120 V or 240 V Mains - which voltage is better?

[Hellbound]

The OP was the origin of the 'one per house'- I suspect it may have been an older article as it also had a lower street voltage than appears to be the current practice
http://science.howstuffworks.com/environmental/energy/power7.htm

It still seems to be only a US based system of having that many street transformers, here we use a substation system where most of a suburb will have only one or two major substations feeding it

Oh, we have substations too, pretty much like you're describing. I think it's just a matter of we have more "step-down" spots. It'll hit various stations and substations, each one leading off lower voltage lines to other locations. We just do the final step-down closer to the end point.

 

[novaphile]

This thread is fun.

Some more grist for the mill from Oz.

In my street there are two layers of power lines. The top layer is 11kV.

The lower layer is three actives and a neutral, 240V.

This house used to have two phase power, (2 actives and a neutral), and two power meters. The second meter was for the hot-water system, which was the only thing that used both phases.

When my solar PV system was installed, they installed a three phase meter, and only connected two phases.

Later the entire service was replaced with a 100 amp single phase.

(the water heater had been replaced long ago with a solar/gas hot water heater).

The internal wiring is determined by the expected current draw. Hence lighting circuits have different cable.

I've had a 64 amp cable laid to my workshop and shed (in case anyone connects up a couple of arc-welders) (each of those buildings also has a separate breaker board).

I also have a couple of dedicated 15 amp services, one for recharging my car for example.

The thing that really makes my eyes roll... My home has a couple of "earth stakes" and the earth cable of all plugs connects to an earth circuit that connects to those stakes.

But the neutral side of the breaker board at the house is also tied to that earth circuit.

There are lots of earth leakage detectors, also called "safety switches" in the breaker boards, each one provides power to about three regular breakers.

Can't wait to see what happens next when I buy a home battery setup.

...and yes, 32 cents per kilowatt/hour is pretty common.

 

[Dabop]

This thread is fun.

Some more grist for the mill from Oz.

In my street there are two layers of power lines. The top layer is 11kV.

The lower layer is three actives and a neutral, 240V.

This house used to have two phase power, (2 actives and a neutral), and two power meters. The second meter was for the hot-water system, which was the only thing that used both phases.

When my solar PV system was installed, they installed a three phase meter, and only connected two phases.

Later the entire service was replaced with a 100 amp single phase.

(the water heater had been replaced long ago with a solar/gas hot water heater).

The internal wiring is determined by the expected current draw. Hence lighting circuits have different cable.

I've had a 64 amp cable laid to my workshop and shed (in case anyone connects up a couple of arc-welders) (each of those buildings also has a separate breaker board).

I also have a couple of dedicated 15 amp services, one for recharging my car for example.

The thing that really makes my eyes roll... My home has a couple of "earth stakes" and the earth cable of all plugs connects to an earth circuit that connects to those stakes.

But the neutral side of the breaker board at the house is also tied to that earth circuit.

There are lots of earth leakage detectors, also called "safety switches" in the breaker boards, each one provides power to about three regular breakers.

Can't wait to see what happens next when I buy a home battery setup.

...and yes, 32 cents per kilowatt/hour is pretty common.

Are you sure that you had 2 phases for your HWS?- thats fairly unusual, even in Oz...

Most houses had 2 meters if they had offpeak electricity- one for the 24/7 electric supply to the house on one meter, the second meter was for the offpeak supply to the HWS, that had a special 'relay box' (usually had a little red light in one corner) but both meters usually ran off the same single phase

from http://greenforcesolar.com.au/knowledge-base/smart-meters/ (not hotlinked)
earlier ones like pictured (the offpeak controller is the bottom right) used a clockwork timer, later ones use control tones sent over the power wires (they can sometimes be heard in running ceiling fans as changes in motor pitch noise) that switch the control relay box on and off at selected times
eta- in the picture, you can actually see the main fuse top left- it has the street feed (single wire at top) and underneath two wires coming out- one to each meter

