Blue Sea Add a Battery

[Lou C]

Interesting and one thing I have noticed in looking at wiring diagrams…Merc has a fuse at the battery connection on the starter solenoid whereas Volvo & OMC did not. I have read reasons why the starter circuit shouldn’t be fused (safety concerns of not being able to start the engine in an emergency) yet due to the amperage draw on a starter circuit it would seem to better to do so for (other) safety reasons….

 

[Bob Sander]

Interesting and one thing I have noticed in looking at wiring diagrams…Merc has a fuse at the battery connection on the starter solenoid whereas Volvo & OMC did not. I have read reasons why the starter circuit shouldn’t be fused (safety concerns of not being able to start the engine in an emergency) yet due to the amperage draw on a starter circuit it would seem to better to do so for (other) safety reasons….

Yeah... exactly... the wild west.
I got into this topic years ago when I found some winches came with circuit protection and others didn't. It's the same thing with cars, some come with fusible links in the starter circuit, and some don't have anything at all.

Winches can pull anywhere from 300 to 500 amps. You can see the complications involved in protecting a circuit with such loads along with the false circuit interruptions that come in these circumstances... but then you can also see the fire it would cause if things ever went south. Because of the lack of regulations though, some choose to err on the side of caution while others play the ole' risk vs reward game. That leaves the consumer standing there scratching the head every time this topic comes up.

 

[Lou C]

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looks like on their new V6s they are still using a 90 amp fuse on the starter circuit....

 

[poconojoe]

When installing an electrical device, whether it be a 240 volt electric clothes dryer or a 12 volt windshield wiper motor, one always determines the amperage draw of the device first. With that information, you then determine what the wire and fuse/breaker size and should be.

 

[poconojoe]

You can't just feed a motor directly without fuse protection. You don't omit fuse protection due to a surge during initial startup.
When it comes to motors, the use of time delay fuses are neccessary due to the initial motor startup.
There are also motor controllers for large motors. These are not just mystery boxes with fancy lights and switches.

 

[bruceb58]

You can't just feed a motor directly without fuse protection. You don't omit fuse protection due to a surge during initial startup.

LOL...you have a fuse going from your battery to your engine starter motor?

 

[bruceb58]

Interesting and one thing I have noticed in looking at wiring diagrams…Merc has a fuse at the battery connection on the starter solenoid whereas Volvo & OMC did not. I have read reasons why the starter circuit shouldn’t be fused (safety concerns of not being able to start the engine in an emergency) yet due to the amperage draw on a starter circuit it would seem to better to do so for (other) safety reasons….

You really think that is for the starter current? It's not. That is for the power going to the rest of the boat's power...not for the starter.

 

[Lou C]

No I didn't because I'm sure the starter draws more than 90 amps.

 

[bruceb58]

When installing an electrical device, whether it be a 240 volt electric clothes dryer or a 12 volt windshield wiper motor, one always determines the amperage draw of the device first. With that information, you then determine what the wire and fuse/breaker size and should be.

That's actually not how it works. For example, a home 120V circuit's amperage is determined by the wire size. When you wire up a home circuit you could have a 1A device attached to it or a 20A device attached to it. You don't know. Typically, if the device attached to the circuit needs it's own protection due to smaller sized wiring within it, that device will have it's own fuse protecting it.

 

[bruceb58]

No I didn't because I'm sure the starter draws more than 90 amps.

Volvo uses a circuit breaker from a wire that attaches to the starter solenoid. They do that instead of the Merc fuse that was done awhile ago. I don't believe my new Mercruiser does that fuse anymore. In fact, on my Mercruiser, they wire up the ignition and fuel injection straight from the battery to lower voltage drop due to the starter pulling current through the battery cables. That wire is fused though.

 

[Bob Sander]

That's actually not how it works. For example, a home 120V circuit's amperage is determined by the wire size. When you wire up a home circuit you could have a 1A device attached to it or a 20A device attached to it. You don't know. Typically, if the device attached to the circuit needs it's own protection due to smaller sized wiring within it, that device will have it's own fuse protecting it.

