Originally Posted by David472
So, in the interest of engineering accuracy, you will see in the attached thumbnail, for the V130LA20B MOV, when voltage reaches 350 volts, the MOV will be drawing about 30 amps (that much clamping action). If this event duration last for more than a few milli-seconds, which it could, this extra MOV current draw through the main breaker, will trip that breaker.
OK. 30 amps creating 350 volts for 20 milliseconds means the MOV is degraded on a first surge (see datasheet charts). Anything longer will probably create 'completely unacceptable' catastrophic destruction. I cannot say more because a transient that long is not even listed in those charts. Transient that long violates what MOV manufacturers intend. And may create a human safety issue.
Meanwhile, a 30 amp transient on a 20 amp circuit takes between 20 and 200 seconds to trip (numbers for various Square D 20 amp breakers). The MOV would have vaporized in flames before that circuit breaker even thought about tripping. That was my point. MOVs are not installed to trip circuit breakers or fuses.
MOVs are thermal fused. A 30 amp transient through an MOV causes an unacceptable (catastrophic) failure that endangers human life. A tiny thermal fuse would disconnect the MOV long before any fire and before any circuit breaker tripped. An effective surge protector is for transients that are hundreds or thousands of amps. And that occur in microseconds.
Surge Guard is a switch that disconnects from AC mains if prolonged AC voltage exceeds (for example) 132 volts.
MOV protector and the Surge Guard are for two completely different events. MOV based protector is for a microsecond transient. And requires a short connection to earth ground. The second is for an anomaly that may occur for seconds or hours. And does not require any earth ground.
Bottom line: Not listed are solutions for other anomalies such as power factor, frequency variation, harmonics, neutral failures, rapid power cycling, etc. For RV shore power, Surge Guard addresses a most common problem. A surge protector at the pedestal addresses a different and rare anomaly that is also so catastrophic. Two completely different solutions for two completely different problems.