Re: [electricboats] Grounding.

Very cool to share this Thomas, thanks.

Your last point is very important---'which negative?', since it's very possible to have a floating 12v or a 12v that is derived from the 48v but having the positive rail in common.  Similar thing with controllers---most (all?) DC brush motor controllers switch the negative rail with the full, unswitched pack voltage passed to the motor.  A strong case therefore could be made for grounding connections being made to Pack Positive, at least, that is, in/near the motor enclosure.  From a human safety perspective, that would make most sense---I have several such Batt+ exposed connections under my outboard cowling and probably just 1 nearly buried connection to Batt-.  My personal safety would be at greatest threat to tie the outboard housing to Batt-.

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of THOMAS VANDERMEULEN
Sent: Sunday, December 6, 2020 7:14 AM
To: electricboats@groups.io
Subject: Re: [electricboats] Grounding.

 

Interested readers will find scans of the ABYC Standards pages relevant to the Grounding discussion and the to applicability of E-30 to 48-volt DC propulsion systems.  I obtained these over a year and a half ago (dated 2018) so it's possible changes have since been made.
Those who believe that the ABYC standards do NOT necessarily represent the most up-to-date knowledge in the industry will likely take exception to one or more of the provisions.  But I felt this would be a pretty good baseline for further discussion and/or argument.
E-11.16.3.1 is a good example of where the standard does not seem to fit well to boats running electric auxiliaries: "The DC grounding bus shall be connected directly to the engine negative terminal or the DC main negative bus."  Most of our boats are going to have both a 48-volt (or higher) system for propulsion and a 12-volt system for accessories and possibly the monitoring circuitry.  So, in the preceding, is the main negative bus the 48-volt system, or the 12-volt system?
[I think it's the 12-volt system that's being referenced since that's what my lighting, instruments, and bilge pump are connected to.]