That's the big point... and probably the most common mistake. Branching a smaller guage wire off of a larger already fused wire and thinking that because the larger wire is fused, then the smaller wire has been safely protected. Ya see a lot of that stuff in cars and aftermarket stuff added... a smaller 18 or 20 gauge aftermarket led wire branched (unfused) from a 20 amp (fused) cigarette lighter circuit. The thought of course being that the led circuit is covered by the cigarette lighter fuse.

 

[bruceb58]

That's the big point... and probably the most common mistake. Branching a smaller guage wire off of a larger already fused wire and thinking that because the larger wire is fused, then the smaller wire has been safely protected. Ya see a lot of that stuff in cars and aftermarket stuff added... a smaller 18 or 20 gauge aftermarket led wire branched (unfused) from a 20 amp (fused) cigarette lighter circuit. The thought of course being that the led circuit is covered by the cigarette lighter fuse.

And that's why I always make branch circuits able to handle the current of a dead short. For example, with a 15A circuit, a 16 AWG wire can handle 22A. You wouldn't use that size wire for the main circuit since you would really want to use 14AWG because of voltage drops if you were pulling 15A. You could actually use 16AWG in a 20A circuit safely if that branch was only pulling 10A in normal use.

 

[poconojoe]

That's actually not how it works. For example, a home 120V circuit's amperage is determined by the wire size. When you wire up a home circuit you could have a 1A device attached to it or a 20A device attached to it. You don't know. Typically, if the device attached to the circuit needs it's own protection due to smaller sized wiring within it, that device will have it's own fuse protecting it.

So you're saying every lamp or other device in your home that plugs into a 120 volt receptacle has it's own fuse/circuit breaker at or in the device? I know you didn't mean that.

Those branch circuits, if protected by a 15 amp breaker for instance, are limited by that breaker. Nothing over 15 amps can operate on that circuit, whether it's one device or a combination of devices. If you plug something in that draws 20 amps, the breaker will trip. So, you DO know what will function on that circuit whether it draws 1 amp or 20 amps. The breaker determines that.

A branch circuit feeding standard convenience receptacles in your house is always limited to 15 amps. The same applies to all your lighting circuits, 15 amp breaker. If you need more amperage, you don't increase the wire or breaker size for these types of circuits, you install additional circuits.

When installing any device, the first thing you do is determine its amperage draw. Then you figure the amperage of the breaker needed and then match the wiring to that amperage. This is how it's done. You don't figure the wire size first. That is the last part you figure.


Only specific circuits for appliances and motor loads can be 20 amp or higher. In your kitchen, you are only allowed two receptacles on a 20 amp circuit and that wire has to be 12 gauge. A window A/C unit that draws under 20 amps should be the only thing on that circuit and it should be 12 gauge wire on a 20 amp breaker.

So the breaker protects against an overload and indeed protects the wires, if the wires are sized correctly.

 

[poconojoe]

That's the big point... and probably the most common mistake. Branching a smaller guage wire off of a larger already fused wire and thinking that because the larger wire is fused, then the smaller wire has been safely protected. Ya see a lot of that stuff in cars and aftermarket stuff added... a smaller 18 or 20 gauge aftermarket led wire branched (unfused) from a 20 amp (fused) cigarette lighter circuit. The thought of course being that the led circuit is covered by the cigarette lighter fuse.

Good point.
And that is why any add-on accessory you "tap" off your cigarette lighter circuit should be immediately fused according to the wire size of that added accessory. This protects that smaller accessory wire and the accessory itself.

 

[poconojoe]

And that's why I always make branch circuits able to handle the current of a dead short. For example, with a 15A circuit, a 16 AWG wire can handle 22A. You wouldn't use that size wire for the main circuit since you would really want to use 14AWG because of voltage drops if you were pulling 15A. You could actually use 16AWG in a 20A circuit safely if that branch was only pulling 10A in normal use.

You cannot protect a 16 gauge wire with a 20 amp breaker. Never assume there will only be a 10 amp draw.

Voltage drop in you home wiring only comes into play when the wire length exceeds 100 feet. Then you need to increase up to the next size.