And yes- the neutral is connected to the earth at the fusebox- In Oz we use what is called the MEN system- or Multiple Earth Neutral, check out the power poles as well, certain poles will have a wire running down and into the ground (usually covered by a pvc conduit where it can be touched from groundlevel to prevent tingles) this wire connects to the neutral wire in the 240v set and is also part of the MEN system

Unusual to have several earth stakes unless you have extremely dry soil ie sandy- most installs only have one- the authorities tend to frown on multiple stakes these days, altho they were more common in older installs if a single stake wasnt sufficient to get a low ohms reading

 

[novaphile]

Yes, quite sure.

When the electrician came out to do the preparation work for the solar installation, he was quite surprised, having not had to work on a two phase system before.

There was also quite a delay while an appropriate multi-phase import/export power meter was found. (To replace the previous pair of meters).

The installation didn't have the usual J-tarrif timer, just the second meter.

Oddly enough the two earth stakes were part of the upgrade that brought the house up to spec.

One is near the meter box outside, and the second is near the primary breaker board which is in the laundry.

The multi-phase meter was replaced with a single phase meter, when the service was upgraded to 100 amp.

The whole service was quite old, this place was built in 1949, and a lot of the hardware looked like it was made in a blacksmith's forge.

Hmm... Just checked the old insulators (I kept them out of interest).

There were four separate wires from the pole to the house. (I have the four house insulators, and three of the pole insulators, the crew broke one of the pole insulators)

 

[Dabop]

Interesting- and I can understand your electricians confusion- especially if it had a 4 wire feed from the street- I would have assumed as soon as I saw that that I was dealing with a 3 phase system (3 actives plus neutral) but yours appears to have only run 2 phases to the meter box, altho 3 to the house???- and the HWS on a completely separate phase....

Weird to say the least

And they added the new earth stake and didnt remove the old one... curiouser and curiouser...
I hope he did his job right and checked the wiring inside that old malleable iron conduit, anything that old could have cotton covered rubber cabling- and by now that rubber would be dangerously decayed if it hasnt had a rewire with more modern TPE wirng

 

[novaphile]

Both earth stakes are new, and yes, all the wiring in the house has/had been replaced.

(I'm not sure, but suspect that the house was originally earthed to the water pipes.)

I'm reasonably confident that all the rubber and cotton clad stuff is long gone.

Oh, and by the way, dry soil is probably another name for "South Australia"

I've been advised to water the earth stakes in summer.

 

[Dabop]

It probably was originally earthed to the then metal water pipes- that was pretty much the norm until about the 60's/70's when a separate earth stake became the preferred method

And you would be surprised, I was installing a new tv antenna and distribution system in an old farm house fairly recently, and I found it still had live cotton and rubber cabling in the roof- some of which had been disturbed and the bare wires were literally just laying side by side fully exposed.....

For an old fella, I can still move pretty quick- I was outta there right quick I can tell you...

eta there is a form of tablet you used to be able to get (some sort of salt I presume), plus I have also seen hollow copper earth stakes (also called copper water pipe IMHO) with holes drilled down them and a hose fitting on top for use in extremely dry areas- where you hook the hose up once a week and turn it on for a few minutes

 

[novaphile]

Believe me, I have checked everything in the roof very carefully.

Similarly, pulled new cables through the conduits to the light switches.

I'm amazed that this place hadn't burned to the ground before I bought it.

 

[EHocking]

I take it you are in WA then as it has for years been a slightly higher voltage thean the rest of the states ...

or Qld, or parts of NSW, or ACT...

 

[Dabop]

or Qld, or parts of NSW, or ACT...

