electrical panel question
 

I have just installed a blue sea dc only panel. Im studying the installation instructions and have a question on running the negative wires. 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. Is there a problem with doing it this way.

There's no electrical reason not to do it as you described BUT you may still want to run each circuit negative as far as possible along with the positive, even twist them together, all the way to the distribution panel. The reason is so the current flowing in the conductor pair (equal but opposite) cancels out the Gauss field surrounding the single conductors. Your compass will be happier.

No problem; just make sure the negative runs are sized the same as the positive. I use a similar panel and a #6 works well for the negative home run.

You can use a ground bus elsewhere, but you still need to run a ground wire to the panel, if for no other reason then making the backlights and indicator lights work ;)

I did something similar, although I used breakers, not a pre-made panel.

Here's the negative side: http://www.moyermarine.com/forums/al...pictureid=1561

Because all my house loads are on this terminal block, the feed and return are sized at full design current, with a healthy margin.

Remember that the size of the conductors have to account for the full length of the circuit, both positive and negative. And while the cable is expensive, you may add loads in the future and you only want to do the feed and return once. Be conservative in your calculations, and then go bigger. :)

Remote ground bus is no problem. Don't forget that the positive lead from the battery to the panel needs circuit protection - the fuse has to be close to the battery (not sure of the max distance).

One more question. At least for now
 

Thank you for the responses so far. This panel has a shunt for an ammeter. My thought was to as per the blue sea app use a #4 wire to the shunt then a 4 from the other side to the first bus bar of the panel. The panel is a 100 amp. Then use jumpers in a series to the secound buss bar and then another to the third and final positive bar. My question is, is this electrically kosher, and if it is can I reduce the size of the wire with each subsequent jump. I would assume that the second jumper would need to be sized for any current down stream of it. And so on. I would make sure that the bus bar screws were long enough to capture two ring terminals. There are also positive and negative wires for a led back lights. Could I simply conect the positive wire back onto the positive bus bar. Trying to make all wire runs as short as possible.

Thanks again for all your advice.

I'm surprised Blue Sea doesn't provide a factory buss bar option to tie the positives together. They do for ganging their switches.

Where's the fuse that protects the #4 positive wire? Should be very close to the battery (nominally <= 7").

That fuse protects everything after, so no, the jumpers should all be #4. You're correct in knowing the nominal loads probably decrease with each subsequent buss bar, but the circuit protection is for full load (E.G. Imagine a dead short from the last bar), and each jumper is only protected if it can also support the full load.

Please post the item number of that Blue Seas panel. If we study it for a bit I think we can give more useful answers to your questions.

Jeff is on it. The fuse protects the downstream wiring, all of it up to the point of the next overcurrent protection so to be Kosher, all wiring protected by your 100 amp fuse should be 100 amp rated.

Didn't think about a dead short. That's why I its so good to ask questions. So if my knowledge is sufficient a dead short on tha last bar in the series will get full amp of whatever battery it's connected to. Hence the fuse <=7 inches away. And the fuse size should be larg enough to handle full load from the panel. I think I can go 150% of the load on the fuse. Not sure about that one. The wire of course needs to be large enough to handle the current I plan to pass through it. Must always remember that's what I'm trying to protect not the load or device. As far as led back light wires the simply emerg from under a circuit board. The tag on the wires state to hook positive to positive and negative to negative. I may decide to hook them up to a switch so the lights are not always on but I'm still thinking about that one. The closest positive source is the positive bus bar to the beakers. So I guess that they don't pre wire them because they may want to be switched. My plan was to go from battery to battery switch then from common from switch to panel and to starter stud. Two wires off of the common stud of battery switch. How am I doing so far. My one concern is where to place the fuse for panel. Only place is after common stud feed wire but may violate 7 once rule based on place of my battery's. Plan on using #2 wire from battery's to battery switch. And from common to starter. Understand it my be excessive.

Use of #2 as you describe is not excessive. Since the panel uses a shunt type ammeter, which will be in the negative loop if it is like other Blue Sea meters, why not put your protection (150 amp breaker) right next to it?

Just to be clear the #2 will be from battery to battery switch. Thinking about a post style fuse for those main branch #2s. I would be pleased to put the panel fuse next to the shunt but that would be about 2-3 feet away from battery. In violation of that 7 inch thing. And the instructions I have on this panel instructs to place the shunt on positive side. What's the difference.

Shunt on the positive side would be new to me, but I do welcome the change if Blue Seas has made it. I would like to study the details on your panel since it seems my knowledge is out of date. Could you say the model number? I will get the instructions on line and refrain from any more statements until I get up to speed.

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.

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.

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.

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.

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.

http://www.moyermarine.com/forums/da...BJRU5ErkJggg==

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?

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.

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.

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.

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