Author Topic: Electrical grounding  (Read 307 times)

Offline HerbP

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  • Name: Herb Potthoff
Electrical grounding
« on: November 04, 2017, 12:31:03 PM »
Does anyone see an advantage, other than the possible length for the wire run, to grounding through the grounded terminal on the battery vs finding a good chassis ground?
1940 LaSalle 5019
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This stuff is FUN!
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Offline Bobby B

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  • Mendham, New Jersey
  • Name: Bob Bender
Re: Electrical grounding
« Reply #1 on: November 04, 2017, 07:09:58 PM »
Herb,
 Hi. There is no reason whatsoever to run a cable all the way back to your battery, as long as you have a good chassis ground with a healthy sized negative battery cable. I would think auto manufacturers do it like this for 3 main reasons....#1-Cost effective, as you would have double the amount of wires in the car, #2-Weight savings, and #3 Possible voltage drop because the longer runs of wire would have to be oversized to handle the current. You can do whatever you want, but as a licensed electrician by trade, I see no advantage to it. Hope this Helps!
                                     Bobby
1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

Offline dochawk

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  • Name: Richard Hawkins
Re: Electrical grounding
« Reply #2 on: November 05, 2017, 04:07:39 PM »
If running a wire to the battery actually made a difference, it would mean that the battery isn't grounded properly!

The chassis will havefar less resistance than any wire.

hawk
1972 Eldorado convertible, 2001 Deville DHS (daughter), 1997 Eldorado ETC (and now my wife wants an Eldorado!)

Offline The Tassie Devil(le)

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Re: Electrical grounding
« Reply #3 on: November 05, 2017, 04:48:26 PM »
Don't forget that one has to remove all the paint that is under the ground strap where it attaches to the chassis.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
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Offline J. Gomez

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  • Name: J. Gomez
Re: Electrical grounding
« Reply #4 on: November 06, 2017, 07:34:14 AM »
There are no issues on using the chassis/frame as you main ground source, it was use on older cars and still in use today.

The issue with older cars lies with the lack of additional ground extensions from the frame (when the battery ground is connected at the frame) over to the chassis. Also using the chassis as the main source for grounding for metal housing, fixtures, etc. with metal-to-metal contact only. One or two ground straps from the engine block over to a point in the chassis is just not enough in my view.

Modern cars have ground wires from all of the electrical devices connected to a main distribution area with is connected to the chassis. These are place around a few areas engine, interior, rear, etc. to aggregate the ground sources via short length of wires.

As stated above these connections would require to be clean for a good bonding to be made for a reliable connection. Older cars with this setup had/have a tendency to be prone to poor grounding, loose connection, corrosion, etc.
I’ve have seen voltage drops of +/- 1 – 2 V on areas (predominant on front/rear light fixtures) where the metal housing was just screw/bolted to the chassis and relying on the fastener for the ground source.

Adding an additional wire(s) on all of these areas to a good metal source is a huge task but it solves some of the intermittent problems and adds an extra layer for a reliable connection.

This is one of the reason folks add a ground wire to the fuel tank to fix the intermittent problems with the fuel sender unit and not relying on the metal fuel line as the main ground source for the fuel tank.

Just my ˝ cent. 
J. Gomez
CLC #23082

Time is irrelevant when you work on your classic car, eventually you will enjoy it..!

Re: Electrical grounding
« Reply #5 on: November 06, 2017, 08:04:39 AM »
If battery is cleanly grounded to the frame and the body is cleanly grounded to the frame, for most electrical loads there would be no advantage to running a ground wire all the way back to the battery terminal. So clean the grounds at the frame, starter, and from body to engine.  All will be well...
Art Gardner


1955 S60 Fleetwood sedan

Offline J. Gomez

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Re: Electrical grounding
« Reply #6 on: November 06, 2017, 08:31:50 AM »
Oops caffeine deficiency this morning, did not read the original post.   :(

Extending a wire for a ground source to the battery terminal is a big no-no it causes what is reference to a “ground loop” if the ends of the connection are somehow attached to the chassis ground at that end.

This causes a different of potential between the frame/chassis ground been at a negative zero and the connection end ground  which could be at a less negative voltage e.g. -2 V between the two, which could affect the overall function at the terminal end.

Back to fill my cup..!   ;D
J. Gomez
CLC #23082

Time is irrelevant when you work on your classic car, eventually you will enjoy it..!

Offline HerbP

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  • Name: Herb Potthoff
Re: Electrical grounding
« Reply #7 on: November 06, 2017, 07:22:01 PM »
Thanks for the replys everyone!  I'm SO not an electrician I was mostly concerned with the technical aspects, and you all answered those expertly...thanks!
1940 LaSalle 5019
.
This stuff is FUN!
:)