single phase from three phase network voltage drop

----------------------- You won't get 208/120V single phase. The 208V is line to line between phases and the 120V is line to neutral- which can be handled as single phase. This voltage will not be in phase with the line to line voltage. If you have loads from line to line and additional loads from line to neutral (on each phase) then you should be looking at unbalanced 3 phase. A lot depends on your feeder and its independence or lack thereof from other loads. Simply fooling around with factors doesn't make any sense unless you know the basis for the factors.

It is time to actually lay out what you are trying to do and get competent advice locally- it may cost.

Don, I'll get two legs and a neutral from the three phase circuit, that's a single phase feeder. It's done all the time. If I need to connect a

208V single phase load to a 208Y/120V three panel board, I simply connect it with a two pole breaker. Similarly, in a residential environment, the utility supplies 208Y120V three phase but each condo gets 208/120V single phase. Dave

As Don said, it is an unballanced 3 phase feeder. The hots are 120 degreees out of phase.

If it was single phase the voltage would be 240/120 and the hots would be 180 degrees out of phase.

You are only using it for single phase loads, but a hot-hot-neutral connection is not single phase.

bud--

snipped-for-privacy@COMCAST.NET wrote:

Condos and apartments in Phoenix are connected every day like this. A service at 208 3 phase is set, 400, 600, or 800 amps, then the meter sockets are connected single phase to the 3 phase supply. Each apartment has its own utility meter and bill. Utilities do not seem to worry about the imbalance.

Do your calculations at the feeder voltage. At least that is what I would do.

---------- In fact the meter is measuring the power in two phases. The meter may be the same as for 120/240, 3 wire single phase but that doesn't make the supply single phase. The utility takes approximate care of the imbalance by trying to balance the customer connections between phases. Over a reasonable area, the load will be reasonably balanced.

Voltage drop calculations will have to account for the fact that the two legs are 120 degrees apart rather than 180 degrees apart so there will be a difference in neutral current i.e. 1.2 KW ,120V resistive load on each leg will result in a neutral current of 10A whereas with a 120/240 single phase setup, the neutral current in the same case will be 0 - there is a difference If the loads are unbalanced, say 0.6KW on one leg and 1.2 on the other, the neutral current will be 8.7A for the 208/120V system vs 5A for the 120/240V system. Not necessarily a big deal but it does lead to higher voltage drops. So why bother? Easy way to balance a buildings load between the 3 phases and also to provide 3 phase for larger motor loads - it all comes down to economics. - Don Kelly @shawcross.ca remove the X to answer