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Old 07-02-2011, 17:52   #1
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Clarifying AC Safety / DC Ground Jumper

Noticed my AC safety (green wires) ground bus and the DC ground buss behind my main panel do not have a jumper wire connecting both together. Boat is a '95. I do have a galv. isolator in the green AC wire at the shorepower plug. Boat is always in marina plugged in to shorepower.

Is the jumper left off do to the yr, thinking it was not the practice in '95, or is there another condition that I may have that dictates not to jump these 2 buses together?
Read the Blue Seas recommendation on this (and the galv.corrosion issue)and it sounds pretty straight forward. Add the jumper and be sure to use an isolator. Is it really just a matter of adding a jumper from the AC to the DC buss grounds?

Thanks,
Jerry
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Old 07-02-2011, 21:06   #2
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Yes, it's that simple however the AC ground wire may also be connected to the engine main negative. Suggest you trace the ground wires from your main AC ground buss to see if it is connected to the DC ground somewhere else. To be in compliance with ABYC, it should only be connected to the main DC negative buss or the engine main negative.

Eric
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Old 07-02-2011, 23:16   #3
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Yes, I do have a heavy green wire attached to an engine block grounding stud of port motor, from the AC buss. (same stud that has the battery ground cable attached to on port motor)

The DC buss ground wire is connected to my battery chargers ground terminal, which in turn connects to the the SB motor's ground stud. Both motors are bonded together by a battery cable. All wiring is factory ran.

So the short of it is; AC safety buss to the port motor, DC gound buss to sb motor. Seem excessive??? The ground cable connecting both motors together at the block studs is the commmon connection here, it appears. Not a direct connection. ?

Does this meet code as it is now, or do they both need to be physically connected at a common point, be it a buss or at 1 of the motors grounding stud.

It would appear I could simply install a short 12" jumper to both busses, to satisfy the CG ruling, leaving 1 wire to go to engine ground and eleminating the second buss grounding wire altoghter.



Hopefully this is easy to understand.
Thanks
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Old 08-02-2011, 06:52   #4
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I don't like the fact that your dc ground wire goes to the sb engine ground. It should go to the port engine ground as that is your common dc ground point. Even though the electrical connection is there via the heavy dc negative starting cable, it's just not kosher in my opinion. I think you would still be in compliance if you wanted to remove one of the cables and use the jumper if that's what you want to do.

Eric
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Old 08-02-2011, 07:00   #5
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Basic DC Neg & Gnd Wiring - Figure 15, ABYC Section E-9 - DC Negative & Grounding Wiring Diagram Cruisers & Sailing Photo Gallery
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Old 08-02-2011, 07:45   #6
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Just to be clear, if the dc ground buss behind your panel is for the negative return for your dc loads, it cannot be used for your ac ground connection. Only a separate dc grounding conductor buss could be used. This may be a little confusing but your dc "grounded conductors" are normally current carrying conductors and your dc "grounding conductors" are normally non-current carrying conductors. Your ac ground is a normally non-current carrying conductor and should NOT be connected in line with normally current carrying conductors.

Eric
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Old 08-02-2011, 16:11   #7
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Ok, do not jump the AC green gnd and DC black gnd busses behind the main distrib panel.

Install a main DC neg buss in the engine compartment.
And to that buss, reroute both the existing AC gnd (green wire) from the port motor stud, and the DC gnd wire(black) from the battery charger neg terminal. Then from that new buss, run a single cable to 1 of the motors studs, or even to both motors as shown in the above pic. Correct?

As I understand GordMays picture (BTW, thanks) I can also run the neg wires from my windlass,(not sure about these as not shown in pic: invertor, stereo amps, and the battery charger neg. side) battery neg post to this new DC main buss? Or do these items need to attach to a yet another 'accessory' gnd buss, which in turn is connected to the new 'main' buss? Or would you recommend I just leave the AC gnd connection to the port stud as it is? I do need to add a DC gnd buss to get all the grd wires off my battery terminals and just have 1 cable going to it.


Confusing, yes it is, when one considers that I can not connect the gnds at 'this' point, but when I follow the cables, in the end they are all still connected together.

Thanks for your help,
Jerry
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Old 08-02-2011, 19:40   #8
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Quote:
Originally Posted by fairbank56
Just to be clear, if the dc ground buss behind your panel is for the negative return for your dc loads, it cannot be used for your ac ground connection. Only a separate dc grounding conductor buss could be used. This may be a little confusing but your dc "grounded conductors" are normally current carrying conductors and your dc "grounding conductors" are normally non-current carrying conductors. Your ac ground is a normally non-current carrying conductor and should NOT be connected in line with normally current carrying conductors.

Eric
This isn't correct at a single point the dc negative is connected to ac protective earth to meet abyc standards.

Dave
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Old 08-02-2011, 19:44   #9
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The main thing to remember here is that all the wires going to the dc main negative bus and any accessory bus's are normally current carrying conductors. All wires going to the grounding bus are normally non-current carrying conductors. The drawing shown is wrong, and yes, it is from the current issue of ABYC E-11 Electrical standard. There are other drawings in the standard that show it correctly. The part that is incorrect is the way the grounding bus is connected. The text of ABYC states that if the negative side of the dc system is to be connected to ground, the connection shall be made only from the engine negative terminal, or its bus, to the dc grounding bus. This connection shall be used only as a means of maintaining the negative side of the circuit at ground potential and is not to carry current under normal operating conditions. In this drawing, the battery is connected to the engine and the grounding bus is connected to the main negative bus. The wire between the engine and the main negative bus is a normally current carrying conductor. The engine should be part of the dc grounding system and the wire connecting the grounding bus to the engine should not be a current carrying conductor. To do this correctly the grounding bus should be connected to the engine. This is how it is shown on the other drawings.

Eric
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Old 08-02-2011, 20:01   #10
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This isn't correct at a single point the dc negative is connected to ac protective earth to meet abyc standards.
I don't understand what you are saying, please elaborate.

This is what ABYC says with regard to the AC grounding connection:

11.5.5.3
The main AC system grounding bus shall be connected to
11.5.5.3.1 the engine negative terminal or the DC main negative bus on grounded DC systems, or
11.5.5.3.2 the boat’s DC grounding bus in installations using ungrounded DC electrical systems.

AND

11.17.1.4
The shore-grounding (green) conductor is connected, without interposing switches or overcurrent protection devices (See E-11.5.5.5), from the shore power inlet to
11.17.1.4.1 an optional galvanic isolator, and then to
11.17.1.4.2 all non-current carrying parts of the boat’s AC electrical system, including
11.17.1.4.3 the engine negative terminal or its bus.
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Old 08-02-2011, 20:03   #11
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ac protective earth.... this is the green wire of the ac circut, which is otherwise commonly refered to as the AC ground, correct? (hot, neutral, ground)

BTW, is there a location on the board where might I find the descritption of the electrical terms, in laymans words, so that there is no misunderstanding on my part?
Thanks
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Old 08-02-2011, 20:15   #12
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Thanks Eric
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