keithkyll said:
Yes it is.
Look out the back door at the wires on the pole. There's 3. That's 3 phases. That's all you get from the power company. Two of the 3 legs are used to send single phase to your house.
The center tap ground (neutral) is from a copper rod driven into the earth locally.
If you are talking your house the three conductors on the service drop from the pole are Edison 3 wire.
Here is how it all works.
At the utility substation they bring in 3 phase.
Incoming is let us say 115,000 Volt phase to phase (primary distribution).
They will often reduce this to secondary distribution say 12,500 phase to phase 3 phase.
FOR COMMERCIAL
GOING OUT they go with the 12.5 to commercial at the service drop they put in a transformer 12.5 primary to say 480 secondary withe the secondary connected wye. They run a 4 conductor drop 3 hots and the common from all 3 phases (also called star point)
AT CUSTOMER SERVICE
3 phases are connected to the hots and the common to the neutral bus. The common can now be called the
neutral (GROUNDED CONDUCTOR) and is BONDED to the ground electrode system consisting of ground rods and or a water pipe. It is white or gray, at ground potential, carries current ie the imbalance between the phases.
This is also where the GROUNDING CONDUCTOR is derived. It is green, is at ground potential and normally carries no current
Both teh neutral white (GROUNDED) and ground (green) GROUNDING are often connected to the same bus ie neutral buss.
The three hots ie phases A B and C are often color coded in order Brown Orange Yellow between any two you will have 480.
Between any phase (Brown Orange or YEllow and the Neutral (GROUNDED Conductor) you will have 277.
Between neutral and ground you should have no potential but there may be some say 2 to 5 volt
and you should always have a fairly low resistance say 2 to 5 ohms.
The same is for 208 / 120 4 wire wye except the commonly colors for phases are Black Red Blue.
Now then for residential
SUBSTATION brings out two legs of 12,5 to the neighborhood. AT your house they put in the transformer with 12,5 primary and a 240 secondary. The secondary winding is centertapped (common) so that voltage from a leg of 240 to common is 120.
This is Edison 3 wire service.
AT RESIDENCE they bring in the 3 wires. Two connect to the hot bus these are often just black but we will do it right and make one black and other red. The common if done right is phase taped white at the mast head and in the panel. It is connected to the neutral bus. The neutral bus is connect to the ground grid - anything connected to neutral bus is at ground potential.
The neutral (GROUNDED) conductor is white current carrying. It will carry the imbalance of current between the two hots on a 240 load (dryer range etc) or will carry a current equal to the hot on a 120 load.
The ground (GROUNDING) green or bare or green with yellow stipe also connected to the neutral buss (in the main panel ONLY)
IN feeder panels fed by the main panel there is a separate bus for the neutral (GROUNDED current carrying white) this is floated ie not bonded to ground (ONLY in main panel) nor to the enclosure and another for the ground (GROUNDING) green etc non current carrying - this bus is bonded is bonded to the enclosure.
Dan Bentler