why is the US not Metric

[Monkeh]

No, it does not. 10 AWG would be sufficient for 10A for residential wiring.
10 AWG copper wire has resistance of 0.9989 Ohm per 1000 feet at room temperature. 10A through 75-feet long circuit branch gives 1.5V voltage drop both ways, which is acceptable.

And 10AWG is ridiculous for a 120W circuit! Nor is >10% drop acceptable by any reasonable standard. How on earth is this better than putting a 12V supply at the point of load, as you can already do? It's more expensive, harder to work with, and less efficient!

10% power loss in the worst case scenario (the maximum distance from distribution box) is far better than typical SMPS losses at the point of load.

And yet you've still got those losses back at the point of distribution - only a little lower in practice, with much higher transmission losses to account for.

Yes, it would be more expensive. Let me guess... Wiring 10 low-voltage branches for lighting receptacles would be $200-300 more expensive in material costs than wiring ten 14AWG lighting branches. That’s a whooping $10 per year, when amortized over 27.5 years period. Jeez...

And it's not going to save you $10 a year, and is going to waste materials which didn't have to be used. 14AWG x 10 circuits is already a stupid waste.

[Rick Law]

Years ago I remember being told that the reason the USA hadn't converted to metric was the cost of retooling, imagine the cost of replacing all those lathes and milling machines, plus the drill bits and everything else.

However............................

Lots of US companies now have their stuff made in Asia, who are quite comfortable working with either system, and the cost of conversion has now shrunk.

re: "Years ago I remember being told that the reason the USA hadn't converted to metric was the cost of retooling..."

I remember the same.  Pride or familiarity was not the main topic of discussion, but the cost vs benefit of having the same units.  The fight was between the importers, exporters, manufacturers, so on.  Manufacturers will be the ones particularly hard-hit in the change because their manufacturing machinery is expensive.

One must also consider, metric is as abstract as any other measurement and there is no intrinsic advantage in using it other than international trade.   Manufacturers/suppliers now adopted a different route to internationalization - with their own units that is even more abstract.  Now a "size 10" shirt from one manufacturer isn't the same size as a "size 10" from another.  Heck, it is not even the same "size 10" a year later from the same manufacturer.

[vad]

No, it does not. 10 AWG would be sufficient for 10A for residential wiring.
10 AWG copper wire has resistance of 0.9989 Ohm per 1000 feet at room temperature. 10A through 75-feet long circuit branch gives 1.5V voltage drop both ways, which is acceptable.

And 10AWG is ridiculous for a 120W circuit! Nor is >10% drop acceptable by any reasonable standard. How on earth is this better than putting a 12V supply at the point of load, as you can already do? It's more expensive, harder to work with, and less efficient!

10% power loss in the worst case scenario (the maximum distance from distribution box) is far better than typical SMPS losses at the point of load.

And yet you've still got those losses back at the point of distribution - only a little lower in practice, with much higher transmission losses to account for.

Yes, it would be more expensive. Let me guess... Wiring 10 low-voltage branches for lighting receptacles would be $200-300 more expensive in material costs than wiring ten 14AWG lighting branches. That’s a whooping $10 per year, when amortized over 27.5 years period. Jeez...

And it's not going to save you $10 a year, and is going to waste materials which didn't have to be used. 14AWG x 10 circuits is already a stupid waste.

Well, I think I toss 1-2 LED lamps a year (they don’t last long in fully enclosed light fixtures that I have, despite being rated for such use), and acquire half dozen power adapters annually (they usually come with electronic devices). That easily covers $10.

Another advantage would be greater safety, fewer electronic waste.

[rstofer]

No, it does not. 10 AWG would be sufficient for 10A for residential wiring.
10 AWG copper wire has resistance of 0.9989 Ohm per 1000 feet at room temperature. 10A through 75-feet long circuit branch gives 1.5V voltage drop both ways, which is acceptable.

And 10AWG is ridiculous for a 120W circuit! Nor is >10% drop acceptable by any reasonable standard. How on earth is this better than putting a 12V supply at the point of load, as you can already do? It's more expensive, harder to work with, and less efficient!

