electrical panel question

[hanleyclifford]

https://www.bluesea.com/products/8378/DC_18_Position
That sould get you to the panel with a link to the instructions. If the link is bad the panel # is 8378. What is the difference between positive and neg loop placement. To my thinking the shunt on positive whould "see" everything after it and after would see before it. I would think intuitively it would be better on positive feed. You would see complete current draw of each load in use.

Now for the caveat. I'm pretty sure I read the schematic correctly.

You did indeed, and I stand corrected and upgraded. Note also they are calling for #2 to and from the panel. If you do use #2 for the panel everything upstream must be #2 or greater. I suggest the use of breakers rather than fuses.

[azazzera]

And I get confused at times. Up stream is the battery side. I or should I say the blue sea app calculated 4 wire based on my wire length of less than 3 feet. There recommended 2 wire was a 10 foot run.

If you or someone can explain the difference between putting the meter in the positive and negative loop.

Thanks again.

[azazzera]

So my couriosity peeked. The instructions say 2 wire but for a 10 foot run the blue sea app gives a calculation of 4 wire. A bit of a discrepancy. Don't know how they come up with the 2 wire size.

[ndutton]

If you or someone can explain the difference between putting the meter in the positive and negative loop.

No difference really, current is current but consider this from your first post:
There is a negative bus on the panel but I don't see the need to run the wire from each load directly back to the panel bus. my plan was to run them to a location close to the panel on a separate wire block then have that block connected back to the battery with a wire that can handle the current of all the wires. I think it will be cleaner and less congested on the panel doing it this way.
Having the shunt in the negative side kinda answers that question itself.

My 2¢: follow the manufacturer's instructions.

edit:
There's no harm in going with larger wire. In fact, there is the advantage of even less voltage drop than the 3% allowable maximum. 1% is better than 3%. Years ago I was wiring city and county parks with insanely long runs between light poles. It was not unusual to run #6 wire for a 20 amp circuit with maybe 10 amps of load to mitigate voltage drop.

[BunnyPlanet169]

If you don't have it already, I would strongly encourage you to get a copy of the Nigel Calder book, "Boat owners Mechanical and Electrical Manual." Note that it's even referenced by Blue Sea in the PDF instructions. It's extremely readable, and contains excellent design and practical information.

For simplicity and bulletproof, you can't go wrong with the terminal mounted Blue Sea fuses. The go right on the battery post, and were designed to meet the nominal <= 7" requirement. No more costly than ANL fuses and holder.

You will not regret using #2 all the way, as opposed to #4. Your time and labor are more valuable than the incremental cost of the cable. And you'll sleep better knowing it's just that much more robust. And it's easier having one kind of lug, one size of heat shrink, one setting on the crimper, etc.

The LED wires are not fused because they're probably 22AWG, and they ARE the fuse. Connect them as described to the bus bars. Just not enough energy to start a fire before the wire is fried.

Both shunt meter wires are fused right next to the shunt because a 16AWG wire CAN start a fire. The shunt meter wires are essentially both at full battery voltage.

[azazzera]

I thought I read at some point that there is a harm in useing an oversized wire. I forget the application I read it in of course. I have vague rememberance reading it in N.C. Book.

So current in equals current out. Other than keeping it simple and neat I would get same reading on both loops. I understand from my quick search about ammeters that the meeter is specific to were it will go as far as positive or neg side?

[azazzera]

Jeff. I agree with your suggestion. It looks like you looked up the panel instructions. The breaker led don't show a fuse but the led from the label backlight system dose show a fuse but gives no amps for it. If I had read the instructions carefully I would have seen were it suggests to connect the positive wire of the backlight system to the panel positive bus. O well. I've enjoyed the conversation. Am very greatfull for it as well. Thanks again.

[ndutton]

I understand from my quick search about ammeters that the meter is specific to were it will go as far as positive or neg side?

