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Old 01-24-2021, 07:27 PM   #1
jg61hawk
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Default Does Gauge of Ground Wire Matter

I bought a disconnect switch locally, the type with a big turn dial OFF/ON. They only had normal 12volt wire in the store. I am breaking the POSITIVE ground. Will it matter if I run the 12volt wire from the frame to the disconnect and then the good 6 volt wire from the disconnect to the battery?

Do ground wires carry current or is just the Negative wire from the battery to the starter the important one?

If the answer is the ground wires need to be 6 volt, do they make a 6 volt disconnect versus a 12 volt disconnect?
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Old 01-24-2021, 08:05 PM   #2
Kurt in NJ
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Default Re: Does Gauge of Ground Wire Matter

It all has to be the "good" 6V wire, the disconnect has to be good for the amperage, how many amps is the switch you want to use rated for?, the 6v starter can draw over 500 amps locked
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Old 01-24-2021, 08:37 PM   #3
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Default Re: Does Gauge of Ground Wire Matter

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Originally Posted by jg61hawk View Post
I bought a disconnect switch locally, the type with a big turn dial OFF/ON. They only had normal 12volt wire in the store. I am breaking the POSITIVE ground. Will it matter if I run the 12volt wire from the frame to the disconnect and then the good 6 volt wire from the disconnect to the battery?

Do ground wires carry current or is just the Negative wire from the battery to the starter the important one?

If the answer is the ground wires need to be 6 volt, do they make a 6 volt disconnect versus a 12 volt disconnect?
Hawk - Wire doesn't really care 6V vs. 12V, it cares about amps. You should have the wire the same size (same gauge) going into the switch as going out. For the Model A, this means you run the thick cable (the one that's the size of your finger) to and from. The original Model a ground was a solid strap but many cars now use a flat braided strap for the ground.

Disconnect doesn't care 6V vs. 12V either. It's also all about amps. You need to look at the disconnect and see what amperage it's rated for. Since you'll be putting starting amperage through it it needs to be rated on the order of several hundreds of amps. If it's designed to be used as a primary disconnect you'll likely find that the terminals are quite large - like 1/4" or 5/16" (the posts, not the nuts). If they're tiny then this is likely not designed to be used as a primary disconnect.

BTW, on a disconnect installation, it's much more common to interrupt the power side, not the ground side. You should interrupt the big honkin' power wire from the battery (negative) to the starter, the power to the rest of the car is distributed from there (the yellow wire that goes up to the terminal box on the firewall).

To answer your other question, yes both negative and positive wires carry current. Think of the wiring as being a closed loop from the negative side of your battery to the positive side. For everything to work, you need to send amps from one terminal to the other. You lose amps along the way if they take an alternate path to ground (like light bulbs grounding against the headlight socket) but for the most part you should consider that both sides need equal capacity. (As an aside, house wiring works the same way - that's why the black wires and the white wires in a wall plug are the same size. I know that's oversimplification and there are cases in house wiring where white wires can be shared between black/red wires of different phases, but that's because house wiring is AC, not DC like the Model A. So let's not go there ).

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Last edited by JayJay; 01-27-2021 at 11:38 AM.
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Old 01-24-2021, 09:42 PM   #4
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Default Re: Does Gauge of Ground Wire Matter

Each side of the circuit carries the same current.

Use the heavier gauge wire. Realistically, the smaller wire will certainly carry the current needs for all your electrical devices except your starter. Your starter will appreciate the heavier cable and you will have one less thing to fail when you are out on the road somewhere.
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Old 01-24-2021, 10:18 PM   #5
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Default Re: Does Gauge of Ground Wire Matter

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Originally Posted by jg61hawk View Post
I bought a disconnect switch locally, the type with a big turn dial OFF/ON. They only had normal 12volt wire in the store. I am breaking the POSITIVE ground. Will it matter if I run the 12volt wire from the frame to the disconnect and then the good 6 volt wire from the disconnect to the battery?

Do ground wires carry current or is just the Negative wire from the battery to the starter the important one?

If the answer is the ground wires need to be 6 volt, do they make a 6 volt disconnect versus a 12 volt disconnect?
Put the disconnect in the ground cable like you planned , That disconnects everything !
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Old 01-25-2021, 07:57 AM   #6
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Default Re: Does Gauge of Ground Wire Matter

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As the fellas said, heavy wire. #1 at least, if not #0.

Any marina should have a heavy 500-600 amp switch if the normal parts stores don't.
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Old 01-25-2021, 08:00 AM   #7
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Default Re: Does Gauge of Ground Wire Matter

Thanks for the replies. I'm going to try to get 0 AWG cables made up. As far a breaking the ground or not an old guy told me break the ground in case I ever drop something on the positive battery to the the car it would not short out.... Again thanks.
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Old 01-25-2021, 09:06 AM   #8
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Default Re: Does Gauge of Ground Wire Matter

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As the fellas said, heavy wire. #1 at least, if not #0.

