VHF/Plotter Wiring Hazard?

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My VHF is wired, via a fuse in the +ve wire, directly to a battery; this seems to be the recommended way of installing VHF’s and is how my boat was set up when I bought it.
All other electronics and electricals connect to fuse panels which are supplied by a positive and a negative heavy duty cable, each with its own isolator switch.

So far so good, except… The plotter that supplies coordinated to the VHF does so via NMEA0183 protocol where it sends the signal over a pair of wires, one is the comms wire and the other a ground (i.e. –ve) wire.
This set-up means that if I switch the heavy duty –ve isolator to “off”, all of the boat’s electronics are still connected to the –ve battery terminal, but via the thin data wire running from plotter to VHF and on to the battery. This concerns me, and I assume that mine is not the only boat to be wired like this.

I plan to disconnect the plotter –ve from the boat’s busbar and connect it directly to the same -ve supply wire that the VHF uses. This will leave the plotter and VHF on their own fuse protected but unswitched circuit.

Is this the usual set-up for a VHF/plotter pairing? Any thoughts or comments are welcome.
 
Why would you be worried about the negative being connected? It is the positive that is switched and the battery isolator switches off the positive supply. Everything else is connected to negative ground anyway.
 
salar said:
Why would you be worried about the negative being connected? It is the positive that is switched and the battery isolator switches off the positive supply. Everything else is connected to negative ground anyway.
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Both the positive and negative cables are switched. When I turn off the negative switch I still get a connection to the battery which I've traced back from the -ve bus bar, via the plotter's NMEA ground connection to the VHF and finally back to the battery.
 
salar said:
Why would you be worried about the negative being connected? It is the positive that is switched and the battery isolator switches off the positive supply...
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Not on my boat, nor on the OP's.

I suggest feeding the VHF from the switched negative bus-bar rather than direct to the battery. In the event of a fire, the individual breakers could be used. You could also run a separate direct negative "emergency" feed terminating in a socket close to the VHF power inputs, with a suitable plug and socket in the standard lead.
 
Good solution on original post - tie the gps to the vhf. It can be a real pain having "ghost" circuits - especially in the return, when trying to source problems in other circuits/devices. Plus, you may end up inadvertently having a high load fed through it even for an instant - you don't want to damage the Nmea link (although they are usually internally protected nowadays.)
Also, in an emergency, the VHF is needed -right? - that's why it's connected direct. Well, what about DSC.........? no use if the gps has gone with the wind.
 
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Am I correct in reading that it is normal to have both +ve and -ve isolators for the batteries? Cos I've had a few boats and none has had a -be isolator...
 
Ardenfour said:
Am I correct in reading that it is normal to have both +ve and -ve isolators for the batteries? Cos I've had a few boats and none has had a -be isolator...
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I wouldn't say it's the norm, but it's not unknown. Not really sure what the rationale is.

Pete
 
The purpose is to ensure a clean power supply to the VHF to minimise the noise from everything else on the boat. For some reason this has mutated into a widely-held belief that the VHF has to be permanently connected to the battery, which is complete b*!!*(£s.

I've got a double-pole switch for the VHF so both +ve and -ve are disconnected when it is off. The -ve is fed directly to that switch and doesn't go via the master switch, so is independent of any other -ve wiring.

In practice, I suspect modern radios aren't that vulnerable to power supply noise anyway. Just to make sure, I've also got the VHF connected to the boat's ground as recommended by the manufacturer (SH). I also fitted the ferrites they supplied onto the power cables.
 
I don't support the VHF direct to battery argument... its a bit counterintuitive... an electrical fire can start in a VHF as much as in any other device, and I want to be able to isolate it quickly... its not a big deal to create a jumper cable with a little thought to provide power to a VHF in an emergency.

I have only one thing connected directly to the battery (bar the +ve busbar) and that is the bilge float switch and pump... (and even that is through a panel switch and breaker) everything else is switched through an isolator switch and panel switch and breaker.
 
lpdsn said:
The purpose is to ensure a clean power supply to the VHF to minimise the noise from everything else on the boat. For some reason this has mutated into a widely-held belief that the VHF has to be permanently connected to the battery, which is complete b*!!*(£s.
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But it is also good practice to not connect the VHF through various "Navigation Instruments" switches and shared circuit breakers that could confuse a crew member in the event of an emergency, or prematurely remove the power to the VHF in a distress situation. The VHF wants to be the last piece of kit to die as the boat sinks under you!!


It's a good tip to consider the earthing situation though. Its a bit like the situation on a 60's car that I had. The earth bonding to the engine fractured, leaving the choke cable the only return path..... it became interestingly hot as the starter slowly churned round..... choke cable...carburettor..... petrol..... Ohhh!!!!
 
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Alpha22 said:
But it is also good practice to not connect the VHF through various "Navigation Instruments" switches and shared circuit breakers that could confuse a crew member in the event of an emergency, or prematurely remove the power to the VHF in a distress situation. The VHF wants to be the last piece of kit to die as the boat sinks under you!!
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That's a different matter, and I agree. I have completely rewired Phoenix from the ground (keel?) up as the wiring was a bit of a mess, with multiple different rated switches in all sorts of wierd locations, all sorts of inappropriate power connections from the 'nearest convenient +ve, and messy cats nest of wiring.... and now a simple clean install, with one switch, one job, and the same for wires, makes it all much easier and safer.
 
Alpha22 said:
But it is also good practice to not connect the VHF through various "Navigation Instruments" switches and shared circuit breakers that could confuse a crew member in the event of an emergency, or prematurely remove the power to the VHF in a distress situation. The VHF wants to be the last piece of kit to die as the boat sinks under you!!
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Hence the double-pole switch I mentioned above, it's labelled "VHF".

If you want it to be the last bit of kit to die as the boat sinks it needs its own battery much higher up than the main batteries, but that a different topic.
 
nigelmercier said:
My VHF and NavTex both have an on-off switch, so I see no need to wire them via the switch panel
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My VHF does have an on/off switch (you press the volume knob inward), but I don't use it. I turn it on and off with the panel switch, which means that the associated GPS puck goes on and off at the same time.

Interestingly, my Navtex doesn't have a switch; the manual says this is because most people will wire it from a panel switch and like you they see no need for both :)

Pete
 
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