Herb40 wrote:
VintageRacer wrote:
Make sure your sub panel does not have neutral bonded to ground. It must separate neutral and ground, the transfer switch must switch both neutral and hot to the inverter, which must bond neutral and ground. Neutral is always bonded to ground at one point only, and that is the source of the power. Remember that GFCI - ground fault circuit interrupter - is a bit of a misnomer. The device does nothing with ground at all and can be installed in a circuit that does not have ground (such is code-allowed for protecting old 2 conductor wiring in old houses). It does trip if there is any difference between the current flowing in the hot conductor and the current flowing in the neutral conductor. Having neutral bonded in two places can create such a difference.
Brian
Brian, my Todd PS250 ATS in our Beaver Monterey is 17 years old. It still works, but the shore power contactor in it looks slightly off-color (burned?) on the outer plastic. I am considering replacing the PS250 with a manual transfer switch. But the manual transfer switches I've found switch only the hot wires, not the neutral. According to what you've written above, it wouldn't be acceptable if I were to simply connect all of the neutrals together (shore, generator, output). What's the deal here? Why does the neutral have to be switched?
Here is an option.
Edit, with regards to the neutral, I copied my response from another thread that this question came up on.
Isolating power sources is not something to be taken lightly. It is not only prudent but also required by code to isolate BOTH the hot and neutral. If done incorrectly there is a health risk.
NEC 551.33 Alternate Source Restrictions. Transfer equipment, if not integral with the listed power source, shall be installed to ensure that the current-carrying conductors from other sources of ac power and from an outside source are not connected to the vehicle circuit at the same time.
In this application the neutral would be considered a current-carrying conductor, and in the previous post the neutral from the inverter is tied to the shore power neutral with no means of disconnect.
NEC 705.20 Disconnecting Means, Sources. Means shall be provided to disconnect all ungrounded conductors of an electric power production source(s) from all other conductors.
With regards to this topic, the grounded conductor(neutral conductor), is ungrounded.
Many inverters actually read 60 volts between the neutral and ground. If this neutral is not isolated from the shore power cord, the shore power cord will also have this 60 volts exposed on the plug! Ouch!
Here is a final reference explaining this.
