Staircase wiring circuit diagram & working

Staircase wiring is a common multi-way switching or two-way light switching connection. Here one lamp is controlled by two switches from two different positions. That is to operate the load from separate positions such as above or below the staircase, from inside or outside of a room, or as a two-way bed switch, etc.

The Staircase wiring diagram in a Traveler system or common system method is shown below,

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A Staircase wiring makes the feasibility for the user to turn ON and OFF the load from two switches placed apart from each other.

Staircase wiring circuit arrangement

 The First pole and second pole of the SPDT switch S1 has connected to the corresponding first and second pole of the SPDT switch S2. That is similar poles of both two switches are connected each other.

The phase of the supply line is connected to the common pole of a switch. And the phase line to the load is taken from the common pole of the next switch.  It makes an arrangement that, to close the circuit both the switches should be in the same position in order to make the two common poles in contact to achieve a closed circuit. Changing ON & OFF condition of a single switch can determine whether the circuit is closed or open. Thus in staircase wiring, we can control the load from both positions. If a truth table has made for the above traveler system output, it will have a result similar to an XNOR gate. That is the light ON’s when both the switches are in the same position.

Similarly, if the connections between the switch s1 and s2 have interchanged, the load will ON when the switches have opposite positions

components required

Component specification Quantity
MCB 250V , 50Hz , 5A 1
Switch SPDT , 250V , 5A 2
Lamp 230V 1

Coast 3-way or California 3-way wiring system

Coast 3-way or California 3-way  wiring and Carter wiring system are another method of connection that can be used for staircase wiring or multiway switching.

In Coast 3-way or California 3-way wiring, the first pole of both switches has the phase line. The common pole and second pole of the first switch are connected to the corresponding poles of the second switch. Then the phase connection to the load connects from the second pole. Thus the lamp L1 will ON if one switch is ON and the other is OFF. While in same switch position, the lamp will be OFF. Coast 3-way or California 3-way circuit shows a Truth table output of an XOR gate, i.e. the output will be high when both switches are in opposite states.

Carter wiring system: A prohibited Multiway switching

Carter wiring is a 3-way wiring or a multi-way wiring method used at the time of old K&T (knob-and-tube) installations, which has been prohibited by the NEC (National Electrical Code) since early 90’s.

In Carter wiring, both phase and neutral lines are connected to the switch. One throw of the two SPDT switches have connected to the phase line and other throws in the neutral line. The load or bulb has connected between the common poles of the two SPDT switches.


The light will be OFF when both switches are in the same position. That is, both of the bulb terminals have either phase or neutral. When the switches are flipped to opposite direction, the terminals get opposite polarity and light gets ON.

Unlike from another multi-way switching, the two socket terminals will not have a fixed phase and neutral points. It changes to either phase or neutral, depends on the position of the switch.

The Carter wiring connection is similar to the H-bridge arrangement used in DC circuits. That is used to alternate the polarity across the load.

When the switch position has flipped to phase at both the switches, even though the bulb does not light, the socket may be charged at both of its terminals. Thus in this wiring system, we can’t even replace a bulb by just turn off the light. Because we can’t predict whether the socket is de-energized or not. During maintenance, a complete isolation of supply line cannot be guaranteed by a switch off. Because we can’t make sure it is in a neutral position at both poles. So we should have to either turn off the main switch or use a tester to ensure an open terminal.

Due to safety issues and high risk of electric shock, the Carter wiring is no longer recommended.

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3 Responses

  1. Neel says:

    Very conceptual! Thank you.

  2. vellaichamy says:

    Thank you sir

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