Fuses Required for Battery Monitor Wires?

[Davidasailor26]

Correct. A wire that is 22 AWG is rated for 1.84 AMPS. The rule of thumb is take the maximum load of the wire and multiply it by 1.5 to determine the fuse size: 1.84 X 1.5 = 2.76 AMPS (fuse size) Which is absurd for a wire that is drawing a maximum of 1 milliamp. Worse, since you are trying to monitor a critical voltage, it is imperative that you have minimum resistance loss to get an accurate reading. Adding unnecessary fuses inline, and the potential for corrosion would just hinder the voltmeter from accurately measuring the voltage. A an ex-electronics technician, I have never seen a fuse in-line with a meter. Ever.

I disagree. The meter will draw about 1mA when everything is working fine, but when part of the wire chafes through and touches a ground, the current through the meter makes no difference - you're going to draw current through the wire until it burns. This is why you do need a fuse in the circuit - it has nothing to do with the meter and everything to do with the fact that you have a wire connected to a battery.

As for any potential voltage drop- since the meter only draws 1mA, you'd need to have a 100 ohm resistor to see a 0.1 volt drop in voltage. Since fuse resistance is measured in milliohms, you're going to see a voltage drop of less than 0.001 volts - way less than the resolution of the OP's meter.

 

[mz4wheeler]

If you want to get minimum resistance, why not use a larger wire? 22GA seems very small. I think ABYC standards call for a minimum of 16 gauge wire. Wouldn't using 16 or even 14 gauge offset any loss associated with a fuse?

If fusing a gauge is really unnecessary, why does the Balmar Smart gauge ship with a 3 amp ATC fuse for each lead and require 14 gauge wiring?

1) 22GA is rated for 1.84 amps, plenty enough for 1 miliamp.

2) because because the Balmar Smart gauge (itself) draws enough current to warrant a fuse. It takes a lot of power to light LEDs and it's circuit board, and internal software.

Also, I was referring to a basic ANALOG meter, which in itself draws 1 milliamp (full scale).

 

[Davidasailor26]

2) because because the Balmar Smart gauge (itself) draws enough current to warrant a fuse. It takes a lot of power to light LEDs and it's circuit board, and internal software. Also, I was referring to a basic ANALOG meter, which in itself draws 1 milliamp (full scale).

Whether or not to fuse has nothing to do with the size of the load on a circuit - the size of the load only affects the size of the fuse. Whether or not to fuse is a risk acceptance decision based on the likelihood that something will go wrong and the circuit will be able to draw more than the wires of that circuit can handle. Given that these meter wires will run in an infrequently inspected space where they could chafe and touch any of the many ground surfaces, there is a risk there, and mitigating that risk by adding a fuse has negligible cost.

 

[Davidasailor26]

Whether or not to fuse has nothing to do with the size of the load on a circuit - the size of the load only affects the size of the fuse. Whether or not to fuse is a risk acceptance decision based on the likelihood that something will go wrong and the circuit will be able to draw more than the wires of that circuit can handle. Given that these meter wires will run in an infrequently inspected space where they could chafe and touch any of the many ground surfaces, there is a risk there, and mitigating that risk by adding a fuse has negligible cost.

slight correction to my statement above - the size of the load doesn't affect the size of the fuse directly, it affects the size of the wire used, and the wire size determines fuse size.

 

[mz4wheeler]

I disagree. The meter will draw about 1mA when everything is working fine, but when part of the wire chafes through and touches a ground, the current through the meter makes no difference - you're going to draw current through the wire until it burns. This is why you do need a fuse in the circuit - it has nothing to do with the meter and everything to do with the fact that you have a wire connected to a battery.

As for any potential voltage drop- since the meter only draws 1mA, you'd need to have a 100 ohm resistor to see a 0.1 volt drop in voltage. Since fuse resistance is measured in milliohms, you're going to see a voltage drop of less than 0.001 volts - way less than the resolution of the OP's meter.

I was referring to corroded contacts of the fuse, not the fuse itself. There are a 1000 different ways to fry any wire on any boat, fused or not.

Why not just connect the meter to circuit breaker? Good enough.

 

[walt]

any time there is a wire gauge change ( larger diameter to smaller diameter) you need to add a fuse.

For example, if you had a 4 gauge wire run, you would need a fuse at the "source" that was sized for the 4 gauge wire.

Then if you tapped off the 4 gauge with a 14 gauge wire, an additional fuse is required where the 14 gauge wire begins and this new fuse sized for the 14 gauge wire.

 

[Maine Sail]

2) because because the Balmar Smart gauge (itself) draws enough current to warrant a fuse. It takes a lot of power to light LEDs and it's circuit board, and internal software.

The Smart Gauge specs claim self consumption is less than 5mA, I have physically measured it at 3 mA, when the display is asleep. Specs claim just 15mA when the display is lit and I have measured it at about 11mA. Most of the time the display will be asleep..


5mA = 0.005A


15mA = 0.015A

The fuse for the Smart gauge is required to protect the wire not to protect the Smart Gauge......

 

[Davidasailor26]

There are a 1000 different ways to fry any wire on any boat, fused or not.

