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What is Intermediate Switch (3-Way in IEC) A.K.A 4-Way Switch in NEC?

4-Way Switch or Intermediate Switch (3-Way) – its Construction, Operation & Applications

What is an Intermediate Switch?

4-Way switch in NEC (also known as 3-way or intermediate switch in IEC following countries) is a very useful switch with four terminals (and optional ground in the US as 4-Way) and commonly used when we need to control a light point (or any other electrical appliances like fan, alarm, in the middle of stair etc.) from three different places. It is used with a combination of two-ways switches to control an appliance from more than two places. In addition, an electric circuit can be controlled from any number of location using intermediate switches (which is known as 3-Way in the UK and 4-Way in the US).

Good to know: Intermediate Switch (3-Way) – IEC is also known as 4-way switch or crossover switch in the US – NEC. The next section will differentiate both of them.

Related Wiring Diagrams:

Construction & Working of Intermediate Switch

In an intermediate switch, there are four terminals by which it changes the flowing of electric current from one circuit to another (see fig 1 & 2) and is also known as Four-Way Switch (Three Way Switch in the UK & EU). It has the ability to ON and OFF the electric supply by two ways or control the single circuit from more than two places.

The four terminals of intermediate switch construction and its operation are shown in fig below where the 4 contact points may be known as A, B, C & D. When the switch knob is up, the terminal contacts of the intermediate switch connect terminal A with terminal C and terminal B with terminal D as shown in fig 1a. On the other hand when knob is down, terminal A is connected to terminal B and C to D then.

What is Intermediate switch, its construction, working principle and uses in different wiring (lighting etc) circuits?
Fig 1: What is Intermediate Switch & How it Works ?

In other words, When the knob of the switch is UP, then the vertical contacts are connected in such a way like AC and BD as shown in fig 1a). And when the knob is DOWN, then the Horizontal contacts are connected (i.e. AB and CD as shown in fig 1b).

Fig 2 shows the basic construction and working of Intermediate switch.

Click image to enlarge

Intermediate Switch or Crossover Switch - 4-Way Switch

There is a little bit confusion about this switch due to regional codes i.e. the same DPDT (double pole, double throw) switch is labeled using different names e.g.

  • UK & EU – IEC = It has 4 terminals for strappers wires to connect to the 2-way switches and known as Intermediate switch & 3-Way switch.
  • US – NEC = It has 4 terminals for travelers wires to connect to the 3-way switches and additional ground terminal and known as 4-Way switch & Crossover switch.

The following figures illustrate the difference (which is not at all) between 3-Way and 4-Way switch.

4-Way Switch - DPDT - US - NEC

Intermediate Switch - 3-Way Switch - DPDT - UK - IEC

The following fig and gif shows how is a 3-way switch or intermediate switch wired with 2-way switches (according to IEC) to control a lamp from 3 places. (Alternatively, a 4-way switch working with 3-way switches to control an LED lamp from three different locations according to NEC)

Click image to enlarge

Crossover or 4-Way Switch - NEC aka 3-Way or Intermediate Switch in IEC

Click image to enlarge

4-Way Switch or Crossover Switch - NEC A.K.A Intermediate Switch (3-Way) - IEC

Here is the short video which shows the working of intermediate (4-Way) switch with 3-Way Switches.

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Application of Intermediate Switch

Intermediate switch is mostly used in large premises & big rooms such as hallway wiring, Hostel wiring, hospital wiring, tunnel wiring, godown wiring & staircase wiring where different lamps are needed to ON/OFF from different places. Moreover, in a multistory building, the lamp at ground floor or in car parking shades can be controlled or ON / OFF from any floor by using an intermediate switch circuit.

How to Control Light Point from Three Places using Intermediate Switch

In Fig 3, a lamp is controlled from three different places by using two, 2-way switches and one intermediate switch.

How to Control a light point from three different places by using two 2 way switches and intermediate switch

Below is the same diagram (Fig 4) to control a light point (lamp) from three different places by using two, two-way switches  and one intermediate switch with different symbols.




The following wiring diagrams show the installation of intermediate switches according to NEC and IEC where a light bulb is controlled from three different locations.

Click image to enlarge

How to Wire 4-Way Switch & Intermediate Switch as 3-Way - IEC & NEC


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Staircase Wiring using Intermediate Switch

Below is a given schematic circuit to control a light point from three different places by using two 2-way switches and an intermediate switch (or two 3-way and one of 4-way switch – US) in the middle of stairs.

Staircase wiring connection using 2 two way switches and intermediate switch
Staircase wiring connection using 2 two way switches and intermediate switch

The following wiring diagrams show the same configurations for both IEC and NEC codes.

How to Wire Intermediate Switch - DPDT or 3-Way Switch

How to Wire 4-Way Switch - DPDT or Crossover Switch

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Controlling of Lamp from Five or Six Places using Intermediate Switch

In fig 5, a lamp is controlled from six different places by using two, 2-way switches and four intermediate switches.

How to control one lamp from six different places

Key Point: You may control a lamp from many different places by adding more intermediate switches such as in the middle of stair or in shared flats (when needed). Also, many other electrical appliances like fans, alarms, machines etc. can be controlled from different places by using an intermediate switch.

Click image to enlarge

How to Control One Light Bulb from Five or Six Different Places - IEC & NEC


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