How do you safely wire a single phase circuit from a three phase circuit? Does the load have to balanced?

Answer 1

Assuming the supply has an earthed (grounded) neutral and the voltages match, you can wire your single phase load between one phase and the neutral.

480v phase to phase will give 277v phase to earth (ground)
415v phase to phase will give 240v phase to earth (ground)
208v phase to phase will give 120v phase to earth (ground)

Its a good idea to try and balance the loads on each phase by sharing the single phase loads evenly through the phases. One small single phase load on a supply that has otherwise large 3 phase loads will be fine.

Answer 2

The most common practice is to run one of the legs through the single phase load to the neutral. For example: 240 volt 3 - phase will give you 120 volts from either of two of the legs to neutral, but one of the legs will give you 240 volts (single phase) to neutral. This is called the high leg. It is also possible to obtain 240 volts single phase across any two legs. Grounding the equipment should be used in all cases for safety. If the current draw is well below the supply circuit, unballance should not be an issue.

Answer 3

That you ask this question means that you need to call in an electrician to safely wire the circuit. Trying to step-by-step you through it, I might miss a step due to an assumption you have knowledge which you do not have, or boring you by being too pedantic and having you miss a step.

It's really nice to have a balanced 3-phase load, but not necessary.

Answer 4

First, check the ampacity and current load of each wire; it if can accomodate additional load, shutdown power supply and install the correct breaker rating of your single phase circuit to the line that will most balance the loading of the three phase circuit. Balance load is necessary to maximize the utilization of electrical materials and minimize power losses.