The so called expensive SURGE PROTECTOR plays a very important role in the RV trailers. It is always ON and looks for bad incoming 120VAC line voltages. When it see's something bad it disconnects your RV trailer from the source to prevent failures.
Actually a small price to pay for protection like this...
You can use RV adapters to get your 30A and 50A service pedestal down to a 20AMP Receptacle and plug in one of these CIRCUIT TESTERs which will detect bad wiring and possible problem areas but does not give you 24HR protection. These are really just a good tool to have around to test the 12VAC Power SOURCE before you hook-up to it.
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I think this is what you may be referring to...
Roy Ken