Neutral Conductor. The conductor connected to the neu-tral point of a system that is intended to carry current under normal conditions.
Neutral Point. The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.
Informational Note: At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point, is zero potential.
This is the best answer really. In days gone by we in the industrial business used more of what is called “common control”, meaning your control circuit voltage was common to the line voltage, ie 480V coils on devices. In that case, none of the control wires were “neutral”, but one of them was always used as a “common” in order to follow the conventional wisdom for the next guy looking at it, the way Russs57 just described it. This convention was laid out in a set of standards called “JIC” (Joint Industry Council) during the boom of the automotive industry after WWI. The old JIC standards later became NFPA 79 and still apply to industrial controls. So all control circuits must have a common side and IF the control circuit uses a neutral, that is supposed to be the common side.The simple answer is that common is the lead that is common to all devices from the same control voltage source. It has no contacts, switches, etc between it and loads. It is run to one side of all devices. It is often grounded (but you should never assume it is). In most ladder diagrams it is the vertical line on the right hand side.
But this is a very simplified answer. For example, cars often switch the negative lead and it is often called the common.
Maybe to make sure they're not accidentally bypassed, disconnected, or otherwise mis-wired while the control wiring is connected.The only caveat is that on NEMA designed motor starters, the OL relay trip contact is always on the common side of the starter coil (neutral or not), for reasons that are now mostly historical.
The simple answer is that common is the lead that is common to all devices from the same control voltage source. It has no contacts, switches, etc between it and loads. It is run to one side of all devices. It is often grounded (but you should never assume it is). In most ladder diagrams it is the vertical line on the right hand side.
But this is a very simplified answer. For example, cars often switch the negative lead and it is often called the common.
I had a question about control wiring. When referring to the common wire, is that always the neutral? ...