Hi.. Just wondering if someone knew how to detmine fuse size for a battery bank. This is the fuse between the battery and the on/off switch + panel. My battery is 215aH and the max amperage on my panel is 100 amps. Thanks... Cris
Fuse Size for Batteries
- Thread starter Cris Hazzard
- Start date
- Status
House fuse
A good common sense approach to fusing is explained in the West Marine catalog. They've condensed info from several books. Following the logic gets you to look at ALL of your 12v requirements.
A good common sense approach to fusing is explained in the West Marine catalog. They've condensed info from several books. Following the logic gets you to look at ALL of your 12v requirements.
How to size overcurrent protection
The primary purpose of any overcurrent device (circuit breaker or fuse) is to protect the conductor. My batteries have 125A fuses at the batteries to protect the #1AWG connecting them to the battery selector switch. If your concern is to protect the switch having a lower current rating, use a smaller fuse sized to protect the switch. Hope that this helps.
The primary purpose of any overcurrent device (circuit breaker or fuse) is to protect the conductor. My batteries have 125A fuses at the batteries to protect the #1AWG connecting them to the battery selector switch. If your concern is to protect the switch having a lower current rating, use a smaller fuse sized to protect the switch. Hope that this helps.
150 amps
I've had the same question for a long time. The most recent answer I found (don't remember where) was 150 amps. (Sorry, but the folks who suggested 20 amps didn't undertsand your question).
I've had the same question for a long time. The most recent answer I found (don't remember where) was 150 amps. (Sorry, but the folks who suggested 20 amps didn't undertsand your question).
Cris
The ABYC says there is no practical way to fuse between the battery and engine. I think that's also the case with the distribution panel.
The ABYC says there is no practical way to fuse between the battery and engine. I think that's also the case with the distribution panel.
Separate Panels
Chris, when I built a new panel for my last boat, I used three commercially available multi-circuit panels side by side. I fused each one's power buss with a 30 amp fuse as a final protection in case one of the pop-out fuses melted down in an over-current situation. On my larger boat's panel (an H-34), I would agree with Fred, you can't practically fuse the panel itself--that's what the main breaker on it is for.
Chris, when I built a new panel for my last boat, I used three commercially available multi-circuit panels side by side. I fused each one's power buss with a 30 amp fuse as a final protection in case one of the pop-out fuses melted down in an over-current situation. On my larger boat's panel (an H-34), I would agree with Fred, you can't practically fuse the panel itself--that's what the main breaker on it is for.
It depends on your Current Draw.
I sized mine for a 2500 watt inverter, refrig, lights, radios, etc. etc. I used a 250 amp fuse on the house system. I don't have a fuse on the start battery. Bill Bell
I sized mine for a 2500 watt inverter, refrig, lights, radios, etc. etc. I used a 250 amp fuse on the house system. I don't have a fuse on the start battery. Bill Bell
Add up your current draws
My surveyor said to add up all the current draw, then add about 20% on top. So I installed 2 large fuse holders between the battery bank switch and the batteries. I attached my ammeter between the holder's terminals in place of a fuse, set the switch to use that bank, then turned each on circuit one at a time. Then just add up the draw for each circuit, multiply by 1.2 and you've got your number. I'm not an electrician, but I just followed the surveyor's instructions and they seemed logical.
My surveyor said to add up all the current draw, then add about 20% on top. So I installed 2 large fuse holders between the battery bank switch and the batteries. I attached my ammeter between the holder's terminals in place of a fuse, set the switch to use that bank, then turned each on circuit one at a time. Then just add up the draw for each circuit, multiply by 1.2 and you've got your number. I'm not an electrician, but I just followed the surveyor's instructions and they seemed logical.
bottom line
The fuse is designed to protect the conductor. I agree that you can't fuse the connection from the battery to the starter motor. I disagree with fred that you can't fuse the conductor going to your panel. whatever the amp rating for that size conductor, that should be the fuse rating for that conductor. What would happen if something abraded through the insulation before the main breaker in the panel and shorted to ground? I use a 175 amp class T fuse right at my battery to protect the 1/0 wiring to the distribution panel.
The fuse is designed to protect the conductor. I agree that you can't fuse the connection from the battery to the starter motor. I disagree with fred that you can't fuse the conductor going to your panel. whatever the amp rating for that size conductor, that should be the fuse rating for that conductor. What would happen if something abraded through the insulation before the main breaker in the panel and shorted to ground? I use a 175 amp class T fuse right at my battery to protect the 1/0 wiring to the distribution panel.
I have two
I have two fuses. One is a 300A fuse, basically to prevent a fire from high amp draw. The second is a 50A master breaker between the on/off switch and the DC distribution panel. I have a 210A house bank of two Group 31 AGM batteries. Hope this helps. Les Murray s/v Ceilidh '86 C-36 #560
I have two fuses. One is a 300A fuse, basically to prevent a fire from high amp draw. The second is a 50A master breaker between the on/off switch and the DC distribution panel. I have a 210A house bank of two Group 31 AGM batteries. Hope this helps. Les Murray s/v Ceilidh '86 C-36 #560
OK, let's think about this for a second,,,
First off I don't know of boat manufacturers installing fuses at the battery to the wire for the distribution panel. I know that runs from the batteries up to a certain length are exempt from fuse requirements.(six feet?) I'm not sure if that is for all equipment not connected via the distribution panel and I'm not sure that the panel is exempt regardless of distance from the power source,,,but, I suspect it isn't done for a reason. A blown fuse interrupting the ships power panel is a major disabling impediment to safe navigation. Maybe a fuse is needed on steel hulled boats but a short on a glass and wood boat is not likely to burn it down. Let me rephrase that. A cable jacket abraded to the conductor is not likely to short to ground on glass/wood boats. Thusly the failed fuse scenario is a larger threat. Whew! But I'm no expert. Gord?! And I do have a 300 amp fuse at the battery for my inverter and a 60 amp fuse at the battery for my LectraSan. But neither of these go through the distribution panel. GORD HELP! So the question remains, are you guys with fuses installing them yourself? Why? Info from a book, underwriter, surveyor, insurance company?