In reply

I take it you are in WA then as it has for years been a slightly higher voltage thean the rest of the states (Actually right from the beginning, due to the manufacturer of their generators was the story I heard as an apprentice, their default was 255v against the rest of Oz's then 240

and definitely this applies

Thats the difference between the real world and the fantasy world a lot of these bureaucrats live in lol
With a stroke of a pen, they can change it to whatever they want- 240 not enough, lets make it a billion volts

Back in the real world, changing the voltage (even by ten volts) can be a major exercise, in some transformers they can adjust the voltage output by changing tapoff points (the ones used in some country areas have this facility to overcome line loses, voltage is a little low, bump it up to the next tap to compensate), others would need to be pulled out and either rewound or replaced... costing millions if not 100's of millions of dollars if not more

A costly exercise, and one that either the taxpayer or the consumer would end up having to shoulder- so basically everyone says 'good job bernie' pats him on the head and simply goes about business as usual with a nod - "we arent 240Vac anymore, we are 'nominally' 230 +- 10% ok"

 

[psionl0]

I know an electrician who has worked in both Australia and the USA. He describes US household wiring as a "mess" and much prefers Australia's 240V system.

I have received some further information about this.

In Australia, the wire colour codes were always Active=RED, Neutral=BLACK and Earth=GREEN. The country later switched to the international standard of Active=BROWN, Neutral=BLUE and Earth=YELLO/GREEN (seems logical enough).

However, the American standard is Neutral=WHITE and Active=BLACK(!!!) This can be a trap for unwary sparkies from across the ocean and I'm guessing that more than a few power points in America are wired backwards because of this. My colleague relates a tale about a fellow sparkie who was re-wiring a power point and found two black wires behind the socket. He ho-hummingly connected both black wires to the socket and later reported that he had the most powerful vacuum cleaner ever (for about 10 seconds).

Apparently, one of the advantages of the lower voltages is safety. As long as your hands are dry, you can't be electrocuted at 120V. My colleague reports that on one job he was getting "slight tingles" from the wires. After completing the job, he checked the meter box and sure enough, the fuses hadn't been removed as he had requested.

Heh, there is no such assurance at 250V. As a kid, one of my tricks was to get free rides from the electric horses you could find outside many shops. I would stick a hair clip inside the box where the coin was inserted and wriggle it around hoping to jag the right connection. Most of the time it worked but one time, I made direct contact with a live wire and was thrown back several feet as if an adult had violently pushed me out of the way. Thereafter, I used an "icy-pole" stick for the same purpose (I can't remember if I ensured that it was dry first).

The way the oldtimers tested for live wires was to lick the back of their hand and then touch the BACK of their hand to the terminal to be tested...- keeping your head out of the way!!!

Interestingly enough, that's exactly what my father did one time when he was re-connecting an electric stove at my aunt's. Unsure if the power had been removed from all of the conductors, he ran the back of his hand across all of the wires (no need to lick the hand first at these voltages) instantly winning the admiration of my aunt and myself for his bravery (which I am sure was the effect he wanted).

He heroically explained that if any of the wires were live, his hand would automatically be thrown off and no harm done. He then pinched one of the wires with his fingers and explained that if the wire were live, his hand would clench and he would be unable to remove it.

 

[Trebuchet]

I'm trying to remember the color codes on the wiring for my little trailer. Better yet, I'll go look....

...ok, white=ground, red/brown = running lights (tail and side), green = right brake/turn, yellow = left brake/turn. Makes no sense at all.

When I assembled the kit I realized that the lights depended on a chassis ground that wasn't going to be any good, so I bought some wire to put in a dedicated ground. Green wire, because that's what I associate with ground.

 

[Doubt]

3 live to neutral voltages each 120 degrees out of phase relative to each other is 3 phase power.

But 2 live to neutral voltages both 180 degrees out of phase relative to each other is NOT 2 phase power. Got it.

If you were to take an oscilloscope and tap the two live phases what you would see is a single sine wave. By being 180 degrees out of phase is how the higher voltage is reached. It does not make any sense to call it two phase because if you remove the neutral what you have is a single underground phase.

 

[Doubt]

Lots of factory control systems in the UK run at 110V AC. The idea is that it's safer even though it involves the extra hassle of 240V (or 400V) to 110V transformers.

