[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

[Peter Gottlieb]

Have a test set here (RF field signal strength meter/receiver) which uses four wet lead acid cells. There is a rheostat to set filament voltage. 

Residential power in the US is generally 240 center tapped with the center tied to ground. Many apartment buildings are fed from 3 phase 120/208 Wye using two of the phases so big appliances like dryers and ovens run at lower power. Con Ed in NY runs an oddball setup with a Delta connection with one leg grounded so you are actually getting 3 phase in those circumstances ( again, not residential except for apartment buildings). 

Most common industrial is 480/277 Wye grounded neutral. Larger facilities are "primary metered" at 13.8 kV and get better rates as the company bought and maintains MV switchgear and transformers. 

What is interesting is how much the ground potential can shift between substations during a fault condition. With modern high power setups the older non-isolated copper circuits couldn't withstand the normal fault scenarios without damage. 


Peter

On Nov 22, 2012, at 9:37 PM, WA5CAB at cs.com wrote:

> I don't recall ever checking on why 5V or 3.3 V were used for logic but always assumed it was at least in part because of inherent voltage ratings of the components and/or was enough lower than 6.3 VDC to allow a regulator to operate properly.
> 
> And the 50/60 cps subject has been beaten enough today so I won't add any comment.
> 
> 6.3V (and 12.6 V and 25.2V) for tube filaments is a result of the characteristics of the lead-acid cell and the fact that early automotive systems were nominally 6 VDC (then 12, then 24) (with engine off of course).  The fully charged voltage of a lead-acid cell (after removal of the surface charge by a slight discharge) is 2.1 VDC.  Three cells in series yields 6.3 VDC and the heavy use in automotive applications made the batteries readily available for battery operated radios (farm sets, and the like).  As the AC operated sets had no particular technical reason (consumer stuff, anyway) to prefer a different voltage, 6.3 volt filaments became common.  
> 
> On the 120/220 VAC question, there never has been a system with those nominal voltages, whether single or 3-phase.  The standards over the years have been 110/220, 115/230, 117/234 and 120/240 for single phase.  Because the standard single phase pole pig has a center-tapped secondary and you can't get 220 volts line to line if the line to CT is 120.  The most common (probably) low voltage 3-phase system is currently 120/208 wye.
> 
> In a message dated 11/22/2012 18:18:10 PM Central Standard Time, 1oldlens1 at ix.netcom.com writes: 
>> 
>> ----- Original Message ----- 
>> From: "Keith Lueck" <kwlueck at swbell.net>
>> To: <notbago at yahoogroups.com>; 
>> <i3detroit-public at googlegroups.com>; <acti at provide.net>
>> Cc: <Greenkeys at mailman.qth.net>
>> Sent: Wednesday, November 21, 2012 12:57 PM
>> Subject: Re: [GreenKeys] History - Why voltages and 
>> frequencies are chosen(5v &3.3v logic, 6.3v filaments, 
>> 120/220 VAC, 50/60Hz etc)
> 
> 
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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