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Old 24 July 2017, 08:55   #1
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Do you really need a circuit breaker?

Hi guys,

Just started to re-wire a converted fro I to O Bayliner with Honda BF150. A bit confused about the wiring. Checked online and find everywhere that I need a 30A circuit breaker. I was running a sailboat with Lister Peter WC2A with 65A alternator with no problems at all. So there is aquestion, do I need a circuit breaker?

Following the manual, the BF150 produces 40A after 2000RPM, so what is the point to fit a 30A breaker? a bit confused

Do all the ribs have circuit breakers and what is the amperage? Thanks for help
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Old 24 July 2017, 09:14   #2
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You don't want a circuit breaker in the charging circuit between engine & batteries. Bad things can happen if the alternator is suddenly disconnected from the battery
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Old 24 July 2017, 10:28   #3
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Originally Posted by Balthazar View Post
Hi guys,

Just started to re-wire a converted fro I to O Bayliner with Honda BF150. A bit confused about the wiring. Checked online and find everywhere that I need a 30A circuit breaker. I was running a sailboat with Lister Peter WC2A with 65A alternator with no problems at all. So there is aquestion, do I need a circuit breaker?

Following the manual, the BF150 produces 40A after 2000RPM, so what is the point to fit a 30A breaker? a bit confused

Do all the ribs have circuit breakers and what is the amperage? Thanks for help
Per ABYC/NMMA standards, fuses or breakers on the battery cables coming from the outboard are not required, as long as the cable run is no greater than 72 inches (1.8M), and is contained within a secondary loom. Also, the cable must be secured at least every 18 inches (0.45m).

http://assets.bluesea.com/files/reso...YCexcerpts.pdf
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Old 24 July 2017, 12:24   #4
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Do you really need a circuit breaker?

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Per ABYC/NMMA standards, fuses or breakers on the battery cables coming from the outboard are not required, as long as the cable run is no greater than 72 inches (1.8M), and is contained within a secondary loom. Also, the cable must be secured at least every 18 inches (0.45m).



http://assets.bluesea.com/files/reso...YCexcerpts.pdf


But he's not in the Good ol' US of A
According to my Ladybird book of boats, no breaker is required & could be positively detrimental.
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Old 24 July 2017, 12:26   #5
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But he's not in the Good ol' US of A
It's a good guideline.

The best boats in the world are built in the US of A to ABYC/NMMA standards.
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Old 24 July 2017, 13:03   #6
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The best boats in the world are built in the US of A to ABYC/NMMA standards.


Good to know
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Old 24 July 2017, 16:10   #7
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Maybe I'm being a bit thick here but surely if a breaker were required in the battery cable it would be the starting load that was critical not the charging load?
Starting load will be many times what the charge load is
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Old 24 July 2017, 18:19   #8
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Maybe I'm being a bit thick here but surely if a breaker were required in the battery cable it would be the starting load that was critical not the charging load?
Starting load will be many times what the charge load is


I'd assumed that it was a separate alternator charging line to the battery & the OP was contemplating putting a breaker inline with the alternator. It's not clear (to me) what the engine arrangement is.
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Old 25 July 2017, 16:47   #9
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My RIB has fuse at battery in transom, then a feed to by BlueSea switch panel at cockpit, which provides 6 individually fused & switched circuits. Also isolation switch at battery in transom.
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Old 26 July 2017, 01:02   #10
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i don't live in the USA but there is no way i would put a fuse or breaker on the battery feed to the engine. If it trips with the engine running, there is a good chance you could damage the ecm/rectifier/regulator on modern engines, then you are stranded. Some engines are worst than others. I have always been warned by dealers not to turn off the engine by using the isolation switch for this reason. Others may disagree. It's important to protect the cable from rubbing through to avoid shorting out by running in a cable trunking, (for instance), and by making sure the ends are protected with rubber boots. Breakers/fuses on all other equipment is a good idea. I'm not a marine engineer but that's what i have been told. I've just fitted a new Honda bf225 and there is nothing in the Honda installation manual which says anything about a breaker/fuse in line and there wasn't one included in the many other boxes that came with the fitting kit? I can also find no mention of in line breakers on the blue sea general wiring advice either?
https://www.bluesea.com/resources/17...l_Applications
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Old 26 July 2017, 02:04   #11
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My RIB has fuse at battery in transom, then a feed to by BlueSea switch panel at cockpit, which provides 6 individually fused & switched circuits. Also isolation switch at battery in transom.
I meant leisure battery.

The engine battery has isolation switch. There are then the standard mercury fuses in engine.
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Old 26 July 2017, 09:14   #12
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But what about the house circuit breaker?

Thanks for your replies, guys, makes sense about the circuit engine-battery

What about this one? My confusion comes from the fact that most of the electrics have already an inline fuse of 10 or 15A. The distribution board on my boat has 10A-15A fuses to all connections.



There is my question, what is the point to fit a 30A circuit breaker as I saw on many wiring diagrams, if ALL the fuses will be already smoking by 15 amps current?
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Old 26 July 2017, 09:28   #13
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Quote:
Originally Posted by Balthazar View Post
Thanks for your replies, guys, makes sense about the circuit engine-battery

What about this one? My confusion comes from the fact that most of the electrics have already an inline fuse of 10 or 15A. The distribution board on my boat has 10A-15A fuses to all connections.



There is my question, what is the point to fit a 30A circuit breaker as I saw on many wiring diagrams, if ALL the fuses will be already smoking by 15 amps current?


Because the "house circuit breaker" protects the cable from the main switch to the distribution board. If you developed a fault on this cable you would probably end up with a fire. Circuit breakers & fuses are to protect cables, not appliances. The circuit breaker needs to be as close to the switch as possible to minimise unprotected cable runs. That's what my Ladybird book of boat wiring says anyway
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Old 26 July 2017, 10:18   #14
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That's what my Ladybird book of boat wiring says anyway
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