Magnetic Starter - Control Stations

One of the advantages of magnetic starters is the ability to add control stations. These stations may be located at any convenient location and duplicated as required. The maximum number of stations and their location is unlimited for all practical purposes. Stations are built using Normally Closed (STOP) and Normally Open (START) momentary contact switches. These switches must be rated for the control circuit voltage at a minimum. Over-rated switches will work fine. Many manufacturers incorporate both Normally Open (NO) and Normally Closed (NC) contacts in a single switch body. By rewiring the switch you can change it from one to the other. Many manufacturers also provide interchangeable buttons in at least red and green.

The last station must always be provided to complete the circuit. The intermediate stations may be repeated as many times as required. Suitable 3 conductor control wiring is required from the starter to each of the control stations in turn (daisy chained).

Air Compressor or Float Pump/3ph Starter/1ph Motor

Line Voltage Control Magnetic Starter controlled by a air compressor pressure switch (NC). Includes Auto/Hand/Off control and low oil switch (NC). Both of these are optional and may not be present in all applications. In some cases, the switch will include only Auto/Off. The Auto/Hand/Off is sometimes an integral part of a factory pressure switch. Auto allows for unattended, automatic starting of the compressor when the air pressure in the tank falls below the preset limit. Hand (manual control) allows the pump to be turned on regardless of the position of the pressure switch. This may or may not be appropriate for all applications and is shown in the interest of completeness only. Hand should be used with caution and due consideration to what is happening in the circuit. Off is self explanatory. If no low oil switch is present, merely remove it from the circuit and continue the wires from the start switch back to the coil.

Incidentally, the same circuit can be used to power a sump pump. The float switch (NO) for the sump would be connected in place of the pressure switch. When the switch detects liquid, the contacts will close and the pump motor will start - assuming that the Start Switch is in the Auto position. Hand is obviously desirable in a sump pump application as it allows the pump to be activated even if the float switch is not functioning.

3ph Starter/3ph Motor/Reversible

Line Voltage Control - double contactor three phase motor starter controlling a reversible three phase motor (rev 08 Aug 2006) (Note: L1 becomes T3 and L3 becomes T1 when the reverse relay is actuated.) The motor must be STOPPED before REVERSING unless the contactor allows for on-the-fly reversing. The coils are locked out via the NC contacts (M1, M2) usually contained within the mechanical interlock. When Coil #M1 is engaged, Coil #M2 is locked out and vice-versa.

3ph Starter/1ph Motor

Line Voltage Control three phase (3ph) motor starter controlling a single phase motor (rev 08 Aug 2006) Some 3 phase Magnetic Motor Starters require current to be seen across each of the three overloads. This may be accomplished by directing the output of second circuit back into the input of the third (previously unused) circuit and feeding the motor off of the output of the third circuit (rather than the second). Wiring then becomes: Line 1 → L1 → T1 → Motor 1 (L1-hot 240v or neutral 120v) Line 2 → L2 → T2 → L3 → T3 → Motor 2 (L2-hot 120v or 240v)

Manual Starter? Merely ignore the control wiring in RED

Over Load Relay

132/33 kv substation

Earthing