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tsweeney 02-12-2008 09:10 PM

Basic Electrical Diagram
 
Howdy All,
I was wondering if folks might look at and comment on the basic electrical diagram I have drawn up (in power point) for an electrical refit of a Fisher 25. The diagram just includes the positive wire for the most part and of course leaves out the branch circuit from the DC panel.
What I'm especially interested in is how other folks have managed switching, fusing and buses. I'm interested in using blue sea systems "terminal fuse block" and hanging those off of the positive distribution bus. Any comments or thoughts would be greatly appreciated as we're getting to the time to start ordering some parts.

it seems until I have made 10 posts I won't be able to have pictures (or clickable links) so y'all will have to go the text route.

(you need to take out the spaces, sorry the forum made me do it!)
www . poodah . com / image / ElecDiagram . jpg

T Sweeney

camaraderie 02-12-2008 10:10 PM

Here ya go T...welcome aboard. www.poodah.com/image/ElecDiagram.jpg

Can you advice what "ACR" is? Battery Selector Switch?

rhaley 02-13-2008 08:12 AM

My guess is ACR=Automatic Charging Relay. Keeps the house bank and starting bank isolated unless charging.

xtatico1404 02-13-2008 01:21 PM

The only comment that comes to mind right now is your Main DC overcurrent protection. You show a "Shunt" on the house batteries and nothing on the starter battery.

By "Shunt" I would take it that you mean a shunt resistor. A shunt does have an Amp rating which burns out at a certain amperage. It does not provide any other type of protection, such a short circuit protection and does not have an "opening speed" type curve. I would highly recommend to put a fuse as DC Main overcurrent protection.

By the way, you mentioned Blue Sea, and their website has a lot of information on their resources section. This is the overcurrent requirements per ABYC:

DC Main Overcurrent Protection Requirements
ABYC standard E11.12.1.1.1 states that each ungrounded conductor connected to a battery charger, alternator, or other charging source, shall be provided with overcurrent protection within a distance of seven inches (175mm) of the point of connection to the DC electrical system or to the battery.

The exceptions to this are:

When the conductor is enclosed in a sheath or enclosure such as conduit in addition to its insulation the 7" dimensions can be increased to 40".
If the conductor is connected directly to the battery terminal and is enclosed in a sheath or enclosure such as conduit in addition to its insulation the 7" dimension can be increased to 72".
The conductor connects to the starter for the engine.
Figure 1 below shows the location of the circuit protection devices per ABYC standard E11.12.1.1.1

camaraderie 02-13-2008 01:51 PM

xta...I assumed the shunt was for a link10 or similar to monitor battery state of charge.
I agree with you on the fuse location and he should use an ANL type block like this one:
http://bluesea.com/files/images/product_lines/129.png

tsweeney 02-13-2008 06:24 PM

Howdy all. Thanks for the responses.
Some points of clarification:
Indeed the ACR is an automatic charging relay.
The shunt is for a battery monitor (XBM probably)
As for fusing:
I'm aware of the rule and had the hoped that I'd be able to position the breakout bus bar close enough to use the terminal fuses (Blue Sea "Terminal Fuse Block") I mentioned in my first post. That may be unrealistic.

The diagram included fuses for all charging sources (and fusing for a windlass should one be added.)

Is the suggestion then to include for both starting and house to include dedicate fuse blocks? IE
house #2 -> fuse -> positive breakout
start batt -> fuse -> post for acr/switch
I further assume that even with these fuses I'd want to continue to include individual fuses for the charger/inv, alternater etc...

Overcurrent protection for the DC panel will be built in (it will have a main breaker)

Thanks again folks.

xtatico1404 02-13-2008 09:16 PM

tsweeney, you got it. Put in place fuses for the batteries. They will protect the batteries under short circuit & overcurrent conditions.

And yes, keep the fuses on each individual circuit, as well as the Main DC panel circuit breaker.

The term for what we are describing is called "selective coordination" of a protection system. For example, you have a fault (short circuit or something else) on the windlass circuit. If you have coordinated your protection, the fuse for the windlass circuit will go off and should contain the problem. Your Battery fuse will keep working and your DC panel will remain energized as well as all circuits, except the windlass circuit, which blew the fuse.

Say you did not put a fuse on each circuit, and only have a battery fuse and DC main breaker. The same condition happens on the windlass circuit, then the only protection will be the DC Main breaker, which should trip. If it trips, then all circuits on the panel will be de-energized, and you will have to fix the problem before you can, say....turn your lights on.

Going even deeper into the situation and something even more important, say you didn't even have a DC Main breaker but have battery fuses, and the same happens. Say your battery fuse is rated at 200Amps. You have a fault on the windlass circuit. Assuming that the short circuit happens to have a current of 180 Amps, the battery fuse will not blow and said short circuit will keep on putting energy and you will end up with a major bonfire :eek:

So, yes, put in place battery fuses, the DC Main breaker as well as fuses for individual circuits.

catamount 02-13-2008 09:53 PM

Quote:

Originally Posted by xtatico1404 (Post 265002)
tsweeney, you got it. Put in place fuses for the batteries. They will protect the batteries under short circuit & overcurrent conditions.

And yes, keep the fuses on each individual circuit, as well as the Main DC panel circuit breaker.

The term for what we are describing is called "selective coordination" of a protection system.