 

[bruceb58]

You cannot protect a 16 gauge wire with a 20 amp breaker. Never assume there will only be a 10 amp draw.

Voltage drop in you home wiring only comes into play when the wire length exceeds 100 feet. Then you need to increase up to the next size.

LOL....then what happens when your lamp with 16AWG wire into a 20A circuit?

BTW, I never said you wire your house with a wire that is below the code required wire size for a certain amp circuit. I am talking about the unfused loads you plug into outlets.

Another BTW, you increase wire sizes far before you reach 100' if you are smart, you keep the entire voltage drop down to 3% and you have to account for the feed and branches.

 

[bruceb58]

So you're saying every lamp or other device in your home that plugs into a 120 volt receptacle has it's own fuse/circuit breaker at or in the device? I know you didn't mean that.

No it doesn't...thankfully a 16 AWG wire can tolerate 22A before it fails.

It's also why the ground wire of 240V and other circuits doesn't have to be the same size as the conductors. It just has to be big enough to not melt before the circuit breaker trips.

BTW...EE here...your background?

 

[poconojoe]

LOL....then what happens when your lamp with 16AWG wire into a 20A circuit?

BTW, I never said you wire your house with a wire that is below the code required wire size for a certain amp circuit. I am talking about the unfused loads you plug into outlets.

Another BTW, you increase wire sizes far before you reach 100' if you are smart, you keep the entire voltage drop down to 3% and you have to account for the feed and branches.

It doesn't matter where you plug the lamp in as long as you use the lamp properly. The lamp was manufactured according to the wattage limit of the fixture, including its cord. There is no fuse in the lamp.

Chances of this happening are are probably nil. An old style 100 watt incandescent lamp (bulb) draws a little under 1 amp at 120 volts. So you'd probably need 10 or 15 of them to overload that wire. In other words, if you somehow adapted 15 incandescent 100 watt bulbs or one 1500 bulb to that lamp, you'd have a problem.

With today's LED lamps (bulbs) having so little wattage draw, the chance of overloading the fixture's capacity is probably next to impossible.

So, basically, if you exceed the wattage to the point past the lamp holder (socket) or cord's capacity, the socket or cord will melt. Once the wires short between each other, the breaker will finally trip.

 

[bruceb58]

It doesn't matter where you plug the lamp in as long as you use the lamp properly. The lamp was manufactured according to the wattage limit of the fixture, including its cord. There is no fuse in the lamp.

Chances of this happening are are probably nil. An old style 100 watt incandescent lamp (bulb) draws a little under 1 amp at 120 volts. So you'd probably need 10 or 15 of them to overload that wire. In other words, if you somehow adapted 15 incandescent 100 watt bulbs or one 1500 bulb to that lamp, you'd have a problem.

With today's LED lamps (bulbs) having so little wattage draw, the chance of overloading the fixture's capacity is probably next to impossible.

So, basically, if you exceed the wattage to the point past the lamp holder (socket) or cord's capacity, the socket or cord will melt. Once the wires short between each other, the breaker will finally trip.

And you missed the point entirely. The point is if you have a fault and you have a short circuit in the wiring feeding the lamp within that cord plugged into the outlet, even if it has a 16awg wire feeding it, it will still blow the 20A or 15A circuit breaker without the rest of the wiring melting.

 

[poconojoe]

No it doesn't...thankfully a 16 AWG wire can tolerate 22A before it fails.

It's also why the ground wire of 240V and other circuits doesn't have to be the same size as the conductors. It just has to be big enough to not melt before the circuit breaker trips.

BTW...EE here...your background?

Great conversation. Only thing is, we basically hijacked the thread! Sorry for that folks!

Grounding is a bit more complicated than that. Then there's bonding, also a bit complicated. And a ground is not the same as a neutral.

I've been around the block and back. I've worked on raising highrise buildings, renovations, power plants, you name it. Everything from IT, fiber optics, security systems to wires the size of your wrists.
I survived 9-11 only because I was working nights that week. I was working on the 110th floor of tower 1. There's no way I would have made it out if I was there during the day.

My background is a retired I.B.E.W. union electrician. New York City, Local union #3. And you?