apartment ?? What no air
    conditioner , deep freezer, refrigerator, stove or Microwave oven never mind
    Washer and Dryer ! and water heater ! I think its most likely a case of no
    grounds on mis-wired replacement outlets

    Yukio Yano
     
  9. Guest

    | Another poster suggested that he would have designed 120VAC to be made uo of two hots (60V
    | lets say each leg), the problem with that is, you would need to switch both lines at a
    | switch, complicating everything, (3-way switches for example), fusing would have to be
    | doubled (as in 220VAC single phase), so simply put, a hot/neutral setup isn't such a bad
    | thing. Same with HV (Canadian industrial is 347/600VAC 3 phase), you can supply an entire
    | row of HV 347 flourescent lamps with one hot, but if you had to do it with two hots, this
    | would complicate matters, unbalanced loads, etc....

    It was I who suggested a "no neutral" wiring system. Actually someone
    else suggested it a while back on another thread and after thinking
    about the idea, it seemed better than anything else. The neutral seems
    to be a legacy thing resulting from a poorly thought out grounding
    system that ultimately had to be replaced.

    Such a system would absolutely have to have a true grounding wire at
    all outlets and fixtures.

    The idea is a center tap on the transformer secondary would be grounded
    so that the voltage potential between any hot and ground is reduced to
    lessen the effect of electric shock, and other hazards. The question
    next would be what voltage. If you used 120 volts between hot wires
    and thus had 60 volts between either to ground, you'd end up having
    electric stoves drawing 100 amps. If instead, you went with 240 volts
    between hot wires and thus had 120 volts between either to ground, then
    you'd have the current demand levels we actually have today for things
    like a stove, but less for things like lights and small appliances.

    The NEMA 6-15R and 6-20R receptacles already work exactly this way now
    at the 240 volt level. There is no neutral connection at all. There
    is a grounding wire (not for carrying load current) and two hot wires
    that have 240 volts between them. The voltage between either hot wire
    and ground is only 120 volts.

    What I would NOT have is multi-voltage system where you have 5 taps on
    a transformer to get more than one voltage to ground. This would make
    things a lot more complicated, and open up some oppotunity to abuse the
    design.

    I don't know that I would necessarily pick 240 volts, were I to go back
    in time where I didn't have legacy equipment designed for a particular
    voltage to keep working. I'd probably go higher, like 300, 360, 400,
    or maybe even 480. But some of that is because I know the level of use
    we make of electricity today. Someone who thought about safety very
    clearly back in the late 1800's to design this would unlikely realize
    the high levels we use today, and might well have chosen a much lower
    voltage. If Edison had his way, we'd all be using 110 volt DC.

    A three phase system would have to work similarly. The transformer
    would be wired in a 3 pole WYE or STAR configuration with the standard
    voltage between any 2 hot wires. So if the standard were 240, each
    hot wire would have 138.5 volts to ground. You can divide by the
    square root of 3 for any other voltage to get those values, and many
    of you probably have some of them well memorized. But the point is
    that there would be simply ONE VOLTAGE to deal with whether the power
    is single phase or three phase, and the voltage to ground would always
    be reduced from that (50% on single phase and 57.735% on three phase).

    The disadvantages to the system that you point out are valid. It would
    require two pole light switches, and two pole circuit breakers or fuses.

    But I disagree about the unbalanced loads you mention. Industrial
    power levels of 480Y/277 in US and 600Y/347 in Canada are not really
    any different than 208Y/120 except for the voltage. You still have to
    run the neutral wire around at the 120, 277, or 347 volt levels. With
    lights operating from 208, 480, or 600 volts, you'd need two hot wires
    but no neutral. You still have to balance things so 1/3 of the load is
    on each phase no matter which way you do it. It's just that with the
    no neutral scheme, you would have hot wire A going to 2/3 of the loads,
    hot wire B going to 2/3 of the loads (half the same as A), and hot wire
    C going to 2/3 (half the same as A, have the same as B). Just wire it
    as if you had delta power, but you can do that on wye.

    In Europe, the voltage is now standardized on 400Y/230 for three phase.
    But they have the advantage that single phase service is one pole 230
    volts, so they don't have issues of something designed for one voltage
    and get something slightly less when they get 2 out of 3 hots from a
    three phase system. But in the US (and presumably Canada, too), some
    people get 2 hot wires at 120 degrees phasing instead of 180, and thus
    they get a lame 208 volts to power devices that usually expect 240.
    And that can cause problems that range from reduced performance to
    equipment destruction (I have seen it happen).

