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Old 12-03-2012, 10:30 AM
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Engine Grounding Points...

Good Morning and Happy Holidays to everyone! As I work through and clean up / correct the wiring in my 1950 Ford I wanted to ask your thoughts on engine grounding points. My understanding has always been the following:
  1. Negative battery terminal to block
  2. Block to frame
  3. Frame to firewall
I know there can be some variations of this, but want to make sure it is right. Also, any better suggestions other than the braided ground straps to ground to frame and firewall?



Thanks!

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Old 12-03-2012, 11:24 AM
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All those are fine, and the braided line isn't necessary, if you are talking about one of these.



Any battery like cable like this is going to doe the exact same thing, but a different look, depending what you are after.



Brian
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Old 12-03-2012, 04:44 PM
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Make sure that you get good metal to metal contact - paint doesn't conduct very well. A large percentage of electrical problems are due to poor grounds.
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Old 12-03-2012, 05:55 PM
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On my stock '75 GM vehicle I know of these grounds:

engine compartment
- Negative battery terminal to block/alternator bracket (standard battery cable)
- Negative battery terminal to radiator support (about a 10 gauge wire)
- Block to frame (braided)
- Block to firewall (braided)

other significant grounds
- Instrument panel to body
- Rear light harness to body (one in the middle and one on each taillight)
- Front light harness to radiator support (one on each side)

Based on past experience, if one of these grounds loosens up I start to have problems with lights and accessories.

Bruce
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Old 12-04-2012, 11:05 AM
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Quote:
Originally Posted by engine24355 View Post
Good Morning and Happy Holidays to everyone! As I work through and clean up / correct the wiring in my 1950 Ford I wanted to ask your thoughts on engine grounding points. My understanding has always been the following:
  1. Negative battery terminal to block
  2. Block to frame
  3. Frame to firewall
I know there can be some variations of this, but want to make sure it is right. Also, any better suggestions other than the braided ground straps to ground to frame and firewall?



Thanks!
Adding a block to firewall ground couldn't hurt.

DC current likes a larger number of finer wire braided into a cable rather than fewer, larger wires bundled into a cable. That's why you see the flat braided ground straps. They might be unsightly to some, but they're effective at what they do.
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Old 12-04-2012, 11:40 AM
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Very interesting, I do like the looks of the big braided cable actually, on a car like my Rambler or my truck with the theme I am after, they are perfect.
But on a more modern "Riddler" type look, the bound and covered cable would make more sense, looks wise.

Just how different could it's operation be?

Brian
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Old 12-04-2012, 12:52 PM
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The finer wire handles vibration better, and is easier to route since it's more flexible. I don't know the physics of fine versus coarse in handling current at low voltages, but have heard high voltages tend to travel more on the surface of the conductor than through it, which would favor the finer wires having more surface area. I used fine wire welding cable for my battery cables because of it's flexibility and better dealing with vibration.

You don't have to give up fine wire to get the cable look - use welding cable.

Last edited by sedanbob; 12-04-2012 at 12:54 PM. Reason: Additional point
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Old 12-04-2012, 01:52 PM
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Quote:
Originally Posted by sedanbob View Post
The finer wire handles vibration better, and is easier to route since it's more flexible. I don't know the physics of fine versus coarse in handling current at low voltages, but have heard high voltages tend to travel more on the surface of the conductor than through it, which would favor the finer wires having more surface area. I used fine wire welding cable for my battery cables because of it's flexibility and better dealing with vibration.

You don't have to give up fine wire to get the cable look - use welding cable.
Good point, welding cable is an excellent example of the type of cable he could use if he didn't want the flat straps.

Someone said welding cable insulation wasn't rated as "good" as automotive cable. IMHO considering the conditions real welding cable must endure I'd expect it to not only be as good but maybe better.

Years ago I went to Skycraft in Orlando (surplus electrical and gadgetry of ALL sorts- the kind of place that you cannot just go in and pick up what you came for w/o taking at least an hour just plundering). There I bought a bunch of welding cable for my '81 Camaro, a friends '72 Camaro and another friend's '78 T/A. At the time I looked up the abbreviations on the cable and there were a lot of mil type specs covering the insulation's abrasion, chemical and temperature resistance that convinced me that the cable would be totally adequate.

But even if there were questions about that, there's flexible PVC conduit that can be used for protection, like if it were to be exposed under the car when mounting the battery in the trunk.

As for any real difference in how fine vs. coarse wire would be, as long as the routing (tight bends, etc.), the type of current (AC or DC), and the voltage/load is taken into account when the size/stranding of the cable is chosen, it matters not.

That said, you will notice a difference in the wire stranding and gauge between cheap cables and good cables, good favoring smaller gauge individual wires bundled into larger gauge cable.

Last edited by cobalt327; 12-04-2012 at 02:04 PM.
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Old 12-04-2012, 01:59 PM
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Thanks for all of the help and information!
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Old 12-04-2012, 09:16 PM
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My sedan is a fiberglass car which means of course there is no grounding through the body. I had to run dedicated grounds for everything. I think I would have wired it the same if it had been a steel body. I ran 1/0 welding cable for both positive and ground from the battery (in the back) to the starter (+) and a bellhousing bolt (-). From that bellhousing bolt, I ran grounds to the chassis, fuse panel, and terminal blocks front and rear. All the grounds from lights, horn, fan, radio, et cetera all go to either the fuse panel grounds, or one of the terminal blocks. All were done with copper terminals crimped, soldered, then covered with glue-filled shrink tube. I also crimped, soldered, and shrink tubed the welding cable. Overkill, perhaps but I don't want problems with bad grounds or weak connections.
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Old 12-04-2012, 11:27 PM
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Is this a stock 50 ford 6v system ?! Guys isn't that a positive ground! I didn't see it stated or not! Is it converted or a street rod with a 12v system I must have read right by it?

Just wondering

Jester
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Old 12-05-2012, 12:41 AM
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Ya, a stock 50 Ford was 6 volt positive ground.
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Old 12-05-2012, 07:25 AM
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Originally Posted by painted jester View Post
Is this a stock 50 ford 6v system ?! Guys isn't that a positive ground! I didn't see it stated or not! Is it converted or a street rod with a 12v system I must have read right by it?

Just wondering

Jester

The car has been converted to a 12v system. Sorry, should have mentioned before.
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Old 12-05-2012, 11:43 AM
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Quote:
Originally Posted by sedanbob View Post
The finer wire handles vibration better, and is easier to route since it's more flexible. I don't know the physics of fine versus coarse in handling current at low voltages, but have heard high voltages tend to travel more on the surface of the conductor than through it, which would favor the finer wires having more surface area. I used fine wire welding cable for my battery cables because of it's flexibility and better dealing with vibration.
The physics of it is that at 12 volts DC, all that matters is the total cross section area of the copper conductor. Lots of electrical installations at much higher voltages than 12 V use solid copper bus bars with no problems. The differences with "high voltages" is at the tens of thousands of volts level - think spark plug voltages. For normal 12V DC ground straps, use whatever works so long as there is enough total copper. The use of braided ground straps for routing simplicity and vibration resistance is fine.
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Old 12-05-2012, 12:23 PM
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The car has been converted to a 12v system. Sorry, should have mentioned before.
"All that matters is the total cross section area of the copper conductor."

He forgot the length of wire increases resistance the longer the wire the hotter it will get!! As length increases you must go to a larger gauge wire! This is very important to remember!

Jester

Last edited by painted jester; 12-05-2012 at 12:30 PM.
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