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pgtips
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Joined: July 23, 2009
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Location: essex
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sctbrd
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Joined: May 06, 2013
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Location: Moravia, Czech Republic
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 Posted: Mon Jun 23, 2025 5:28 am Post subject: Re: Earth strap - how many amps ? |
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Same as negative battery cable should be enough.
Braided is used for some flexibility between tranny and body. |
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pgtips
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Joined: July 23, 2009
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Location: essex
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Wildthings
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Joined: March 13, 2005
Posts: 52281
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| Posted: Mon Jun 23, 2025 5:57 am Post subject: Re: Earth strap - how many amps ? |
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| For the 12+ side the schematic in the technical section shows a DIN 25 which converts to a #4 AWG. I have upped the size of both my battery cables to #1 AWG and run the negative cable to the engine and not the frame so if something goes wrong with the ground strap the clutch cable doesn't see the starter current, thus the actual transmission ground could be smaller, though I am sure whatever I used is much higher rated than it need be. |
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lil-jinx
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Location: New Brunswick,Canada
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raygreenwood
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Location: Oklahoma City
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 13470
Location: West Coast, USA
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| Posted: Mon Jun 23, 2025 6:59 am Post subject: Re: Earth strap - how many amps ? |
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My ammeter showed 120-150 amps at initial cranking, and close to 100 amps for the next few seconds of cranking. This is on my low compression stock 1600 Type 1 with a manual flywheel, fully charged battery, and inductive clamp meter. Your Subaru with a torque converter will draw a little more power.
Good luck,
Robbie
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pgtips
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Joined: July 23, 2009
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Location: essex
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wagen19
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Joined: November 16, 2007
Posts: 650
Location: germany
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| Posted: Mon Jun 23, 2025 7:19 am Post subject: Re: Earth strap - how many amps ? |
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Imo the easiest way would be, just to buy a original or good repro strap. The original plastic cover was ment good, but was the contrary for corrosion.
Have a look on your original ground and plus wire from battery to body and to starter. That diameter should be enough, as long your electrical system is near to original.
If you are nut sure and want it to make more safe than original, thake a stronger wire.
German cars are based on DIN.
Compare:
https://www.google.com/search?q=kabel+25mm2+ampere...s-wiz-serp
Old 6 volt beetles have 25 mm², 356 has 35 mm² (longer wire, battery in front) |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 13470
Location: West Coast, USA
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| Posted: Mon Jun 23, 2025 7:38 am Post subject: Re: Earth strap - how many amps ? |
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| pgtips wrote: |
| airschooled wrote: |
My ammeter showed 120-150 amps at initial cranking, and close to 100 amps for the next few seconds of cranking. This is on my low compression stock 1600 Type 1 with a manual flywheel, fully charged battery, and inductive clamp meter. Your Subaru with a torque converter will draw a little more power.
Good luck,
Robbie |
Thanks Robbie/All
1 AWG is about 7.35 mm and good for appx 110 amps
0 AWG is 8.25mm and is good for 150
00AWG is 9.26mm and is good for up to 190
(from https://www.metersuk.co.uk/american-wire-gauge-awg-cable-conductor-sizes/)
So based on @airschooled post (thank you) 00AWG will be perfect |
00 isn’t going to hurt anything, but it’s way more than you need. The link you posted doesn’t take length into account. Check Ray’s link above- length of wire is a key variable in heavy loads. Ground straps are what, twelve inches max? 1Awg is already plenty useful overkill, unless you’ve come up with a reason for your ground strap to be eight feet long?
I think the braided originals compensated for movement of the powertrain on its rubber mounts. A thicker wire replacement isn’t going to last as long in that situation that requires compliance.
Robbie
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pgtips
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Joined: July 23, 2009
Posts: 879
Location: essex
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| Posted: Mon Jun 23, 2025 7:46 am Post subject: Re: Earth strap - how many amps ? |
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ok. I was just thinking (the wrong way but this is a learning curve on this) that with Subaru engine it might need a upped spec.
Whats actually triggered this is a ebay vendor sold me '70amp' earth strap cable but its 7awg, pointed out earlier that's max 30 amps. I am super wary of ebay sellers on these sorts of things.
then you know how it is, you start to go round in circles.
The reason for not just buying a braided strap is becuase I am also going to replace my battery cable. I have proper crimpers and end rings so figured one cable length and make up 2 cables.
So if 1AWG is ok then I'll buy that instead.... battery and gearbox earth strap can be same.
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1971 356 kit 1600 TP - semi/stickshift
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Trim ring info here -> http://www.thesamba.com/vw/forum/viewtopic.php?t=559668
http://www.thesamba.com/vw/forum/viewtopic.php?t=451210
http://www.thesamba.com/vw/forum/viewtopic.php?t=479721 |
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KTPhil 
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Location: Conejo Valley, CA
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| Posted: Mon Jun 23, 2025 8:54 am Post subject: Re: Earth strap - how many amps ? |
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It needn't be thicker than the battery positive cable. In a closed circuit the current flow through those two cables at the battery is identical by definition.
