[mail box]

In an electrical circuit

[ballengerb1]

Is this a test question on you apprentise testing?

[stanfortyman]

Without getting too technical about transformer phases and such...

In a 120v circuit the current on the neutral is equal to the current on the hot.

A true 240v circuit has only two hots and NO neutral. The current is perfectly balanced on the two hots.

A multi-wire circuit is one with two hots and one neutral. The two hots must be placed on different phases/legs of the panel. This way there is 240v between the two hots.
What happens is if the load is perfectly balanced on the two hots, as in a true 240v circuit, there is 0 current on the neutral. If the load is unbalanced the neutral carries ONLY the amount of imbalance.
Example:
Phase A is carrying 12 amps.
Phase B is carrying 8 amps.
The neutral is carrying 4 amps.

A single phase residential service is just like one big multi-wire circuit. Two hots and a neutral. The service neutral only carries the current imbalance of the two hots.

[Missouri Bound]

Mind if I jump in on this Stan? What happens if the service is 3 phase? How do you calculate the neutral load?

[ohb0b]

Mind if I jump in on this Stan? What happens if the service is 3 phase? How do you calculate the neutral load?

Same principle, only a little more complicated. You balance the load between three phases instead of two, and since the currents are 120 degrees out of phase, you have to add the vectors and the resultant is the unbalanced current.

Please don't make me remember how to add vectors... it has been 30 years since I took trig.

[stanfortyman]

I know right. I could do it if I had to, but I don't want to. LOL.

[stanfortyman]

Here. I cheated. ;)

Calculating Unbalanced Neutral Current in 3p-4w system - Mike Holt's Forum

[tkrussell]

Knowing where to find backup of what you already know is not cheating.

As electricians we rarely care what the neutral current is on a three phase system, as we know that the neutral is to be considered as a current carrying conductor, esp on a multi-wire circuit, and will always use a full size neutral.

When we deal with single phase loads that produce harmonics, we will use a 200% neutral.

Besides we can use power recorders to measure all three live phases and neutral at the same time.