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Author Topic: 220/120 volt Line or Lines for Shack  (Read 4427 times)
W6RMK
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Posts: 650




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« Reply #45 on: October 24, 2009, 08:31:30 PM »

About the 220 or 230 vs 240 thing...
The voltages in use haven't changed in a long long time, but how they're described has.


These days, the higher is the "supply voltage" (e.g. 120V, 240V, 480V).. the lower is the "utilization" or "load" voltage.. for instance, if you look at the nameplate on a motor, it will almost always be 230V, not 240V.  

That's because they are allowing for the voltage drop in the wiring from feeder (at 240) to load.. 230 is 10V or about 5% lower.

For some strange reason, though, light bulbs have the supply voltage (120V) on them.  It's probably all just tradition.
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W6RMK
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Posts: 650




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« Reply #46 on: October 24, 2009, 08:45:26 PM »

Capacitor input filters (to generate the raw bus for a PWM supply, typically) are why the code was changed 10 or so years ago to require a larger neutral in 3 phase Wye connected (e.g. the 208/120 scheme) systems supplying offices/light industrial. In the "good old days" with resistive loads, they'd just make sure that all phases had about the same load, so the neutral current was small.

But with the very peaky current waveform for a lightly loaded capacitor input filter, the neutral would be overloaded, with the pulses at 6*line frequency (3 each positive, 3 negative).  There are some modular office (cube farm) power distribution systems (with too small neutrals) that had real problems.

Modern switching supplies (especially if they're CE marked) have harmonic content requirements (essentially, you can't have the peaky current waveform).  You can look through things like the Vicor catalog and see the prefilters or active compensators. In the late 90s, the harmonic content requirement was often met with lumped LC filters, which are big, heavy, and expensive.  These days, active circuits are more popular (essentially a PWM switcher on the input that makes the current drawn from the line look sinusoidal).  Either way, it means you've got to have some energy storage to smooth things out.

I haven't looked at the CF lightbulb waveform, but I'll bet that either a)they're not covered by the harmonic content rules or b)they're crummy designs that don't meet specs, but as long as nobody complains before the company goes out of business...
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W6EM
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Posts: 774




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« Reply #47 on: October 26, 2009, 06:36:09 AM »

"The voltages in use haven't changed in a long long time, but how they're described has.


These days, the higher is the "supply voltage" (e.g. 120V, 240V, 480V).. the lower is the "utilization" or "load" voltage.. for instance, if you look at the nameplate on a motor, it will almost always be 230V, not 240V.

That's because they are allowing for the voltage drop in the wiring from feeder (at 240) to load.. 230 is 10V or about 5% lower.

For some strange reason, though, light bulbs have the supply voltage (120V) on them. It's probably all just tradition."

The NEMA utilization rating is 115 and 230.  And, appliances are generally expected to operate properly with a 10% tolerance of those values.  Incandescent lamps can be had with different voltage ratings, primarily with the notion that a higher rating of 130V, for example, will extend their life.  However, the wattage and output is based on the label voltage.

Most utilities use the standard supply voltages of 120, 208, 240, 277 and 480 as their nominal voltages to allow for voltage drop in transformers, secondary wiring, and service drops.  Regulation is at the high voltage level.  Most CA utilities are governed by CPUC Rule 2, and maintain a minimum of 114 volts and a maximum of 126 volts at the service entrance.
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W6EM
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Posts: 774




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« Reply #48 on: October 26, 2009, 07:30:48 AM »

"Capacitor input filters (to generate the raw bus for a PWM supply, typically) are why the code was changed 10 or so years ago to require a larger neutral in 3 phase Wye connected (e.g. the 208/120 scheme) systems supplying offices/light industrial. In the "good old days" with resistive loads, they'd just make sure that all phases had about the same load, so the neutral current was small."

No, it wasn't so much light commercial 120/208 three phase distribution, but because of industrial 480/277 three phase systems with large amounts of variable frequency motor drives.  Many, many kVA of distortion, not a few desk top PCs.

The "old" code allowed reduced neutral sizing for good reason.  If the design was done properly, there was no reason to waste additional investment in a full sized neutral.  Especially in industrial environments when most all of the load was three phase and ineherently balanced motor loads.  That is, before the widespread use of harmonic current generating variable speed drives.

The term "capacitor input filter," as I recollect, has long been used by hams to differentiate a pi-network  capacitor-inductor-capacitor power supply filter from an L-network inductor-capacitor filter.  All power supplies that I know of have filter capacitors.  It seems counterintuitive to use the term unless to make a pi verses L distinction.


"But with the very peaky current waveform for a lightly loaded capacitor input filter, the neutral would be overloaded, with the pulses at 6*line frequency (3 each positive, 3 negative). There are some modular office (cube farm) power distribution systems (with too small neutrals) that had real problems."

