All utility grade photocontrols should have some sort of surge protection.

Air Gap Arrestors

AC relay controls usually have an air gap type "lightning arrestor". These arrestors are inexpensive, have about a 2.0 - 2.5 KV spark over and provide bare minimum protection for photocontrols and luminaires.

MOVs / Metal Oxide Varistors

Much better protection can be obtained from metal oxide varistors or MOVs. MOVs are reliable, have clamping voltages under 1,000 volts and are available from all photocontrol vendors. They will dramatically reduce the number of surge related photocontrol failures on your system. A properly rated MOV has a much longer service life than an air gap arrester. All manufacturers of electronic controls use MOVs to protect the control and luminaries; they are optional on conventional controls.

Over the years, DTL has witnessed utilities that use conventional controls get reduced failures when Engineering switches to MOV surge protection. However, MOVs have to be specifically written into your utility specification. MOV's energy rating is given in joules and maximum surge current is given in amps. Most utility specs call for 160 joule ratings. This rating works well in 90% of the United States.

In areas of extreme lightning, such as Florida, many utilities specify 320 joule, 10,000 amp MOV's. Although more expensive, these large MOV's reduced surge failures to almost nothing. In recent years, more utilities are switching to 320 joule MOVs

If your service area has repeated high energy line surges and if you are seeing photocontrols fail due to surge damage, consider upgrading from a 160 joule MOV to a 320 joule MOV. Of course, if you are still using older style air gap arrestors, most likely all you need to do is specify a standard 160 joule MOV.

CAUTION: Some photocontrol makes are playing a MOV Rating Game. They publish high ratings based on one-time surge withstand. Thus a MOV that is really 100 Joule when tested per ANSI C136 with multiple surges will be put in a control as a claimed 220 joule part. DTL now suggests that a current rating be added to user specifications. Example: 160 joule, 6500 amp or 320 joule, 10,000 amp.

End users that are serious about preventing surge failure of controls should require the following:

"Control manufacturers shall be able to provide lab test results that the control
and MOV pass surge tests per ANSI C136.10-1996, High Surge Section."