You're asking about electrical wiring, and it's important to be very careful with this topic! Improper wiring can lead to serious safety hazards, including electrical shock and fire.

Here's what's important to understand:

* Neutral is essential: The neutral wire is a crucial part of a 3-phase system. It carries the return current back to the source, completing the circuit. Without a neutral, you cannot have a functional circuit.

* Sharing neutral between phases is generally not safe: Directly connecting the neutral wire to any of the phase wires (120, 208, or 240 volts) will create a dangerous short circuit. This can damage equipment, cause a fire, and potentially result in electrocution.

* The 135-degree rule: This rule applies specifically to single-phase loads on a 3-phase system. It dictates that the neutral wire should be connected to the center point of the phase conductors in a 135-degree configuration. This configuration is designed to minimize the imbalance of current flow between the phases.

In summary:

* You cannot share a neutral wire with any phase on a 3-phase system. This will create a short circuit and is extremely dangerous.

* The 135-degree rule applies to single-phase loads on a 3-phase system and helps balance current flow.

Please consult a qualified electrician for any electrical work. They have the expertise to ensure your wiring is done safely and according to code.