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Old 14-11-2011, 08:57   #1
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Recommended Breaker Size for Ignition Switch ?

In going threw some wiring, I discovered the ignition switch takes current without a breaker in the circuit. It has been 40 years like this.
The ignition switch has to supply power to several items like

ignition coil
starter solenoid
choke coil
engine gauges water temp
AM-FM radio, which might just be a trigger on circuit.
I dont know what else, the electric fuel pump is not in that circuit.

I was thinking a 20 amp breaker would be plenty of power. So what is typically used here?
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Old 14-11-2011, 09:04   #2
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Re: recommended breaker size for ignition switch?

MY boat has a 40 amp breaker.
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Old 14-11-2011, 09:28   #3
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Re: recommended breaker size for ignition switch?

Breaker size?

Found this reference to a 20 amp breaker used for this.
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Old 14-11-2011, 09:30   #4
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Re: recommended breaker size for ignition switch?

If you really want to add a breaker then it is based on the maximum current your starter motor draws. Not all starter motors draw the same amount of current...it varies dramatically. The other electrical loads that the engine draws are relatively nothing by comparison.

After you determine how much current your starter motor draws, you then want to add some till you come up to the next sized breaker.

The downside to adding a breaker is that you have added a potential fail point to the engines start system.

I don't have a fuse on my starters. I just make sure that the chance of them grounding is next to zero by installing chafing wrap and routing and securing them carefully. I know this is contrary to what ABYC recommends. I figure the new fail point (a breaker and its holder) is more likely to fail than the start wire is likely to ground out.
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Old 14-11-2011, 09:47   #5
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Re: recommended breaker size for ignition switch?

David,

I think ABYC actually agrees with you on the point of not having a breaker on your starter motor for exactly the reason you stated. You don't want to be in an emergency situation where you need to turn the engine on in a hurry and have the breaker flip on you. However you do need to secure the wire and loom them to reduce the chance of chaffing or vibration and they recommend a battery switch to turn it off. Everything else should have a breaker and remember the point of the breakers is to protect the wire.
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Old 14-11-2011, 09:58   #6
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Re: recommended breaker size for ignition switch?

I thought ABYC did recommend a breaker for the starter cable but you are probably right. Would someone like to look up reference to the ABYC recommendation?
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Old 14-11-2011, 10:05   #7
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Re: recommended breaker size for ignition switch?

Guys, it is not the starter motor, it is the starter solenoid relay coil I am talking about. The coil pulls the bendix gear in and the solenoid takes the current load from the battery. That activates when turning the key, push button what have you.

I sort of agree with not fusing the large main wire, it is not fused on my boat.
I bet a 400 amp fuse would be ok here, except on a large diesel.

I have bought these before and they work fine, good prices.
http://www.drillspot.com/products/14...ircuit_Breaker

This one has a screw terminal
http://www.drillspot.com/products/14...ircuit_Breaker
except the reviewer said it does not have screw terminals

one that auto resets.
http://www.drillspot.com/products/14...ircuit_Breaker

Do you think an auto reset is a good idea when used for the ignition circuit?
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Old 14-11-2011, 10:13   #8
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Re: recommended breaker size for ignition switch?

It was my understanding that you fuse to the wire, not to the devices being fed by the wire. I've read that the real purpose of the fuse is to protect the wire from overheating and catching fire/melting. The wire is what should be correctly sized to the things it feeds. So wouldn't the more appropriate thing to do be to size the wires to these devices correctly and fuse the wires according to the very standardized tables that show the acceptable fuse ratings?

I'm new to 12v DC, so go easy if I'm misguided here.
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Old 14-11-2011, 10:15   #9
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Re: recommended breaker size for ignition switch?

David,

ABYC doesn't require a breaker or fuse in the starting circuit, i.e., the large cable from the start battery to the starter solenoid.

However, many marine electricians and experts (including Nigel Calder) think there's no good reason NOT to put in a healthy sized fuse. I do on my boat, and on customer's boats. I think it's a safety factor, and if you use an appropriately-sized ANL fuse it's highly unlikely to blow. Mine hasn't in over five years since I installed it.

However, the OP wasn't talking about this circuit, but the starter switch circuit.

Bill
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Old 14-11-2011, 10:23   #10
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Re: recommended breaker size for ignition switch?

Quote:
Originally Posted by btrayfors View Post
David,

ABYC doesn't require a breaker or fuse in the starting circuit, i.e., the large cable from the start battery to the starter solenoid.

