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

[Dabop]

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.

Amazing- them lot over there havent stuffed (much) with the trailer wiring colours....

(apart from that red/brown business)
its pretty easy (although I have wired so many trailers/plugs up over the years I dont even need to look em up
pin1 brown tail/clearance lights (dull red looks brown, bright red like brakelights looks red)
pin2 yellow left hand indicator (yellow lens so easy to remember)
pin3 green right hand indicator(nearest colour to yellow so its the other indicator)
pin4 red brake lights (red lens)
pin5 blue electric brakes
pin6 white earth

 

[Dabop]

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.

A fairly common practice on large contactors is the pullin/holdin twin coils, I cant understand why it would have caused you trouble, unless either the wiring was undersized and too long a run, or your psu was of insufficient capacity to handle the coil loads (doubtful, they dont consume THAT much current) or you had high resistance joints somewhere in the circuit
In the mines we had truly massive contactors in the switchroom, capable of handling thousands of amps at thousands of volts, their pullin coils did have issues, but the coils were literally the size of garbage cans and had to be magnetically shielded

 

[BillC]

Volts don't kill you at all.

Consider the Taser, it has a wallop of about 50,000 Volts.

What will kill you is the Amperage, about 100-200 mA across the heart.

This statement, while sort of true, is missing some of the details. The current across the heart is driven by the voltage, and although the impedance is highly non-linear, the higher voltage, in principle the higher the current. While a shock from a Taser might carry 50kV, it is non-lethal, while a shock from a 50kV power line is almost certain to be. What makes the difference is the impedance of the internal circuit and how long that voltage is maintained. A Taser has a high internal impedance and delivers its voltage in short duration pulses. The power line has a very low impedance, and will sustain its power flow until external protection kicks in and trips the circuit, by which time the shock is likely lethal.

 

[CORed]

This could perhaps justify its own thread, but I'll start it off here and see what others come up with.

• Wire gauge
• Camera aperture settings
• Star brightness (magnitude)
• Paper sizes (maybe not in America, but in Europe we have the 'A' series where A4 is half the area of A3, and A5 half the area of A4 and so on)
• UK knitting needle sizes

Fish hooks (in the USA, anyway. I don't know what the rest of the world does).

 

[bruto]

I would point out (probably unnecessarily) that camera apertures are, while odd and seemingly backwards, a specific calculation (ratio of focal length to aperture size) that sort of makes sense, in that the effective aperture of a lens is not an absolute size, but a relative one.

Of course I suppose they could have done the ratio backwards and at least had the numbers go in the right direction.

Similarly, the numbering of book sizes makes sense if you think of the folds, or pages to the standard sheet, but if not, the larger numbers indicate the smaller books.

Shotgun gauges are also backwards. As usual, there's a sort of explanation from long ago, but it makes little sense now. Interestingly, though the gauge of shotguns is backwards as is the gauge of wire, the two are derived completely differently.

 

[elgarak]

I would point out (probably unnecessarily) that camera apertures are, while odd and seemingly backwards, a specific calculation (ratio of focal length to aperture size) that sort of makes sense, in that the effective aperture of a lens is not an absolute size, but a relative one.

Of course I suppose they could have done the ratio backwards and at least had the numbers go in the right direction.
Similarly, the numbering of book sizes makes sense if you think of the folds, or pages to the standard sheet, but if not, the larger numbers indicate the smaller books.

Shotgun gauges are also backwards. As usual, there's a sort of explanation from long ago, but it makes little sense now. Interestingly, though the gauge of shotguns is backwards as is the gauge of wire, the two are derived completely differently.

Direction for what? (for photographic aperture sizes)

You mis-understand which way the calculation was used primarily.

Same with paper sizes: You cannot fold a small sheet into a large one. You have to start with the largest size, and then go from there. The series can go very far in the direction of smaller sizes (but not the other way), hence you start with 0 for the largest.

 

[Doubt]

A fairly common practice on large contactors is the pullin/holdin twin coils, I cant understand why it would have caused you trouble, unless either the wiring was undersized and too long a run, or your psu was of insufficient capacity to handle the coil loads (doubtful, they dont consume THAT much current) or you had high resistance joints somewhere in the circuit
In the mines we had truly massive contactors in the switchroom, capable of handling thousands of amps at thousands of volts, their pullin coils did have issues, but the coils were literally the size of garbage cans and had to be magnetically shielded

In the end we were never really sure either. All wiring was to code and we tried everything AB said to try. We also replaced the original 24VDC units with new ones.

After wasting a lot of time on a secondary system the decision was made to go with AC and just get it done.

Then again, on the same assignment I triggered an Allen Bradly recall on limit switches. we had a large number of switches that became unreliable over a two month period. Turned out that they had moved manufacturing from the US to the Dominican Republic and ran into some quality issues. I had two machines with a 127 limit switches each and had to replace 60% of them.

