Posted by Peter Kennedy on 12/16/2025 to
Battery Chargers
The latest revision of the ABYC standards changes the requirement for inverter charger case ground terminals. This is covered in section A-31 of the standard published at the end of July 2025 with a compliance date of August 2026. Here is the text:
A-31.7.5 DC Grounding Connections
31.7.5.1 The DC Grounding conductor shall be connected from the metal case or chassis to:
31.7.5.1.1 the engine negative terminal or the DC main negative bus for grounded DC systems, or
31.7.5.1.2 the grounding bus for isolated DC systems
31.7.5.2 The DC grounding conductor shall have a minimum size as specified in Table 1 based on the size of the DC overcurrent protection device for the battery chargers, inverter and inverter chargers
It goes on to say that this isnt necessary if the case is made of plastic or other non-conductive material.
This is a change from the previous version of the standard. It means that if you take an example of the Victron Energy PMP122305122 MultiPlus-II 12/3000/120-50 120V inverter/charger that uses a recommended fuse of 400 amps the size of the case ground connection can be 3 awg. The previous version of the standard said the case ground conductor had to be a minimum of one wire size less than the main DC Cables. For a 400 amp fuse these would be 4/0 awg and so in the previous version of the standard the DC Grounding conductor would have had to be 3/0 awg. This is quite a difference and will make the installers job a bit easier.
If you wondered what the purpose of this conductor is the main purpose is a safety ground in the event the DC Negative comes loose. If there were a fault the charger might try to put the DC Charge current to the battery via the AC Ground wire. This would be way too much current for that wire.
Although the primary purpose of this wire is safety in the event of a fault it does have some other functions: It serves as a lightning ground for the device. By keeping all the large metal components in a boat at the same electrical potential with appropriately sized wires the possibility of internal lightning within the boat is greatly diminished.
The photos below show the DC Grounding Terminal on various Victron chargers and inverter chargers.
Peter Kennedy has been in business since 1991 designing, installing and servicing marine electrical systems. The purpose of this blog is to offer support to both professional installers and do-it-yourself boat owners who wish to undertake this work themselves.
SEARCH
You can subscribe to get automatic notifications of new blog posts, this is separate from a newsletter subscription.