100 Amps for a microwave.  We have 2.  2 HP Garbage disposal.  6 kW stove.  That’s 500 Amps,
12V is ridiculous!

[vad]

No, it does not. 10 AWG would be sufficient for 10A for residential wiring.
10 AWG copper wire has resistance of 0.9989 Ohm per 1000 feet at room temperature. 10A through 75-feet long circuit branch gives 1.5V voltage drop both ways, which is acceptable.

And 10AWG is ridiculous for a 120W circuit! Nor is >10% drop acceptable by any reasonable standard. How on earth is this better than putting a 12V supply at the point of load, as you can already do? It's more expensive, harder to work with, and less efficient!

100 Amps for a microwave.  We have 2.  2 HP Garbage disposal.  6 kW stovue.  That’s 500 Amps,
12V is ridiculous!

Add a tumble drier, air conditioner, a fridge, a washing machine, a gaming desktop computer and a hair dryer. That makes it 9 appliances that need 120V or 240V. Almost everything else can be powered from low-voltage low-power supply. I have many dozens of LED A19 lamps alone

[boffin]

In the same vain pentax never changed their camera lens mounts, others did. Some people select the camera brand because they have an old lens that would cost a fortune to replace and is still seviceable. No one will buy a new camera for even a few thousand if it means changing a whole lens kit worth more than the camera body. Good telephoto lenses can cost more than the camera body.

Sure they did. A long time ago they used a screw mount on older spotmatics

[Simon]

I tend to use Fahrenheit for higher weather temperatures and Celsius for the lower ones.

In the UK we still have road distances and speed limits in miles despite having most other things in SI units... strange really.
... and when it is really hot the tabloid papers say... "Oooo what a scorcher <big number>F"... I seriously doubt many people understand F in the UK now... not me anyway. 

That's true, especially with higher temperatures. The BBC gave the temperature in both Fahrenheit and Celsius, when the heatwave in the summer just gone, broke the UK temperature, by reaching  38.7°C (101.7°F), yet the record breaking temperature in winter, at 21.2°C was only given in Celsius.
https://www.bbc.co.uk/news/uk-49157898
https://www.bbc.co.uk/news/uk-47374936

I wonder if it's because 101.7°F sounds more impressive than 70.2°F?

I think we should all use Kelvin for temperature. Celsius is no better than Fahrenheit because both scales have negative numbers which are totally unnecessary.

the C/K conversion is easy and for the average person and general convenience having 0 as water freezing is nice. Kelvin would still not solve everything with negative numbers or rather conversions. Auto standards do not go lower than -40C. In a CAN bus message where you only have 8 bits available for temperature and want to go as high as engine temperatures the 0 starts at -40C. In kelvin a similar translation would be required. No one will ever have to work with near 0K temperatures so it's a bit pointless using that as the starting point in every day life.

[Simon]

here in Australia everything is Metric,  like most of the world.

WRONG.

Most engineers in Australia, including me, still use the term "0402", "0603", "0805" etc for surface mount resistor sized. There is some crossover in name sizes between imperial and metric which just adds confusion. But I can live with this.
 
But what is really annoying is engineers in Australia who use an imperial grid for schematic symbol grid lines in Altium. So when my schematic symbols have a 2.50mm grid pattern and I have to use them to modify some imperialist's 0.1" grid, the bloody pins don't line up.

Australians should abandon the antiquated imperial measurements once and for all. And use kPa rather that PSI.

I think the only countries that have not moved to metric are Liberia, Burma and, you guessed it... the USA

Yea I did the same. Really bad idea. Stick with 2.54mm. I actually went for 3mm to make the divisions make more sense and because if you want to drow nice detailed symbols you want a 1/10 resolution but CS would not do 0.25mm, it had to be over 0.254mm. So I went for 3mm grid and regreted it. I now use KiCad and just stick with their standart 0.1" or 2.54mm. I can live with that.

[Simon]

here in Australia everything is Metric,  like most of the world.

WRONG.