As I understand it, the reason for each of these fuses/breakers in sequence is to protect each bit of wire "downstream" from each fuse. You need a fuse at the battery to protect the wire that runs from the battery to your main buss (unless it's less than 7" or somesuch). The wire running from your buss to you panel might be a different (smaller) guage and so will require a different (smaller) fuse. The wires running from the panel to each of your fixtures will be smaller still, requiring still smaller fuses/breakers, and then fixtures (e.g. electronic instruments) may have still smaller wires in them, requiring their own fuse as well! You probably all know all this already, but the point is that it all starts at the battery, so you need fuse protection starting there, too. Am I right?

xtatico1404 02-14-2008 10:41 AM

catmount, you got the general idea.

Yes, the fuse is intended to protect the wire AND to a certain point, the load (whatever is connected to it). I say to a certain point, because it protects the load to faults (short citcuits) outside of the load itself. It will not protect the load from internal faults.

Also, the fuse size is NOT based or related to the the wire size/gauge. The fuse size depends on the amperage of the load that is connected to it. Say you have a lighting load that draws 5 Amps. According to wire ampacity tables http://www.ancorproducts.com/support..._Amperage.html
you can wire it with #18AWG (if less than 3 conductors and not taking into account wire length), which will give you 20 Amps outside engine areas, but your fuse will have to be a 5 Amps fuse at a minimum. However, recommended practices call for a fuse or breaker to operate at 75-80% of it's rated capacity. So 5Amps + 20% = 6 Amps, so you would have to go with the next size up which is 7.5 Amp fuse.

Also, please first look at the recommendation of the equipment manufacturer as to wire size & fuse size. When you are talking about electric motors (pumps, cooling/heating equipment, windlass, etc) the protection requirement is much higher. A respectable manufacturer will tell you what wire & fuse size to use.

As to why starting on the battery, because that's where you have all your enegy stored onboard. Say you accidentally short the wires on a battery, if the fuse is not in place, the short circuit will continue until the battery depletes it's energy, and once again we go back to the big bonfire thing :eek:
Think of it as the lock on your front door, you have to start protecting from the very begining.

Just to give you a good idea of the energy dissipated on a short citcuit:
http://teslamania.delete.org/frames/...#500_kV_Switch
http://teslamania.delete.org/frames/longarc.htm#Blowup - the fire you see is caused by the oil inside the transformer that escapes under pressure and gets ignited

And just in case you thought that it only happens at high voltages, here is a 480V short circuit...the lower the voltage, the higher the current.
http://teslamania.delete.org/frames/...volt_arc_flash

Serious stuff, so take electrical systems seriously. Be safe please.

rhaley 02-14-2008 11:56 AM

Quote:

Originally Posted by xtatico1404 (Post 265275)
catmount, you got the general idea.

Yes, the fuse is intended to protect the wire AND to a certain point, the load (whatever is connected to it). I say to a certain point, because it protects the load to faults (short citcuits) outside of the load itself. It will not protect the load from internal faults.

Also, the fuse size is NOT based or related to the the wire size/gauge. The fuse size depends on the amperage of the load that is connected to it. Say you have a lighting load that draws 5 Amps. According to wire ampacity tables http://www.ancorproducts.com/support..._Amperage.html
you can wire it with #18AWG (if less than 3 conductors and not taking into account wire length), which will give you 20 Amps outside engine areas, but your fuse will have to be a 5 Amps fuse at a minimum. However, recommended practices call for a fuse or breaker to operate at 75-80% of it's rated capacity. So 5Amps + 20% = 6 Amps, so you would have to go with the next size up which is 7.5 Amp fuse.

Also, please first look at the recommendation of the equipment manufacturer as to wire size & fuse size. When you are talking about electric motors (pumps, cooling/heating equipment, windlass, etc) the protection requirement is much higher. A respectable manufacturer will tell you what wire & fuse size to use.

As to why starting on the battery, because that's where you have all your enegy stored onboard. Say you accidentally short the wires on a battery, if the fuse is not in place, the short circuit will continue until the battery depletes it's energy, and once again we go back to the big bonfire thing :eek:
Think of it as the lock on your front door, you have to start protecting from the very begining.

Just to give you a good idea of the energy dissipated on a short citcuit:
http://teslamania.delete.org/frames/...#500_kV_Switch
http://teslamania.delete.org/frames/longarc.htm#Blowup - the fire you see is caused by the oil inside the transformer that escapes under pressure and gets ignited

And just in case you thought that it only happens at high voltages, here is a 480V short circuit...the lower the voltage, the higher the current.
http://teslamania.delete.org/frames/...volt_arc_flash

Serious stuff, so take electrical systems seriously. Be safe please.

There are a few points that I disagree with here, one of which is that the fuse size is not related to the wire size. The wire size most certainly dictates the maximum size fuse. You may fuse the wire at a lower current rating than the wire itself, but the fuse protects the wire, not the load. The 80% rule of thumb for the protective device applies to the rating of the wire, not the device on the other end. As before, you can fuse lower if you prefer. A short circuit between the source and the load will expend it's energy before the current reaches the intended load (hence the name) and at the relative voltage levels found on most boats, will have no effect on the load other than not providing it with enough energy to function.

One point I absolutely agree on is the fusing of the battery as close to the battery bank as possible. As xtatico1404 points out, this is the beginning of all your stored energy and a short circuit there has a huge fire risk. This should be non-negotiable and standard practice every time you start to layout an electrical system.

Good Luck!


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