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

[TheGnome]

Ah yes. So they are metric. But if you can't unscrew a nut, you don't care if it's of metric or imperial size. You just have to notice that it's left threaded.

Happened to me a few times with certain makes or models of TV sets where the picture tube was attached to the case with left threaded bolts.

Damn if I know why they did this.

 

[Speedskater]

Bicycles have one pedal reverse threaded. With a normal thread, the pedal would loosen itself over time.

 

[CORed]

Ah yes. So they are metric. But if you can't unscrew a nut, you don't care if it's of metric or imperial size. You just have to notice that it's left threaded.

Happened to me a few times with certain makes or models of TV sets where the picture tube was attached to the case with left threaded bolts.

Damn if I know why they did this.

I have no idea why they would use a left-hand thread for picture tubes. Some older cars (mostly Chrysler products, IIRC) used to use left-hand threads on the wheel lug nuts on the left side if the car, I believe so that inertia would not loosen them when braking. It could make trying to change out a flat difficult if you didn't know they had to be turned the "wrong" way. I think this was abandoned because, as long as the nuts are properly tightened, they won't come loose anyway, and it probably cost less to use the same studs and nuts on all the wheels.

ETA: I've also run into left-hand threads attaching fan to water pump, where the direction of rotation was such that the water pump could unscrew itself from the fan with a right hand thread.

 

[bruto]

Ah yes. So they are metric. But if you can't unscrew a nut, you don't care if it's of metric or imperial size. You just have to notice that it's left threaded.

Happened to me a few times with certain makes or models of TV sets where the picture tube was attached to the case with left threaded bolts.

Damn if I know why they did this.

To keep people like you from getting the picture tube out and cutting yourself?

Left threads make a certain sense in certain applications, among them bicycle bottom brackets and pedals. The pedal threads (also several different types) are always, or at least almost always, left threaded on the left, but bottom bracket threads, despite the sense of it, are not if they are French or Italian.

Some things, like the left side wheel lugs of automobiles, should be, and used to be in many cases, but rarely are nowadays.

 

[ceptimus]

British Association screw threads are some of the weirdest around. B.A. fasteners are still used by model makers as they often look more like full-size fasteners scaled down to model scale than any of the alternatives.

From Wikipedia

They are unusual in that they were probably the most "scientific" design of screw, starting with 0BA at 6.0mm diameter and 1.0mm pitch and progressing in a geometric sequence where each larger number was 0.9 times the pitch of the last size. They then spoiled this by rounding to 2 significant figures in metric and then converting to inches and rounding to the thousandth of an inch. This anticipated worldwide metrication by about a century. The design was first proposed by the British Association in 1884[1][2] with a thread angle and depth based on the Swiss Thury thread,[3] it was adopted by the Association in 1903.

 

[MRC_Hans]

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.

Mmm, impedance is not all. Of course, a high impedance source can deliver little current, even with a high voltage, but it is also a question of capacity, or very often, capacitance. A taser delivers quite a bit of current, but with very short duration. The amount of energy supplied is also important.

Hans

 

[psionl0]

Mmm, impedance is not all. Of course, a high impedance source can deliver little current, even with a high voltage, but it is also a question of capacity, or very often, capacitance. A taser delivers quite a bit of current, but with very short duration. The amount of energy supplied is also important.

I think BillC was referring to the impedance of the source - not the body. Capacitance is also part of the body's impedance anyway.

 

[psionl0]

It takes the same time for a 120V kettle to boil as a 240V kettle if they have the same power rating.

I didn't know that. I had heard differently. I wonder why Americans are so resistant to the things?

The "if they have the same power rating" was quite a big caveat. The maximum current in the US isn't double the current in the UK (UK 13A, US 15A or 20A, you don't want to exceed it so manufacturers are likely to design for 15) so the overall power available is lower (P=VxI). Referring just to the voltages is easier when explaining it casually to someone who doesn't need the details.

http://wordpress.mrreid.org/2012/04/16/why-kettles-boil-slowly-in-the-us/

This exchange took place on the UBI thread (of all places). I thought it also had a place here as well.

This thread has focused mainly on the supply side of electricity. I assumed that 120V or 240V was mostly the same difference when it came to appliances. This was especially so since heavy duty appliances could still be powered from 240V.

