can i detect if the hot and neutral lines reversed?

ebp

Joined Feb 8, 2018
2,332
Prior to the abundance of power supplies made by rectifying and filtering AC, "power factor" was pretty much universally thought of as sinusoidal voltage and current that were not in phase with each other. This, of course, is what you get with linear reactive loads. If you have an excess of inductive loading you can correct the power factor by adding capacitive reactance (perhaps with "synchronous condensers" that are big machines that pretend to be capacitors). You can't use linear reactance to compensate for the very non-linear behavior of a capacitively filtered rectifier circuit. The peak of current is temporally very close to the peak of voltage, but for most of the half-cycle the current is zero. There are passive techniques that can improve power factor, but not at the dangling end of the power cord.

Active power factor correction, or active harmonic filtering as it is often called in Europe, generally is done using a boost switch mode converter designed so that the instantaneous input current is directly proportional to the instantaneous input voltage but inversely proportional to the average input voltage. - which is a little tricky. A typical single-phase APF converter will boost to about 385-400 volts DC and to do a good job it needs to accomplish that boost for the entire AC cycle - big boost near zero crossings, small boosts at peak. The last time I designed such a beast, 100 kHz was a fairly popular switching frequency, being a reasonable compromise of the usual "everything is in conflict with everything else" nature of switchers. It is APF that makes lots of higher power switchers "universal input" - accepting anything form about 85 to 265 VAC (actual, not nominal) or equivalent DC.

A moderator might like to move this and a bunch of previous posts off to another thread, since they are non-responsive with regard to the original topic.
 

MrAl

Joined Jun 17, 2014
8,253
`All 100% true the NET is always right isn't true here. In an Explorer's Post at HP (Hewlett-Packard) I wa sin my teens and knew which wire should go to the middle of a glass fuseholder. My mentor didn't.

The three prong line cords don't have the wide blades when 3 prongs are present. What about the guys that cut the third prong off. Fortunately, I don;t see any non-polarized duplex outlets anywhere, but I do have some (unconnected ones) at home.

Many a times, I would grab a line cord, orient it as though I was plugging it in and take a meter to figure out whether or not brown or blue was hot or neutral. I still haven't learned.

When RED became ALWAYS NEGATIVE and I didn;t know any better, you learn. In the thermocouple world RED is negative. Then with copper tubing fittings, a 7/8 elbow is a 3/4 elbow. Same exact fitting. Just depends on where you buy it.

The last annoying thing I ran into was that a machinist measures flat head (overall length) and pan head (thread length) screws differently. In another discipline (eyeglasses) all screws are measure OAL.
Hi,

Yes i forgot about the three prong plugs having both prongs the same with a U shaped ground prong.
I had to take the plug and plug it into a three prong outlet socket to see which one was which because i wanted to switch the hot wire not the neutral. The sockets have the wider hole for the neutral.
You have to be very careful how you call the wide (or narrow) prong as to handedness depending on if you look at the plug from the front (where you see all three prongs) or the back (where you are looking at the wire side of the plug not the prong side) and if the U is right side up or upside down.
 

MrAl

Joined Jun 17, 2014
8,253
One 'Slight' exception was when the regulation for kitchen duplex outlets were required for each to be wired across 240v, IOW top one L1 & N, bottom L2 & N.
Because each Live is out of phase to each other a single N was allowed, in this case IF the load on each were equal the N current is Zero!
Max.
Hi,

Oh yes that's a catch there. Three phase systems also have that character in certain circumstances.
In the single phase or two phase system if you measure the current right out of the socket though it will be equal to the hot wire current even with both phases taking the same current. That's because they dont cancel in the appliance, they only cancel at the point where the two neutrals are tied together. In other words for a two phase system a ground fault interrupter should work just fine on both lines.
But yes, where the two neutrals connect the currents cancel with equal loads.

That way of remembering things (wide prong takes more current so it should be hot) was not right anyway though and i like WBahn's idea so i'll try to remember it that way from now on.
 

MrAl

Joined Jun 17, 2014
8,253
I wonder, in the age of highly non-linear loads, is it now possible for the neutral current in such an arrangement to actually be greater than either of the live wires?

Or even with linear loads, what about if one is capacitive and the other is inductive? I wonder if the standard allowed for that possibility, or chose to discount it because of the unlikelihood of its occurrence in such a way as to be an issue.
Hi,

Yes that's an interesting question and we can guess the answer ;-)

The question was whether to run a single 3 wire cable or two 2 wire cables. I think a lot of do it yourself handbooks had shown a three wire cable, which of course only has one neutral and it's the same gauge as the other two (one red and one black, with a white neutral and maybe a green or bare wire ground).

We could run the numbers with one full capacitive load and one full inductive load.
 

WBahn

Joined Mar 31, 2012
26,398
A moderator might like to move this and a bunch of previous posts off to another thread, since they are non-responsive with regard to the original topic.
That will largely be the call of the TS, who may or may not find the meanderings useful and/or distracting. If they would like them split off then we will likely honor the request.
 
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