Alan-I know you were tired when you wrote:
but the Neutral is tied to Earth(green/green-yellow)back at the switchboard.
In fact, neutral (white/blue) and safety
ground (green/green w/yellow) are only tied together at sources; generators, inverters, and shore power
at the mains transformer. NEVER at the switchboard.
The new ABYC standards require a “Status Monitor” feature, requiring additional circuitry.
There is another option, not requiring a status monitor
, that was developed in ABYC A-28 a few years ago.
A bit of history
. While GIs, when made of quality components, did their job well, there was a concern within the ABYC that placing a semi-conductor based device in the critical safety
ground wire could lead to loss of the safety ground path if the semi-conductors failed open, their normal mode of failure. Thus the well intentioned requirement for a monitoring system was developed.
Several manufactures (Professional Mariner, among others) brought some sophisticated monitoring systems to market. These monitoring systems checked the ground path at least once every 24 hours and alarmed for a couple of faults, the most critical being for loss of continuity in the safety ground path. If an alarm
condition occurred, the alarm
sounded and could not be silenced for more than five minute. Unfortunately, these monitoring systems did a fine job of verifying the condition of the shore side portion of the safety ground system...and found that this side of the system was in bad shape!
So, the law of unintended consequences had reared its head
Enter the fail safe GI. These have been around in the dairy and pipeline protection industry for years. They are constructed of extremely robust components and, unlike their less robust nephews, will fail closed if subjected to an otherwise incapacitating surge so there is no need for the monitoring system. The extremly rigorous testing requirements for candidate fail safe GIs was developed (A-28) and each candidate must be certified by an independent laboratory (UL, AMMANA, etc.)
The fail safe units have been on the marine
market for some time and are the only ones that I will install.
Hope this helps,