devices for surge protection

pianotuna wrote:
If I add a MOV type device in parallel to the shore power cord will it offer some down stream protection to my RV?

Please step back a minute. Ignore everything posted. First grasp these basic facts. Then read everything to separate half truths from actual facts.

First, this will discuss one type of surge that typically damaged appliances in an RV and appliances in a home. This transient is a current source. That means it has near zero voltage if connected low impedance (ie within feet) to earth ground (not a receptacle's safety ground). It can be 20,000 amps. It is typically a microsecond event.

That means anything that foolishly tries to block it causes voltage to increase even destructively. If anything tries to disconnect from a surge, well 300 consecutive surges could pass through before a disconnect even starts. That means every informed reply always says where hundreds of thousands of joules dissipate.

Second, MOVs in a Progressive only address this anomaly (different from other anomalies also called a surge) if that PI connects at the pole. A protector is only as effective as its earth ground. Only earth ground does that protection. MOVs in a PI are only connecting devices to what does protection.

Third, MOVs are more than fast enough. MOVs will respond in nanoseconds. These type of surges are microsecond anomalies. (BTW, nobody sees the surge. Most confuse the construction of a plasma path that may take hundreds of milliseconds with a surge that is done in microseconds.) However, if MOV leads have sharp bends or that connection to earth ground is too long (ie protector located inside an RV), then that response time increases. Again, protection is about impedance (not resistance).

Four, assume those MOVs in a Progress (inside an RV) are rated at 330 volts (let-through voltage for 120 volt service). Assume a surge is approaching on a hot (black) wire that is 5000 volts. What does that protector circuit do. Now that surge is 5000 volts on that hot wire, and 4670 volts on the safety ground (green) and neutral (white) wire. Where is this protection? Again, protector does not define protection. A majority never get this. Quality of earth ground and its connection defines protection.

Five, why would MOVs need replacement? How many joules does it claim to absorb? Hundreds? A thousand? Potentially destructive surges can be hundreds of thousands of joules. What happens when a protector tries to 'absorb' or 'block' that energy? Effective (properly sized) protectors do not fail. If a protector fails, it was undersized for that venue. Must be replaced by one with larger ratings.

Six, of course, how often do destructive surges occur? Maybe once every seven years. A number that can vary significantly even in a same town. A number determined by relevant factors such as geology.

Why do protectors for RVs typically ignore this type of surge? Progressives address other anomalies that are called surges - such as high voltage, low voltage, open ground, floating neutral, or reverse polarity. Type of surge technically defined above is rare in campgrounds. But is often blamed when others have no idea what else to blame.

Reread those others posts. Any useful recommendation (for this anomaly called a surge) will always say where hundreds of thousands of joules are harmlessly absorbed. Since a protector is only as effective as its earth ground - including impedance of that connection.

One final point. Do not install your own MOVs. Fire and other dangers exist. So many protectors were so badly designed that UL repeatedly upgraded UL1449. UL1449 says nothing about protection. It is completely about human safety issues (including fire) created by so many plug-in protectors.

How many knew even half of this or discussed any of those numbers?