Circuit breaker for main power? How many amps?

How many amps is typically pulled through the main power feed to the ignition switch?

I want to put a circuit breaker on the power going to my ignition switch, and i'm wondering what it needs to be rated at. 50amps or so? Car will have 2 power windows and a normal stereo, not much else.

Damn wiring caught fire today, i'd like to get some protection on it while i'm redoing that ignition wiring!

Also, anyone have any good sites about how to wire in relays? Best way to configure the wiring?

 

Why don't you put in an ANL fuse holder and start the car with everything on with the coil wire pulled..........I would start out with about 250 amps and go up from there. You want to pull alot of load, cranking the car with the stereo one and the lights and windshield wipers on and pop the main fuse after about 6 to 8 seconds........................then replace your main fuses with breakers..........

 

The way you're supposed to do it is to size the breaker or fuse so it protects the wire (the breaker trips/fuse blows before the wire gets hot enough to cause trouble). Typical ratings are 30 amps for 10 gage wire, 20 for 12 gage, 15 for 14 gage, etc.

 

Automobiles didn't typically fuse the main power supply to the fuse box.....Later model cars have used fusible links to supply the fuse box power.

Think of it like your house....there is not any fuses between the pole and the house.

I think 14 ga. fuseable wire is rated at 30 amps....if you used circuit breakers you could always split them up for the various circuits. i.e. one 50 amp breaker for the first 5 circuits and another 50 amp breaker for the next 5 circuits and then use appropriate fuses for each circuit

 

My house has a main breaker at the service entrance panel, sized to protect the wires that run from that panel into the distribution breaker box inside the house. There's also a fuse on the pole between the high voltage line and the transformer.

Same thing with cars....if there's a #10 wire feeding the fuse box, then that wire should have a #14 fusible link in it to protect the #10 wire. The smaller fusible link will melt before the larger wire gets hot enough to cause problems.

 

What i did for my truck when some friends of mine rewired it is got a re-setable breaker from a stereo shop reated for 150 amps. I have a 105 amp alternator and figured that would me more than enough for my setup. The good thing is you can disable the system by pulling the trip on it making it unable to start, kind of a poor mans alarms I guess. Worked good so far with no problems and I used a E-Z Wiring 12 circuit setup.

Michael

 

That 150 amp breaker won't do squat to protect the wiring.

 

Generally speaking, if you short home wiring at the weatherhead, before it reaches the breaker box, everything concerned is SOL.

Any fuseable links or circuit breakers will have to be installed as close to the battery as possible or feasable.

 

There may be some confusion about amp draw when starting......all of that would be carried by the postive batt cable, and wouldn't be fused anyway.

 

The OEM set-up my son's OT '93 Ford Probe has a 100 amp main breaker in the power box under the hood along with a series of 50 and 30 amp breakers/fuses to feed "larger" circuits....and off those larger circuits smaller circuits (with smaller fuses) are used for the individual devices.

The marine industry uses 50 amps for the feed going to the start circuit and 50 amps for the feed for everything else.

Nobody protects the main line from the battery to the starter/starter solenoid as it can draw up to the cranking amp capacity of the battery.

-Bigchief.

 

That's right, lately the fuse/relay boxes are located in close relation to the battery, rather than underdash. The reasons have been though out a little more carefully.

 

thanks for the info!

I'd really like to move everything to the engine compartment, like the germans do with benz and bmw. I have a 10ga wire running from the solenoid to the ignition switch, and off the accessory on that switch everything is about 14 or 16ga. The car previously had a 20amp breaker/switch on it, and I removed it some time ago when I was fixing the wiring. Like a dummy, I never replaced it with anything else. My own damn fault it caught fire. Gonna redo it, might as well do it right.

I'm thinking a boat style Buss 30amp breaker/switch for the feed from the solenoid to the ignition switch. Does that sound about right?

The power windows kit comes with a 25amp fuse just for those guys. I don't know if I like running that through the ignition switch though. I have a 30 or 40 amp relay, I just need to figure out how to wire it.

Alternator is 100amp, is a 120amp breaker too much for it? Gonna run 6ga from the alt to the solenoid, I figured the wire would burn at anything more than 120amp anyway. Only thing in this car is power windows, and a mild stereo at some point. Maybe an electric fan later on.

 

Why ya need a 10 gauge to the ignition switch? Most of them aren't rated to carry much current, and shouldn't.

 

Make sure you get 32V fuses/breakers. The higher voltage (250V) fuses will give you erroneous failures.

Just remember that any wire between the short and the fuse (if mounted at the battery) will melt or burnup if the fuse is overrated. If the fuse is placed between two wires, one from battery and one to load and the fuse is overrated, then one or both wires will burnup. Now if the load is rated at 28A and the fuse is 30A and you have used underrated wire, then the wiring will burn up, even though the load is OK. Electricity takes the path of least resistance!

