If modern standed outlets can do 240 then why do we still have the big 240 outlets?
Yes, a standard outlet (I’m assuming you’re in the US) could handle 240 volts if you wired it that way, but the electical codes specify that that type of outlet is rated for ~110 volts. We have the 240v outlets for ovens, dryers, etc. which are (by design) different enough that you don’t accidentally plug a 110v appliance into them.
If you’re talking about the US, the large 240 V receptacles are for high-current appliances like electric ranges and heavy-duty driers. They have to be physically large to handle the load without overheating. There are also 240 V receptacles which are about the same size as typical 120 V ones, but with a different plug configuration so you can’t inadvertently confuse the two; these are typically used for smaller 240 V appliances, like large room air conditioners.
A link to the column is appreciated. It’s How come the U.S. uses 120 volt electricity, not 240 like the rest of the world?
The voltage I understand, but why 50 Hz in Europe and 60 Hz in the USA?
A friend told me that many of the old subway and trolley systems used bizarre electrical standards.
I’ve never found a good cite for how we ended up with 60 Hz. When I worked for a power company, an old engineer there said that one of the early test systems was designed to run at 50 Hz but wouldn’t produce enough power for the test, so they cranked the generators up to 60 Hz to get a bit more power out of them.
In the early days, there were a lot of oddball systems with varying voltages and frequencies. Over time, 120 Volt 60 Hz systems became the most popular, and once that became the standard, most of the oddball systems eventually went away. There was an early system at Niagara Falls for example that ran on 25 Hz, and there were some 40 Hz systems as well. The main reasons we all ended up at about 50 or 60 Hz is that frequencies below that starts to have noticable flicker when used with lighting, and frequencies above that have much more noticable hums from things like transformers. I think there is still some 25 Hz equipment running at Niagara Falls, or it may have been only recently retired. You’ll probably still find some oddballs elsewhere in the country as well.
Some of the other theories I’ve heard:
Safety - AC at about 50 or 60 Hz or so is really good at stopping your heart. We really couldn’t have chosen worse frequencies to use from a safety standpoint. Anyone who claims that 50 or 60 is safer is wrong, though. Both are equally good at screwing up your heartbeat.
Clock frequencies - I don’t buy this one either. You can gear a 50 Hz motor to run a clock just as well as you can gear a 60 Hz motor and have them both be equally accurate.
Compatibility with the rotation speeds of existing steam engines - don’t know if this one has any truth to it or not.
There’s also the old English vs. Metric units of measurement. 60 Hz fits in nicely with 60 sec, 60 min, etc. for time, and 50 fits in better with metric style units since it’s half of 100 and metric folks like powers of ten. Make of that what you will.
It’s not a root cause, but it is one reason why it’s tough to change it. Changing the frequency of the power grid would require replacing millions of clocks across the country (among, presumably, many other changes).
Heck, in the 60s, the clock in mainframe computers ran off the line frequency. 50Hz models counted by six and 60Hz models counted by 5, so that either type would look to software as though it were running at 300Hz.
Our Garrard turntable in the 50’s had an international choice of three or four motors, many of which had several jumper options to cover several power supplies. Until this thread, that was the only time I ever heard of 40Hz power.
Note that a change in frequencies has other effects. Televisions used to synch. off it – I don’t know if they still do – and there are differences in power capacity and efficiency. Starting in the very late 60s, many IBM mainframes required 400Hz power; for the more expensive models, you had to purchase a motor-generator unit from Westinghouse or G.E; IBM supplied the less expensive ones.
The original questioner’s premise is also somewhat mistaken. This site shows about 40 countries using electricity ranging from 100-127 volts. Still in the minority, but certainly not unique.
Also, Cecil mentioned that New York is unique in using two legs off a three-phase generator to supply 208 vs. 240 volts. Is this only New York City? I looked at my home’s hookup, and as far as I can tell, we have two legs off a single-phase transformer.
You can find 120/208 residential service in many places in the US, but outside of New York they will be very rare and definately won’t be the “standard” for that power system. The vast majority of homes outside of New York are fed by single phase 120/240.
I thought three phase was a normal arrangement. (See my thread) I am interested in what other countries use a similar system – other than Australia and New Zealand.
Three-phase distribution is the norm in the US, but residential installations generally use a single-phase-fed transformer, called split phase, with a center-tapped secondary to supply individual houses.