Re: Isolation transformer and connection to ground


Good point, Steve. Has a lot to do with the trip curve of the pedestal-mounted circuit breaker, but that's usually beyond the reach of boaters to change.

A step up from your manual (and probably bullet-proof) solution might be to use a simple 120 VAC, SPST relay with coil directly across the transformer primary and a 100 watt light bulb in series with the transformer hot wire. The relay's contacts would short the bulb when the inrush current dissipates and the relay coil is energized. A shortcoming is that the relay is energized whenever the transformer is in use.

Another step up would be to insert a manual SPDT switch so as to select either the light/bulb relay circuit or a direct connection. That way the light bulb/relay circuit could be reserved for those cases where inrush is tripping shore power breakers.

Probably $15 worth of parts and 20 minutes to do the job.

It should be simple enough to design a better circuit that would automatically drop the relay out after initial inrush.

Caution: these are lethal voltages and the wiring is best left to professionals for those uncertain of their skills and understanding.

Chuck




Steve Lusardi wrote:
The real problem, that no one has yet mentioned, is inrush charge current. If the transformer is sized correctly for maximum shore load, the initial inrush will most certainly pop the breaker at most marinas. The solution I use works very well, if anyone is interested.

Tie in series with the primary coil of the transformer a standard light bulb socket. Insert a 100 watt light bulb of the appropriate voltage and connect a switch capable of handling the maximum current of the transformer in parallel across the lamp socket. In use, open the switch and connect the transformer to shore power, then close the switch before applying secondary load. Initially the bulb will light and then fade out. Anytime after that bright phase, it is safe to throw the switch shorting out the lamp.
Steve


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