Generator/invertor and bonded neutral


Old 02-19-16, 07:06 PM
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Generator/invertor and bonded neutral


I am planning a backup system to power my “boiler” during a power outage. I’ve done a lot research. The wiring is figured out and I have the load requirements of the boiler. I am trying to install the most versatile system. I have yet to purchase a generator or inverter, and the transfer switch. The only issue I have left deals with the bonded/floating neutral. I would like to be able to use a generator [b]or[\b] inverter. Generators may or may not have their own bonded neutral, depending on model. Inverters may or may not have their own bonded neutral, depending on model. (It seems most inverters have a bonded neutral, and is complicated if a GFCI is used).) Some generators can be configured either way, or a “bonding plug” assembled by connecting the ground to the neutral and plugging it into the outlet on the generator. I plan on using a pure sign inverter as the boiler does have a circuit board and processor (and pure sign inverters seem more versatile, better made, output 120 VAC on the hot rather than possibly 120 split between hot and neutral). The house load center is bonded neutral. I will be using a single circuit transfer switch. Per code there can be only one bonded neutral in a separately derived system. If the transfer switch only switches the hot, the generator/inverter side of the transfer switch cannot be bonded. If the transfer switch switches both the hot and neutral, the generator/inverter side of the transfer switch must be bonded. I plan on using a short extension cord to connect the generator/inverter to the transfer switch (or power inlet box). Backfeeding will not be considered.

The transfer switch is the issue. Switches such as the EZ Generator Switch can purchased either way - switched or non-switched neutral. I believe the switched version could be quickly rewired so the neutral bypasses the switch, thus allowing for a single bonded neutral if a floating neutral generator/inverter is used.

Thoughts? I am missing something? Again, my goal is to create the most versatile system that is independent of the type of generator or inverter.

I know the bonded neutral and generators and inverters issue is not new. If this has been answered before, please point me to the correct thread.
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Old 02-21-16, 05:47 AM
Join Date: Mar 2010
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The best way to assure proper neutral-ground bonding is to have none downstream of the transfer switch. The neutral-ground bond for utility power would be upstream of the utility power leg of the transfer switch, perhaps within the transfer switch assembly. The bond for generator power would be either in the generator or using a bonding plug (supposedly vaguely resenbling a 3 prong to 2 prong adapter in appearance) as you mentioned. With a neutral switching transfer switch, this also gives the most versatile system.

In practice, many homeowners with portable generators ignore the requirement for neutral-ground bonding in one place only, connecting any generator of their choice to the transfer switch generator leg. However they will unhook a neutral-ground bond inside the generator as needed if that procedure is easy.

Last edited by AllanJ; 02-21-16 at 06:10 AM.
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