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Discussion Starter #1
Been reading some of the helpful posts about installing a power outlet. I'm going to mount a weather-proof 12v cig-lighter socket in the tray, and connect it to the battery leads, with an inline fuse. It will be used to power a small compressor for inflating tires.

My question is about the socket I bought...

It has a white and grey wire, instead of the usual red and black. Can I assume that standard would be white = center pole positive, and black = ground/negative?

Thanks in adavnce.
 

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FORUM GODFATHER.....R.I.P. PAT
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That's probably it but it's a better idea to check. If you don't have a voltmeter, get a 9v battery. Touch one pole to the outer metal case which is ground. The ground wire will make little spark when touched to the other pole as it completes the circuit.
 

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That's probably it but it's a better idea to check. If you don't have a voltmeter, get a 9v battery. Touch one pole to the outer metal case. If the grey wire really is the hot, it will make little spark when touched to the other pole.
I think you meant "If the grey wire really is the negative," ? (The outer metal case of the cig lighter is the ground)
 

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Discussion Starter #4
Thanks...


My next step was to use a piece of wire and a flashlight to see if the grey lead gave me conductivity to the shell of the connector.


One other question I just thought about...

What amperage fuse do you guys recommend inline with the power outlet?
 

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FORUM GODFATHER.....R.I.P. PAT
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I think you meant "If the grey wire really is the negative," ? (The outer metal case of the cig lighter is the ground)
Yes. I was thinking of testing for power in an installation rather than continuity. I'll change it. Thanks.
 

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What about the fuse amperage, what do you gurus recommend for this application?
I'm no guru, but it should be fused for the wiring leading to the cig lighter (and the rating of the lighter) - the larger the wire, the larger the fuse can be. (you want the fuse to blow before the wire melts). I wouldn't fuse it much over 15 amps (assuming 14 awg wire), likely 10 amps would be best....
 

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For future reference:
from the national fire protection assosciation standard (NFPA 79)
wire gauge: Ampacity:
24_________2A
22_________3A
20_________5A
18_________7A
16_________10A
14_________15A
12_________20A
10_________30A
All current capacity is for wire in a cable or raceway with a 75 degree C rated insulation in a temperature of 30 degrees C.
This is a good conservative guide for fuse values. Use the value for the smallest gauge (largest numerically) that you have in the circuit.
 

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FORUM GODFATHER.....R.I.P. PAT
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That table is for power transmission or 120VAC house wiring. Chassis wiring if a different beast. Do be aware that we are normally using bundled wire so values closer to power transmission values are best observed. See http://www.powerstream.com/Wire_Size.htm
 

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That table is for power transmission or 120VAC house wiring. Chassis wiring if a different beast. Do be aware that we are normally using bundled wire so values closer to power transmission values are best observed. See http://www.powerstream.com/Wire_Size.htm
WRONG! It's for internal wiring of industrial equipment. I do this for a living.
 

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FORUM GODFATHER.....R.I.P. PAT
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Okay. House wiring uses 10ga for 30a, 12ga for 20a and 14ga for 15a circuits. I didn't look closely enough.

Electricity works is the same regardless of what you do with it. Safe capacity is all about how well the environment allows cooling of the wiring. Heavier wiring means less resistance which means less heat. Bundling, running in conduit, or running in walls packed with insulation all reduce the ability of the wire to radiate heat away. Maybe the most valuable part of that site is the calculator that indicates voltage drop by size and length.
 

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Okay. House wiring uses 10ga for 30a, 12ga for 20a and 14ga for 15a circuits. I didn't look closely enough.

Electricity works is the same regardless of what you do with it. Safe capacity is all about how well the environment allows cooling of the wiring.
Good point. That is why NFPA79 is a good practical tool that errs on the conservative side. The spec is for wire in a raceway or in a cable, which means it is a good guide for our bikes as well, which tend to have tightly bundled wiring in an enclosed environment.
Heavier wiring means less resistance which means less heat.
Absolutely, but that is a different thing altogether. Fusing is to protect wiring. Lower resistance and voltage drop deal more with design intent and maximizing power transfer. One thing often overlooked is connection resistance, which can be a killer. I have been working with a circuit lately in which the connection resistance was more than the wire resistance! Needless to say, when you put 40 amps through it, the connections get quite warm.
Bundling, running in conduit, or running in walls packed with insulation all reduce the ability of the wire to radiate heat away. Maybe the most valuable part of that site is the calculator that indicates voltage drop by size and length.
I would agree. There are many standards out there dealing with this type of thing. In the controls environment I work in, we use NFPA79 and the NEC for our standards. NFPA79 tends to deal more with panel and controls wiring, NEC more with power and building wiring. How and what standard you apply to your application is up to you, and what your end-user needs. I just offered up NFPA79, as it is a good spec that is applicable to determining fusing values. You can't go wrong with it in this case.
 

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FORUM GODFATHER.....R.I.P. PAT
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Yeah. It's very conservative, but I'd rather be conservative than have my bike catch fire.
 
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