electrical and ignition Should we trust the wire sizes shown in the wiring diagrams?

[Healey3000]

Hi,

 

The wiring diagrams list the area of wires used as well as the color codes.  Are these numbers reliable, from your experience?

 

For example, the main positive cable that goes from battery anode into the harness near the radiator is listed as 6 mm^2 in area.  That translates to a diameter of 2.75 mm.  Looking up charts, this wire can support about 60 amps, which seems okay, perhaps.  Looking at the wire in my car, it sure seems larger than 2.75 mm but perhaps that's because it has unwound some over the years.  If anyone can confirm this I'd appreciate it.

 

The battery to starter cable is listed as 16 mm^2 in area.  That's only 4.5 mm in diameter, good for just over 100 amps.  That does not seem big enough, sparking doubts (pun intended) about the veracity of the sizes in the diagrams.

 

Thanks.

 

 

[xr4tic]

4.5mm is roughly equivalent to 5 gauge, which is fine for 100 peak amps.  Keep in mind it's not a constant load, just a few seconds

[Preyupy]

Also remember that wire diameter was specified for a 18" run from the battery to the starter on a STOCK car.  If you are going to mount the battery in the trunk you need to recalculate because of the resistance/foot of the small diameter wire. Higher compression ratio engines also require a few more amps to start. 

[Healey3000]

4 minutes ago, Preyupy said:

Also remember that wire diameter was specified for a 18" run from the battery to the starter on a STOCK car.  If you are going to mount the battery in the trunk you need to recalculate because of the resistance/foot of the small diameter wire. Higher compression ratio engines also require a few more amps to start. 

Indeed.  I'm keeping the battery in the stock location but going with a smaller AGM type that I can lay on its side.  That will buy me added clearance to put an airbox on top of the battery, poking out that hole in the front sheetmetal.  Still, I'd feel better with at least a 4 AWG or perhaps 2 AWG cable to the higher output starter.

[Preyupy]

For that short of a run a 4AWG will be more than enough. 

[jgerock]

4 hours ago, Preyupy said:

For that short of a run a 4AWG will be more than enough. 

+1.   Look for flexible cable like this 4AWG marine cable I bought at West Marine.  They have the connectors too (also can be found at Auto Parts stores).

 

[Healey3000]

There are a few vendors on ebay who will fabricate custom cables to order.  You pick color, length, gauge and eyelet size and they do the rest.  Seems very cost competitive versus buying the parts myself and trying to crimp properly.  Peace of mind since they have the correct crimp tools.  Nice looking cable from West Marine.  Did you put the terminals on yourself?

[jgerock]

5 minutes ago, Healey3000 said:

There are a few vendors on ebay who will fabricate custom cables to order.  You pick color, length, gauge and eyelet size and they do the rest.  Seems very cost competitive versus buying the parts myself and trying to crimp properly.  Peace of mind since they have the correct crimp tools.  Nice looking cable from West Marine.  Did you put the terminals on yourself?

Yup.  Cut the sheath with an Exacto knife, spun on the terminal and used a chisel and hammer on both sides to crimp the ends.  Didn't feel like spending $$$ for a cool crimping tool but bet it would work great.

[Buckeye]

Alternative to crimping is Fusion copper lugs or similar. Come ready to use, pre-measured and loaded with correctly metered flux and solder in a solderable tin plated copper connector.

I used Fusion positive battery connector with my existing cable and it worked great.

 

https://www.delcity.net/store/Straight-Barrel-Fusion-Battery-Terminals/p_804069

 

https://www.delcity.net/store/Fusion-Heavy-Wall-Copper-Lugs/p_807161