GET THAT FUSE (and wiring) RIGHT!

Squirrel knows what he is talking about.

 

I use the 50 amp. fuse like the ones in the newer cars. This will protect system and starter will not blow them.

 

I always use fuses instead of a fusible links.... ever tried to chnage a fusible link on the side of the road at midnight....?

 

The next time you have a tornado, look outside and see if there isn't power lines skating across the lawn on fire....any fuses, circuit breakers, etc. contained within the transmission grid (either in transformers, fuses on 7200 volt transmisson lines or circuit breakers in sub stations) are intended to protect the grid, not your house. Engineering sometimes makes it impossible for the grid to know whether the line is on fire or somebody just turned on their air conditioner.

I don't think you can go wrong by puttting fusible links (fusible wire with male spade terminals on each end) in circuits to feed any number of fuse boxes. The wrecking yards are full of neat little do-dads to get the job done.

 

Not much different that having a blown fuse and no replacement. I once heard of a Darwin award winner that used a loaded 22 shell for an emergency fuse replacemant. Needless to say an empty case would have gotten him home while the loaded one just blew his fuse panel to bits. Could have been worst.

 

I'm running 10ga just for overkill, and because I had it laying around. Not sure what it would need, so I figured best to have too much wire than not enough.

If an alternator is rated at 100 amp, should I put a 100amp breaker on it, so it catches it right as it goes over, or a little bit more (110 or 120 amp breaker) for a failsafe?

thanks for the tip about 32v, i'll see if I can find that somewhere.

 

In answer to the 100 amp alternator queston. NO, that isn't material. you have to figure out what the loads in the circuits are.

The power windows draw X amount but only when they are running up or down.
The sterio draws X amount.
The headlights/tail lights will draw X amount.

The only power that the start circuit draws through the switch is what it takes to engage the solenoid. The main battery cables carry the rest.

The 100 amp battery means that it will keep the battery fully charged when your total electrical system is drawing up to 100 amps.

Meaning that if you have a big souind system and ac going at the same time along with super bright Halogen lights it should keep up with all of them and still keep the battery charged. It doesn't push 100 amps through the circuits unless you have a 100 amp draw.

It also keeps your lights brite at low speeds and still keeps the battery charged.

Too big a fuse or too high a rating on a circuit breaker is no different than no circuit breaker of fuse if it allows the protected item to fry before blowing or tripping.

Go back and read what Squirrel wrote, as usual he got it right the first time. Normally if he answers a question you don't have to read the rest of the answers and get confused.

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I would just run a 10 gauge wire from the alt to the batt +

Normally the proximity of the alt and battery is short and the wiring can be run in such a way (shielded and secured) that it would be unlikely to come into contact with a ground

I would study a good current flow diagram in order to determine your specific needs.

Most good diagrams or flow charts will tell you wire sizes and fuse needs.

 

This is why I love the HAMB. The internet is full of partial and mistaken information, but here, there's people who has been there and done that. Squirrel's information was a big help, i've read his post over several times.

That's good to know about the amp draw. It looks like i'm going backwards... I need to account for the draw, and setup the power circuit in anticipation for that then.

This car is a OT late 60's Ford. The way it was wired when I got it, is the battery positive goes to the solenoid, then power comes off the solenoid, and to the ignition switch. That's the only solenoid switched power going out. There's an "accessory" pole on the center of the ignition switch, and it appears that everything that needs ignition switched power (dash lights, gages, radio, power windows) comes off of that pole. At least from what I can see from a wiring diagram. Is this incorrect? I understand it's a bad idea to run a large amount of draw through that ignition switch.

I'll put a 30amp breaker on the power to the ignition switch to protect that wire, per Squirrel's post. Is there are a chart or anything anyone has come across that shows what size breaker or fuse to use for what size wire?

 

There are a couple decent "How to Wire Your Hotrod" books out there that cover the basics. I recommend grabbing one or two and go through them. They've got example layouts with expected loads.....diagrams and pics too.

-Bigchief.

 

Look in the factory manual, there should be a schematic in there, see how the factory originally did it, and wire it that way, takes all of the guess work out of it. Ford starter solonoids draw very little amperage in comparison to what goes through them on the starter circuit. Remember that they are 2 seperate and distinct circuits inside that solonoid.

 

Here is a guide......if you keep the main supply cable (10 ga.) less than 7 feet long you can use a 30 or 50 amp breaker....won't make any difference......the 50 will allow more capacity for future expansion.

 

But there is a trip switch at the transformer that will trip if a house pulls too many amps from a direct short. Your power company will come out and reset it. Ask me how I know.

