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High voltage is the key to reducing losses in transmission. Back in the day, there was no easy, economical way to boost DC to a higher voltage for transmission & than back down to a safer voltage for consumer use. AC used simple transformers to do that. That's why AC won out in for utility distribution.Originally Posted by Curt Harms
Member
In the second picture, the wire that looks like it burned the pole is a ground. It goes to the Lighting Arrestor, H1 is tied to the LA's primary. If there is a lighting strike on the primary, the LA bleeds it to ground before it gets to the transformer. It's sort of a big spark plug. Why it flashed to the pole is anyone's guess.
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2A9253EF-C1D7-4CDD-95E2-71905DA7A0AC.jpgAttachment 451507I tested a 20 amp circuit, 12 gauge wire, about 50 feet using the third/last receptacle in the run.
120.2 volts with no load
added an 18 amp load
116.5 with 18 amps.
About a 3 percent voltage drop.
Last edited by Bruce King; 02-07-2021 at 1:00 PM.
Moderator
Many single phase AC motors will run on somewhat lower voltage. The potential problem is, they will then draw more current to generate the same output power. A little of this is usually not a problem unless the voltage is so low that the current it draws is so high the feed wires and motor windings also overheat. (Heated wires have higher resistance which further reduces the voltage making things worse.) At some point the motor is damaged. This can happen from a voltage drop from a wire that is too long.
Many years ago my brother-in-law burned up three motors by running 110v through long wires to the pump in his spring. Instead of running a larger wire, he solved the problem by supplying 220 volts and switching the new motor to run on 220v instead of 110, cutting the current draw in half. He never burned up another pump motor.
I don't know how this applied to 3-phase motors driven by a VFD.
JKJ
Contributor
It would be interesting to run that same test on the closest outlet - with the shortest wire run - and see what drop you get.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Member
With good connections it’s all going to be pretty close to this calculator. The length of the wire is not always known if it’s behind drywall.
https://www.calculator.net/voltage-d...s=15&x=63&y=27
Member
That’s not a load tester.
Over the past five years I’ve checked out over a hundred homes with mine, and the voltage drop is typically in the 3 to 7 percent range with a 15amp load, with some variation outside of that. That’s an observed reality.
Most of this was while looking for a new home that I would be satisfied with, given that I’m very particular about some stuff (that might touch on electrical, which would inevitably require some modifications.) Finally found one, BTW.
Moderator
I had to put a buck/boost transformer on my slider because for a time period the voltage from the street was either too high or too low...I don't recall at this point and it was tripping the circuitry that monitored for that. The saw would just stop working until I did the labor to get inside and reset things. My point here is that some tools are designed to support a very specific range of voltage fluctuation and if the "line steps over the line"...you get no sawdust. Sam Blasco helped me diagnose that back when it happened. The power company later found a degrading transformer feeding our property and rectified it.
--
The most expensive tool is the one you buy "cheaply" and often...
Member
That’s a current meter. I also had a load and a volt meter. Your load tester combines all that in one tool. My measurements and technique is perfect and agrees with published data. Your load tester is probably using a higher load than the 15 amps you posted or the cable length is very long or loose connections.
Last edited by Bruce King; 02-07-2021 at 4:02 PM.
Contributor
The major reason back then was that AC voltage could be stepped up and stepped down with a simple transformer. So you could step up the voltage to a very high level for long distance transmission and then step it down to a voltage for local transmission and finally to residential voltage.
You couldn't do that with DC back in the early days so DC had to be carried at the user voltage level which implied very high currents and high losses.
Today, we have the technology to convert between AC and DC at a reasonable cost and efficiency so DC can be used for long distance transmission at very high voltage levels.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Member
I have both the Extech and the Ideal SureTest, and they’re consistent with one another. (The Ideal is good for bootleg grounds, but I prefer the Extech because it plays nice with AFCI.) It sounds like you’ve got a lot of connections there, and a few data points. I have many more data points, across a broad range of structures. You seem to be indicting the whole of the residential wiring trade, across many decades. :^)
Anyway, the point is that what appears at the receptacle is not always what you think it should be.
Member
AC or DC, very high voltage (and proportionally less current) always has an advantage in long distance power transmission lines. The lower the voltage, the higher the current (and vice versa), and resistance losses in transmission lines are proportional to current, not voltage.
The early advantages of AC over DC had to do with the difficulty (= cost), in that era, of efficiently changing DC voltages, compared to using a simple transformer to change AC voltage. Since DC voltage could not easily be raised for efficient transmission voltages (or reduced for safe consumption at the end users), transmitting it over long distances was cost-prohibitive.
Modern electronics have drastically reduced the cost of changing DC voltages at very high power levels, though only enough to make long distance DC transmission more cost effective overall. It is still cheaper to change AC voltages with a transformer, especially at high power, but when the combined conversion and transmission costs are considered, DC now wins for very high power and/or very long distance applications.
As an illustration of the relentless pursuit of efficiency, high power generator armatures are spun in hydrogen atmospheres, to reduce mechanical resistance losses. Helium, while advantageously inert, would have twice the viscosity of hydrogen. A vacuum is not practical because of the lack of an insulating atmosphere (electrons at the potential in these generators can fly around rather easily in a vacuum.) So they just have to make sure there is no oxygen mixed in with the hydrogen. At those power levels, even small percentage losses are still big losses, and seemingly extreme measures are cost-effective.
-- Andy - Arlington TX
Contributor
Hydrogen atmosphere is used in large dynamos to cool the windings, not to insulate them. There is no practical difference in the electrical insulating effect of hydrogen vs air vs vacuum - the hydrogen being only .025% more dielectric than a vacuum. Hydrogen is, however, a significantly more efficient thermal medium than either air (or Helium) - easier to move with fans, and much better thermal conductivity. That's why it's used to cool dynamos.
Contributor
You both are correct BTW!! Andy is not necessarily correct about the insulating properties of hydrogen but one of the reasons it's used is definitely because of the viscosity of the gas not just the efficiency of it's thermal conductivity. There is much less drag in hydrogen than in air therefore Andy is correct in that there is much less mechanical resistance! But Steve is also correct in that hydrogen is much better at dissipating heat.
Contributor
Jeff
I don't know if you're still keeping track of your post, but after 4 pages of academic discussion the simple answer is, yes, treat them the same, as long as you live in the continental US.
"The first thing you need to know, will likely be the last thing you learn." (Unknown)
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