The life of the reed switch is typically 106 - 109 operations, dependent upon load conditions. The special reed blade material is selected to ensure a mechanical life of at least 3 x 109 operations. Contact Protection: The specified value of switching current and/or voltage must never be exceeded, even for very short periods. It is strongly recommended that contact protection be used whenever there are capacitive or inductive loads (long leads and relay loads). High inrush loads caused by filament lamp switching or capacitances may be compensated for by using current limiting resistors. These should limit the current to that acceptable to the reed switch.

Electrical current overload is a common cause of failure for liquid level switches utilizing reed switch technology. Reed switches are rated for a steady-state current. Devices such as motors, solenoids or coils can produce capacitive or inductive electrical loads. When power is applied or removed from these devices, it can produce a current spike from 4 to 10 times the switch's steady-state current. This spike in the current can arc across the contacts of the reed switch, causing the contacts to fuse together or stick. When this occurs, the switch may fail or appear unreliable. To prevent this type of failure, a circuit can be wired in conjunction with the switch to protect it from the current overload caused by capacitive or inductive devices. A resistor/capacitor network or varistor can be used for AC loads, and a diode can be used for DC loads.

When trying to switch loads (capacitive or inductive) that exceed the maximum steady-state current rating of the reed switch (see UL Current & Voltage Rating Chart below), Madison recommends the use of general-purpose/isolation relays or controllers to protect the switch from current overload. This will prevent the contact of the reed switch from fusing together, thereby increasing the lifespan and reliability of the switch. Madison offers the R1 general-purpose DPDT relay for switching simple loads, as well as the R2 controller to perform pump-up or pump-down control when used with at least two levels. Keep in mind that any relay or controller that you use should be rated to handle your supply voltage and have a current rating greater than your maximum supply current.

• Click here to read more about Voltage Ratings.
• Click here to read more about Tank Level control and to view our Wire Color Guide.

Contact Madison today to learn more about our liquid level float switch offerings!