What I hadn't considered was the difference in the power ratings of the power outlets. Australian power outlets are typically rated for 10A which means that they can power appliances at up to 2400W. (You can also get outlets rated for higher currents - they have a larger earth pin). However, US outlets are rated at 15A meaning that they can only power appliances at up to 1800W.

This has implications when it comes to electric kettles and portable heaters which must necessarily be lower power if you wish to plug them into a standard power outlet (not so portable otherwise). That gives 240V a distinct advantage.

 

[lauwersw]

The situation in Belgium (I don't know about the rest of Europe) is different. There's a rating on the outlet of 20A, but most appliances are only rated for 16A. The reason is that the fuse on the outlet is not there for protecting your appliance, but for protecting your wires and outlets. It kind of makes sense as you can connect multiple appliances to the same wire, so there's some extra margin. Most appliances don't draw 16A. Still sometimes you can end up in a situation where you consume too much and the fuse trips.

Building code here says up to 8 "outlet points" are allowed on a single fuse, but there's no limit to how many outlets you can actually have at each point. Some things don't make much sense

Many houses here have 3 phase 380V connections (even though that's getting less common). We have an induction stove for example that can draw up to 7.2kW on 3 phases. Gets a pot of water boiling in 3 minutes, I love that!

 

[elgarak]

As far as I can tell, there's no mentioning of the electricity being AC – alternating current. Which means that there's a frequency attached.

The USA (and some surrounding contries) uses 60 Hz. Europe and the rest of the world 50 Hz.

From what I understand, the household voltage in the USA of 120/130 V was set because the frequency of 60 Hz is more dangerous to humans than the 50 Hz elsewhere. It's closer to the natural heart rate of most humans, and therefore more likely to cause heart problems when shocked.

 

[P.J. Denyer]

As far as I can tell, there's no mentioning of the electricity being AC – alternating current. Which means that there's a frequency attached.

The USA (and some surrounding contries) uses 60 Hz. Europe and the rest of the world 50 Hz.

From what I understand, the household voltage in the USA of 120/130 V was set because the frequency of 60 Hz is more dangerous to humans than the 50 Hz elsewhere. It's closer to the natural heart rate of most humans, and therefore more likely to cause heart problems when shocked.

If 60Hz is closer to your heart rate than 50Hz, you already have bigger problems than being electrocuted! This smacks of a post hoc rationalisation by someone who doesn't know the difference between Hz & BPM becoming an "Internet Fact".

 

[P.J. Denyer]

The use of 50 versus 60 Hz is purely due to historical reasons, with companies in the US making 60 Hz equipment and those in Europe making 50Hz equipment so that they have a monopoly. This rivalry led to the split you see today.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.djtelectricaltraining.co.uk/downloads/50Hz-Frequency.pdf&ved=2ahUKEwiyz_quwbzmAhWkUhUIHcsdDi8QFjABegQIDRAG&usg=AOvVaw2oa2-TuWR6XSLtfHE6-JXb

 

[Speedskater]

...........................................
What I hadn't considered was the difference in the power ratings of the power outlets. Australian power outlets are typically rated for 10A which means that they can power appliances at up to 2400W. (You can also get outlets rated for higher currents - they have a larger earth pin). However, US outlets are rated at 15A meaning that they can only power appliances at up to 1800W.
.......................................................................

While not as common as 15A receptacles, 15/20A receptacles are seen in kitchens, bathrooms & laundry rooms. That would be a 2400W max.

 

[DuvalHMFIC]

One of the things I've had to do a lot over the years as a fitness repair tech is to wire a dedicated 20 amp circuit to power treadmills in people's homes. So the US certainly has the capability for 20 amps at the outlet, it's just not common.

Oh yeah-I see Speedskater just addressed this.

 

[bruto]

One of the problems, though, is that one cannot always tell whether a 20 amp circuit and outlet are correctly done. There's nothing to prevent putting a 20 amp receptacle on a 15 amp circuit, and nothing to prevent putting a 15 amp receptacle on a 20 amp circuit. These days many houses are wired with 20 amp outlets and circuits, some simply to allow more outlets on a circuit, rather than to allow higher-amperage outlets.

If you can't see the cable, you have to trust that wiring has been done correctly, and that, for example, amateur maintenance has not resulted in the wrong outlets.

