Also referred to as the breakdown voltage or dielectric strength, this is the minimum voltage that can be applied between any of the device’s selected pins before breakdown occurs.

These ‘selected device pins’ are typically those connected to the device’s switch. However, the standoff voltage is also the dielectric strength between the pins connected to the reed switch and the pins connected to the coil.

In a high voltage reed relay, the standoff voltage (and switching voltage) is primarily determined by the size of the contact gap and the quality of the vacuum. Regarding the latter, a perfect vacuum is very difficult to achieve, but high-grade switch manufacturers can get close. The further away from being a true vacuum, the more gas atoms/molecules will be present in the tube. These can be electrostatically attracted to the contact gap as the voltage increases and then provide a path for the voltage to cross.

In addition, the quality of the plating on the blades can be an issue. The plating material can outgas slightly, which can cause the standoff voltage to degrade slightly over time.

For this reason, it is always good practice not to use a high voltage reed relay close to its rated standoff voltage. Always allow a margin.

Note: Pickering reed relays are tested to between 500 and 1000V above the ratings given on the datasheets. Even so, we urge users to operate comfortably below the specified standoff voltage.

If you would like advice on this or any of the other issues discussed above, please contact us.