SMTCapeCod

So- the copper ground strap from the block to the ground point on the pass side body...I've been replacing mine regularly, I have a new one and the installed one is showing its exposure.

Aside from the usual hollow mantra that Porsche knows best- are there any arguments for leaving the copper strands exposed to the elements vs. trying to seal with vulcanizing tape & etc...or using a different coated strap?

mike77

Mine gets coated in rust proofing spray which is suitable for electrical connections while I do other parts under the car. That said I keep meaning to replace mine as I think it is original.

MainePorsche

Bump for the Ones who know.
I've wondered about this too, for there must be a reason it is bare.
I keep the contact points clean, but find I have to spray the twined cable with Deoxit semi-often as it soils. Would have to be losing a bit of conductance.
What say you...

Alan

It will get wet, so better that it air dries (as it will due to engine heat) than stays wet behind insulation/cover/wrap. That way you can also much more easily evaluate condition visually while in situ.

Alan

dr bob

I've considered replacing with a factory-sealed 2ga lug-to-lug cable, but don't know how well the jacket would do in the heat. It would also preclude visual inspection. So far, those things have kept the original open type strap in place.

There are marine-rated cables easily available with fine-strand tinned-copper conductors that would do the trick nicely, especially since jackets and insulation have improved a lot. Maybe a piece of Firesleeve over that would solve the worry things on my "potential problems" list.

Were I engineering this today... I'd have short braided straps as jumpers around each motor mount. Maybe instead of the factory piece, but at this point I'd look to just leaving the factory piece in place.

MainePorsche

Thanks Alan. I did wonder why. Simple logic was the answer. That's electricity

Tomkat80222

I changed this cable this last week and what a difference. I have no ideas about the age, but the cable looks good. It had some green corrosion, but not much. The ends were not corroded. No resistance with the volt meter. With the old ground the volt meter ranged from 13.5 to 14. With the new strap the meter ranges between 13 and 13.5. Higher voltage means higher resistance. Anyone try to clean these straps with vinager and salt or baking soda?

Alan

Not sure your conclusion here makes so much sense... if the old ground strap had high resistance you would be dropping some voltage over it. This means there is a difference between the engine related grounds and the chassis related grounds. If the Alternator is producing then it will be referenced to the engine ground.

Generally we measure voltages wrt the chassis ground points - its easiest.

Here measuring a voltage wrt chassis ground it might seem to be lower than if it was referenced to engine ground. Then eliminating this resistance with a better ground strap should then make the same measurement voltage appear to go up (not down).

If the voltage across chassis related grounds does go up after replacing the ground strap then the circuit current will also go up and this loading may make the alternator voltage actually drop - especially at idle. So if you do measure voltage wrt engine ground replacing the engine ground strap may make the actual generated voltage lower. This effect should typically not be apparent @ >2K engine RPM.

Clearly the results you get here depend very much on the ground reference you use for measurements.

Truest ground for engine non-running cases is the battery negative terminal, truest ground when the alternator is generating and charging the battery is the alternator case. We rarely actually reference these points directly - so we almost always have a ground offset to any equipment of interest - fortunately the difference is usually quite negligible. A 0.5V difference is a very big offset indeed!

To the earlier questions on sheathing, there is a (newish to me) heavy duty clear heat shrink tubing (available at Waytek Wire) that allows good visual inspection that might be a good idea to use here. I like it so much I stripped my waytek battery ground strap of the self vulcanizing tape wrap I had installed on it and covered it with this instead - for largely the same reasons.

DSG Canusa CPX 100 1500 CLEAR Polyolefin Heat Shrink in 48" lengths
2:1 shrink, Flame retardant, MIL-1-23053/5 Class 2 specs
257°F (135°C) - 67°F (-55°C), Wall Thickness: .040"

Alan

UKKid35

Anyone happen to know what the length and connector sizes are?

Thanks

UKKid35

I can confirm that it is 12" and has M8 fittings

The cable I have purchased is 50mm sqd or 0 AWG and cost £7

Hopefully it won't be too awkward to fit

FredR

Easy to fit if the body pan is removed or non existant. 50mm2 sounds about right [4mm diameter?]

dr bob

FWIW, the aftermarket motor mount set I received from 928 International a few years ago included metal straps that connect top and bottom electrically. I didn't even try to fit them inside the factory brackets, but probably should have.

Hey_Allen

I'm fairly certain that 1/0 AWG wire is closer to 8 mm diameter, plus the insulation.
I checked one of the engineering handbooks, and 4 mm diameter wire is between 6 and 7 gauge.

That said, while it might be a bit harder to route the wire, it can't hurt to have a better ground path between the engine and chassis.

FredR

You are spot on- my decrepit mental arithmetic forgot to convert radius back into diameter- no wonder it seemed suspect

UKKid35

This 12" earth strap is slightly shorter but significantly heavier

Hope it isn't too awkward to fit