Fusing the Battery Cable

[FrankZ]

Blue Sea has a nifty little weblet that helps in picking out cabling.. and fuses.

[Ziggy]

Originally Posted by sailingharry

Actually, you've hit on two of the problems with fusing the starter wire. The fuse should be rated for the wire. But starter wire is allowed to have MUCH higher current than the same wire for other purposes because of the short duty cycle. So, to meet the surveyor's "ding," I'd need a 175A fuse as you suggested. But, someone else here said that a ~30HP diesel can take upwards of 300A to start. The cable can take it, the fuse can't.
Harry

You should check that 300A figure. Just for comparison, the max surge current on a Yanmar 3YM30 (30 HP) starter is 200A. While the Volvo may be more, you should take the 300A with a grain of salt until you can verify the starter spec. If the max surge current is really higher than 175A and you're concerned about the surveyor's dings, you should upgrade the starter cable to #1 or 1/0 and fuse it accordingly.

[Ziggy]

By the way, you can find the Volvo shop manual here: http://www.bluemoment.com/manuals/Vo...1C_D_17C_D.pdf. While it does not give the max starter surge current, it does specify #1 AWG cable.

[Cacique]

A freind recently chartered a new (Less than 1 year old) French boat, after starting the engine the starter jammed and started working as a generator and overheated the wiring starting a serious fire, fortunately they stopped the engine and extinguished the fire with no injurys.
If the starter cable had a fuse it would have probably saved the day.

[CharlieJ]

...and that is exactly why there is an ABYC requirement for a battery switch in the B+ conductor to the starter.

[btrayfors]

A similar event occurred 120 miles offshore on a client's boat just last month. It was a new-to-him 42-footer, U.S. built, 1982 vintage.

As best they could reconstruct, the starter position on the ignition key jammed in the "start position", unbeknownst to the crewmember who had started the engine.

This started a serious fire, which they were very lucky to discover in time and extinguish. It destroyed the wiring harness, the starter, the alternator, and the solenoid. It did not damage the heavy start cables.

Understand that even if the starting circuit is fused, it may not protect against this eventuality. The solenoid circuit is wired for, and meant for intermittent service, not continuous service. The wiring overheated easily in continuous service, drawing less amperage than the fuse's rating. As it was bundled with the harness, it damaged other wires closeby.

One needs to consciously and continually be on guard against such circumstances.

A similar event can happen with, e.g., an electric motor with a frozen rotor. Unless the fuse is carefully matched to the manufacturer's LRA (locked rotor amperage), the frozen pump will NOT draw a lot more than normal amperage...it will just sit there and get hot and, eventually, catch fire. We have demonstrated this effect recently with a small bilge pump at a West Marine seminar.

A disconnect switch won't be helpful in preventing the fire, unless you're right there and catch it early.

You gotta be very watchful and very careful with this electric stuff :-)

Bill

[CharlieJ]

Originally Posted by btrayfors

A disconnect switch won't be helpful in preventing the fire, unless you're right there and catch it early.

I certainly did not mean to imply that the disconnect switch required by the ABYC would "prevent" a fire in the starting circuit. It will, however, provide the means for disconnecting the hung starter from the battery without resorting to physically unbolting the starting cable from the battery terminal or bus bar. And, if the abnormal condition is caught soon enough, the damage may be minimized.

Charlie

[btrayfors]

Charlie...

Yes, absolutely. I didn't mean to imply that the switch wouldn't be useful or help prevent greater damage. However, in the case I mentioned -- which is very rare in my experience -- the fire started in the solenoid wires in the harness due to a hung solenoid and/or starter.

Normally, one would think that someone on board would have heard something amiss with the starter, but this was a new-to-them boat and they were relatively inexperienced. Somehow, they didn't notice, until smoke started pouring out of the engine room.

Even worse, on this boat the starter was connected to the house battery bank, and the new owner(s) hadn't found the disconnect switch yet :-(

BTW, I'm just paranoid enough to have a big ANL fuse in my starter circuit, as well as the ABYC-specified disconnect switch. Experimented a bit until I found one big enough, and I have bigger ones and jumpers available "just in case".

