Wiring VHF Radio on Music system supply?

[Steve_Brennan]

Hi

Have just purchased my first power cruiser. It has a brand new Raymarine Ray70 VHF radio installed below the new music system in the cabin but its not been connected or used. I powered up it up to test and all works fine. The Music systems has a fixed supply directly back to the switch panel. Mty Questions is, can I also connect the VHF radio on to the same supply feed as the music system? Effectively T off the + and - wires? Will the two on together draw to much current on the 12v supply cables?

Steve

 

[duncan99210]

Provided you have the right fuse in the supply wires, I don’t see why you couldn’t use the audio system supply for the VHF.

 

[peteK]

It would work but a vhf radio should be wired seperate as it may need to be used in an emergency.

 

[VicS]

Hi

Have just purchased my first power cruiser. It has a brand new Raymarine Ray70 VHF radio installed below the new music system in the cabin but its not been connected or used. I powered up it up to test and all works fine. The Music systems has a fixed supply directly back to the switch panel. Mty Questions is, can I also connect the VHF radio on to the same supply feed as the music system? Effectively T off the + and - wires? Will the two on together draw to much current on the 12v supply cables?

Steve

How much current does the music system take?
.

 

[Steve_Brennan]

How much current does the music system take?
.

The documentation says 3A max.

 

[PaulRainbow]

How much current does the music system take?
.

How is that relevant without knowing the size of the cables and the fuse fitted at the supply end ?

 

[PaulRainbow]

Hi

Have just purchased my first power cruiser. It has a brand new Raymarine Ray70 VHF radio installed below the new music system in the cabin but its not been connected or used. I powered up it up to test and all works fine. The Music systems has a fixed supply directly back to the switch panel. Mty Questions is, can I also connect the VHF radio on to the same supply feed as the music system? Effectively T off the + and - wires? Will the two on together draw to much current on the 12v supply cables?

Steve

It can be done, but, the cable current rating has to be rated high enough for both devices and the fuse at the panel end has to also be rated high enough for both devices. You then have to fit two fuses where you "T" off at the equipment end, each rated for the relevant device.

In my opinion, it's not a good solution for wiring the VHF, which is an important piece of safety equipment. I would connect it straight to the panel with its own cable. No need for a switch at the panel, but it does need a fuse.

 

[st599]

There's also a small chance that a short in the music system will render the VHF inoperable.

It's a similar argument with using one antenna in to two systems, you either have a lossy diplexer (which will lose half your transmit power) or an electronic switch which can fail following a power spike or similar.

 

[alahol2]

It can be done, but, the cable current rating has to be rated high enough for both devices and the fuse at the panel end has to also be rated high enough for both devices. You then have to fit two fuses where you "T" off at the equipment end, each rated for the relevant device.

I thought we are always being told that the fuse should be set to protect the wiring not the device?

 

[PaulRainbow]

I thought we are always being told that the fuse should be set to protect the wiring not the device?

Not always, there are exceptions. But, even if the primary purpose of the fuse is to protect the wiring from overload/short circuit, it doesn't mean the fuse has to be rated for the current carrying capacity of the cable. It needs to be rated between the max current the circuit will be required to carry and the max current rating of the cable.

1) Sometimes, you might be taking several cables from a fusebox to various devices. The cable suppying power to the fuse box will need to be rated for at least the combined load of all the devices, probably much greater to counter voltage drop, and this cable will need fusing accordingly. You could use all 2.5mm cables (provided nothing needs anything greater of course) and if they all have loads less than 10A you could use all 10A fuses. One roll of cable, one size of fuses, a couple of spares will do nicely, simple.

2) Let's say you wire your fridge with 10mm cable to counter voltage drop. 10mm cable is rated at 75A, so your fuse could be anything from about 15A to 75A. It would be a bit daft to fit a 75A fuse though, so you'd fuse for the fridge max current, which by default protects the cable.

In the case of post #7, the first fuse, at the panel, is there to protect the wiring, but obviously has to be rated to carry the combined current of both devices. When the cable is split for the two devices you then have to reduce the fuse ratings, or one device could disable both devices. You would not want a fault with the stereo blowing the main fuse so you lose the VHF.

 

[alahol2]

In the case of post #7, the first fuse, at the panel, is there to protect the wiring, but obviously has to be rated to carry the combined current of both devices. When the cable is split for the two devices you then have to reduce the fuse ratings, or one device could disable both devices. You would not want a fault with the stereo blowing the main fuse so you lose the VHF.

It was this bit that I couldn't follow.
Thanks for the explanation.