Most engineers in Australia, including me, still use the term "0402", "0603", "0805" etc for surface mount resistor sized. There is some crossover in name sizes between imperial and metric which just adds confusion. But I can live with this.
 
But what is really annoying is engineers in Australia who use an imperial grid for schematic symbol grid lines in Altium. So when my schematic symbols have a 2.50mm grid pattern and I have to use them to modify some imperialist's 0.1" grid, the bloody pins don't line up.

Australians should abandon the antiquated imperial measurements once and for all. And use kPa rather that PSI.

I think the only countries that have not moved to metric are Liberia, Burma and, you guessed it... the USA

At least we drive on the right side of the road, unlike people of Botswana and Bangladesh.

Don't forget:

<iframe width="560" height="315" src="https://www.youtube.com/embed/BYeMotNIIGs?start=81" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[syau]

In commerical aviation (ie Boeing & Airbus) all tooling are in imperial unit but all measurement in Airbus is metric 

The worst thing is the wire gauge size AWG vs mm, due to slightly different in diameter, 2 set of wire stripper is required

[mariush]

I agree with low voltage, but I'd go with 24v or 48v DC

24v is low enough to allow cheaper switching regulator ICs that work at higher frequencies allowing for smaller inductors and capacitors. 48v would mean less current, so thinner wires to each led bulb or to devices.

No conversion at the house panel would be needed, you could still have 110v or 230v for your big appliances. You could have a small 24v ac-dc converter on top ceiling or hidden in the lamp somewhere, or hidden in the fake wall by the power switch on your wall. 

Internal dc-dc converters inside the led lamps would be more efficient than AC-DC (especially those capacitor dropper psus) and they'd be able to do brightness adjustment more easily and with less flicker ...

You could also have some 24v..48v DC outlets ... imagine you have your laptop that has a 18.5v DC charger ... usb power delivery allows up to 20v , so you could have the laptop powered using a small 24v..48v ->20v usb power delivery charger.
We're using more and more super efficient laptops and tablets that work with 10-20w and charge within hours, so maybe you don't need 65-90w adapters with lots of mains filtering in them

Small wallwarts for 5v / 9v / 12v for various devices would also be more efficient and smaller and cheaper to make,  powering off individual outlets in an automated way would also be easier and cheaper (not having to deal with AC high voltage relays and all that)
 
 Also less worry about people using shit chargers with shit isolation on the transformers inside, and people dying from using such chargers in bathrooms, or wallwart blowing up due to shorted transformers
Less zapping yourself due to those Y capacitors between primary and secondary , less radiated noise etc etc..

You may not even have to hide these AC-DC converters in the walls ... you could have extension cords, power strips with built in 110v->24v..48v DC ... ex.. sell a power strip with 5 outlets and 250-500w (ex 24v..48v 10A)

We may be getting there with usb power delivery if 20v becomes more popular... we have already chargers with multiple usb ports which can do 65-100w on the ports.

[vad]

I agree with low voltage, but I'd go with 24v or 48v DC

24v is low enough to allow cheaper switching regulator ICs that work at higher frequencies allowing for smaller inductors and capacitors. 48v would mean less current, so thinner wires to each led bulb or to devices.

No conversion at the house panel would be needed, you could still have 110v or 230v for your big appliances. You could have a small 24v ac-dc converter on top ceiling or hidden in the lamp somewhere, or hidden in the fake wall by the power switch on your wall. 

Internal dc-dc converters inside the led lamps would be more efficient than AC-DC (especially those capacitor dropper psus) and they'd be able to do brightness adjustment more easily and with less flicker ...

You could also have some 24v..48v DC outlets ... imagine you have your laptop that has a 18.5v DC charger ... usb power delivery allows up to 20v , so you could have the laptop powered using a small 24v..48v ->20v usb power delivery charger.
We're using more and more super efficient laptops and tablets that work with 10-20w and charge within hours, so maybe you don't need 65-90w adapters with lots of mains filtering in them

Small wallwarts for 5v / 9v / 12v for various devices would also be more efficient and smaller and cheaper to make,  powering off individual outlets in an automated way would also be easier and cheaper (not having to deal with AC high voltage relays and all that)
 
 Also less worry about people using shit chargers with shit isolation on the transformers inside, and people dying from using such chargers in bathrooms, or wallwart blowing up due to shorted transformers
Less zapping yourself due to those Y capacitors between primary and secondary , less radiated noise etc etc..