Not sure where they were/are making the contactors.

 

[bruto]

Direction for what? (for photographic aperture sizes)

You mis-understand which way the calculation was used primarily.

Same with paper sizes: You cannot fold a small sheet into a large one. You have to start with the largest size, and then go from there. The series can go very far in the direction of smaller sizes (but not the other way), hence you start with 0 for the largest.

Of course it makes sense as it's done, but it still is counterintuitive if you are not thinking in terms of why the numbers are as they are. Similarly, gauges of one sort or another have a rationale. Wire is gauged as a theoretical number of narrowing draws, more draws making for a smaller wire. Shotguns are gauged by the number of balls you can make from a pound of lead, the smaller the bore, the more balls.

In the case of camera apertures, although the formula makes sense, since it's a ratio, there's no great reason why it could not be the other way around. Purely as a ratio, 1:2 is the same as 2:1 as long as you know what the terms are. That way, although the numbers would still not be linear, at least a bigger hole would lead to a bigger number, rather than the other way around. The result would be trivial and it's easier just to remember the stops anyway, but it would theoretically have been possible once.

 

[Trebuchet]

Amazing- them lot over there havent stuffed (much) with the trailer wiring colours....

(apart from that red/brown business)
its pretty easy (although I have wired so many trailers/plugs up over the years I dont even need to look em up
pin1 brown tail/clearance lights (dull red looks brown, bright red like brakelights looks red)
pin2 yellow left hand indicator (yellow lens so easy to remember)
pin3 green right hand indicator(nearest colour to yellow so its the other indicator)
pin4 red brake lights (red lens)
pin5 blue electric brakes
pin6 white earth

Not all that different, except that we've only got four pins in a "flat four" connector. Brake and signal lights are combined per side. No brakes on a simple trailer. The alternative is a larger round connector which I've got no idea of.

The "Red/brown" thing is because there's been some solar fading and I can't really tell what color it was supposed to be.

 

[Planigale]

This statement, while sort of true, is missing some of the details. The current across the heart is driven by the voltage, and although the impedance is highly non-linear, the higher voltage, in principle the higher the current. While a shock from a Taser might carry 50kV, it is non-lethal, while a shock from a 50kV power line is almost certain to be. What makes the difference is the impedance of the internal circuit and how long that voltage is maintained. A Taser has a high internal impedance and delivers its voltage in short duration pulses. The power line has a very low impedance, and will sustain its power flow until external protection kicks in and trips the circuit, by which time the shock is likely lethal.

I previously posted it is the energy delivered that is biologically important (timing is also important obviously the same energy delivered over a year is not an issue as opposed to over 0.1s), so power is significant. Timing is also important in that the heart varies in its sensitivity to shocks in the cardiac cycle. A lot of electric injury is thermal, so how quickly heat disperses is important. Electricity and consequent thermal injury follow conductive paths so nerves and blood vessels are more damaged than fatty tissue.

 

[Tomtomkent]

Just something I have been wondering about recently.

Most appliances can just as easily be designed for 120V mains as 240V mains so it is six of one and half of the other. More heavy duty appliances will require a higher voltage and sometimes, only three-phase will do (for example, I used to have a three phase motor to pump bore water).

Most places in the world have a 240V mains. The local power lines carry that voltage on 3 lines (plus one for neutral) and it is only necessary to tap into the line to supply the house with either single phase or three phase electricity.

America, Canada, Japan and a few other countries use a 120V mains. There the setup seems a little more complicated. As I understand it, the local power lines carry 7,200V and pole top (or underground) transformers convert it to a "center tapped" 240V supply (http://science.howstuffworks.com/environmental/energy/power7.htm). Each transformer supplies a single house with two phase 120V electricity (although residential complexes may share a transformer). Heavy duty appliances like washing machines can easily be accommodated with 240V but if a household needs a three phase supply then I guess they need an extra pole top transformer.

About the only advantage I can see of a 120V system is that local power lines can be thinner since they carry less current. 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 was wondering if anybody involved in power distribution would like to weigh in.

For all intents and purposes you won't really notice a difference at all based on voltages. As an everyday consumer the chances are the differences you would notice if your how is wired on a ring main with spurs, independent spurs from a hub. Even then, your house will have a consumer unit, with a distribution board of protective devices, and you may notice if the plugs are fused or not.

Most stuff you plug in will be white goods keyed for the local supply, or electronics which will reduce the power supply to a few DC volts anyway. Either way, there is a good chance they are well insulated to the point of having a dummy earth connection.

 

[bruto]

Psion, with regard to three phase power, even a pole top transformer is not enough. The high voltage supply is also split phase, and in order to have three phase it must be three phase to the pole also.

