Circuit breaker required when fuse present?

demonboy

demonboy

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I'm now close to wiring my Icom 710. I wanted to see what the required CB rating was but note that it actually has two fuses, one for + and one for -, rated at 30a each, in the back of the unit. The official Icom manual indicates that the unit is wired directly to the battery.

What to do? Should I do as instructed or should it go via a circuit breaker as well?
 
If you wire directly to the battery and you leave the boat with the VHF on accidentally, then you may return to flat batteries.

Mine is wired after the battery switch, but not on its own breaker, so the normal end of trip turn of the battery switch ensures everything goes off.
 
I think the idea is that the fuses protect the radio while the circuit breakers protect the wiring. The fuses will blow much quicker than the trip speed of the breakers. The fuse on the 0 volt connection will presumably protect against someone connecting the aerial ground to 12volts. Not very likely but I suppose it could happen.

It's concerning though when the fuses are likely to be hard to get at in an emergency. And will you be able to find a spare fuse?
 
Ruffles is right the fuses in the back of the unit protect it. It says so in the manual. A circuit breaker , or another fuse, as close as possible to the connection to the battery will protect the wiring.
 
I dont agree. I built test rigs for circuit breakers in my youth. One of the tests was to ensure that the breaker tripped out on the first 1/2 wave where the current exceeded the design load. I doubt you'd find a fuse that fast.
 
Hi again

As always there is no simple answer. It depends a bit on when and how you plan to use the radio. On transmit (if I remember) it draws about 25amps hence the 30amp fuses.

Reason for fuses on both red and black is re electrical spikes both sides are protected (Just leave it no need to worry and certainly not breakers on both sides)

Wiring it directly stops any power supply problems Ie. loss in the circuit. but doesn't stop small cable wire melting etc only shorts.

If you have a battery monitor then you can manually check the state at any time. The issue always is "am I killing the batteries". If you have a good domestic bank, and check it regularly then no problem.

Given that you have a watermaker, fridge............. etc and an ssb you could be drawing significant amps all at the same time so if you are chinwagging on the ssb there maybe a problem.

After all the above waffle it comes down to:

SSB direct wired (no circuit breaker) and check battery status to make sure they don't drop below the 70% level.

I don't know you electrical setup so difficult to comment further.

BTW was the link any good re the grounding and other issues they were not specific to the product as you ATU is a coupler.

Peter
 
[ QUOTE ]
25 amps is huge. Do you mean 25w?

[/ QUOTE ] No its not a VHF its an HF radio.

Google and you'll find the operators manual for it!!
 
Power hungry well not really. The 25 amps drawn is when actually speaking on transmit. ie about 50% of the time you are transmitting. If it is used for essential communication then transmit time is quite low. If you use it for data or as ham who waffles on then yes the total drain can add up.
The high current must be considered in terms of cable size and volt drop but not so much inj terms of battery capacity.
olewill
 
Peter,

All good so far, thanks for your assistance. Regarding water maker, fridges, SSB: I have in my head some kind of routine for each one where none are running together. All are going via the battery monitor so at least I can see what I am drawing.

Thanks to everyone else for interesting info on the subject. Managed to install the wiring so far (that took a day, stopping for frequent coffee breaks). Next step today.
 
Couple of points, a power feed with no protection is a very bad thing. I once spend a day in a burnt out engine bay tracing why it had caught fire. Turned out a retro-fit gen set had no protection in the starter motor feed cable. A minor falt else were had caused a cable to melt, this melted others,that melted the 35 sq mm feed cable to a main earth, and thus a fire. So though the feed to the radio may be ok, a fault in another circuit could cause a fire in that unprotected cable.

Circuit breakers have trip curve, so the higher the fault current, the faster the trip. This could span a time period of 10 seconds to a 0.5 second trip time, depending on fault current. All manufactures print the curves, and you can get various options for a given design and rating. This allows you to match the protection to your application.

Brian
 
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