You may not even have to hide these AC-DC converters in the walls ... you could have extension cords, power strips with built in 110v->24v..48v DC ... ex.. sell a power strip with 5 outlets and 250-500w (ex 24v..48v 10A)

We may be getting there with usb power delivery if 20v becomes more popular... we have already chargers with multiple usb ports which can do 65-100w on the ports.

I totally agree. The example of 12VDC / 10A that I gave was a marginal case, just to show feasibility even at such low voltage. Higher DC voltages (24...48V) can deliver greater power and would be less expensive both in installations and material costs. 12-14AWG that is commonly used for residential wiring is 2-3 times less expensive than 10AWG needed for 12V / 120W, and is easier to work with.

[Monkeh]

I totally agree. The example of 12VDC / 10A that I gave was a marginal case, just to show feasibility even at such low voltage. Higher DC voltages (24...48V) can deliver greater power and would be less expensive both in installations and material costs. 12-14AWG that is commonly used for residential wiring is 2-3 times less expensive than 10AWG needed for 12V / 120W, and is easier to work with.

Would you make up your mind?

He suggested point of load converters. Which we already have, and you already rejected.



12V, 150W, and no need for running 10AWG around the place. Already exists, already used, we have USB capable of 100W for devices.

[Simon]

The worst thing is the wire gauge size AWG vs mm, due to slightly different in diameter, 2 set of wire stripper is required

Yea, I hate that but have to work with it.

[bdunham7]

240V is a two-phase system with a neutral wire and two hot wires running at 180 degrees phase shift.

No.. it's definitely single-phase centre-tapped.

What makes "phases" must be 120 degrees apart from each other?

They don't have to be 120 degrees--the original polyphase , aka 'two-phase' had phases 90 degrees apart.  And you don't necessarily have to evenly space them, I suppose...

However, the real point of understanding is knowing when equivalence by superimposition occurs.  We all understand that compass readings of 0 and 360 degrees are equivalent, but in power phases, this equivalence occurs at 180 degrees.  In other words, simply reversing the polarity of a phase doesn't give you another phase.

[james_s]

Add a tumble drier, air conditioner, a fridge, a washing machine, a gaming desktop computer and a hair dryer. That makes it 9 appliances that need 120V or 240V. Almost everything else can be powered from low-voltage low-power supply. I have many dozens of LED A19 lamps alone

Do you have any idea what you're talking about? Have you looked into the cost of 10AWG wire or calculated the losses you'd end up with? There's a good reason that aircraft and large trucks have historically been 28V and there is talk to changing cars to 48V. What do you think 12V would solve for lighting? Are LEDs going to magically run cooler if the driver is fed by 12V instead of 120V? My house is almost entirely LED since I changed it out in 2011-2013 and I think I have had 3 bulbs fail in that time, all of which were in enclosed fixtures, I have since found some bulbs that don't seem to mind that. Nobody in their right mind with any understanding of EE would contemplate wiring a house for 12V. Try living in an RV or boat for a while and you'll quickly realize what a hassle it is to be stuck with such a low voltage. A 2V sag under load is no problem for 120V but it's completely unacceptable for 12V.

If we were to contemplate changing anything it would be far more sensible to increase the household voltage to 240V rather than reduce it to something stupid. Incandescent lamps are for the most part obsolete so the major disadvantage of the efficiency penalty for higher voltage incandescent lamps is gone. Voltage conversion is cheap and efficient now so it can be done at the point of use when needed. Less copper, lower losses, lower cost, there are lots of advantages. But not really enough to change it at this point, 120V works fine.

