Fusing starting Battery

[34atlantic]

Redoing my starting circuit and was wondering if anyone is installing fuses on the starting batteries. I am switching from 1 4d battery that was used to start both motors to 2 group 31 deka agm batteries with 2/0 awg  for both grounds and positives.   

 

Should have said this earlier this is for 2 Cummins 6bta 370hp motors. 

If a fuse is recommended what size?  From what I read it is recommended to fuse the circuit with the max wire amps which on 2/0 ga is 280 amps. 

Topic

[34atlantic]

After reading the comments and doing a little more research I plan to either use an ANL fuse or like Tont stated an on off switch that is easily accessible in case of an issue. 

[Tony Athens]

Fusing a batteries output

I am basically 100% on board with Gene’s thoughts.. As to fusing the starter motor  main cable, we use a on-off   HD battery switch  should something “stick-on” . 

Fusing the + to the boats DC distribution panel = YES–usually something in the 100-150A range that also has a on-off   built-in switch

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Patrick Mangum

[Gene Fuller]

Fuses are intended to protect the wiring, not the source or the downstream load.

Since an alternator cannot send excessive current there is no need for a fuse at the alternator end. (Various bad things can happen at the alternator, but that is a different topic.)

However, the battery can provide a very large amount of current so a fuse at the battery end of the circuit is required.

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Patrick Mangum

[Patrick Mangum]

Alternator to Battery Isolator Fuse?

While on the topic, do you fuse between the alternator and the battery isolator?  I saw the diagram under Tony’s Tips and I don’t see a fuse along that 4AWG cable but wanted to be sure as I’m also taking a look at some of this stuff of my boat.  

[bluebyu]

Just to help a little, different engines.

We have 6CTA8.3.

Grid heater, 190 amps

Starter, 600 amps

Total load when engine is starting is 790 amps.

We use 4/0 cables from each bank to starter, NO fuse.

Starboard engine bank is 6 ea., 6 volt  golf cart from Interstate (same as trojan T105)(2 in series, 3 in parallel)

Port engine is one 4D.

Hope this helps

[34atlantic]

I will look into the clamp meter. The grid heater is disconneected and installed pan heaters. 

[Rob Schepis]

The grid heaters will also come into play for total cranking amps.  As to total amperage draw the best way to know for sure is to pickup a 1000A Clamp Meter.

[34atlantic]

Thanks for the reply. Yea, I never had fused before I was just looking to see what the others have done. 

 

By chance are there any specs that give the starter cranking amps of the starters? I been looking and wasn’t able to find any info? 

[Rob Schepis]

ABYC does not require an OCPD on a starting circuit and it is not commonplace to see them installed optionally either.  If you decide to, be sure it is well above the starter cranking amps but within range of what the circuit wiring is rated for.

[Author]

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