For these reasons this method has long been non-compliant, and should not be used.Īnother common requirement is to allow one or more lamps to be switched by multiple PIR sensors, say for example automatically turning a a driveway lamp on when approached from both ends of the drive. It also feeds line and neutral to the poles of a switch, and switches do mechanically fail, creating the risk of a short. This approach will with some switch settings leave both terminals of the lamp holder "live" even when the lamp is not lit, creating a shock risk for someone changing a bulb. Thus, depending on the switch settings the lamp can see either 2 neutrals, 2 lines, or one of each. Power is fed to the circuit in the same way, however the lamp is connected between the COM terminals of the pair of two way switches. Its called the Carter system (other names are also used).īoth the standard and alternative variations can be configured as a Carter system. Sometimes two way switched circuits are more likely to give rise to occasional flashing problems when used with low power CFL or LED lamps.Īnother two way switching method exists and is occasionally encountered. Needless to say this practice will cause unexpected trips when a modern consumer unit incorporating multiple RCDs or RCBOs is installed. upstairs lamp powered from the downstairs circuit and vice versa), also the not uncommon practice of "borrowing" a neutral connection from a circuit other than the one providing the line connection. They are included here as they are often encountered in older wiring.Ĭaution: Something to watch out for on circuits wired in this way, is lamps being powered from unexpected circuits (e.g. The alternative circuits appear to require one less wire but in reality it is usually necessary to return the COM connection at the second switch position to the first switch or the rose or light fitting which typically needs a wire. It is also less likely to cause interference problems with electronic systems (the example given in the electrical regulations is inductive hearing loop systems but similar considerations apply to computer networks and other wired systems).Ĭaution: Two way light switches in this switching arrangement will carry live wires from two independent circuits. that feeding other lights on the same storey). The first example given in each case is the preferred connection method, as it ensures the light is powered from the expected circuit (i.e. This is an alternative deprecated form (see above for the reasons) of the multi way switch wiring: Any number of intermediate crossover switches may be added to give three or more switching positions.Īlternative method of Three Way Switching.The switches at each end are 1 pole 2 way switches. In fact any number of intermediate switches can be added, to add as many extra switching positions as required.Īn application of above using multiple switching positions to switch multiple lamps: The addition of an "intermediate" cross over switch allows a two way switched lamp to be controlled from a third position. This can cause interference with inductive loop hearing aid systems for example. This is not only dangerous, but often incompatible with RCD protected circuits.Īnother failing of this layout is that it may generate additional electrical interference and "noise" since the current flow in the link cable between switches is unidirectional (most circuit cables have currents flowing in opposing directions in their separate wires). One potential problem here is where the two switches are in locations covered by different circuits, you may end up with a live feed on one circuit connected to a neutral on a different circuit. This method is also sometimes seen, although its use is deprecated since live and neutral are connected at two different locations. In the above diagram, the black core of the 3&E has been connected to the COM terminal, and the Brown to L1 and the Grey to L2. Two way switches usually have terminals marked COM, L1 and L2. (in the above example the landing light would be switched off, and the hall light would be on) An implementation that allows both lights to be controlled from both locations could look like this: To achieve two way control the usual single switch is replaced with one of the following circuits:Ī typical application is that of being able to switch the hall and landing lights on and off from both upstairs and downstairs. Some manufacturers (especially Hager) put an additional, insulated terminal in the switch, which can be used for looping through the Neutral. NOTE many single way switches will have a space for the L2 terminal, even though it is not fitted since the same plastic casing is usually used for both types. The terminals on a dual gang two way switch
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