# Punching through the firewall...



## Ziggythewiz (May 16, 2010)

lowcrawler said:


> That said, I figure I'll ask before I cut... is there any reason to run two smaller holes vs one larger?


No. Mine has 6 holes for bolts supporting my mounting plate, and one larger that a single 2/0 cable goes through.

Just be sure to use some kind of grommet to protect the cable where it passes through the firewall, you don't want it rubbing on metal.


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## lowcrawler (Jun 27, 2011)

Oh, right, I just meant hole(s) for cabling... I'll obviously have a few holes in there for mounting my component mounting board.

Basically -- is there anything bad about running two large cables through a single large (grommeted) hole? ... or would two be better?

(obviously we are getting to the point of diminished returns here... but hey, it's cold out!  )


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## dtbaker (Jan 5, 2008)

lowcrawler said:


> Basically -- is there anything bad about running two large cables through a single large (grommeted) hole? ... or would two be better?



well, it is BETTER to run + and - next to each other to help reduce the EMF that forms around high-amp cables.... but in specific, I'd have to ask why you are running traction-pack cables thru the firewall.

You REALLY don't want traction cables anywhere near people in the cabin if you can help it. They should be run under the center of the car if you have a pack in the rear, and hopefully straight up and into the rear box with NO CHANCE of exposing passengers in cabin to high voltage.


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## lowcrawler (Jun 27, 2011)

The batteries are behind the back seat (battery box mounted to the firewall) and the controller is mounted on the otherside of the firewall (ie: 6 inches away). About as far from 'people' in the car as possible and the cables will only be in the car for about 3 inches (positive) and about 8 inches (negative).


Sounds like no issues running them in the same hole. I was thinking about cable wear, sound coming through, or something like that...


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## piotrsko (Dec 9, 2007)

OK dumb question: fire wall, in the back of the car; right??

The Big ugly square connector on the upper left side has numerous taps for all sorts of odd functions replicated up front. I forget if 70's have one or not. A good wiring diagram is in order here.

Since the fire wall no longer serves an anti gasoline fire function, hole size and quantity would matter not. One thing though: a 3/4 dia grommet is easier to buy than a 1 1/2 dia ditto. when you remove the under seat heat boxes, you get this built in 2" dia hole on both extremes of the engine compartment and can run wires in the defrost floor channels into the front Trunk area.


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## lowcrawler (Jun 27, 2011)

piotrsko said:


> OK dumb question: fire wall, in the back of the car; right??


Right; 1970 VW bug.


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## piotrsko (Dec 9, 2007)

Just checking.


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## dtbaker (Jan 5, 2008)

lowcrawler said:


> Right; 1970 VW bug.



I missed that part and was thinking of traction cables down around your feet in front....

I would NOT run cables under doors, especially not together.... in case of accident requiring 'jaws of life', you don't want to have a saw cut electrocute everybody if the blade could short across both +-.


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## Woodsmith (Jun 5, 2008)

The only reason I can see for cables though the same hole is to prevent eddy currents in the metal.
Two holes would have current passing one way though one hole and then the other way through the other hole, a bit like one turn of wire around the metal between the holes.

I would put two cables through one big hole or, if space prevents it, put two holes next to each other and then saw a slot in the bit of metal between them so they become one 'dog bone' or 'dumbell' shaped hole.

I would do this for all cable holes in any component.

Gromits are a must to prevent wear on the cable.


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## lowcrawler (Jun 27, 2011)

dtbaker said:


> I missed that part and was thinking of traction cables down around your feet in front....
> 
> I would NOT run cables under doors, especially not together.... in case of accident requiring 'jaws of life', you don't want to have a saw cut electrocute everybody if the blade could short across both +-.


Meh, it'll happen... it's kind of weird. 

I agree -- no keeping the high-voltage out of the jaws-of-life areas.  (actually one of the reasons I went with the area behind the back seat rather than the rather worthless front trunk)


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## Ziggythewiz (May 16, 2010)

Front's certainly not as convenient as the nice shelf in back, but it has more room than the shelf does.

Can you fit all the batteries you need on just the shelf?


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## lowcrawler (Jun 27, 2011)

Ziggythewiz said:


> Can you fit all the batteries you need on just the shelf?


Yep, I don't need much range -- 48 100Ah CALB cells fit back there perfectly. If it turns out I need more range, I'll parallel another set.


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