What component was used in early AC door operators to limit voltage?

In early AC door operators, resistance was commonly used to limit voltage. This is largely due to its simplicity and effectiveness in controlling the current passing through the circuit. By introducing resistance into the system, the voltage across the door operator components could be reduced, helping to ensure that the machinery operated within safe limits. This method effectively prevents overload and reduces the risk of damage to the electrical components.

Other components, while they have applications in electrical systems, were not typically used for voltage limiting in early AC door operators. Capacitors primarily store and release electrical energy, transistors serve as switches or amplifiers in modern applications, and diodes control current flow in one direction but were not the primary method for voltage limiting in these older systems. Thus, resistance stands out as the most appropriate choice for this context.