New Electrical System Questions

[Maine Sail]

Originally Posted by ramblinrod

I certainly do not suggest the on/off battery switch is bad design, for all the reasons stated.

Per ABYC, 11.6.1.2.1, a battery disconnect switch is not required if the battery CCA is less than 800 Amps. (According to Calder, this is because a stuck starter motor will kill the battery before it overheats and catches fire.)

I disagree with your statement, "But you have just given up any ability to isolate a bad bank (internal short etc.), stop a wiring short or stop a stuck starter."


Another way to disconnect a start (or any battery) in an unusual event, is to remove the battery terminal. This is an effective (albeit slower response) to a possible but highly unlikely occurrence.

I too prefer all battery banks be current limited, which prevents the risk of fire in the event of a battery short circuit.

So installed, if such an occurrence takes place, the fuse blows and battery is disconnected, long before the user ever gets to an on/off switch or battery terminal.

So IMHO, the on/off switch is a convenience feature, but not required (except for ABYC compliance for start batteries greater than 800 CCA).

Anyway, great discussion, but I hafta get to work now.

Ramblin

Absolutely, any discussion that gets a good safety discussion going is worthwhile even when there is disagreement.

I think you might be looking at an outdated version of E-11 it now says (July 2015 edition) 800CCA or 100Ah because they recognize that many boats are using deep-cycle batteries, even for starting, and they may not have a CCA or MCA rating but they likely have an Ah rating.

Pretty much any boat with a G-31 AGM or flooded Group-31 deep cycle or starting battery will require a switch.. If an actual starting battery is used even G-24 flooded start batteries are often hitting 800CCA. Group 24 or 34 and larger Northstar or Odyssey AGM's exceed 800CCA as do most of the Optima spiral wound AGM's... The Odyssey or Northstar group 24 or 34 is capable of throwing 3100A into a dead short..

Sure we can always find a battery smaller than 800CCA to sneak by the exception to the rule (essentially this is allowed to stand for small skiff builders) but I'd much rather install a $25.00 switch regardless of bank size....

I prefer to treat the standards as a minimum and don't like to use exceptions, when going above and beyond can be safer.

Course sometimes the exceptions are safer such as the 150% exception for over-current protection. No over current protection at all, or sized to the 150% rule? I think I will take 150% of ampacity every single time rather than zero protection. In a perfect world I would talk the owner into the proper size wire but this is not always cost effective and even at 150% you are still within the rule and safer than no over-current protection at all...

[ramblinrod]

Originally Posted by Maine Sail

Absolutely, any discussion that gets a good safety discussion going is worthwhile even when there is disagreement.

I think you might be looking at an outdated version of E-11 it now says (July 2015 edition) 800CCA or 100Ah because they recognize that many boats are using deep-cycle batteries, even for starting, and they may not have a CCA or MCA rating but they likely have an Ah rating.

Pretty much any boat with a G-31 AGM or flooded Group-31 deep cycle or starting battery will require a switch.. If an actual starting battery is used even G-24 flooded start batteries are often hitting 800CCA. Group 24 or 34 and larger Northstar or Odyssey AGM's exceed 800CCA as do most of the Optima spiral wound AGM's... The Odyssey or Northstar group 24 or 34 is capable of throwing 3100A into a dead short..

Sure we can always find a battery smaller than 800CCA to sneak by the exception to the rule (essentially this is allowed to stand for small skiff builders) but I'd much rather install a $25.00 switch regardless of bank size....

I prefer to treat the standards as a minimum and don't like to use exceptions, when going above and beyond can be safer.

Course sometimes the exceptions are safer such as the 150% exception for over-current protection. No over current protection at all, or sized to the 150% rule? I think I will take 150% of ampacity every single time rather than zero protection. In a perfect world I would talk the owner into the proper size wire but this is not always cost effective and even at 150% you are still within the rule and safer than no over-current protection at all...

Well, the majority of cruising sailboats I work on that have a dedicated start battery, have a grp 24 std lead acid start battery under 800 CCA and the installed cost of an on/off switch is much more than $25.

Great discussion, have to get to work.