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Old 10th May 2012, 05:16 PM   #11
AndrewT is offline AndrewT  Scotland
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I have seen numerous posts claiming that North America does not use the 3phase system and that they have a split phase system.
Poppycock.

Look outside at the cables strewn across the country. They are in groups of three for the three phases. Just like everywhere else that uses a 3phase system.
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Old 10th May 2012, 05:22 PM   #12
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North America does use the 3 phase system. We also use the split phase system.
The split phase system also requires three wires. 120, neutral, 120.
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Old 10th May 2012, 05:24 PM   #13
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The Crown MacroTech 10,000 used 3-phase power input. Output was low, like 1/2 ohm, recommending 0-guage speaker wire. Used them at the Indianapolis Speedway if I'm not mistaken? Some of the high-power audio-range class-d 3-channel amps from Techron division also used 3-phase input, but those were moslty used for MRIs. So if you find someone scrapping an old MRI, grab the 3 power amps for your subwoofers!
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Old 10th May 2012, 05:26 PM   #14
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We've had discussions on this beast and it's bigger brother several times here. You remember? Both feature 3 phase power supply as standard.

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Old 10th May 2012, 05:40 PM   #15
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A company I sometimes work for supplies a large piece of film equipment all over the world including North America. We don`t change the voltage rating for 110 volts (the current would be too great), the customer just runs it across the two phases and it works fine.

Last edited by barrymagrec; 10th May 2012 at 05:54 PM. Reason: spelling
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Old 10th May 2012, 05:51 PM   #16
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by AndrewT View Post
Look outside at the cables strewn across the country. They are in groups of three for the three phases. Just like everywhere else that uses a 3phase system.
But only one phase is available in any given house. They're not going to put 3 transformers up on the pole just for me - unless I'm planning to spend more than $1000 a month on electricity.
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Old 10th May 2012, 07:26 PM   #17
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Wow, how this audio forum continues to degrade when power systems are discussed. Bring up isolation transformers, and hang on for the ride.

In the US, setting aside HVDC transmission, which is irrelevant in this discussion, all power is generated with three phase generators, stepped up with 3p xfmrs, carried over 3p transmission lines, stepped down with 3p xfmrs, and distributed with 3 phase distribution lines.

Typical 3p distribution voltages range between 24.9 kV (line-line) and 8.32 kV. Normally, the utility has a grounded wye secondary at these voltages; ungrounded or high impedance systems exist, but are either being phased out or are unique and rare. The 'neutral' conductor is carried through and grounded often at regular intervals. This helps with ground fault sensitivity.

Commercial installations will use a 3p transformer to provide 3p service at less than 600V. Some regions of the US also allow primary rate customers who own their own step-down.

Residential customers are provided with split single phase, ALMOST WITHOUT EXCEPTION. The utility provides a single phase transformer and connects it up to the 3p system, normally line-ground (another reason why the neutral is carried through). This is the most cost effective way to provide single phase; yes, they could install a transformer suitable for line-line single phase primary, but the extra bushing adds to the cost. Secondary winding simply has a grounded center tap, 120/240V.

More remote areas will only provide a single 'hot' and a neutral at distribution voltage, supplying all those customers from the same phase. A well designed system will split up these single phase taps equally, such that the overall loading on the 3p line and substation transformer are reasonably balanced.

It is my understanding that across the pond they do it differently, and 3p service to the residence is fairly common. Consider yourselves lucky.

Last edited by zigzagflux; 10th May 2012 at 07:28 PM.
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Old 10th May 2012, 08:29 PM   #18
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The other draw back of 3 phase is that the hum is 3x the basic frequency or 180hz
Or even 360hz
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Old 10th May 2012, 08:45 PM   #19
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Quote:
Originally Posted by myhrrhleine View Post
The other draw back of 3 phase is that the hum is 3x the basic frequency or 180hz
Or even 360hz
If we use a three phase bridge rectifier (six diodes), the resulting hum frequency ist six times the mains frequency, i.e. 300 Hz in Europe or 360 c/s in U.S., respectively. Ripple is only about 14% of peak voltage - even without any filter cap. This is the reason for the relatively low filtering capacitance used in these Philips beasts.

From Wikipedia:

Click the image to open in full size.

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Old 10th May 2012, 11:03 PM   #20
benb is offline benb  United States
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Originally Posted by Arty View Post
This question is bugging me from time to time,
why shouldn't 3 phase powersupply be used for high end audio amplifiers?
Supposedly smoother DC could be achieved, seems quite reasonable.
Might some PA system be using this setup, I'm not realy into those.

Any opinion ?
By "high end" I wonder if you really mean "high power." It seems that's the main reason to use 3-phase in anything.

If you want 3-phase in a (USA) home, there are companies such as this one that make "phase converter" products of many sizes:
Rotary Phase Converter, Static Phase Converter, and CNC Phase Converters - Phase-A-Matic

I can see this for serious home woodworkers with big machinery that use 3-phase motors, but that's all.

For a stereo (or even mono) amp? It seems overkill. The advantage is obvious if 3-phase is easily available, but I don't see where it's a big deal. We got plenty of big enough electrolytic capacitors for 50-60Hz single-phase full-wave power supplies.

It seems the main reason for using 3-phase is for high power, as in motors substantially larger than 1 horsepower, and as others said, 3-phase service is limited to industrial areas where such higher power devices are used.

120V with the usual (in the USA) 30A circuit breaker gives 3.6kW Use one power circuit for each channel, and you can get loud sound with even the most inefficient speakers.
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