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Old 26-10-2010, 10:45   #1
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Location: Potomac Shores, VA USA
Boat: Formosa 51 Aft Cockpit Ketch - "Beausoleil"
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Cable Size for AC Grounding Bus to DC Neg Main Bus ?

I've scanned the ABYC e11 recommendations, but can't find it. What size cable should be used to connect the AC Grounding Bus bar back to the Engine / DC Main Negative Bus bar?

I was doing a little DC re-wiring the other day, and it finally hit me that when my electrical system was installed three years ago, the installer connected the AC Grounding bus to the DC negative bus bar mounted behind the combined AC/DC panel. He disregarded the installation diagrams... I've seen the connection many times when adding new power connections, but I'd never really noticed it.

The distance from DC panel bus bar to the DC Main negative bus bar is about 15', and uses 1/0 cable. The AC Grounding bus is located behind the AC/DC panel, next to the DC panel bus bar, and is connected to it using #2 cable.

What size cable should I use to correct the installation error? The length would be basically the same length as the DC panel bus bar connection to the DC Main Negative bus bar. #1/0 would be way overkill for the AC system, as I believe #2 would be. But would #10, the same size as the AC Mains cables coming from the shorepower connector and galvanic isolator (no, not an isolation xformer yet), be sufficient?

I'm suspecting that the mis-connected AC ground is a significant contributor to the 60Hz hum I hear in my DC-powered PC's sound system and the Sony marine DC stereo system whenever the Magnum MS-2800 inverter/charger is in charging mode...
Cap'n Jon (KB1HTW)
S/V Beausoleil -1979 Formosa 51 Ketch
"If it's gonna happen, it's gonna happen out there." - Captain Ron
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Old 26-10-2010, 11:19   #2
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Location: Fort Myers FL
Boat: Irwin 40
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As I recall the rule is the ground can be 1 size smaller than the feed. So if you are using a #6 feed you could use a #8 ground. Remember this is to provide a path for fault voltages only so would not be higher than the input voltage and Amperage ie 120VDC 30 AMP or 240 50 AMP VAC. As for the hum it is common to inverters in charge mode I get it on my SSB but not the stereo. It is the result of a AC ripple put in the DC as it charges. You could try a ferrite choke. not sure that would help for this though. Maybe someone else could jump with thoughts

Good luck
Capt. Wayne Canning, AMS
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