 

<TABLE cellSpacing=0 cellPadding=2 width="80%" border=0><TBODY><TR><TD>To choose an adequate wire gauge, determine the amp draw (amperage) that the wire circuit will carry. Then measure the distance that the wire will travel (length) including the length of the return to ground (the ground wire running to the ch***is or back to a ground block or battery. Using these two numbers, Amps and length, locate the nearest gauge value in chart below. For 6 volt automotive systems typically a wire gauge 2 sizes larger than what is shown should be used.
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<TABLE cellSpacing=0 cellPadding=0 width="80%" border=1><TBODY><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf rowSpan=2>Amps
@ 12 Volts</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca colSpan=7>LENGTH OF WIRE
American Wire Gauge (AWG)</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#dbdbca>3'</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca>5'</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca>7'</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca>10'</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca>15'</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca>20'</TD><TD borderColor=#00467d align=middle bgColor=#dbdbca>25'</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>0 to 1</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>1.5</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>2</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>3</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>4</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>5</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>6</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>7</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>8</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>10</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>11</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>12</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>15</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>20</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>22</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>24</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>30</TD><TD borderColor=#00467d align=middle bgColor=#f3fed3>18</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>36</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>40</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#be8bf8>8</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>50</TD><TD borderColor=#00467d align=middle bgColor=#ddfc81>16</TD><TD borderColor=#00467d align=middle bgColor=#f7dd86>14</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#be8bf8>8</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>100</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f9a784>12</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#a4a4ff>6</TD><TD borderColor=#00467d align=middle bgColor=#a4a4ff>6</TD><TD borderColor=#00467d align=middle bgColor=#4aaeff>4</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>150</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#be8bf8>8</TD><TD borderColor=#00467d align=middle bgColor=#be8bf8>8</TD><TD borderColor=#00467d align=middle bgColor=#4aaeff>4</TD><TD borderColor=#00467d align=middle bgColor=#4aaeff>4</TD><TD borderColor=#00467d align=middle bgColor=#00ffff>2</TD></TR><TR><TD borderColor=#00467d align=middle bgColor=#ddbfbf>200</TD><TD borderColor=#00467d align=middle bgColor=#f797f9>10</TD><TD borderColor=#00467d align=middle bgColor=#be8bf8>8</TD><TD borderColor=#00467d align=middle bgColor=#be8bf8>8</TD><TD borderColor=#00467d align=middle bgColor=#a4a4ff>6</TD><TD borderColor=#00467d align=middle bgColor=#4aaeff>4</TD><TD borderColor=#00467d align=middle bgColor=#4aaeff>4</TD><TD borderColor=#00467d align=middle bgColor=#00ffff>2</TD></TR></TBODY></TABLE>​

<TABLE cellSpacing=0 cellPadding=2 width="80%" border=0><TBODY><TR><TD>Also see:
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yeah, the 6 volt info appears ****ed in my previous post, thanks for pointing that out

 

Like roadrunner said, voltage drop (VD) can be a bad thing but you will have this in any vehicle. There are so many connections and lengths of wire and it is all wired in a big loop (from the power source to the device and then back to the power source).

What some people overlook is the ground paths. My look at this is if I am adding a 4 gauge wire to the battery to power something I will either run the same gauge (4) from the device back to the battery negative or if the device is grounded to a large metal conductor like a frame and it is solid from the rear of the car back up to the front I will pick up at the front part of the frame and add a 4 gauge wire from there up to the battery negative post.

A lot of vehicles have the main battery ground cable going directly to the engine block for mainly a return path for the starter as it draws so much current. The factory then had a smaller gauge wire or braided cable to tie either the engine to the body of the car or this smaller wire from the battery negative cable to a spot on the fender. If you run a 4 gauge wire to something in the car and then ground it to the body of the car the restriction becomes this small original ground connection and there will be a big voltage drop across this connection as it is undersized.

As far as putting a fuse on a wire I always size the fuse to what the wire can handle. You can easily put a 100A fuse onto an 18 gauge wire but that's not the right size for it. When I put a 30A fuse onto a wire it will be 10 gauge or larger. If I install a 60A fuse on a wire it will be 8 gauge or larger. For 4 gauge I normally limit that to 120A fuse and for 1/0 I only go up to a 300A fuse. Some of this might be a little too high or a little low but I'm normally running the wiring and can position it so there is less of a chance of it being pinched and shorted.

I've blown fuses before and I normally find out what caused the problem and don't feed the circuit more good fuses hoping the problem will correct itself. On some of my installs I give the customer an extra fuse or wire tie it close to the fuse block and explain how a fuse works. If they come back saying they want a third fuse because the original one and the spare blew I tell them I want to inspect the car and see what is going on.

Jim