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Sat Mar 16, 2024 9:14 pm

On my 1971 SB race car, I will be running a wire from the B post on the new alternator to the starter. Lee than 4 feet long. I have seen wire sizes quotes from 2 ga to 8 ga.
I am curious as to why the B post is so small if that big of gauge is required.
What size did VW use for the original cable?

Sat Mar 16, 2024 9:28 pm

4.0 or 12 awg no need for more.

Sat Mar 16, 2024 9:46 pm

In fact your running a wire from the B terminal to the battery, using the starter as a junction block. It has only the current the regulator can give it.

Sat Mar 16, 2024 10:56 pm

That is what I was thinking. Thanks for the comfirmation.

Sat Mar 16, 2024 11:05 pm

FunracerCO wrote: On my 1971 SB race car, I will be running a wire from the B post on the new alternator to the starter. Lee than 4 feet long. I have seen wire sizes quotes from 2 ga to 8 ga.
I am curious as to why the B post is so small if that big of gauge is required.
What size did VW use for the original cable?

It is closer to a 10ga wire, than a 12ga wire. 12 is good to 20amps 10 is good to 30.

Sun Mar 17, 2024 6:42 am

VW_Jimbo wrote: FunracerCO wrote: On my 1971 SB race car, I will be running a wire from the B post on the new alternator to the starter. Lee than 4 feet long. I have seen wire sizes quotes from 2 ga to 8 ga.
I am curious as to why the B post is so small if that big of gauge is required.
What size did VW use for the original cable?

It is closer to a 10ga wire, than a 12ga wire. 12 is good to 20amps 10 is good to 30. Yes it is closer to 11awg. The nec limits 12awg to 20amps but its good to 25.

Sun Mar 17, 2024 10:32 am

bsairhead wrote: VW_Jimbo wrote: FunracerCO wrote: On my 1971 SB race car, I will be running a wire from the B post on the new alternator to the starter. Lee than 4 feet long. I have seen wire sizes quotes from 2 ga to 8 ga.
I am curious as to why the B post is so small if that big of gauge is required.
What size did VW use for the original cable?

It is closer to a 10ga wire, than a 12ga wire. 12 is good to 20amps 10 is good to 30. Yes it is closer to 11awg. The nec limits 12awg to 20amps but its good to 25.

You always round up in electrical systems. 11 gauge is not availed in electrical wiring, that I have ever seen.

Smaller the gauge number, the LARGER the wire. The larger the wire, the more amperage it can handle.

All system wiring is UNDERRATED for safety! A good rule of thumb is 20%. You are confusing the full rating with the safe to use rating.

Sun Mar 17, 2024 6:14 pm

Yes you are correct about going to the next size larger. 10awg in this case although some diagrams show 6.0mm so now where at 8awg. If the charging system is working correctly I would have a hard time believing that B+ to the battery would ever have more than a 16 amp load. It would be interesting to see an amp draw on that wire.

Mon Mar 18, 2024 6:59 am

The ampacity of a conductor is based a number of factors e.g., length of wire,insulation type,time constant,ambient temperature and load cycle. NEC is not a guideline for automotive wiring.

Mon Mar 18, 2024 8:36 am

Schatzievw wrote: The ampacity of a conductor is based a number of factors e.g., length of wire,insulation type,time constant,ambient temperature and load cycle. NEC is not a guideline for automotive wiring.

Correct, unfortunately automotive cables have no universal standards/guidelines. VW uses what's called VW60306-1.

Mon Mar 18, 2024 3:22 pm

Quote: automotive cables have no universal standards/guidelines

of course they do...

https://www.iewc.com/resources/technical-guide/automotive-industry-wiring-standards

https://www.jocacable.com/faq-items/understanding-automotive-wiring-standards-organizations/

https://www.sae.org/standards/content/j2202_201912/

then there is my standard...bigger is better 8)