    In the 1900's my design would complicate 3-way light switches. But now
    days there is some trend to centralized relay switching of lights, even
    with dimming controls, and the switches are wired at very low voltage
    as merely control/signal devices. I'm working on a house design now
    and I plan to have all switches work this way, using momentary contact
    switches that go either up or down and spring back to the center when
    released. That way, all switches always have the expected on or off
    orientation. What lights I would have dimmers on would be based on
    the time the contact is made and go up or down gradually as the switch
    is held in position. Many systems today a smart programmed with scene
    lighting that at the push of a specific button changes many lights to
    pre-programmed levels for a particular mode or usage pattern. And then
    there are motion detectors that can ensure a light comes on in the room
    you are entering. Light controls can even be put in the bathroom shower
    using fiber optic cabling.


    | The whole moral of the story, a properly wired outlet is important.

    Of course. If a contact is expected to be neutral, then it absolutely
    must be wired that way, without exception. My design simply makes a
    system where nothing will expect a neutral. Things that do now are
    just a legacy of the past.
     
  10. Myron Samila

    Myron Samila Guest

    people get 2 hot wires at 120 degrees phasing instead of 180, and thus
    they get a lame 208 volts to power devices that usually expect 240.
    And that can cause problems that range from reduced performance to
    equipment destruction (I have seen it happen).

    In 3 phase, the potential between two hots is 208 (120 degrees out of phase, to start 3
    phase motors, change one phase direction, the motor changes direction).

    In single phase, the potential between two hots is 220V (180 degrees out of phase)

    Typically, devices that are designed to work on 220V must function at 208V as mandated by
    CSA and cUL, cETL. Current must not exceed the 220V spec at 208V.

    What I meant about unbalanced loads is as follows (3phase)

    (BTW: we do not have 600V industrial lighting, none that I've seen anyhow, it is all 347
    with a neutral).

    If you have three rows of lights, and you pick off

    Row 1 (use phase X, Y)
    Row 2 (use phase Y, Z)
    Row 3 (use phase ?!? to balance it?)

    In 347V, you'd use a phase per row of lamps + your neutral.

    You also simplify wiring, as you run 3 hots and ONE neutral back to the panel, not 6
    wires. The Neutral would be the same gauge as the hots you are running, in certain
    regions in Canada, properly installed conduit or rigid EMT can be used as the ground
    conductor, some installations require a dedicated ground.


    I've run dimmer setups for professional stage lighting (touring) in 100K+ packs, and
    balancing is VERY important.

    BTW: Interesting to note, the UK is 240V, and the rest of Europe is 230V. Which makes
    life hard on quartz lamps when touring in the UK using European fixtures/lamps.

    Thank goodness Edison didn't get his way with DC, AC is fantastic.... step up, step down,
    isolate...... fantastic. But, I still think our system is safe, you should hear what
    Europeans think about NEMA U-Ground connectors!!! (they don't like them).
     
  11. Guest

    |
    |>> But in the US (and presumably Canada, too), some
    | people get 2 hot wires at 120 degrees phasing instead of 180, and thus
    | they get a lame 208 volts to power devices that usually expect 240.
    | And that can cause problems that range from reduced performance to
    | equipment destruction (I have seen it happen).
    |
    | In 3 phase, the potential between two hots is 208 (120 degrees out of phase, to start 3
    | phase motors, change one phase direction, the motor changes direction).
    |
    | In single phase, the potential between two hots is 220V (180 degrees out of phase)

    You're actually using 2 different nominal voltages to get those values.
    But those are probably the voltages more people think of for those kinds
    of circuits.

    Line-to-neutral line-to-line
    110 volts 190 volts (closer to 191)
    115 volts 200 volts (closer to 199)
    120 volts 208 volts
    125 volts 216 volts (closer to 217)
    127 volts 220 volts (standard in Mexico)
    138.5 volts 240 volts (a wye config for 240 volt 3 phase loads)
    220 volts 380 volts (closer to 381)
    230 volts 400 volts (closer to 398)
    231 volts 400 volts
    240 volts 416 volts (lots of military surplus gensets have this)
    250 volts 433 volts
    254 volts 440 volts
    266 volts 460 volts
    277 volts 480 volts (US industrial)
    318 volts 550 volts (I wonder if anyone ever used this)
    332 volts 575 volts
    347 volts 600 volts (Canadian industrial)
    577 volts 1000 volts (once used in mines, probably 25 Hz)


    | Typically, devices that are designed to work on 220V must function at 208V as mandated by
    | CSA and cUL, cETL. Current must not exceed the 220V spec at 208V.

    Is that for 3 phase or 1 phase.

    I've experienced single phase motors designed for 240 volts (presumably)
    burning out in just a week or two under heavy use. A 208 volt model was
    finally special ordered and it worked fine. For whatever reason, the A/C
    system was installed using single phase power, even though 208Y/120 was
    there. Apparently A/C systems designed for single phase assume it is
    because the voltage is 240/120 and they optimize for it.


    | What I meant about unbalanced loads is as follows (3phase)
    |
    | (BTW: we do not have 600V industrial lighting, none that I've seen anyhow, it is all 347
    | with a neutral).

