| If you live in certain apartment or condo complexes in the US, you | might be stuck with 208/120 volt service instead of the traditional | split-phase 240/120 volt service common to single family houses. (The | 208 V. transformer secondary voltage is the result of a more | economical 3-phase wye connection scheme available in urban areas that | balances the load to a three-phase primary.) The upside of the | 208/120 service is that 3-phase power is available for elevators, | pumps, etc.
I'd rather see them run the "big stuff" on 480/277 or even 600/347. If it needs some "umph" to go, it could use some 480 or 600.
Then put in 3 transformers to drop 480 or 600 down to 120/240 and divide the place up into 3 roughly equal sections. All the out of reach HID security lighting could be run directly on 277, 347, 480, or 600.
The utility might not like the extra transformers involved, though. OTOH, some very large buildings do have transformers at various levels. I know the college dorm I lived in for a couple years had a transformer closet every 3 floors (and the lock on the door was NOT a part of the building master key system). I have no idea what the supply voltage was (whether it was 600 volt class or higher). But I do know the elevators were supplied by 480/277.
| Just how readily available are electric dryers, for example, that | operate on full-power at 208V instead of 240 V? | | I am aware that you can operate a 240V dryer on 208V, but the heating | element will operate at 20% less capacity than at the higher voltage. | The dryer is likely to run longer to get the clothes to dry.
Not accounting for resistance change due to temperature, at 208 volts there would be only 75% of the power used. So that would mean a 25% reduction. But at the lower temperature, the element would draw a bit more current since it would have slightly less resistance. But is that effect enough to put this in the 20% range? I don't have the formulas to figure that out. Is that where you get "20%"?
| Googling around, I found that there are some dryers that can be | ordered full power (lower resistance) at 208 V. (One source says that | this is illegal or at least highly discouraged in Canada).
You can get replacement heating elements designed for 208 volts for many models of dryers, stoves, water heaters, and I presume also for central heating systems. I don't know how well that addresses the increased current that would be drawn.
But see below.
| I can understand that if you move your 208 V. dryer to a new home and | put it on a 240 V. circuit, you may have a serious overheating | problem.
Maybe. If the heating is thermostatically controlled, especially with solid state switching at a fast rate, it should be possible to have an element that handles a wide voltage range.
My current kitchen stove has cooktop and oven elements that even at the highest settings are not on more than about 2/3 of the time. It seems to me they could handle 208 volts by being on for a longer time.
Keep in mind that although an element designed for 208 volts would draw more current than one designed for 240 volts, when used at the design voltage, to produce the same heat, one that is thermostatically controlled would not matter so much. While it would have a higher current at the higher voltage and a lower current at the lower voltage to achieve the same heating, the heating effect on the wiring that supplies it, and on the thermal element in the breaker that protects that wiring, would follow the same pattern on average. It just needs to switch on and off fast enough to avoid heat surges. For a range of voltage from 208 to 240, on and off every 10 seconds or so could be enough.
| In general, I didn't find a lot of specific information on the | Internet that addresses this concern about the difference in voltage. | | When these multi-unit buildings are constructed, do the developers | actually specify and insist on 208 V. appliances or do they just | install the more common 240 units and hope that no one notices or | complains?
Apparently the latter happens a lot. But do not assume malice where mere incompetence can explain it. The developers might well not even know the issue at all.
If I were developing a large building for residential purposes like that, though, I would be fighting to get normal genuine 120/240 in each unit.
| Finally, is it the same deal for electric ranges that are connected to | 208/120 instead of 240/120 voltage? Are there full power 208 models | that are readily available?
Absolutely yes, at least for older stuff (see above).
My grandfather managed to get three phase power for his wood shop. But he made the mistake of getting it all on a single drop (the wood shop was a detached building, though not as easily reached by an overhead service drop). Apparently it was 208/120 wye/star, instead of 120/240 center tapped delta. It was well known that the stove and electric water heater were always "slow". The A/C worked, but was especially sensitive to brownouts. The house was built around 1956.