Why it's Generally a Bad Idea:
* Increased Risk of Short Circuit: If the insulation on the phase wire fails, it could come into contact with the neutral wire inside the conduit. This would create a direct short circuit, potentially causing a fire or electrocution.
* Increased Risk of Ground Fault: If a ground fault occurs (e.g., a live wire comes in contact with a metal surface), the fault current will flow through the neutral wire. Having phase and neutral together increases the likelihood of this fault current reaching the neutral wire and potentially creating a hazardous condition.
* Interference: Having the phase and neutral wires close together can lead to electromagnetic interference, which can disrupt the operation of sensitive electronic devices.
Why It's Allowed in MWBCs:
* Code Compliance: The National Electrical Code (NEC) allows for phase and neutral wires to be grouped together in a metal conduit only when they are part of a multi-wire branch circuit. This circuit type has specific requirements:
* Shared Neutral: Both hot wires share the same neutral wire.
* Balanced Loads: The loads connected to each hot wire should be roughly equal to prevent overloading the shared neutral.
* Proper Grounding: The neutral wire must be grounded at the electrical panel.
Important Note:
Even in MWBCs, it's crucial to ensure the wires are properly insulated and there are no potential points of contact between them. It's also a good practice to use conduit that is rated for the specific voltage and current of the circuit.
In summary:
While there are exceptions in specific circumstances, it's generally not safe to run phase and neutral wires together in a metal conduit. This practice increases the risk of short circuits, ground faults, and interference. Always refer to the National Electrical Code (NEC) for specific wiring requirements.
