Which type of fuse?

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mikecontessa26

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Hi, i'm planning on installing a seperate block of fuses for GPS, Wind Instrument, Depth and Log transducers and AIS etc. off a single switched 3A circuit breaker called Instruments. I plan to route these to a fuse bank located in the back of the switchboard panel.

My question is what type of fuses to use for this sort of thing? Are car fuses suitable for marine use?

Many thanks as always for any advice.

Michael
 
Perhaps using circuit breakers would make your life easier than having to worry about having the right type of spare fuse. If you must have fuses I would suggest standard glass fuses as the holders fit in circular holes so easy to make and you have a wide choice of values and a choice between fast annd slow blow.
 
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Depth and Log transducers

[/ QUOTE ]Why do you want to fit fuses in your depth and log transducers? Fusing individual instrument heads I can understand but why anyone would want to fuse "transducers" leaves me a little puzzled. /forums/images/graemlins/grin.gif
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Artificial Intelligence is no match for Natural Stupidity
 
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you know what i meant..... /forums/images/graemlins/tongue.gif

[/ QUOTE ]Did / do I?... /forums/images/graemlins/ooo.gif

In answer to your question car type fuses are a no-no. you will need low amperage fuses so I would look at either breakers or radio type PCB mounted fuses - Maplin would be a good place to start.

Also individual switches so you can turn off what you don't need when at anchor overnight.
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Artificial Intelligence is no match for Natural Stupidity
 
What do other people use for this purpose? As mentioned the smallest fuse rating is 3Amp. If I connect them to a 3A circuit breaker and ensure the wire is greater than 3A is this sufficient?
 
They seem to be the same fuse holders as fitted to the marine switch panels sold in swindleries. I have used them without any obvious problems, though I would not recomend pouring salt water over them.

When fitting ensure you have access for the screw driver to relaese the cap.
 
It seems an odd arrangement. The beauty of a circuitbreaker is that you just reset (when you have fixed the fault). I can see why you want your instruments separate - so that you don't loose all at once. But the arrangement you propose will mean that you loose the advantage of a breaker, because the fuses must be sized to blow before the breaker trips - otherwise you are wasting your time completely. If a fuse blows, you have lost a instrument and then need to go digging around to find the fault.


Given that you have a nice low value breaker, why not just use switches for each of the instrument groups - say 1.sailing instruments, 2.GPS and 3.AIS. Then when the breaker trips , just switch all off, reset breaker and see which trips it when you switch back on ?
 
ok, heres my logic, please explain where i'm going wrong.

The smallest breaker is 3A but some instruments recommend a lower fuse value, will the breaker trip if there is a 1amp fault? I'd much prefer as suggest to have AIS & Wind & Depth Instruments on one breaker and GPS on another breaker with no need for additional switches or fuses? If the wire to the instrument can take say, 5Amps then where is the danger?
 
There is no danger at all. It is just less convenient to have fuses as well as breakers. In general I prefer breakers over fuses because they are re-settable and rusting fuses with loose fittings to their holders are common sources of problems.

Above you seemed to describe 1 breaker plus 3 fuses. That is safe but I think inconvenient. 2 breakers no fuses is also perfectly safe. 1 breaker with 3 switches is marginally simpler and gives 3 groups which will fail together but the faulty circuit can be quickly isolated. In fact, I have a similar arrangement but I can switch off my AIS by pulling out the power plug! Needs no extra components at all!
 
ok sorry for labouring the subject but i'm confused, the wind instrument for example recommends a 0.25amp fuse, if i connect this to a 3amp circuit breaker what happens if there is a fault in the instrument? Could there be a risk of fire from the instrument itself? The wire would be able to handle at least 5 amps?
 
Yes mike you are right. However it is unlikely that a fault in the instrument itself will cause a serious fire. The internal fault if connected to 3 amp protection in stead of .25 am protection will cause more damage to the internals of the instrument but given that this kind of fault will probably require replacement of the instrument (given even simple repair costs) why worry?

So if the instruments have their own switches on their control panels then I would advocate just connecting all instruments to the circuit breaker. If the cb operates yes it will require that the wires be disconnected individually to identify the culprit but I consider this a remote possibility. Fitswitches only as necessary.

The simpler the system the more reliable it will be. My own boat has one 5A fuse at the battery. This protects lights GPS and solar charging all at once. I have never had a fuse "blow" in 25 years. but i have had lots of fuse holder corrosion problems. olewill
 
Realistically, the chances of a fault which causes a current of between 0.25 and 3A is vanishingly small. If it did happen, you could in theory suffer more damage in the instrument. But it is not worth loosing any sleep over as long as you are protected by a fuse or breaker sized to trip below the max current rating of the circuit itself. The instrument is not going to cause a fire with a current of 3A.

Let's face it, 99.99% of faults are simple short circuits caused by 'operator error' or dodgy installation. What's more, if you have both a 3A breaker and a 0.25 fuse in the same circuit and short it out, I have no idea which will 'go' first. It depends on the characteristics of the fuse and breaker.

So, as the poster above says, keep it simple and arrange it out so you won't loose everything in the event of a single fault. And remember that a fuse is a very common cause of faults. Especially those awful screw-in panel fuses. Look at any boat with that type of fuse on its main board and I predict you will find 1 dodgy fuse connection and 2 fuses packed out with silver foil to improve their contact!
 
I have fuses and when my Simrad tillerpilot let the rain into itself and shorted out, the resulting electrical disturbance killed the electronics in my (separately fused) NASA DUET Log/Depth.

NASA fixed the DUET for £14 and recommended that I fit fast blow fuses in future - which I have done. (I had to sue to get recompense for the Simrad tillerpilot.)

Question.
Will a breaker trip as fast as a fast blow fuse?
 
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I have fuses and when my Simrad tillerpilot let the rain into itself and shorted out, the resulting electrical disturbance killed the electronics in my (separately fused) NASA DUET Log/Depth.

NASA fixed the DUET for £14 and recommended that I fit fast blow fuses in future - which I have done. (I had to sue to get recompense for the Simrad tillerpilot.)

Question.
Will a breaker trip as fast as a fast blow fuse?

[/ QUOTE ]

It depends on the current vs. time performance of the devices. For example it will take many hours at 3.1 A to blow a 3 A fuse.
 
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