Bosch RSR Battery Switch wiring questions

[keith]

I'm wiring the Bosch battery switch according to this diagram, and need some input:



On my '75, the hot leads from the battery other than the starter cable (which bypasses the Bosch switch) are 4.0mm, 4.0mm, and 6.0mm. Accordingly, I'm trying to determine the proper wire size for the single wire from the battery to the Bosch switch - any advice from those more electrically savvy than I?

The wire will end up being approximately 4.5-5 feet long to get to the switch in the speaker location.

[keith]

anyone know what 4+4+6 = ?

[davep]

a wee bit bigger than 8

[keith]

was hoping it was 8, but the extra length on the 6 was a concern...

[keith]

on the other hand, since I'm doubling the length of the 6, should I step it up a size also?

[keith]

OK, so here's what I did:

I made the 6.0 that feeds the fuse panel from the battery into an 8.0 (which incidentally is an 8 AWG) because I doubled the length when I moved it to the kill switch in the speaker location.

I was looking for something equivalent to 14 mm^2 (4.0+4.0+6.0) in AWG which should be a 6 AWG, but its cross-section is actually 13.3mm^2 for some reason - and being that I'm risk-averse, I bumped it up to 4 AWG, which is the same size as the battery cable in the 1975 911 (25.0). [EDIT- it's actually smaller than the main battery cable - 21.2mm^2 vs. 25.0]

I probably could have used a 6 AWG cable safely, but since I'll be using the 901 611 311 00 battery clamp (which is a 2 cable clamp) and I felt better clamping two cables of the same size for cable retention - they are a bit large for this particular clamp, but I think it'll all work nicely.

The clamp also has an additional ring terminal bolt - in case I need to power something else directly from the battery in the future (like Marchal relays, for instance )

I'm sure this is overkill on the wire sizes, yes?

[keith]

In the interest of entertaining myself, I'm continuing to post on this thread.

I found this online calculator, which alongside this handy conversion table tells me that I indeed went overkill on my wire sizes.

[keith]

I do have a question; what boots are everyone using on the terminals? The starter cable boot is ridiculously large on the cable entry side, and I'm concerned it is going come off and slide down the wire eventually.

UPDATE - I ended up using the starter cable boots - nothing else worked very well at all!