Probably not too much so in an office environment with transformer ballasts and air conditioning load that contains no motor speed control.  On the other hand, a rather large data processing center may show considerable neutral load from current distortion even without speed control on three phase HVAC load.  Doubtful it would be enough to overload the neutral as would likely be the case in large structure HVAC systems with variable frequency drives employed on air handlers.

"Modern switching supplies (especially if they're CE marked) have harmonic content requirements (essentially, you can't have the peaky current waveform). You can look through things like the Vicor catalog and see the prefilters or active compensators. In the late 90s, the harmonic content requirement was often met with lumped LC filters, which are big, heavy, and expensive. These days, active circuits are more popular (essentially a PWM switcher on the input that makes the current drawn from the line look sinusoidal). Either way, it means you've got to have some energy storage to smooth things out."

Yes, the key is to make the current envelope look sinusoidal.  But, as I said earlier, PWM motor drive outputs are pulse strings and those are the animals that caused the problem to be recognized in the first place.  Rich in 3rd order harmonics.  Even with PWM inverters, LC filtering is necessary when the problem is huge.  Its filling in the gaps between the pulses that is the problem.

"I haven't looked at the CF lightbulb waveform, but I'll bet that either a)they're not covered by the harmonic content rules or b)they're crummy designs that don't meet specs, but as long as nobody complains before the company goes out of business..."

Probably so.  Finding the company in China might be a fun exercise as well.  The reason I entered the foray here was that JI seems to believe a linear power supply is a huge generator of current distortion.  Its not.  And, again, the use of the term "capacitor input power supply" was taken issue with as we amateurs use the term to differentiate between filter configurations.

You CA hams have a problem facing you.  A state Energy Commission ruling that forces linear supplies out of existence.  Or, at least that was the case a while back.  Any exceptions to the rule?
As is usual, government made a decision without examining all of the consequences.  Are HV supplies going to be given an exception or will those be noise generating switchers as well?  I'd surely not want a switching power supply putting out several kVA to an amplifier sitting in my shack.  Talk about a noise problem.  HF would just about be useless!!!!!

"Wall warts" being left unattended could be a problem, but a better solution would have been a mandated auto disconnect feature if left unloaded.  Insisting on the demise of transformers due to idling current losses is a bit absurd.  CA, love it or leave it.  I left it.......

73.
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AE5NE
Member

Posts: 91




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« Reply #49 on: October 27, 2009, 02:30:09 PM »

A common neutral between two legs of the 240V circuit is fine. This is how 240V power is normally delivered.  If 20A is flowing on Line A and 20A on Line B - there is zero amps on the neutral.
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VK2GWK
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Posts: 196


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« Reply #50 on: October 31, 2009, 05:35:38 AM »

After reading five pages of confusing and contradictory advice about 110 and 220 (or is it 240V)....why the heck has the US not adopted 240V as a standard.... like the rest of the world.....
Can someone - knowledgeable - explain that?
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W8JI
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Posts: 9304


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« Reply #51 on: October 31, 2009, 06:06:28 AM »

The USA has standards for all feeds, but people are sloppy with their terminology. The standard residential USA supply is single phase 120V/240V with +- 5% tolerance. That is 228 to 252 volts. The transformer is a grounded center tap hence the split voltages. It has been 120/240 60Hz single phase since the 1950's.

The typical large home is single phase 200 ampere 240V, smaller homes now range down to 100 amperes. Our typical feeds use a short LV runs from transformer to house, unlike those in your area where a very large transformer might feed several people over several hundred feet.

The problem in this forum is people misunderstand or misspeak.

The correct term for residential service, and there is only one correct term, is 120v/240v. it's been that way since I plugged my first toy train set into an electrical outlet.

Tom
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K8SOR
Member

Posts: 55




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« Reply #52 on: October 31, 2009, 06:11:38 AM »

Well I read all the advice everyone offered.  I've been a ham for almost 50 years, electrician/electronic tech for 40 years.  
You are making something simple into something hard.  
You said "money is no object" for such a small project.
Simple, run a couple 12/2 wg for the 120 volt receps, and a 12/3 wg for the 240v recep.  Use 20 amp single pole breakers for 120v, and a double pole 20a breaker for the 240v.  Some may say that you need larger wire and bigger breakers.  The load will determine the wire and breaker size.  20 amps at 240 volts times 80% is 3840 va or about 3840 watts.  This should run any legal amp made. 80% (Full load continuous should not exceed 80% of breaker and wire ampacity)  2-20 amp 120v circuits will give you another 3840.  
Even in today's high tech world, it's still best to use the old KISS method.  KEEP IT SIMPLE S.....
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