    I haven't seen 480 volt lights in US, either ... just 277 (or lower).


    | If you have three rows of lights, and you pick off
    |
    | Row 1 (use phase X, Y)
    | Row 2 (use phase Y, Z)
    | Row 3 (use phase ?!? to balance it?)

    So row 3 would have Z-X.


    | In 347V, you'd use a phase per row of lamps + your neutral.

    X-N, Y-N, Z-N


    | You also simplify wiring, as you run 3 hots and ONE neutral back to the panel, not 6
    | wires. The Neutral would be the same gauge as the hots you are running, in certain
    | regions in Canada, properly installed conduit or rigid EMT can be used as the ground
    | conductor, some installations require a dedicated ground.

    Why run 6. Run just 3 wires and put it all on a 3 phase breaker rated
    for 1.732 times as much.

    I personally would not depend on the conduit for the grounding wire even
    where the code allowed it.


    | I've run dimmer setups for professional stage lighting (touring) in 100K+ packs, and
    | balancing is VERY important.
    |
    | BTW: Interesting to note, the UK is 240V, and the rest of Europe is 230V. Which makes
    | life hard on quartz lamps when touring in the UK using European fixtures/lamps.

    At least it is being standardized on a common voltage. There was a lot of
    220V (maybe still is the change is taking place).

    Lots of Europeans also get 400Y/231 three phase at home, too.


    | Thank goodness Edison didn't get his way with DC, AC is fantastic.... step up, step down,
    | isolate...... fantastic. But, I still think our system is safe, you should hear what
    | Europeans think about NEMA U-Ground connectors!!! (they don't like them).

    I'm not that fond of them, either.
     
  12. Mjolinor

    Mjolinor Guest

    | BTW: Interesting to note, the UK is 240V, and the rest of Europe is
    230V. Which makes
    UK is 230 / 400. In reality they didn't change anything except they changed
    the tolerance to the same as the rest of Europe and that meant that we
    satisfied the spec. to be quoted as 230 so that is what we now have. It's
    been 230 for about 4 years I think but as one gets older history alllways
    seems more recent than it was (is?):)
     
  13. Guest

    |> | BTW: Interesting to note, the UK is 240V, and the rest of Europe is
    | 230V. Which makes
    |> | life hard on quartz lamps when touring in the UK using European
    | fixtures/lamps.
    |>
    |
    | UK is 230 / 400. In reality they didn't change anything except they changed
    | the tolerance to the same as the rest of Europe and that meant that we
    | satisfied the spec. to be quoted as 230 so that is what we now have. It's
    | been 230 for about 4 years I think but as one gets older history alllways
    | seems more recent than it was (is?):)

    So what is the lowest and highest voltage considered to be within tolerance,
    now? How far below 220 (380) and how far above 240 (416) is the voltage
    allowed to go?
     
  14. Any device or cord with a two prong non-polarized plug will not be
    bothered b reverse polarity or no ground. Amps and stuff could be a
    safety hazard because your microphones and input jacks are at chassis
    ground, which should be an absolute ground, i.e. green wire.
     
  15. Any device or cord with a two prong non-polarized plug will not be
    bothered by reverse polarity or no ground. Amps and stuff could be a
    safety hazard because your microphones and input jacks are at chassis
    ground, which should be an absolute ground, i.e. green wire.
     
  16. john KB5AG

    john KB5AG Guest

    )
    it's not all that common, but 480v HID lighting is available from most
    industrial lighting manufacturers in the US. We see it where very long
    circuit runs are necessary. A few of the newer fluorescent technologies (T5
    fluorescent, for instance) are also available in 480v versions, since
    they're trying to cut into the HID market.

    John KB5AG
     
  17. Guest

    | )
    |> |
    |> | (BTW: we do not have 600V industrial lighting, none that I've seen
    | anyhow, it is all 347
    |> | with a neutral).
    |>
    |> I haven't seen 480 volt lights in US, either ... just 277 (or lower).
    |>
    |>
    | it's not all that common, but 480v HID lighting is available from most
    | industrial lighting manufacturers in the US. We see it where very long
    | circuit runs are necessary. A few of the newer fluorescent technologies (T5
    | fluorescent, for instance) are also available in 480v versions, since
    | they're trying to cut into the HID market.

    A single street light might run on 120 volts tapped into the nearest power
    transformer. But in areas like big traffic mixers with roads everywhere,
    it is not practical to run distribution voltage (above 10 kV) and install
    transformers everywhere just for some lights. Instead, they use 480 volts
    for that very commonly, and just run the lights directly at 480 volts.
    Long streets with no other power will usually have a higher voltage like
    this running along the street lights.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-