Switches and Relays


Switches are devices that regulate the flow of electricity; when open they allow current to flow and when closed they prevent current from flowing. Switches that contain mercury can be used to regulate electricity flow based on changes in pressure, temperature, or position.

Some temperature or pressure sensitive and mechanical switches may contain mercury. Typical examples may be found in the hood and trunk light switches in some cars made before 2000, silent wall switches, garage door openers, clothes dryer lids, microwave ovens, proximity or position sensors found in irons and space heaters, sump pumps and bilge pumps.

The average mercury-containing switch may have as much as three grams of mercury; however, large switches can contain up to 70 grams.

In many cases, non-mercury, electronic alternatives are available.

Useful Information:

Listed below are common types of switches:

Float Switches

Use: Float switches monitor liquid levels. Float switches are most frequently used in sump pumps. They are also found in bilge pumps, boilers, sewage treatment plants, and pumping stations.

Description: Two basic types in use are buoyant floating switching products, activated by rising and falling liquid, and stationary devices, actuated by the lack of or the presence of a liquid (Galligan et al., 2002).

Identification: The mercury will be contained in a cylindrical or global outer casing within the interior in a sealed ampoule. When the device is manually moved, a sloshing sound/movement will be heard or felt. A rolling sound or feel will be a good indication that the device is not mercury but a metal ball.

Mercury content: Mercury content can vary significantly depending on the size of switch. Normally, the content is below 1 gram per switch; however, float switches can have as much as 15 grams per switch.

Alternatives: Mechanical switches may be used to replace mercury switches for most applications. If in doubt, contact the manufacturer regarding mercury alternative availability and practicality. The prices of mechanical float switches are normally similar to mercury-containing float switches.

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