Cheers,

Bill

[clearsea]

Originally Posted by btrayfors

A similar event occurred 120 miles offshore on a client's boat just last month. It was a new-to-him 42-footer, U.S. built, 1982 vintage. As best they could reconstruct, the starter position on the ignition key jammed in the "start position", unbeknownst to the crewmember who had started the engine. This started a serious fire, which they were very lucky to discover in time and extinguish. It destroyed the wiring harness, the starter, the alternator, and the solenoid. It did not damage the heavy start cables. Understand that even if the starting circuit is fused, it may not protect against this eventuality. The solenoid circuit is wired for, and meant for intermittent service, not continuous service. The wiring overheated easily in continuous service, drawing less amperage than the fuse's rating. As it was bundled with the harness, it damaged other wires closeby. One needs to consciously and continually be on guard against such circumstances. A similar event can happen with, e.g., an electric motor with a frozen rotor. Unless the fuse is carefully matched to the manufacturer's LRA (locked rotor amperage), the frozen pump will NOT draw a lot more than normal amperage...it will just sit there and get hot and, eventually, catch fire. We have demonstrated this effect recently with a small bilge pump at a West Marine seminar. A disconnect switch won't be helpful in preventing the fire, unless you're right there and catch it early. You gotta be very watchful and very careful with this electric stuff :-) Bill

This is an important post. If a boater revising their boat's wiring understands everthing here, they have achieved a lot of key, basic know-how, methinks.

[James S]

This is not directly aimed at start batteries fusses...but for those of you who are as green behind the ears as I electrically… here is a picture of what may be involved...the various types of fusses required was the biggest surprise in my rewire.
I'll qualify the picture by saying that two switches and slow burn fusses on the bottom left are going to a switch box (full of contactors)for my 24v bow thruster (I'm a 12v system) that puts part of the battery bank into 12v/12v series.
Please keep in mind that none of these parts were available in country (Lebanon) so if we wanted to change or further optimize something it meant weeks of delay in a very tight schedule.

[s/v Jedi]

James,

Good installation. The only thing I did differently is the main switch and class-T fuse: I have them swapped with the fuse at the bus bar and the switch between fuse and main-panel. I can't tell for sure if that's a requirement but I think it is...

ciao!
Nick.

[Joli]

We had this happen with a Vacuflush head. The vacuum pump jammed and became "quite" warm. My crew asked, "who had the hot ****?".

All toilets are now manual.

Originally Posted by btrayfors

A similar event occurred 120 miles offshore on a client's boat just last month. It was a new-to-him 42-footer, U.S. built, 1982 vintage.

As best they could reconstruct, the starter position on the ignition key jammed in the "start position", unbeknownst to the crewmember who had started the engine.

This started a serious fire, which they were very lucky to discover in time and extinguish. It destroyed the wiring harness, the starter, the alternator, and the solenoid. It did not damage the heavy start cables.

Understand that even if the starting circuit is fused, it may not protect against this eventuality. The solenoid circuit is wired for, and meant for intermittent service, not continuous service. The wiring overheated easily in continuous service, drawing less amperage than the fuse's rating. As it was bundled with the harness, it damaged other wires closeby.

One needs to consciously and continually be on guard against such circumstances.

A similar event can happen with, e.g., an electric motor with a frozen rotor. Unless the fuse is carefully matched to the manufacturer's LRA (locked rotor amperage), the frozen pump will NOT draw a lot more than normal amperage...it will just sit there and get hot and, eventually, catch fire. We have demonstrated this effect recently with a small bilge pump at a West Marine seminar.

A disconnect switch won't be helpful in preventing the fire, unless you're right there and catch it early.

You gotta be very watchful and very careful with this electric stuff :-)

Bill

[James S]

Thanks Nick, but I cant take the credit, CharlieJ and his wife spent almost 6weeks with us this summer in Lebanon...He did a hell of a job, and was a real pleasure to work with....they were also lots of fun to have around.
Thanks again Charlie

[CharlieJ]

اهلا وسهلا بكم ، يا حبيبي.

[hellosailor]

And let's not totally ignore an insulated-handle bolt cutter (or good lopping shear) or the old fashioned fire axe. A great way to disconnect whatever is causing a bother.