5 amp fuse keeps blowing?

[Hoohaa]

I have recently installed a new AIS and splitter. We wired in a bus, which takes its power from the instrument switch on the pannel. If everything is running, the fuse will blow after a minute or so. I suspect we are overloading the 5 amp fuse but would like some input on what size I should be running. Note that the fuse does not blow if the AIS is switched off.
Here is a list of the equipment currently using that fuse and the manufacturers power consumption specs.

Class B Icom AIS MA-500TR, with its own gps antenna - Uses TX 1.5 amps & RX 0.7 amps (could someone explain what TX & RX mean?).

GME AIS Splitter (AISS120) - uses 1.15 amps.

Garmin GPS map 550S plotter with a Transducer - uses 1.25 amps.

If this data is correct then its a total of 4.6 amps..

Thanks for your help.
Jeff

[TurninTurtle]

Shouldn't each of those have its own dedicated fuse?

TX = Transmit
RX = Receive

[Hoohaa]

Originally Posted by TurninTurtle

Shouldn't each of those have its own dedicated fuse?

TX = Transmit
RX = Receive

You might be right..?? Open to advise here..

[TurninTurtle]

Each of those should have come with an in-line fuse holder and fuse of the correct size.

If you've got them all mixed up then check their manuals as they should indicate the correct fuse ratings.

[pesarsten]

In a perfect world, everything would be individually fused. Perhaps impractical in some cases. But, have you checked what the voltage is at the devices, a corroded connection in the supply line could cause a problem. It looks like you consume about 48 watts ( 12 volts x @ 4 amps). A poor connection that drops you supply to 10 volts would result in 4.8 amps draw. Too close for a 5 amp fuse. This would need to be adressed.

Perhaps put the AIS and Splitter on a separate 5 amp fuse for reliability.

[skipmac]

First question, is the fuse that's blowing connected to the switch on the panel or an inline fuse? If the later where is it located?

If the fuse is in the panel then if I understand you have a wire from the "Instrument" switch on the panel to a bus bar and then feed the instruments from the bus bar. I assume + and - wires to the bus, both from the panel?

If this is correct then what size wires are running from panel to bus bar and from bus bar to the instruments?

The reason for all this, the purpose of a fuse that feeds a bus bar is not to protect the instruments but to protect the wires, if you have a very small wire you need a very small fuse because a big fuse might allow enough current to heat the wire, melt the insulation and start a fire.

So if your wires are say 10-12 gauge you could easily and safely use a 15 amp fuse.

If you are trying to protect the equipment then an inline fuse on the hot wire to the device is where that should be. In that case use the size fuse recommended by the manufacturer.

[StuM]

Fuse or circuit breaker? If CB, how old is it?

CB gets weaker with age and use.

As a rule of thumb, you shouldn't load circuit breakers consistently over 80% - doing so can cause them to trip after a while.

[Hoohaa]

Originally Posted by TurninTurtle

Each of those should have come with an in-line fuse holder and fuse of the correct size.

If you've got them all mixed up then check their manuals as they should indicate the correct fuse ratings.

Surprisingly they do not have an in-line. But if I install them it will still not solve my original problem. Yes the devices will be protected but they are still getting power from the original switch with the 5 amp fuse.
Am I thinking this through correctly. If I increase the fuse size without having the recommended in-line fuse for each of the items, then they could be damaged before, lets say 10 amp fuse blows?

[TurninTurtle]

US Navy Electrical Safety Inspector (In a previous employment) says:

Each of these devices NEEDS to be individually fused because when you have a bunch on one fuse and it blows ITS DISABLING ALL OF YOUR NAV/SAFETY ELECTRONICS. (even though adding up the demands says it should work).

You don't know which one is drawing more than its supposed to... Just that the math says it should work.

Do it right.

For equipment reliability and fire prevention.

**************

Its OK to have a 10 amp rated line, with 10 amp fuse that then splits at a bussbar to the individual device fuses. Not ideal... but keeps you from running as many lines.

[Hoohaa]

Originally Posted by skipmac

First question, is the fuse that's blowing connected to the switch on the panel or an inline fuse? If the later where is it located?


If the fuse is in the panel then if I understand you have a wire from the "Instrument" switch on the panel to a bus bar and then feed the instruments from the bus bar. I assume + and - wires to the bus, both from the panel?


Correct. But the - is connected to a main earth which runs directly to the battery bank, not back to the panel.

If this is correct then what size wires are running from panel to bus bar and from bus bar to the instruments?

The reason for all this, the purpose of a fuse that feeds a bus bar is not to protect the instruments but to protect the wires, if you have a very small wire you need a very small fuse because a big fuse might allow enough current to heat the wire, melt the insulation and start a fire.

I can't tell you exactly what the wire gauge is, but they are substantial, so I am shore they will be able to cope. the equipment wiring is what came with the equipment. I am fairly shore that the Splitter and AIS do not have an in-line fuse supplied with it. but I did get the AIS second hand.

So if your wires are say 10-12 gauge you could easily and safely use a 15 amp fuse.

If you are trying to protect the equipment then an inline fuse on the hot wire to the device is where that should be. In that case use the size fuse recommended by the manufacturer.

The fuse is connected to the switch on the panel.



Jeff

[Adelie]

Originally Posted by Hoohaa

You might be right..?? Open to advise here..

Turtle is right.

[Hoohaa]

Originally Posted by StuM

Fuse or circuit breaker? If CB, how old is it?

CB gets weaker with age and use.

As a rule of thumb, you shouldn't load circuit breakers consistently over 80% - doing so can cause them to trip after a while.

Its a fuse..

[Hoohaa]

Originally Posted by pesarsten

In a perfect world, everything would be individually fused. Perhaps impractical in some cases. But, have you checked what the voltage is at the devices, a corroded connection in the supply line could cause a problem. It looks like you consume about 48 watts ( 12 volts x @ 4 amps). A poor connection that drops you supply to 10 volts would result in 4.8 amps draw. Too close for a 5 amp fuse. This would need to be adressed.

Perhaps put the AIS and Splitter on a separate 5 amp fuse for reliability.

I have checked the voltage, as far as I can see it all looks good.

[cal40john]

Originally Posted by Hoohaa

Surprisingly they do not have an in-line. But if I install them it will still not solve my original problem. Yes the devices will be protected but they are still getting power from the original switch with the 5 amp fuse.
Am I thinking this through correctly. If I increase the fuse size without having the recommended in-line fuse for each of the items, then they could be damaged before, lets say 10 amp fuse blows?

From your manual -

One fuse is installed in the DC power cable. If the fuse blows,
track down the source of the problem, have it repaired, and
replace the damaged fuse with a new one of the proper rating.
(There's a picture following in the manual.)

Click on manual at this link
MA-500TR Class B AIS Transponder - Features - Icom America

You'll probably find all your electronics manuals will describe an inline fuse

Read #6 again about fuses protecting wires or devices.

[smac999]

your instrument fuse should be large. say 15amp. I normally run 30a breakers for nav gear. then run cable to bus bar, then each unit has it's proper size fuse from bar based on the manual. or buy a blue sea fuse block to feed from the switch. https://www.bluesea.com/products/502..._Bus_and_Cover