Problems caused by reversed AC polarity

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

Chris posted:

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

On Fri, 09 Apr 2004 15:39:27 +0200 Bjoern Rost wrote: | 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.

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.

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.

can

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.

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

"Chris" wrote in message news:Tqxdc.1$ snipped-for-privacy@news.nyc.globix.net...

amps.

| 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.

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).

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

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.

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?):)

On Sat, 10 Apr 2004 19:51:18 +0100 Mjolinor wrote: |> | 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?

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.

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.

anyhow, it is all 347

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

On Sat, 17 Apr 2004 13:43:01 -0400 john KB5AG wrote: | ) |> | |> | (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.