Any marina should have a heavy 500-600 amp switch if the normal parts stores don't.
I used double ought 00 wire I got from a welding shop. The difference in starting was remarkable.
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Old 01-25-2021, 10:12 AM   #9
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Default Re: Does Gauge of Ground Wire Matter

I made a long story short...The car had a disconnect but it dawned on me the wires are probably 12volt. So here is the disconnect (see photos) says 500 INT and 300 cont. I think that's good?? The wires I had were as follows...1 gauge from battery neg. to starter and then 2 gauge from battery positive to disconnect and 2 gauge to frame from disconnect. So I'm ordering all new 0 AWG. Sound good?
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File Type: jpg Battery Disconnct a1.jpg (23.0 KB, 66 views)
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Old 01-25-2021, 10:30 AM   #10
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Default Re: Does Gauge of Ground Wire Matter

The heavier gauge is important. My 6v car was starting poorly, then I noticed how small my negative cable to the starter was. I put a new one on from Brattons and it transformed starting! The old cable was smaller than a #4 under the insulation.
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Old 01-25-2021, 11:37 AM   #11
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Default Re: Does Gauge of Ground Wire Matter

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It says 500 INT and 300 cont.?
INT = intermittent
cont = continuous
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Old 01-25-2021, 11:40 AM   #12
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Default Re: Does Gauge of Ground Wire Matter

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Originally Posted by jg61hawk View Post
I made a long story short...The car had a disconnect but it dawned on me the wires are probably 12volt. So here is the disconnect (see photos) says 500 INT and 300 cont. I think that's good?? The wires I had were as follows...1 gauge from battery neg. to starter and then 2 gauge from battery positive to disconnect and 2 gauge to frame from disconnect. So I'm ordering all new 0 AWG. Sound good?
Hawk - 300 amps continuous and 500 amps intermittent (i.e. during starter load) is great. I think (happy to be corrected) that the original wire was the equivalent of today's #2 AWG, so #0 AWG (which is higher ampacity than #2) should be fine.

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Old 01-25-2021, 11:50 AM   #13
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Default Re: Does Gauge of Ground Wire Matter

Thanks....I ordered cables from this site...I'll keep you posted.

https://www.batterycablesusa.com/?ms...20Cables%20USA

1/0 Gauge Battery Cables (0 AWG)
1/0 GAUGE BATTERY CABLES (0 AWG)

I found this quote searching around here: Dyke's Automobile & Gasoline Engine Encyclopedia notes that the Model A's starter should normally turn at 1500 RPM drawing 175 Amps @ 6V, and produce a torque of 3 lbs-ft.

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Old 01-25-2021, 12:41 PM   #14
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Default Re: Does Gauge of Ground Wire Matter

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Thanks for the replies. I'm going to try to get 0 AWG cables made up. As far a breaking the ground or not an old guy told me break the ground in case I ever drop something on the positive battery to the the car it would not short out.... Again thanks.
Uh - the positive IS the ground, so dropping a wrench on it won't short anything out. It's already grounded. Or am I missing the logic here?

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Old 01-25-2021, 02:24 PM   #15
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Default Re: Does Gauge of Ground Wire Matter

He told me that about my 1961 Studebaker....If you do hold a wrench on a Model A negative to the frame or something does it spark? I never tried...probably won't try but now I'll wonder...
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Old 01-25-2021, 04:10 PM   #16
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Default Re: Does Gauge of Ground Wire Matter

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Uh - the positive IS the ground, so dropping a wrench on it won't short anything out. It's already grounded. Or am I missing the logic here?

JayJay
Break the ground so if you drop something on the hot post it wont spark is what he is trying to say.

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Old 01-25-2021, 04:57 PM   #17
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Default Re: Does Gauge of Ground Wire Matter

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He told me that about my 1961 Studebaker....If you do hold a wrench on a Model A negative to the frame or something does it spark? I never tried...probably won't try but now I'll wonder...
Oh yeah, it will spark, big time, as long as the ground terminal (the positive) is connected to the frame. Negative is the hot terminal. If you've interrupted the ground (as you propose) then no, it won't spark if you drop a wrench on the negative terminal.

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Old 01-25-2021, 06:41 PM   #18
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Default Re: Does Gauge of Ground Wire Matter

any welding supply can make up whatever guage cable with whatever end fittings you require.
I believe that most NAPA stores can make cables also.
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Old 01-25-2021, 09:40 PM   #19
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Default Re: Does Gauge of Ground Wire Matter

Welding cable is larger than battery cable.
You need #0 ends for #1 welding cable.
I never buy welding cable ends (terminals): they don’t look right.
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Old 01-26-2021, 08:54 PM   #20
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Default Re: Does Gauge of Ground Wire Matter

It's kinda like links of a chain. "It is only as strong as the weakest link "
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