Sorry to belabor the point, but, really there's only 1 way to fry any wire on a boat - to put more current through it than it can carry. If the wire is properly fused (at its current source), then that one way is simply not possible.

As Stu might say - OP's boat, OP's choice, but I think the OP made the right decision to fuse. I would do the same, accepting the risk of loss in meter accuracy if fuse contacts ever corroded, vs the risk of burning down the boat.

 

[Jim 5757]

"to Fuse Or Not To Fuse... That Is The Question...!"

 

[Ron20324]

"There are a 1000 different ways to fry any wire..."

"...really there's only 1 way to fry any wire on a boat....

"

No, he was right- there are a THOUSAND ways. Thus the "MILLI" amp usage.

 

[dlochner]

"

No, he was right- there are a THOUSAND ways. Thus the "MILLI" amp usage.

Not sure I follow, since the prefix "milli" denote 1/1000, so that would be less than one way.

The prefix "kilo" means 1000. So a kilo amp would be 1000 amps. But I've never heard that term.

One more thing, if you are not fusing your boat properly, please dock next to someone else.

 

[mz4wheeler]

One more thing, if you are not fusing your boat properly, please dock next to someone else.

Again.. I have never seen a meter "fused" in any schematic diagram I've ever worked with.

Can you? Sure. Do you really need no? If you are going to add a fuse in a 1 milliamp voltage measuring circuit, it must be physically at the battery to be effective. But isn't going to do ANYTHING to protect the meter.

What about a NMEA/Seatalk wire? Should you fuse that? It's a wire, right? Funny, I don't see any fuses on the raymarine diagrams for seatalk. Those wires go all around the boat, rubbing all kinds of different wires.

Do you think there is a fuse in the main power line from your battery to the breaker panel? If the philosophy is to "always protect the wire" then there should be a fuse inline, right?

I guarantee you I can fry that wire by shorting any part of it to ground, or doing something stupid like dropping a screwdriver between terminals.

There are a 1000 ways of being stupid with boat wiring, no amount of fusing will protect all possibilities. However, it DOES catch quite a few.

Fuse a 1 milliamp circuit if it makes you feel better.

 

[dlochner]

Do you think there is a fuse in the main power line from your battery to the breaker panel? If the philosophy is to "always protect the wire" then there should be a fuse inline, right?

Yes. One of these guys. One for the house battery, one for the start battery.


https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A

And then there is a circuit breaker at the on/off switch and another breaker at the panel.

 

[mz4wheeler]

Yes. One of these guys. One for the house battery, one for the start battery.

Yup, I have those too. However, I must admit that I haven't verified that they were installed properly by the PO. After all, there are a 1000 ways to screw it up.

 

[capta]

Has anybody considered that this unit may be a load tester? It appears from the picture that there may be more in this circuitry than just a meter. It quite plainly says "test" on it, which would indicate to me that it does more than read the static voltage.
Therefor, I would certainly fuse it.

 

[JamesG161]

I have noticed the "NO's" are certain and the "YES's" are almost all...

why not's
or
I thinks so's
or
I would's

I did note that the electricians or electronic types all said NO.

Science is almost certain.
Jim...

 

[Maine Sail]

I have noticed the "NO's" are certain and the "YES's" are almost all...

why not's
or
I thinks so's
or
I would's

I did note that the electricians or electronic types all said NO.

Science is almost certain.
Jim...

I believe I am the only practicing ABYC certified marine electrician here and I did not say no fuse.... This is exactly what I said on the first page of this thread..

This definitely requires a fuse, under current US safety standards..

This is why land based electronics techs, EE's or electricians need not present marine based statements as "facts" unless they are specifically trained in marine standards. It is extremely clear from this thread that those who said no have little understanding of marine wiring standards and practices. The rules and standards for land, while similar, are NOT the same. A fuse is REQUIRED in this instance....

It is a requirement under marine safety standards and would be a flag in an insurance survey, IF you had a competent surveyor.

 

[Johnb]

I have noticed the "NO's" are certain and the "YES's" are almost all...

why not's
or
I thinks so's
or
I would's

I did note that the electricians or electronic types all said NO.

Science is almost certain.
Jim...

No, those of us who actually know anything about electricity all advised for fusing.

And can explain why.

 

[Davidasailor26]

Has anybody considered that this unit may be a load tester? It appears from the picture that there may be more in this circuitry than just a meter. It quite plainly says "test" on it, which would indicate to me that it does more than read the static voltage. Therefor, I would certainly fuse it.

If you're right and it is a load tester, then it will draw much more current than a plain voltmeter, and would require much larger gauge wire. It would need a fuse regardless of whether it's a load tester or a voltmeter, just a different size fuse, based on the wire gauge.

Personally I still think it's a plain voltmeter, just with the test switch to close the circuit and see the voltage so that it's not drawing current all the time.

 

[Maine Sail]

Has anybody considered that this unit may be a load tester? It appears from the picture that there may be more in this circuitry than just a meter. It quite plainly says "test" on it, which would indicate to me that it does more than read the static voltage.
Therefor, I would certainly fuse it.

It is nothing more than a volt meter with a 4 way selector switch to monitor the voltage of four different banks. The only load is the analog meter. Still needs a fuse at the source, or step down in wire size, to protect the wire...