No. The meter is specific to the type of shunt and since they were packaged by the mfr. you're good. Line and load connections on the shunt are specific and in the negative loop may be (I think) reversed. Again, that's why I suggest following Blue Seas' instructions and intent.

[tac]

Ammeters and Shunts

1. Most ammeters that measure over a few amps use a shunt, and are actually millivoltmeters, not ammeters. A shunt is no more than a precision, high wattage, low resistance resistor. They are large in mass, and often finned, so the heating effect of large currents on the resistance is minimal. Standard shunts are sized to give a voltage drop across this resistance of 50 millivolts for a given full scale current. A 100A/50mV shunt would have 50 millivolts out with a current of 100 amps through the shunt. Plugging this into Ohms law gives shunt resistance of R = .050V/100A, or .0005 ohms.

2. Analog meters used with a shunt are sized so the meter scale reads in amps the same as the shunt, and that scale maximum is when the input voltage is 50mV. As in the above shunt example, an analog meter matched to a 100A/50mV shunt would be marked, generally on the back, "50mV full scale", and the meter scale on the front would be marked 0 to 100 amps. This means you can buy a Simpson 0-100Amp/50mV meter to go with a Yokagawa 100A/50mV shunt.

3. Because an analog ammeter is measuring the voltage drop, or the differential voltage, and that can be a floating voltage (not referenced to ground), across the shunt, it doesn't care if it is on the positive side or negative (return) of the circuit. Nor does it care if neither side of the shunt is connected to ground.

4. Most low priced digital ammeters with shunts are different. Again, they are actually millivoltmeters. But they do not actually measure the voltage drop across the shunt, they measure the voltage of the shunt with respect to ground (battery return). Therefore, most (but not all) can only be used in the negative side of the circuit where one side of the shunt is connected to battery negative, with the other side connected to all the return wires for the circuits you want to measure. They are sized the same way as the analog meters.

5. The reason for this is that digital meters contain one or more instrumentation operational amplifiers, and analog-to-digital converters. They are expensive and can be susceptible to noise, so design and construction of micro/millivolt signal conditioners and A/D converters is much more expensive than analog meters, which contain no electronics. These electronics require a good battery return as a reference, which an analog meter doesn't. The simplest and cheapest answer to these problems is to require one side of the shunt to be grounded. Good industrial digital ammeters that will measure a floating differential voltage do exist, but are much more expensive.

6. Some nice things about using shunts, and either analog or digital meters:
a) Generally you can use anyone's shunt with anyone's meter as long as you match the amp scale and shunt millivolts. Don't like the Blue Sea meter face? Get a Yokagawa
b) The shunt is a resistor and has no polarity, so how you connect the main power leads is unimportant.
c) For a digital meter the two small leads to the meter can be hooked so that the meter reads negative when the circuit is drawing current, and positive if there is a charger. Or hook it so it reads a positive number when current is drawn. You can do that with an analog meter only if you have a center-zero scale meter. They exist, but are expensive and hard to find.

[ndutton]

If diverting from the Blue Seas instructions (shunt in the negative side), I'd pay careful attention to the instructions as you modify.

[hanleyclifford]

1. Most ammeters that measure over a few amps use a shunt, and are actually millivoltmeters, not ammeters. A shunt is no more than a precision, high wattage, low resistance resistor. They are large in mass, and often finned, so the heating effect of large currents on the resistance is minimal. Standard shunts are sized to give a voltage drop across this resistance of 50 millivolts for a given full scale current. A 100A/50mV shunt would have 50 millivolts out with a current of 100 amps through the shunt. Plugging this into Ohms law gives shunt resistance of R = .050V/100A, or .0005 ohms.

2. Analog meters used with a shunt are sized so the meter scale reads in amps the same as the shunt, and that scale maximum is when the input voltage is 50mV. As in the above shunt example, an analog meter matched to a 100A/50mV shunt would be marked, generally on the back, "50mV full scale", and the meter scale on the front would be marked 0 to 100 amps. This means you can buy a Simpson 0-100Amp/50mV meter to go with a Yokagawa 100A/50mV shunt.