[rstofer]

the C/K conversion is easy and for the average person and general convenience having 0 as water freezing is nice. Kelvin would still not solve everything with negative numbers or rather conversions. Auto standards do not go lower than -40C. In a CAN bus message where you only have 8 bits available for temperature and want to go as high as engine temperatures the 0 starts at -40C. In kelvin a similar translation would be required. No one will ever have to work with near 0K temperatures so it's a bit pointless using that as the starting point in every day life.

Just so the US doesn't get stuck with C and Kelvin, we have Rankine as our absolute zero referenced temperature (like K) but scaled in Fahrenheit.  Oddly, it wasn't discussed in my grandson's Physics course.  I'll bet it comes up in his Thermodynamics class.

[mariush]

What do you think 12V would solve for lighting? Are LEDs going to magically run cooler if the driver is fed by 12V instead of 120V? My house is almost entirely LED since I changed it out in 2011-2013 and I think I have had 3 bulbs fail in that time, all of which were in enclosed fixtures, I have since found some bulbs that don't seem to mind that. Nobody in their right mind with any understanding of EE would contemplate wiring a house for 12V. Try living in an RV or boat for a while and you'll quickly realize what a hassle it is to be stuck with such a low voltage. A 2V sag under load is no problem for 120V but it's completely unacceptable for 12V.

Not 12v but 24v or 48v.
Much simpler circuit inside the bulb: you won't have bridge rectifier, no bulky fuse, no common mode chokes for filtering, no primary high voltage capacitor, no need for transformers with double insulated wires or with space between primary and secondary, no cutouts in pcb under transformer ... a simpler and cheaper inductor instead of bigger transformers...
Better factor correction, you can have a 120-230v -> 24/48v that's 90%+ efficient, with 95+ factor correction instead of separate ac-dc converters in each bulb with 70-90 pfc.

Most led bulbs use small leds, let's say up to 100mA ... so 24v or 48v would be fine for having multiple leds in series, even if using cheapest linear led driver, losses would be very small. ex have 7 x 3v 0.1A in series, then 2-3 of these in parallel  for 21v 0.3a ... you get 7.2w in, 6.3w out .. 88% efficiency with cheapest linear led driver out there.

Cheaper bulbs, or maybe better heatsinked leds for longer life, as the led driver inside may be more efficient and generate less heat. 
much easier to produce 3.3v or 5v for an integrated IC that could do dimming based on signals on the DC input line or from bluetooth / wireless signal.

Less waste that won't be recycled properly...

[Simon]

why don't you just have a seperate thread on this?

[Monkeh]

What do you think 12V would solve for lighting? Are LEDs going to magically run cooler if the driver is fed by 12V instead of 120V? My house is almost entirely LED since I changed it out in 2011-2013 and I think I have had 3 bulbs fail in that time, all of which were in enclosed fixtures, I have since found some bulbs that don't seem to mind that. Nobody in their right mind with any understanding of EE would contemplate wiring a house for 12V. Try living in an RV or boat for a while and you'll quickly realize what a hassle it is to be stuck with such a low voltage. A 2V sag under load is no problem for 120V but it's completely unacceptable for 12V.

Not 12v but 24v or 48v.
Much simpler circuit inside the bulb: you won't have bridge rectifier, no bulky fuse, no common mode chokes for filtering, no primary high voltage capacitor, no need for transformers with double insulated wires or with space between primary and secondary, no cutouts in pcb under transformer ... a simpler and cheaper inductor instead of bigger transformers...
Better factor correction, you can have a 120-230v -> 24/48v that's 90%+ efficient, with 95+ factor correction instead of separate ac-dc converters in each bulb with 70-90 pfc.

Most led bulbs use small leds, let's say up to 100mA ... so 24v or 48v would be fine for having multiple leds in series, even if using cheapest linear led driver, losses would be very small. ex have 7 x 3v 0.1A in series, then 2-3 of these in parallel  for 21v 0.3a ... you get 7.2w in, 6.3w out .. 88% efficiency with cheapest linear led driver out there.

Cheaper bulbs, or maybe better heatsinked leds for longer life, as the led driver inside may be more efficient and generate less heat. 
much easier to produce 3.3v or 5v for an integrated IC that could do dimming based on signals on the DC input line or from bluetooth / wireless signal.

