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 Post subject: Mast and chainplates part of common ground?
PostPosted: 06 Mar 2018 13:34 
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Skipper

Joined: 24 Sep 2013 09:20
Posts: 321
Is everyone's mast and chainplates part of the common ground of the DC electrical system (through the wire that bonds everything together throughout the bilge and behind the cabients)? I had always seen the wire that bonds everything together for the zincs and I guess lightning protection too. I only just realized that if I touch a volt meter to a positive somewhere, and then touch the black probe of the meter to the mast or chainplates, I'm getting whatever the battery voltage is through my DC system (13V, e.g.).

Is that right? Or do I have something going on that needs attending?

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Zach Duncan
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 08 Mar 2018 06:58 
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Tactictian

Joined: 16 May 2009 08:06
Posts: 103
I think that is right. I am pretty sure my bonding wire ties into the electrical ground through a buss bar in the engine sump.

Chip


 
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 08 Mar 2018 08:51 
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Skipper

Joined: 24 Sep 2013 09:20
Posts: 321
This question came about while I was trying to fix a VHF transmitting hum. I was disconnecting the radio, and when I pulled the black ground wire off the 12V panel, the radio still would power on. I found that the coax antenna cable was carrying strong DC ground to the radio. Also, I found that with any of the mast lights off, their red positive wires would also read as weak DC negative grounds (10-11.5 V, I'm guessing light contact of exposed wires with the mast). When you flip them on they read as normal positives and the lights operate as normal.

So, I'm guessing I should go up there and insulate around all the light connections (steaming, foredeck, anchor, tricolor) and also insulate the VHF antenna bracket? Anyone else had to track this down before? If our masts are all part of the common ground, seems like a bunch of us would have this going on unless we all had really great previous owners.

Incidentally, this wasn't the source of the radio transmit hum. So, it really isn't causing a problem that I can tell. Leave as is?

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Zach Duncan
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 09 Mar 2018 07:01 
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Tactictian

Joined: 16 May 2009 08:06
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Hopefully the electrical engineers will step in here but I THINK with everything off, the red wires in the mast will read the resistance of the bulbs to ground. Iím not sure how that translates to DC voltage.


 
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 09 Mar 2018 08:29 
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Skipper

Joined: 24 Sep 2013 09:20
Posts: 321
I didn't explain that part too well. I touched the red of the volt meter to the red positive of something else powered on (my Wi-Fi router), then touched the black of the volt meter to each of the reds of mast lights that were off. That's how I was getting a low volt reading (10-11.5 V). Normally, I would think, nothing would show on the volt meter there. I haven't checked resistance yet.

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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 09 Mar 2018 19:01 
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Tactictian

Joined: 16 May 2009 08:06
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So Iím still hoping that someone who knows what they are talking about chimes in but.....I think you are reading the voltage potential between the active 12VDC circuit and the ground that is being seen through the resistance of the light bulb. With the 12 volt circuit to the masthead fixture open, the red wire connected to the bulb is still connected to ground through the bulb. The resistance of the bulb is what causes the lower voltage reading (10-11 volts vs 12-13 volts).


 
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 09 Mar 2018 21:31 
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Skipper

Joined: 24 Sep 2013 09:20
Posts: 321
Ah, got ya. So, I got a new VHF radio in today, and now my transmissions are perfectly clear. So, my old radio was bad, and I'm not having any noticeable problems.

Still curious about the electrical going up the mast as well if anyone knows for certain.

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Zach Duncan
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 09 Mar 2018 21:40 
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Tactictian

Joined: 16 May 2009 08:06
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I am 80% certain that the bonding wire that runs all through the boat (a single strand #12+/- copper wire) is connected to the mast step. That would provide a connection to all of the standing rigging. That wire is connected to a buss bar in the engine sump that ties the whole boat together. Iím pretty sure that is a factory installation.


 
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 10 Mar 2018 08:27 
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Skipper

Joined: 24 Sep 2013 09:20
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So, my main wonder is even though the VHF is now working, should the antenna really be carrying the ground back to the radio so much so that I can unplug the black wire from the panel and it still powers on.

Should I try to insulate the antenna from the mast or just leave it alone (thinking it could cause damage over time or a weaker signal)?

I was thinking about it (in my very amateur electrical mind), and even if I did insulate it, obviously ground inside the radio body goes from something to the antenna connection. So, the 12V system ground would reach the antenna that way anyways, right (from the black connected in the panel, to the radio, across whatever is connecting them in the radio body now, and up the coax to the antenna)?

I'm probably just thinking gibberish at this point.

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Zach Duncan
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 Post subject: Re: Mast and chainplates part of common ground?
PostPosted: 10 Mar 2018 08:51 
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Tactictian

Joined: 16 May 2009 08:06
Posts: 103
Falling back on my usual disclaimer, I believe electricity will divide its path to ground according the paths available and the path of least resistance. If you have a properly sized wire running each circuit to ground, the system should not rely of the ground side of the coax. I wouldnít mess with it.


 
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