Webster defines coordination as "harmonious combination or interaction". This definition can apply to anything from marriage to the operation of a presidential election-polling location. As we have seen in recent days not all planned events go smoothly, most fail because of lack of coordination between all parties. Surge protection and its relationship to the electrical system is much the same.

When multiple Surge Protective Devices (SPDs) are introduced into an electrical system the devices ultimately alter the transient voltage response characteristics of that system. Installing surge protective devices without regard to coordination can have undesirable consequences. References on this subject are available from the IEEE (Institute of Electrical and Electronics Engineers www.ieee.org)

The most common method for insuring proper coordination of surge protective devices is to use the clamping voltage. Underwriters Laboratories (UL) tests surge protective devices using a common standard to allow the consumer to compare different products. The clamping voltage of the device refers to the voltage the device maintained during a six thousand volt test surge. The clamping voltage is required on the ID label if the product is listed and should be included in the literature.

Surge protection begins at the electrical service entrance where the severity of surge transients is expected to be the greatest. A surge protective device chosen for this location should be capable of diverting significant amounts of surge energy safely to ground. Surge protective devices have clamp voltage levels they let through even though voltage levels vary with the size of the transient event. This residual energy is usually insignificant to electromechanical devices like washing machines, but can cause harm to sensitive electronic equipment like a DVD player or surround sound system. In this case, a second layer of surge protection is required.

The second layer, or secondary, surge protective devices are installed to minimize the effects of residual energy passing the primary protector and internally generated surge transients on sensitive equipment. The clamping voltage of the secondary device should be within the primary surge protective device. If the clamping voltage of the secondary device is too low then the secondary device will attempt to divert large surges before the primary activates resulting in damage to the secondary surge protective device. If the clamp is too high, it may not protect sensitive equipment.

A properly applied surge protection plan will have coordination between a primary device diverting large transients and a secondary device diverting residual voltages. In essence these devices should work together to consecutively step down the surge events to levels that will not damage equipment.