First off I don't know of boat manufacturers installing fuses at the battery to the wire for the distribution panel. I know that runs from the batteries up to a certain length are exempt from fuse requirements.(six feet?) I'm not sure if that is for all equipment not connected via the distribution panel and I'm not sure that the panel is exempt regardless of distance from the power source,,,but, I suspect it isn't done for a reason. A blown fuse interrupting the ships power panel is a major disabling impediment to safe navigation. Maybe a fuse is needed on steel hulled boats but a short on a glass and wood boat is not likely to burn it down. Let me rephrase that. A cable jacket abraded to the conductor is not likely to short to ground on glass/wood boats. Thusly the failed fuse scenario is a larger threat. Whew! But I'm no expert. Gord?! And I do have a 300 amp fuse at the battery for my inverter and a 60 amp fuse at the battery for my LectraSan. But neither of these go through the distribution panel. GORD HELP! So the question remains, are you guys with fuses installing them yourself? Why? Info from a book, underwriter, surveyor, insurance company?
Fred
My boat came with an inline 60 amp fuse at the battery. (hunter 260) Granted, it's not as complicated as your boats distribution system, I installed a larger panel for more goodies and upped the wire size and fuse from the battery to the panel. The way I see it if you have an overcurrent situation that will blow the fuse, and there is no fuse, the wiring is going to overheat and eventually melt down. That is also a hazardous situation. As far as glass vs. steel you have a point, but most boats I've seen run the ground and the positive right next to each other. What if something metal rubs thru both? I'm no expert on boats, but almost all automobiles have a fuse link at the battery, houses have a primary fuse at the transformer, and all the large commercial stuff I've been around have an overload device at the source of power. To me, it just makes sense. I've been around off grid solar installations with large battery banks and all the ones I build have a large fuse as close to the battery as possible. I saw an installation that wasn't protected, 48 volt 1500 amp/hr bank that overloaded, melted the 4/0 battery cables together, and melted down. It looked like a small nuke went off in the mechanical room. The only thing that kept the house from burning down was the fact that the mechanical room was cement block construction.
My boat came with an inline 60 amp fuse at the battery. (hunter 260) Granted, it's not as complicated as your boats distribution system, I installed a larger panel for more goodies and upped the wire size and fuse from the battery to the panel. The way I see it if you have an overcurrent situation that will blow the fuse, and there is no fuse, the wiring is going to overheat and eventually melt down. That is also a hazardous situation. As far as glass vs. steel you have a point, but most boats I've seen run the ground and the positive right next to each other. What if something metal rubs thru both? I'm no expert on boats, but almost all automobiles have a fuse link at the battery, houses have a primary fuse at the transformer, and all the large commercial stuff I've been around have an overload device at the source of power. To me, it just makes sense. I've been around off grid solar installations with large battery banks and all the ones I build have a large fuse as close to the battery as possible. I saw an installation that wasn't protected, 48 volt 1500 amp/hr bank that overloaded, melted the 4/0 battery cables together, and melted down. It looked like a small nuke went off in the mechanical room. The only thing that kept the house from burning down was the fact that the mechanical room was cement block construction.
Surveyor actually recommends another fuse
I just had an insurance survey done on my boat. One thing the surveyor mentioned was the need for a fuse between the alternator and the batteries due to my boat having an external 3-stage regulator. He says this is an ABYC recommendation to prevent overcharging the batteries from a faulty regulator. Just some more food for thought. Les Murray s/v Ceilidh '86 C-36 #560
I just had an insurance survey done on my boat. One thing the surveyor mentioned was the need for a fuse between the alternator and the batteries due to my boat having an external 3-stage regulator. He says this is an ABYC recommendation to prevent overcharging the batteries from a faulty regulator. Just some more food for thought. Les Murray s/v Ceilidh '86 C-36 #560
Les and Reudi
Les, that's right about the alternator wire to the regulator. My Balmar harness has such a fuse. Reudi, all good points in their application, but let's stick to our boats. When a house blows a fuse you don't have to worry about finding your way home or being seen. I'm just asking if a fuse in the distribution supply wire is needed or wise if the boat has a breaker panel that's properly installed. By 'proper', I also include one of your mentioned 'burn-down' possibilities ie; both conductors touching and potentially melting together. On my boat I kept the wires separate.
Les, that's right about the alternator wire to the regulator. My Balmar harness has such a fuse. Reudi, all good points in their application, but let's stick to our boats. When a house blows a fuse you don't have to worry about finding your way home or being seen. I'm just asking if a fuse in the distribution supply wire is needed or wise if the boat has a breaker panel that's properly installed. By 'proper', I also include one of your mentioned 'burn-down' possibilities ie; both conductors touching and potentially melting together. On my boat I kept the wires separate.
- Status