This has become a big issue around here, as the phase of power lines is a limiting factor on the capacity of solar installations. Needless to say, the power company is reluctant to do the expensive work in extending three phase service to places where it does not exist. Now this in some ways turns out to be an advantage where the unbridled uglification of plots of land is beginning to show as solar developers look for the cheapest and least obstructed old fields on which to build. Commercial viability is lessened, and smaller solar farms more suitable. Of course, there is no real reason why a big solar farm cannot be well designed, but alas, it is not always so.

 

[Speedskater]

While on the subject of sizes. In the US, a 10AWG wire is larger than a 12AWG wire, yet a #10 bolt is smaller than a #12 bolt.

 

[CriticalThanking]

Amazing- them lot over there havent stuffed (much) with the trailer wiring colours....

(apart from that red/brown business)
its pretty easy (although I have wired so many trailers/plugs up over the years I dont even need to look em up
pin1 brown tail/clearance lights (dull red looks brown, bright red like brakelights looks red)
pin2 yellow left hand indicator (yellow lens so easy to remember)
pin3 green right hand indicator(nearest colour to yellow so its the other indicator)
pin4 red brake lights (red lens)
pin5 blue electric brakes
pin6 white earth

Yeah - trailer wiring connections are frustrating. We seem to be moving toward a more standard connection type, but I frequently see trailers with multiple connectors wired up because you never know what the towing vehicle will have. When I go into a trailer supply store, I often take pics on my phone of the standard wiring for multiple types so I can at least take an educated guess when fixing/rewiring.

I only play with that stuff every few years - just enough to forget the lessons of last time and for the wires to have faded colors.

CT

 

[Trebuchet]

While on the subject of sizes. In the US, a 10AWG wire is larger than a 12AWG wire, yet a #10 bolt is smaller than a #12 bolt.

While at the airplane company, we had assemblies that used tiny microswitches installed with #2 screws. You can almost see them.

 

[CORed]

While on the subject of sizes. In the US, a 10AWG wire is larger than a 12AWG wire, yet a #10 bolt is smaller than a #12 bolt.

The number sizes for US, bolts and screws have always seemed strange to me. The larger sizes are designated by diameter in fractions of an inch, which is reasonable if you must use inches as your unit of measure, but when you get below 1/4 inch you have weird sizes like 10-32, 10-24, 8-32 ir 8-34 (the last number I think is pitch in threads per inch), and I have no idea what the first numbers reference.

 

[CORed]

While at the airplane company, we had assemblies that used tiny microswitches installed with #2 screws. You can almost see them.

No doubt the people that had to service those things had some interesting things to say about the engineers who designed them.

 

[Trebuchet]

The number sizes for US, bolts and screws have always seemed strange to me. The larger sizes are designated by diameter in fractions of an inch, which is reasonable if you must use inches as your unit of measure, but when you get below 1/4 inch you have weird sizes like 10-32, 10-24, 8-32 ir 8-34 (the last number I think is pitch in threads per inch), and I have no idea what the first numbers reference.

Threads per inch is correct. And annoying, because especially in those small sizes you're about equally apt to encounter coarse and fine threads. A 10-24 nut doesn't work well on a 10-32 screw. The first number is basically an arbitrary series, although #10 is actually 3/16 diameter. Generally anything smaller than 1/4 isn't referred to as a bolt, but rather as a "machine screw".

No doubt the people that had to service those things had some interesting things to say about the engineers who designed them.

Who, me?
They aren't that difficult, you just need a small Philips screwdriver. And a supply of screws to replace the ones you lose. The teeny switches in question were actually more reliable and carried more current than the next size up.

 

[Galaxie]

The number sizes for US, bolts and screws have always seemed strange to me. The larger sizes are designated by diameter in fractions of an inch, which is reasonable if you must use inches as your unit of measure, but when you get below 1/4 inch you have weird sizes like 10-32, 10-24, 8-32 ir 8-34 (the last number I think is pitch in threads per inch), and I have no idea what the first numbers reference.

The number sizes are determined by the formula: Major diameter = Screw # × 0.013 in + 0.060 in
So a #10 screw is 0.190".

Strangely, there is a #14. It's 0.242". That's awfully close to 1/4". It's a good thing that size has fallen out of use for the most part.

 

[Trebuchet]

The number sizes are determined by the formula: Major diameter = Screw # × 0.013 in + 0.060 in
So a #10 screw is 0.190".

Strangely, there is a #14. It's 0.242". That's awfully close to 1/4". It's a good thing that size has fallen out of use for the most part.

Wow, I didn't know either of those factoids! #12 is also fairly uncommon.

A pet peeve of mine is that my former employer somehow decided that everything should be decimalized, including screw sizes. So a #10-32 is .1900-32. Sheesh.

When I'm King of the World (KotW, (TM)) we'll stop counting on our fingers and go to octal or hexadecimal numbers. Probably octal, so we don't have to use letters. Then the nice common fraction will have simple octal equivalents.