I must be missing something, and as I Google, I am just more confused. My neighborhood has 50 houses, and let’s assume all 50 houses are downstream from one step-down transformer. That said, after years of accepting parallel circuits at face value, I am trying to understand how could the house furthest from source have the same voltage (110 VAC) as the house closest to the source…due to line losses? Ok, you’d say the wire gauge is selected to negate line losses…but wait! I Googled such charts, and it appears they ALL assume voltage is constant, and amps drop!!! Huh?
So, what’s the SD here? There must be more to the story than what they convince us of in high school physics. What’s the rest of the story?
let’s assume all 50 houses are downstream from one step-down transformer.
Why would you assume that? As I remember it, there’s a transformer for every house from the 7,200V distribution line to 240V house service. Not sure, but that was the way in my old neighborhood that had exposed lines on poles.
Because I should have mentioned this is a newer neighborhood with all wiring underground, and there is only one box…I think. I will look again, but even if there are 5 boxes spread around the neighborhood, there are still voltage line losses, not amp losses…right? The amp-gauge charts are to size a line to carry the amperage without overheating the line…not for line losses. Am I misinterpreting the purpose of these charts? (Again, remember I noticed the voltage on these charts is expressed as a constant.)
Amps and voltage are related. The voltage drop at zero amps is zero. I’m not sure which tables you are looking at. It is probably maximum amps per wire size before you experience significant voltage drop. If you want to be able to provide more amperage and not lose voltage you need to use larger wire.
The voltage supplied is nominal. A house closest to the transformer might be receiving 115 volts @ 100 amps while the house furthest away might be getting 105 volts @ 100 amps.
A single 240v split-phase transformer like this usually serves only a small number of houses - sometimes just two or three. They’re mounted on a pole (or underground) pretty close to the actual house, usually right out front. So the voltage drop from the transformer is minimal. The standard is 120v per leg (not 110, I have no idea why people keep saying that) plus or minus 5%. So you can get anywhere from 114 - 126 volts and be within spec.
As others said, there’s a transformer for 1-3 houses, not fifty. If a transformer powered 50 houses, the loss would probably be mostly due to trying to run 240v over that long of a distance. That’s the reason we have transformers. There’s loss loss to resistance over distance at higher voltages. Also, there probably just wouldn’t be enough juice to run all 50 houses, but they all experience the same problems, not just the ones furthest away.
Ignoring all that, with parallel circuits, each load gets the same voltage. Look at the diagrams you were googling. Why wouldn’t they? The house (or load) closest to the power source is connected to the same wire as the furthest one. Ignoring line loss, why would one several hundred feet down have any less voltage? If they were wired in series, that would be different, but it’s not the case.
It’s no different than in your house. If you put three lights in the same circuit, the one furthest away isn’t dimmer since it’s connected directly to the power source the same way the first one is. If it was in series, the power would have to travel through each load before going to the next…that would cause issues, but that’s not how it’s done.
Imagine each of these circles is a house. If you put a meter across the wires, you’ll get a reading. It’s not going to matter where you place the meter. Right next to the source, at the end of the line, in the middle, right next to a load. You could even put on probe next to the load and one on the other line at the next to the last load.
It’s the same reason you get (more or less) 120v no matter where in your house you check for voltage even though there might be hundreds of feet and plenty of loads hooked up to that circuit. The voltage will be the same.
In fact, if the voltage did drop as you’re thinking, that could (I’d imagine) cause an issue because there’d be a potential difference from one end of the line to the other. Not just that, but I think it would be a mess for all the linemen wondering each time they find a wire that has less than 120 or 240v and trying to figure out what’s going on with it.
Yes there are line losses. The house closes to the source might have 240 VAC and the house at the end of the line might be only 228 (a 5% loss) during heavy draw times. Wire is sized to carry the full load amps with out over heating. That also means that there will be low line losses. Remember the heat is I2R, or IV. The higher the voltage drop the more heat.
In urban UK, the local transformer (11kv in - 330v out) will supply up to 100 houses. They, however, are not stand-alone units, but part of a unified network.
The cable that is under my street carries 330 volts three phase and the supply to each house will be from two phases, giving us a 220 volt supply. All household appliances are 220/240 volt here.
Out in the country, the supply is likely to be on poles and a transformer will serve only a few houses. A farm, for example would have 220 volts for the house, but a three phase supply for machinery/plant, all from a single transformer up on a pole.
It’s fairly rare for single family homes in the U.S. to get fed by two legs from a 3 phase line. There are places where 3 phase is used like this, but they aren’t common, even in urban areas. Parts of New York and Chicago and a few other places still have it and there’s still a few other areas around the U.S. but most other homes in the U.S. are fed from a split single phase transformer (aka a center tapped transformer). The split single phase transformer gives you 240 volts from line to line and 120 volts from either line to the center tap, which is used as the neutral. Homes fed by 2 legs of a 3 phase system have 120 volts from either line to neutral, but only 208 volts from line to line. The lower line to line voltage means that electric ovens take longer to heat up to temperature and electric clothes dryers take longer to dry clothes, but otherwise it doesn’t make too much difference. Ovens and clothes dryers are about the only common things in a typical U.S. house that run on 208/240.
Distribution voltages in the U.S. vary quite a bit. Older areas tend to run at lower voltages, anywhere from around 3,000 to maybe 7,200 volts, typically, though maybe up to 9,600 in some places. Newer areas tend to use higher voltages, typically in the 9,000 to 15,000 volt range. As was already mentioned, each transformer typically feeds a small number of houses, maybe 3 or 4 max.
The math doesn’t make sense here. What’s 330v three-phase? 330v from each phase to neutral? If so, then if you measure between two phases you’d get something like 570v. If it’s 330v between each phase, then an additional step-down transformer would be needed to step it down to 220v. And while I know that everything electrical in the UK is supremely wacky, I’m dubious that a 2/3-phase system is commonly distributed to residences. (Perhaps in large buildings which receive 3-phase power and distribute 2/3 to each residential unit. That used to be common in NYC and my (old) building has that feature.) But I’m pretty sure the standard UK residential service is a single-phase with 230v to ground.
So the three phase would be 400 to 415 volts RMS…
(the maximum voltage would then be 1.5 times higher… up to 600 volts… this might be required for designing insulation … )
Having spent most of my adult life living in rural Arkansas, I believed each house had a step down transformer, but in town we share one with our neighbor.
I think the main thing to remember is that power is the product of voltage and current. With very high voltage, the current is low. Resistive voltage loss is V = IxR, so with high voltage and large wire, the voltage drop is small.