The drawback of this 55V - 0 - 55V idea is that you have to put fuses in both of the 55V wires. When a fuse blows and a panel is apparently 'dead' the other fuse often hasn't blown so you often get people tinkering around trying to find the fault when they suddenly surprise themselves by shorting the remaining wire to ground with the accompanying sparks and curse words!

The other drawback is that you end up with a floating voltage that makes troubleshooting more difficult. I was quite happy when an automaker in the US that has a name the rhymes with Ford finally changed their standards for control and went to a grounded 110VAC system.

Also the trend now is to just use 24VDC for control. Works well for most things. But large contractors connected in series don't work very well with it.

 

[psionl0]

If you were to take an oscilloscope and tap the two live phases what you would see is a single sine wave. By being 180 degrees out of phase is how the higher voltage is reached. It does not make any sense to call it two phase because if you remove the neutral what you have is a single underground phase.

And if you remove 2 active wires from a 3 phase system you also get single phase.

It has already been explained that the preferred term is "split phase" and there is no need to revisit this argument.

 

[Trebuchet]

The other drawback is that you end up with a floating voltage that makes troubleshooting more difficult. I was quite happy when an automaker in the US that has a name the rhymes with Ford finally changed their standards for control and went to a grounded 110VAC system.

Also the trend now is to just use 24VDC for control. Works well for most things. But large contractors connected in series don't work very well with it.

I believe you meant "contactors". Which is like a relay but for transferring power rather than information. And if you're connecting the coils in series, you're doing it wrong.

 

[Doubt]

I believe you meant "contactors". Which is like a relay but for transferring power rather than information. And if you're connecting the coils in series, you're doing it wrong.

Correct on the first part about the botched language. And now that I think about it, I described the situation wrong. They were parallel connected. Still had a problem. These fairly large contactors used 2 coils each. One to pull them in and one smaller one to hold them in. The problem being when they both powered up together one would pull in and the other would fail. The initial inrush was not enough to get action out of both of the larger coils together.

 

[Trebuchet]

Need a little time delay relay so they don't both go at once. Or a bit more power on the control circuit, of course. Possibly just heavier wires.

 

[Doubt]

Need a little time delay relay so they don't both go at once. Or a bit more power on the control circuit, of course. Possibly just heavier wires.

We tried the time delay trick. It did not work. Allen Bradly had a number of solutions that did not work. Either one worked if we disabled the other one. We went back to 120VAC for those contactors. We already had it in the cabinet for combustion safety circuits.

 

[bruto]

In the US system, the same wires are used in the 120V and 240V parts of the system.

================
NEC Article 310

It's true up to the input end of the breaker box, but not after that usually in households.

Normal breaker boxes are designed so that the two legs of the circuit alternate, allowing either two 120 volt breakers side by side, or a single 240 occupying both legs. 240 volt circuits use ganged breakers because if only a single breaker goes, the circuit will still be hot even though it is not working. It's against code to use the separate 120 volt sides of a system to provide 240, or to use two adjacent 120 volt breakers in the box. Although many breakers have holes in the switch to allow a pair to be ganged together mechanically, that is also now against code, I think.

Generally speaking, 240 volt household circuits are only used for high current devices, such as dryers and stoves, and so it's normal for them also to be heavier gauge wire as well. A dryer generally uses a 30 amp circuit and a stove 50, whereas ordinary outlets are 20.

In uses other than household, it is not uncommon to use lower amperage wiring for 240 volt circuits, and indeed then one can use the same wire as usual. A lot of shop machinery works on 240 volts with 20 amp plugs and breakers, but I've never seen them further into a house than the basement or garage.

However, just to add: the original statement is correct in theory. It's only the "ampacity" that determines the type of wiring, and either voltage will use the same wire for an equivalent amperage. It just happens in practice that you rarely see the same wire in both uses, and I just wanted to make sure that it's understood that although the same kind of wire is used, the way they're connected will vary at the fuse or breaker box end.