Why choose 120 volts?

Wed May 27 13:28:13 UTC 2009

The early problems with distance transmission of DC really didn't have
anything to do with the inherent properties of DC current, but with
the fact that, at the time, there was no good way to convert DC
voltages up and down in a similar fashion to the function performed by
transformers with AC.

The inability to step DC up to high voltage for distant transmission
was the real killer for early use of DC.  Lately, very high voltage DC
is actually a better performer than AC for some long distance
transmission situations.  In particular, DC can be used to move power
between unsynchronized grids without the usual problems, and to
transmit power through undersea cables, where AC capacitance losses
would add up.  See:

http://en.wikipedia.org/wiki/High-voltage_direct_current#Advantages_of_HVDC_over_AC_transmission

The main thing that has changed since the early days is that much
better semiconductors are available to make the voltage conversion
feasible...

-Dorn

2009/5/27 Brian Raaen <braaen at zcorum.com>:
> As a Holder of two different FCC licenses I can tell you voltage is not
> what kills, it is amps and location that kill. Actually in certain cases
> as long at you have good electrical isolation, high enough dielectric
> breakdown voltage, and good grounding higher voltages can be safer and
> more efficient. Also, Thomas Edison was the one that discovered that
> trying to deliver DC more than a few feet was not a good idea.
>
> --
> -----------------
> Brian Raaen
> Network Engineer
> email: /braaen at zcorum.com/ <mailto:braaen at zcorum.com>
> FCC GROL (General Radiotelephone Operators License)
> FCC Amateur Extra Class KG4CXN (Also certified volunteer examiner with
> CAVAC and ARRL)
>
> Alex H. Ryu wrote:
>> Also, adding followings.
>>
>> 5) availability from local power provider(s)
>>
>> 6) local regulation such as fire department safety rules...
>>
>> 7) for your own safety... (120V may not kill people, but 240V can do...)
>>
>>
>> If you want better, why not just have everything to DC power ?
>> Something like 48V...
>>
>> Alex
>>
>>
>> Wayne E. Bouchard wrote:
>>
>>> 1) Equipment used to not be dual voltage
>>>
>>> 2) For smaller scale, 120V UPS and distribution equipment is usually
>>> cheaper
>>>
>>> 3) 120V embedded itself into operations as a result.
>>>
>>> 4) We're all lazy and hate change.
>>>
>>> On Tue, May 26, 2009 at 12:39:10PM -0700, Seth Mattinen wrote:
>>>
>>>
>>>> I have a pure curiosity question for the NANOG crowd here. If you run
>>>> your facility/datacenter/cage/rack on 120 volts, why?
>>>>
>>>> I've been running my facility at 208 for years because I can get away
>>>> with lower amperage circuits. I'm curious about the reasons for using
>>>> high-amp 120 volt circuits to drive racks of equipment instead of
>>>> low-amp 208 or 240 volt circuits.
>>>>
>>>> ~Seth
>>>>
>>>>
>>> ---
>>> Wayne Bouchard
>>> web at typo.org
>>> Network Dude
>>> http://www.typo.org/~web/
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>