However, many marine electricians and experts (including Nigel Calder) think there's no good reason NOT to put in a healthy sized fuse. I do on my boat, and on customer's boats. I think it's a safety factor, and if you use an appropriately-sized ANL fuse it's highly unlikely to blow. Mine hasn't in over five years since I installed it.

However, the OP wasn't talking about this circuit, but the starter switch circuit.

Bill
Bill,
Yes, the wrong question was answered...woops.

But in getting back to the wrong question, I think it comes down to deciding if adding a potential fail point is better or worse than the potential problem that it cures. It seems to be mostly a question of your philosophy about complex systems with lots of possible failure points versus keeping things simple, and possibly worse?

Nigel seems to like complex systems which is not necessarily a bad thing.
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Old 14-11-2011, 10:40   #11
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Re: recommended breaker size for ignition switch?

Quote:
Originally Posted by David M View Post
Bill,
Yes, the wrong question was answered...woops.

But in getting back to the wrong question, I think it comes down to deciding if adding a potential fail point is better or worse than the potential problem that it cures. It seems to be mostly a question of your philosophy about complex systems with lots of possible failure points versus keeping things simple, and possibly worse?

Nigel seems to like complex systems which is not necessarily a bad thing.
David,

I share your concern about KISS. I, too, believe in keeping things simple and straightforward.

HOWEVER, I've seen boats which have experienced a short in the starting circuit, and it's not pretty. One of my clients on a 42' sloop had a major engineroom fire when several hundred miles off the coast, and only just managed to save the boat and crew. A proper CPD could have prevented that.

Anyhow, seeing that up close and thinking about it was enough for me: I got religion!

And, re: failure of devices, I've never seen an ANL fuse fail below it's rated amperage. Other types? Maybe..due, especially, to lousy holders and contacts. But a Blue Sea Systems ANL fuse with a BSS ANL fuse holder, properly installed, is highly unlikely to fail. At least not before everything else on your boat fails :-)

Bill
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Old 14-11-2011, 10:44   #12
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Re: recommended breaker size for ignition switch?

Depends on your engine system. There may already be a fuse/breaker somewhere in the engine wiring harness. Is the starter solenoid fed directly off the start switch (not likely) or from a slave relay? An example is a Yanmar 4JH4AE system with gauges, start/stop relays, intake heater relay, alternator excitation and fuel pump all fed from a 5amp breaker. The gauges themselves fed from an additional 3amp fuse in the harness. Best to check with an ammeter in the circuit and take some measurements. A lot of engine wiring harness's have relatively small gauge wiring that might not be well protected by something as large as a 20amp or larger breaker.

Starter bendix drives haven't been used for years. More likely you have the typical overrunning-clutch pinion arrangement.

Eric
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Old 14-11-2011, 10:51   #13
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Re: recommended breaker size for ignition switch?

A really easy way might be to put a clamp ammeter around the circuit, use the circuit and see what the peak amount of current was. Then fuse it for a little more than the peak measured current...maybe 20% more provided it is not more current than the wire is capable of carrying. Otherwise, fuse it for the current carrying capacity of the existing wire, so long as it is not for less than what the clamp ammeter measured.
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Old 14-11-2011, 10:59   #14
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Re: recommended breaker size for ignition switch?

Quote:
It was my understanding that you fuse to the wire, not to the devices being fed by the wire. I've read that the real purpose of the fuse is to protect the wire from overheating and catching fire/melting. The wire is what should be correctly sized to the things it feeds. So wouldn't the more appropriate thing to do be to size the wires to these devices correctly and fuse the wires according to the very standardized tables that show the acceptable fuse ratings?
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Quote:
one that auto resets.
http://www.drillspot.com/products/14...ircuit_Breaker

Do you think an auto reset is a good idea when used for the ignition circuit?
No, I don't and such practice is not in accordance with ABYC Standard E-11 so I would not recommend this path.

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Old 14-11-2011, 17:44   #15
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Re: Recommended Breaker Size for Ignition Switch ?

IF you fuse the starting motor circuit.

What happens if the starter motor lugs,
The oil is really cold and the motor really stiff.
Battery voltage is low and engine is cranking slowly.
The engine hydrolocks or cant spin at all for whatever reason.

Will that fuse blow if those things occur?
I know that if the starter motor is under great load, the current flow goes way up. I can imagine a nuisance if the fuse blows.
I have actually fuel hydrolocked gas motors couple of times.
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