Lately, I have had several inquiries about whole house surge protectors.
Over the years I've installed a few but never really knew or cared how effective they are
I would like to get some of the opinions of the forum on them.
- Do they work?
- Is there a brand or model that's proven to be better than any other.
-Etc.
I see that some make claims that they will reimburse the user for damaged electronics in the event of an incident. That I find hard to believe simply because there are so many variables that could be at play.
Any thoughts appreciated.
I am an electrical engineer and I have spent my career designing utility, industrial, and commercial power systems. Most large power systems do employ surge arrestors because they reduce the risk of over voltages damaging both the power system and the utilization equipment. Over voltage events can be predicted in aggregate using statistics (average number of times per year in the UK that one kilometer of 11kV distribution circuit will experience an over voltage) , but we cannot predict the details of a specific event with any level of certainty at all (how long until the next over voltage at my house, how large with that next over voltage be, etc.) Specifying arrestors to protect a power system requires statistical data for the location as well as a preference of what percentage of typical overvoltage events we will protect against. It’s not practical or cost effective to install equipment that will protect from 99.999% of overvoltages, but we can protect over 99%.
Most people that apply surge protection in residences do not understand the statistical side of overvoltage events and overvoltage protection - to many either a surge protector either works or it doesn’t work, which is not a correct interpretation of the physics and randomness of lightning phenomena.
I will attempt to answer your questions, understanding that there are many statistical shades of grey involved with the level of protection provided.
Q: Do they work?
A: Yes, surge protectors from electrical distribution equipment vendors that have been tested to IEC, UL, or IEEE standards do work to reduce the likelihood and magnitude of power system damage due to overvoltage events.
Q: Is there a brand or model that’s proven to be better or is preferred?
A: Almost all surge arrestors produced for 50 or 60 Hz power systems in the last few decades are “gapless” metal oxide varistor (MOV) type arrestors. The zinc oxide compound that makes up the MOVs is very similar across all manufacturers. For the voltage ratings used in a residence there may be a few dozen brands on the market but they are only manufactured by a few companies, they go through the same tests, but they are marketed under different names, different form factors, and with different ratings. Purchase a unit that has been certified/listed by the local testing agency, which should be UL or Enertek/ETL in the US. Some models will list the surge current rating, which is derived from the cross-sectional area of the MOV device. More area means more current can pass through the MOV with the same level of voltage protection. Clamping voltage is another rating, although most residential devices will have very nearly the same clamping voltage rating so this is probably not useful for comparison. An arrestor energy rating in Joules is also provided on some arrestors, but this can be deceiving. For a given surge current, a device with less protection (higher clamping voltage) will dissipate more Joules of energy during the surge event. A higher Joule rating may not be meaningful if it accompanies a higher clamping voltage. For the same clamping voltage and same surge current rating, a higher joule rating may indicate the MOV has more thermal mass, which is useful.
Spark gap type arrestors are used for high frequency protection today but are rarely used on power systems. The poster above indicates correctly that spark gaps can handle more restrikes than MOVs before they become thermally damaged, however current industry standards for MOV-based arrestors take into account the typical frequency of lightning strikes, the thermal mass, surface area, and cooling time of the arrestor as part of the IEEE standards that govern the product design and testing. In practice, when MOV arrestors are applied in accordance with IEEE C62.22 they very rarely fail from thermal endurance (too many operations too close together). The most common failure modes are from water ingress, mechanical/accessory problems, or misapplication. Arrestors’ typical life is measured in decades. At 20 years in service some users start to test the arrestors with a DC hipot or Megger to verify they will still work correctly. For inexpensive arrestors it may cost the same to replace them instead of testing them. Any surge arrestor that only lasts a few months or a few years was likely misapplied or was not built and tested to industry standards.