Mercury switches

The contacts of a mercury switch are hermetically sealed in a glass envelope. Contact wear is, for all practical puposes, non-existent by virtue of the fact that the rupture of current takes place in an atmosphere of specially prepared hydrogen.

Selection of switches
Mercury switches can handle heavier loads and greater surges without contact deterioration than can metal contactors which break in air. They can also operate with a much higher temperature rise than
conventional switching devices. For inductive loads such as motors and transformers, it should be remembered that the peak value of current on switching “on” may be from five to 10 times the final load figure and a larger size switch must be selected according to prevailing conditions of use. For such applications, a switch with a porcelain liner must be used.
The fused-in liner type mercury switch consists of a conventionally shaped tube with bottom or top entry connections. Between the electrodes, a porcelain liner is sealed into the glass tube, becoming one with the glass wall. Such constructions adds greatly to the general mechanical strength of the switch and gives complete arc protection. These switches will withstand 100 per cent momentary overload and surge currents many times their normal rating without risk of damage.
Unlined glass switches are intended only for use on non-inductive AC circuits for voltages not exceeding 250 volts and similar DC circuit voltages not exceeding 50 volts. Never use a plain glass unprotected switch on full line voltage DC. When a very rapid operation is anticipated, choose a switch of ample size and a large cooling area.

The following are the lengths of standard leads fitted to mercury switches, unless specified otherwise.
1 - 10a amp - 150mm         15 - 60 amp - 230mm
For larger switches details are available on application.

All switches may be fitted with the following leads and insulating materials:
Plain copper                                                                      Plain copper, covered with single viscose Rayon
Plain copper, covered with double viscose Rayon            Plain copper, covered with silicone rubber
Plain copper, covered with standard                                 Tinned copper, covered with PVC

Terminal tags are fitted only if specified.

Listed below are some of the standard flexible, plain copper cords available and their current ratings. Unless instructed otherwise, we will select the lead most suitable for a particular rating.
60/002 up to 5amps                        80/002 up to 6amps
4/80/002 up to 13amps                  3/50/002 up to 13amps
3/7/002 up to 30amps                    7/69/002 up to 15amps
4/7/60/002 up to 40amps   

Special applications

As the contacting medium is a fluid, the mercury switch lends itself to the impulsing either each way of tilt, or one way only ie no pulse on return. One or more pulses can be supplied in a single tube and the period can be varied within wide limits by the angle of tilt, length of tube etc.