Boat Electrics Question

[GAJ52]

I have recently bought a 1987 Birchwood with I suspect original electrics. The main switching panel is made by Axon and appears to be a circuit breaker type system.

Having worked on cars for many years I am fairly familiar with 12 volt DC electrical systems, i.e. Battery , Alternator, Fuse Box, Relays etc. Apart from this Axon circuit breaker switch panel my boat doesn't seem to have any fuses or relays - is this normal for boat electrics of this vintage ?

The reason I ask is my boat has a powerful spotlight with the main switch on this Axon panel. When I investigated why it didn't work a previous owner had cut the electrical wires close to the lamp. I presume to use the power for something else but I can't find the old power supply cable. Anyway going back to my car days a powerful light like a Headlight would always go through a Relay - but my boat doesn't have any ??

Is this normal with boat electrics ?

Glen

 

[pvb]

Anyway going back to my car days a powerful light like a Headlight would always go through a Relay - but my boat doesn't have any ??

Is this normal with boat electrics ?

Cars use relays so that switchgear needn't be so heavy-duty, and so that a lot of the wiring to the switches can be much thinner. Boat equipment tends to be wired directly to a distribution panel.

It would be wise to fuse the panel's supply cable at the battery.

 

[boatmike]

Cars use relays so that switchgear needn't be so heavy-duty, and so that a lot of the wiring to the switches can be much thinner. Boat equipment tends to be wired directly to a distribution panel.

It would be wise to fuse the panel's supply cable at the battery.

PVB is right but it is still good practice to use a relay on heavy draw items. I think many boats are built to be just good enough I am afraid! Regardless of this all items should be individually fused and it's also good practice to have a large capacity fuse on the main supply as near to the battery bank as possible in case of flooding or other nasties...... The most frightening thing that can happen on a boat is fire....

 

[GAJ52]

That makes sense. thinking about it the wires are quite chunky, although I thought relays also protected the switches, but maybe this Axon panel caters for this as part of its design.

 

[GAJ52]

PVB is right but it is still good practice to use a relay on heavy draw items. I think many boats are built to be just good enough I am afraid! Regardless of this all items should be individually fused and it's also good practice to have a large capacity fuse on the main supply as near to the battery bank as possible in case of flooding or other nasties...... The most frightening thing that can happen on a boat is fire....

Good point, I must check the supply from the battery to the Axon panel.

 

[William_H]

If the switch for the light is part of the switch panel and uses a combined switch and circuit breaker then obviously all the lamp current goes through the switch/cb and a relay is not necessary or used. If on the other hand you want to use a small switch then a relay and fuse or circuit breaker would be needed.
Re need for a fuse at the battery
The wire which runs from the battery or better the main power isolation switch is not always fused. The wire should be short direct and with no chance of it contactting or shorting the negative wire in which case you take the risk that it will not short. If however theree is a short to negative say in the switch box then the wires from the battery to the switche/fuses will get red hot. So you need to ensure that red hot will not cause a worse fire. Any doubts in this area and you fit a fuse as close to the battery as possible which will fuse before the wiring can get red hot. Cars and most boats have some wiring not protected by fuses. ie battery to starter to fuse box. However with the heavy wiring there is also the point that the battery being smaller can not provide enough current for long enough to start a fire. Or if it does only the wiring will burn.
So fit an isolation switch or fuse at the batterry if you think it necessary for safety or understand the risks. good luck olewill

 

[JSYmartini]

Your most commonly seen Carling toggle switch is good for up to 20A so there's not many circuits on a small boat that couldn't run directly through one.

 

[GAJ52]

You always get good advice on this forum - many thanks for your help guys.

Glen