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raygreenwood
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Joined: November 24, 2008
Posts: 23098
Location: Oklahoma City
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| Posted: Mon Jun 23, 2025 8:58 am Post subject: Re: Earth strap - how many amps ? |
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| pgtips wrote: |
ok. I was just thinking (the wrong way but this is a learning curve on this) that with Subaru engine it might need a upped spec.
Whats actually triggered this is a ebay vendor sold me '70amp' earth strap cable but its 7awg, pointed out earlier that's max 30 amps. I am super wary of ebay sellers on these sorts of things.
then you know how it is, you start to go round in circles.
The reason for not just buying a braided strap is becuase I am also going to replace my battery cable. I have proper crimpers and end rings so figured one cable length and make up 2 cables.
So if 1AWG is ok then I'll buy that instead.... battery and gearbox earth strap can be same. |
I posted a link to this a few times over the past years or two.
If you are going to use an original braided strap.....which has PLENTY of amp capacity.....go one step better than factory.
Copper braided strap is very high capacity as it has hundreds of interconnected individual wire filaments. This makes for very high mass. But it's form makes it very flexible compared to a round, tight packed wire. BUT.....braided Copper strap has one problem.
As braided copper strap is constantly exposed to oxygen and moisture....it starts getting that Copper penny colored patina all over it even in the minute spaces between the filaments where they interleave and interconnected.
That oxidized "Copper penny" color patina....while it is still conductive.....it is an order of magnitude higher resistance (actually potential is a better word). If you test it's resistance with a VOM....it will still read low or no resistance because there is a lot of Copper mass there fo conduct.
But if you start pulling amps through it.....the resistance is much higher and it can get warm (that is the potential factor at work). Still not a huge issue....yet.
But as the strap gets older and you start seeing that greenish or whitish corrosion forming down inside of the braid.....that Copper patina is 100%.....a NON-CONDUCTOR.
The corrosion gets into the crossing spaces in the weave, becomes non-conductive and the ground strap resistance goes way up.
How to fix this?
You can cheaply buy silver plated braided copper ground straps. Silver will also develop tarnish/patina.....but silver tarnish/patina is CONDUCTIVE.
This is why in my industry we are required to use silver or gold plating and conductors on medical device and certain aerospace printed circuits.....so that they will not lose connectivity or develope serious resistance problems due to weathering and oxidization.
You can also buy "tinned" braided copper which will resist corrosion for a lot longer but tin plating is a factor of about 10X higher surface resistance.
I will try to dig up my links later today if you are interested.
Ray |
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pgtips
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Wildthings
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Joined: March 13, 2005
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| Posted: Mon Jun 23, 2025 10:16 am Post subject: Re: Earth strap - how many amps ? |
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| For a late Vanagon, they use a 70 DIN (2/0+) cable for the (+) hot side and a 25 DIN (4 AWG) cable for the negative. The hot cable is about 8' long which accounts in part for its large size. |
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Shonandb
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Joined: January 12, 2019
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Location: Vancouver, BC
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| Posted: Mon Jun 23, 2025 10:54 am Post subject: Re: Earth strap - how many amps ? |
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I went with the "more is better" mentality when planning the grounding of my Subaru engine in my swap. I used all the existing grounds that attached to the engine as well as ran a 30" 4 gauge negative cable from the normal ground bolt to the starter bolt at the engine, a 12" 4 gauge negative cable from the ground bolt to the A/C bracket mount bolt on the engine, and a 6" 4 gauge cable from the Auto transmission to the torsion tube to replace the braided ground strap.
This way, both ends of the transmission have a solid ground and the main current goes from the starter pos through the starter to the starter neg cable at the starter bolt and not go through the transmission to the torsion tube.
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SGKent
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| Posted: Mon Jun 23, 2025 12:20 pm Post subject: Re: Earth strap - how many amps ? |
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the hard thing with thick wire is going to be mounting it. By the time you buy lugs and a industrial crimper that has handles 18" - 24" long, it would have cost less to buy a new transmission or battery strap. I run one between the battery and frame, the one between frame and transmission, and an extra one between the engine and transmission. There is also one at the back between the frame and engine. It isn't just for the starter. I want the lowest amount of noise in the system possible for the best results from the FI ECU.
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lil-jinx
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SGKent
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| Posted: Mon Jun 23, 2025 3:24 pm Post subject: Re: Earth strap - how many amps ? |
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The crimp needs to be about twice that size or the wires simply break in the middle and pull out the sides. I know this because I had to buy a big honky ass crimper to fix one someone did like that.
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Abscate
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| Posted: Mon Jun 23, 2025 7:54 pm Post subject: Re: Earth strap - how many amps ? |
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If you have West Marine in your neighborhood you can crimp your own stuff on their handy rigging crimper they have in their store for us sail boaters.
They also carry Ancor line of electrical stuff which is top shelf quality - heavy guage wire, lugs etc.
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