by Art Hebert
The bypass switch allows the owner to send power to inverted loads (usually electrical outlets, heaters, dehumidifiers etc.), by sending electric current around the inverter. This is great for periods of extended absence by the boat owner. Without the bypass, when power is lost on the boat, the inverter will try to support the heaters and dehumidifiers and will operate on BATTERY POWER until the batteries are DEAD. The bypass will still send power to the inverter so that it can satisfy the need for charging but the outlets will be fed from the bypass. The loads will only operate while the boat is plugged in but at least the batteries are safe from critical discharge.
Many older boats that did not have an inverter when they were new, have issues when they moor up at a marina that has new electrical wiring (ELCI wiring). Many times this issue is caused by an inverter that was not completely installed. Without getting too far in the weeds, when an inverter is installed it is required that all neutral conductors be collected and placed on the INVERTER Neutral bus bar, which is separated from the boat system neutral bus. This key step is regularly missed by installers that are not electricians. It can be very time consuming depending on the complexity of the boat AC panel and how well wires are
labeled. The bypass switch allows the owner to bypass the problem inverter and use the shore power without causing the shoreside ELCI to be effected by improper neutral – ground connections. Warning, this may not fix every boat but it could be a cheaper alternative to an isolation transformer.
Many vessels that travel outside the area and use freezers and refrigerators that are powered by the inverter when voyaging, run the risk of not having a functioning freezer in the event of an inverter failure. If these critical loads are fed exclusively by the inverter, and the inverter fails for whatever reason, there is no “simple way” to send power to the loads. Often the boat owner falsely assumes if they plug the boat into shore power or run their generator they can pump down the refrigerator/freezer; this is not true with an inverter failure, all loads fed from the inverter are isolated from onboard or shore power sources. If the boat is wired with the Bypass switch the critical electrical loads could be fed by the onboard generator, while inconvenient it can buy time for the boat owner to get a new inverter.
The photos below show two versions of the bypass switch. It can be installed anywhere but is most economical when next to the inverter. The switch on the left uses a pair of interlocking circuit breakers to bypass the inverter. The rotary switch on the right does the same thing with a single move.
Arthur Hebert is a 28 year veteran of the U.S. Coast Guard. He served on a wide variety of the Coast Guard ships and participated in many Search and Rescue missions. He holds a 100-ton Master Inland License and is an ABYC Master Tech. He is a part time instructor at Skagit Valley College Marine Trades program and during the summer you can find him on his 30 ft Fisher motor-sailer.