120/208 Y is a very advantageous setup to have if your loads are not large and you also can benefit from having 3 phase. There is no wild leg to be concerned with and you only need one service panel. Sure, in some cases you may need to up your wire gage to account for the reduced voltage but this would be far less than the cost of a seperate panel for your 3 phase loads.
I've seen house power stated as 110, 115, 117, and 120 volt. Ive seen three phase motors marked 440, 460 and 480 volt. However according to my Electric supplier, PPL Corp. (Allentown PA) Power is supplied at
120, 208, 240, 277, or 480 volt all of which are +/- 5%.
Where did all these other numbers come from, or in some parts of the US can you actually get 110V residential or 440Volt 3 phase power?
My shop is right at the +5% limit. 126, 251V (my meter is not true RMS)
The 120 and 240 are the nominal supplied single phase configurations. The 208, 277, and 480 volt figures are all various 3 phase configurations.
In the 'old days', the nominal line voltage was 110 volts, 220 volts, and 440 volts depending on the service. The power companies discovered they could get more power (watts) through the same wires with higher voltage. This has led to voltage creep over the last century or so. This is where you get your "110, 115, 117, and 120 volt" figures. Currently, my residential line comes in at a pretty consistent 123 or 124 volts.
During heavy load conditions (heat wave and air conditioner load), you will get voltage sag so your power co may deliver 126 volts in the early morning, 114 volts in the afternoon, and still be in tolerance. Some older systems may allow the sag to get below 110 volts, that starts to cause motor overheating.
The guys working 2nd shift in our weld shop doing fussy work on thin tubes during the summer would be constantly readjusting their machines as the voltage levels rose from the peak system load time of around 4 pm to light loading at midnight.
So, I would guess this was an increase by the power co's at the primary voltage level and secondary voltages just went up accordingly. Back in the 80's I worked at AT&T in Allentown PA and at about 3:30 in the morning there was a big explosion on the lower floor. Turned out to be some type of suge arrestor. They changed out every one of them in the plant, when I checked them out (there was a dumpster full) they were marked 9800 volt max, the plant was fed with 12,470 volts. some time in the past the voltage was upped and nobody noticed the little details, took years to fail........
The small percentages are a voltage creep over the years. Your example is more like a major upgrade to the lines and someone forgot to make ALL the necessary changes.
In rural areas it was common to have the feeder lines running at 4100 volts, then to the step down transformer in the farm yard. These got bumped to the current 8KV that we usually see. A lot of transformers went to the scrap yard on that changeover.
I never realized there was a powder charge involved, or that the intention is to blow out the arc. It definitely makes sense. I've been there for a few "moments of truth" when the primary splice is put to the test...
Can't say, That was the sticker on the side of the conduit and on the switchgear. The arestors were connected to ground, not phase to phase, so maybe is was just age, not overvoltage that caused one to fail. Never saw what was put in, just the dumpster full of old one's.
And it also gives them more of a cushion for voltage sag before they get into the 'damaging customer equipment' territory. I'd much rather have it come in a little hot than a little low.
Oh, and a "True RMS" DVM will read a bit higher than an old 6" panel meter at the substation that traces it's roots to a Simpson 260.
Depends on whether that switchgear belonged to the utility or to AT&T. The utilities are pretty good on noticing and correcting those little details, but some Pointy Haired Boss at AT&T might have deleted the line item for replacement arrestors figuring 'it's not critical.'
Amazing thing that Utilities noticed when usage grows, if you double the voltage you cut the current in half - or double the capacity on the same lead. And all you have to do is change out the insulators to handle the higher voltage and make sure you have sufficient clearance, the wire stays the same. Lots of distribution lines were bumped from
2,400V to 4,800V, 9,600V to 34,500V...
The replacement might have been prompted by fine print on the surge arrestor label that said something like "Mfg Date Apr-1952, Replace by Apr-1972" and this was 1988. Oops...
There are some high-voltage switches and circuit breakers that use SF6 gas (sulfur hexaflouride?) to blow out the internal arc. If the gas has leaked out over time it's not the arc that blows out, it's the whole breaker - and rather violently at that.
Moral: If it has a "freshness date", or even a production date, there's usually a reason.
The sulfur hexaflouride gas in SF6 breakers is pressurized to a few hundred psi. They all have a pressure sensor or switch that prevents opening the breaker unless a minimum pressure is present. In medium voltage breakers, the gas does not blow out the arc, it is merely present in the chamber where the contacts part. It is extremely resistant to ionization and has a high heat capacity, all of which help to suppress the arc formed between the contacts in a few cycles.
Lately Ive been unable to use the VFD on my Gorton MasterMill...single phase 220 coming into the property has been running at 245 volts. The vfd shows an over voltage condition and refuses to start up. A call to PG&Es office brought out a tech, who measured, shrugged and said that was "normal" in my area.
Im about ready to stick in a buck boost.... the bastards......