Less waste that won't be recycled properly...

Where's the significant advantage over existing 12V PoL systems? There's little to gain by upping the voltage over a 2-3m run.

[james_s]

Not 12v but 24v or 48v.
Much simpler circuit inside the bulb: you won't have bridge rectifier, no bulky fuse, no common mode chokes for filtering, no primary high voltage capacitor, no need for transformers with double insulated wires or with space between primary and secondary, no cutouts in pcb under transformer ... a simpler and cheaper inductor instead of bigger transformers...
Better factor correction, you can have a 120-230v -> 24/48v that's 90%+ efficient, with 95+ factor correction instead of separate ac-dc converters in each bulb with 70-90 pfc.

Most led bulbs use small leds, let's say up to 100mA ... so 24v or 48v would be fine for having multiple leds in series, even if using cheapest linear led driver, losses would be very small. ex have 7 x 3v 0.1A in series, then 2-3 of these in parallel  for 21v 0.3a ... you get 7.2w in, 6.3w out .. 88% efficiency with cheapest linear led driver out there.

Cheaper bulbs, or maybe better heatsinked leds for longer life, as the led driver inside may be more efficient and generate less heat. 
much easier to produce 3.3v or 5v for an integrated IC that could do dimming based on signals on the DC input line or from bluetooth / wireless signal.

Less waste that won't be recycled properly...

Not really. Have you looked at the drivers used in modern line voltage LED lamps? They are not much more complex than lower voltage DC drivers. They are low cost and very efficient, many are now using a single IC. Bluetooth is a train wreck, you are seriously suggesting a low voltage DC lamp that requires built in bluetooth and a separate voltage converter is simpler and cheaper than the $3 LED bulbs we already have that work perfectly well from existing line voltage? And this is going to be worth replacing the existing domestic wiring with something completely new that is far more expensive to install due to much more copper being required for a given amount of power and still won't work for all the large loads? What are you smoking and where can I get some of it? And what does any of this have to do with the metric system?

[tooki]

Sigh... Until American children are taught metric the Imperial system will persist, simple as that. It's not about what is better, it is about what is familiar, and in the US the Imperial system is by far the most familiar one.

As an American who went to school in USA: I was taught the metric and imperial systems in elementary school. And that was in the 80s, long after the US abandoned metrication.

yes but we don't have mixed measurements in the same industry like the US space industry did

How would one transition an industry from one system of units to another, if not to start converting? It’s impossible to shift everything instantaneously, so there will necessarily be a period when some things are still in the old system and others are in the new one. It’s a no-win situation: if USA retains the old system, the haters accuse of us being backwards and lazy and arrogant (neither is true), but if USA does switch to metric, then the haters accuse of us being reckless for switching. 🙄

[tooki]

In the US we typically have a separate 15A branch circuit per bedroom.

I’m American, I’m well familiar with US wiring, thanks.

So 120W low-voltage circuit per bedroom is plenty enough for LED lights - with 100 lpw devices you can light up bedroom with 12,000 lumens - equivalent to 15 x 60W incandescent bulbs - far more than anyone would need.

And for this you want to double the amount of wiring in a house, again, right as the cost of copper has never been higher? 

But moreover, it’s not just lights. What about the 12W phones and tablets, the 90W laptops, and all the other myriad gadgets we use and charge? It’s easy to exceed the 10A you’ve budgeted.

240V is a two-phase system with a neutral wire and two hot wires running at 180 degrees phase shift.

No, it is not. There is only one phase (240V), and it’s divided into 2x120V by a center tap in the transformer on the pole or in the green box near the sidewalk. While it is somewhat common to refer to this as a “two phase” system, that is a misnomer, and the correct nomenclature is that it is a split-phase system. True multiphase power does exist in USA, but isn’t really used residentially. (Unlike in Europe, where true multiphase power is commonly used for home ovens, stoves, and some laundry machines.)

[schmitt trigger]

And don’t get me started on Miles per Gallon vs Kilometers per Liter vs Liters per 100 Kilometers.

[Simon]

litres per 100km alwoys confused me. I mean why?