My current house, for example, has a mishmash of wiring covering a period of nearly a hundred years (th0ugh thankfully all the knob-and-tube wires have been superseded), and one must assume a circuit is 15 amp unless it's one I've put in, but outlets are all sorts, not all correct. Rather than rewire or replace, I just test and label, but it's not great. I've also seen new construction in which the wrong combinations were used, grounds omitted, outlets mis-wired, and so forth.

I heartily recommend that anyone dealing with unknown new wiring buy one of the cheap little outlet testers. You can buy a little gadget that plugs into an outlet and lights different lights to identify if it's correct.

 

[DuvalHMFIC]

I don't disagree about checking....but even if you have a 15 amp receptacle, it should be wired with 12 gauge wire, and still able to safely deliver 20 amps. This is where you need to make it dedicated, though, so that it is no longer sharing a breaker with other outlets.

Your 15 amp receptacles all come from 20 amp breakers, but there are usually several together since most objects don't require a high ampacity.

 

[bruto]

I don't disagree about checking....but even if you have a 15 amp receptacle, it should be wired with 12 gauge wire, and still able to safely deliver 20 amps. This is where you need to make it dedicated, though, so that it is no longer sharing a breaker with other outlets.

Your 15 amp receptacles all come from 20 amp breakers, but there are usually several together since most objects don't require a high ampacity.

Yes, but I'm presuming that one is in a house whose history and age may not be so easily determined. Since current codes and best practices are not retroactive, and as I mention I've seen some pretty disastrous mistakes even in new construction, I'd check.

My wife in a former life lived in a house whose entire electrical system was not grounded. The house was wired by licensed electricians. There was no earth ground at all. It was a log house, with wiring routed through the solid walls, and a couple of switches and lights never worked. Nobody could figure out what was connected to what. I managed at least to prevent her from getting a constant shock from the washing machine when I belatedly installed a ground stake.

My former in-laws had a house built, wired by licensed electricians, and I donated a used refrigerator that had been working just fine for some time. The compressor immediately fried, and fuses blew. It turned out the refrigerator had a small ground fault, which a normal circuit bled off harmlessly, but the kitchen outlets were wired wrong - the hot and neutral reversed.

My current house had some three prong outlets installed on old two-wire ungrounded circuits.

If you have something done watch them do it. Otherwise, test!

 

[BillC]

From what I understand, the household voltage in the USA of 120/130 V was set because the frequency of 60 Hz is more dangerous to humans than the 50 Hz elsewhere. It's closer to the natural heart rate of most humans, and therefore more likely to cause heart problems when shocked.

I'm an electrical transmission engineer, not an electrician, but I have never heard this, and am sceptical that it is the case. 60 Hz is 3600 beats per minute, or 7200 bpm if direction is unimportant. I doubt that corresponds to anything going on in the body.


ETA: I see this is already covered, and that the difference is attributed to the much more likely 'historical accident'. At higher frequency, losses are slightly higher, but physical equipment can be made smaller, which is an advantage in some contexts.

 

[lauwersw]

One of the problems, though, is that one cannot always tell whether a 20 amp circuit and outlet are correctly done. There's nothing to prevent putting a 20 amp receptacle on a 15 amp circuit, and nothing to prevent putting a 15 amp receptacle on a 20 amp circuit. These days many houses are wired with 20 amp outlets and circuits, some simply to allow more outlets on a circuit, rather than to allow higher-amperage outlets.

That's why here in Belgium ALL outlets need mandatory 20 A wiring (2.5mm2) and fuses. Lights can on 16A (1.5mm2) wiring. It's allowed to mix lights and outlets, but then all wiring must be rated for 20A. No mix ups possible that way.

 

[psionl0]

While not as common as 15A receptacles, 15/20A receptacles are seen in kitchens, bathrooms & laundry rooms. That would be a 2400W max.

Are they 120V outlets or 240V? I understand that washing machines and airconditioning in particular operate on 240V.

My old house had a 240V 15A outlet wired on its own separate fuse for the air conditioner. It had a larger than normal earth pin. You could still plug ordinary devices into them but you couldn't plug the air conditioner into an ordinary outlet.

This still doesn't address the question of kettles and portable heaters. These are typically rated at in excess of 2000W here. You couldn't plug a 120V appliance like that in an ordinary US socket without overloading it.