3. Because an analog ammeter is measuring the voltage drop, or the differential voltage, and that can be a floating voltage (not referenced to ground), across the shunt, it doesn't care if it is on the positive side or negative (return) of the circuit. Nor does it care if neither side of the shunt is connected to ground.

4. Most low priced digital ammeters with shunts are different. Again, they are actually millivoltmeters. But they do not actually measure the voltage drop across the shunt, they measure the voltage of the shunt with respect to ground (battery return). Therefore, most (but not all) can only be used in the negative side of the circuit where one side of the shunt is connected to battery negative, with the other side connected to all the return wires for the circuits you want to measure. They are sized the same way as the analog meters.

5. The reason for this is that digital meters contain one or more instrumentation operational amplifiers, and analog-to-digital converters. They are expensive and can be susceptible to noise, so design and construction of micro/millivolt signal conditioners and A/D converters is much more expensive than analog meters, which contain no electronics. These electronics require a good battery return as a reference, which an analog meter doesn't. The simplest and cheapest answer to these problems is to require one side of the shunt to be grounded. Good industrial digital ammeters that will measure a floating differential voltage do exist, but are much more expensive.

6. Some nice things about using shunts, and either analog or digital meters:
a) Generally you can use anyone's shunt with anyone's meter as long as you match the amp scale and shunt millivolts. Don't like the Blue Sea meter face? Get a Yokagawa
b) The shunt is a resistor and has no polarity, so how you connect the main power leads is unimportant.
c) For a digital meter the two small leads to the meter can be hooked so that the meter reads negative when the circuit is drawing current, and positive if there is a charger. Or hook it so it reads a positive number when current is drawn. You can do that with an analog meter only if you have a center-zero scale meter. They exist, but are expensive and hard to find.

Thanks for the excellent discourse. My experience is with digital meters and shunts for which Blue Seas specifies using the negative side whereas the analog can use either positive or negative.

[azazzera]

Thanks Neil. I realy have no intention on deviating from published instructions. My questions come from a desire to understand how this all works. knowledge Is power after all. I'll be back to fill my brain From time to time.

[tac]

My windy discourse on shunts and meters was of a general nature, since this problem has come up before. Of course Neil is correct to advise following the Blue Sea instructions.

Since the panel in question has an analog ammeter/shunt, if the shunt power leads are hooked up backwards, the voltage drop across the shunt will be reversed and the meter will try to read negative and can't since it will hit the mechanical stop at just below zero. If the meter leads from the shunt are hooked backwards, the meter will also try to read negative. If both are hooked backwards, the meter will read correctly (two wrongs make a right?). So, if you see the meter try to read negative, the easiest thing to do is swap the meter leads, they're smaller. But if you hook to the instructions there should be no problem.

[hanleyclifford]

My windy discourse on shunts and meters was of a general nature, since this problem has come up before. Of course Neil is correct to advise following the Blue Sea instructions.

Since the panel in question has an analog ammeter/shunt, if the shunt power leads are hooked up backwards, the voltage drop across the shunt will be reversed and the meter will try to read negative and can't since it will hit the mechanical stop at just below zero. If the meter leads from the shunt are hooked backwards, the meter will also try to read negative. If both are hooked backwards, the meter will read correctly (two wrongs make a right?). So, if you see the meter try to read negative, the easiest thing to do is swap the meter leads, they're smaller. But if you hook to the instructions there should be no problem.

Paragraphs 4 and 5 of your discourse explain something I had not known until now - why I could not use my digital Blue Seas ammeter to measure in the positive side. Now I know: thanks again.

[ndutton]

Azazzera, it's all about a successful result for your installation and anticipating problems before they emerge. If you ever remember where you read that oversized wire was harmful please refer the source. That ought to be entertaining.