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Old 02-16-2010, 06:56 PM
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Can there be electrical interference when grouping wires?

I'm trying to group all my wires going through my firewall into 2 bundles. Then I began to wonder if there could be any electrical inference if I put the wrong 2 wires close to each other. I was mainly concerned about the alternator cable being close to wires for my ignition controller. Are there any wires I need to keep separate from the others? Thanks...

Mike

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Old 02-16-2010, 08:14 PM
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12 volts DC doesn't really create any interference in adjacent wires, so it should not be a problem to put them in a bundle.

The only exception is the alternator, (which is really AC) which might cause some whine in a sensitive radio.

Bruce
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Old 02-16-2010, 08:29 PM
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Not a problem.

Vince
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Old 02-16-2010, 08:58 PM
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Quote:
Originally Posted by 75gmck25
12 volts DC doesn't really create any interference in adjacent wires, so it should not be a problem to put them in a bundle.

The only exception is the alternator, (which is really AC) which might cause some whine in a sensitive radio.

Bruce
The alternator if working properly does not produce ac current on the output. Internally it is an AC device but it is completly rectified.The only thing close to ac would be wiring for an ignition box and it would be pulsating DC
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Old 02-17-2010, 06:51 AM
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I personally wouldn't be running the output for my alt inside anyway unless that's where your bat is. It should be ran directly to the + side of your battery min of 10ga wire.
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Old 02-17-2010, 06:55 AM
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you should twist the ignition wires together to prevent eddy current cross flow just as a precaution , if you have a alternator loose a Phase it can cause problems as it will be only 2 phases and the dc will have a real bad pulsing effect .
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Old 02-17-2010, 09:17 AM
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Some wires do cause interference, but unless you have EFI, the interference is mainly static on the radio. As an example, many factory tach wires were shielded to prevent radio interference.
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Old 02-17-2010, 10:10 AM
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Alt feed into the car requires a 50amp fuse or breaker at the alt post to prevent a wires fire in the whole bundle!!!!
(alt output is batt direct hot all the time)

this is minor but it's "heat" in the bundle you want to pay attention to....

the hotter the wire is,, the more (ohms) resistance there is,,, to cause voltage drop/amps loss (and copper is a darn good heat conductor)...

a loose bundle of wires with air gaps,,,bundle mounted where there is good cooling air circulation and not contacting hot engine parts at all,,,is a good plan....

use one size larger wire than required on the high amps (= heat) devices will help keep the bundle cooler...
you also do want shortest (practical) wires lengths...

just for the idea:
if the wires do get hot,,,the alt "will" put out enough more amps to overcome the added "heat" resistance to operate the devices....
but why work the hell out of the alt and have less than best voltage at the device,,,,which degrades device performance (like ign spark) when cooler wires would solve it and costs nothing except some planning/thinking....

just a example/comment/my $.02:
a big part of why newer cars resale value is in the toilet is due to "expected" electrical repairs costs...due to how they are wiring the cars!!!
(amazing they don't croak sooner with how the harnesses are routed and bundled)
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Old 02-17-2010, 01:44 PM
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I can hardly believe some of the wiring I'm seeing these days on some of these new cars, used to be the only time there was problem with the wires themselves was if somebody hacked them, it was terminals and terminal ends that were troublesome sometimes, but more and more, I'm finding broken wires in perfectly intact harnesses. Another thing, if you measure almost any alternator output, you WILL measure a certain amount of AC current, on GM cars, anything over about 300MV will cause driveability problems.
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Old 02-17-2010, 06:23 PM
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What's the thing about the twisted ignition wires and eddy currents? I noticed that the pair of wires from my Crane HI-6 ignition box that go to the magnetic trigger distributor are twisted together for their entire length. I was thinking of untwisting them to get them to fit in the split cable wrap better. Maybe this twisting is for a purpose?
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Old 02-17-2010, 07:04 PM
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Quote:
Originally Posted by boris_thespider
What's the thing about the twisted ignition wires and eddy currents? I noticed that the pair of wires from my Crane HI-6 ignition box that go to the magnetic trigger distributor are twisted together for their entire length. I was thinking of untwisting them to get them to fit in the split cable wrap better. Maybe this twisting is for a purpose?
I believe I should keep the ignition wires twisted together. Here's a quote from an MSD technical bulletin I found:

"Routing the magnetic pickup wires can be very important to your engine’s performance. Since the pickups are delivering a voltage signal to trigger the ignition, it is important that the wires are routed away from other wiring, electrical components and spark plug wires. This is especially important in today’s performance world with aftermarket EFI systems, electric water pumps and more.
Notice that the pickup wires are twisted around each other in the PN 8860 harness that MSD supplies with the ignition. This helps create a field around the wires for protection and should be done with any other wiring of the pickup. Also try to route the pickup wiring as close to the engine block, frame or chassis of the car. These parts serve as large ground planes so there is less electrical activity near their surface.
Following these guidelines will help ensure the proper trigger signal from your pickups. MSD also offers a special Shielded Harness, PN 8862. This harness features a special ground shield that protects the trigger wires from external interference.
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Old 02-18-2010, 04:31 AM
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boris
leave the ign leads twisted,,,(it was done for a purpose)

http://en.wikipedia.org/wiki/Twisted_pair
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Old 02-18-2010, 01:15 PM
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the twisting of the wires helps prevent a magnetic flux ( which forms around wires that carry current ), if you lay two wires next to each other , one with current , the other without , part of the curent can transfer to the other wire , I cannot explain it as well as my father as he was a electrical Engineer , but there are stories of farmers running fences parallel to hi wires and the flux charging the fence enough to seriously hurt people when they touch them ( like a true electric fence) or farmers borowing power from Hi lines by doing the same thing but using cable on poles , enough power was pulled the utilities noticed it and they where lighting lightbulbs with it . I twist the wires on any of my high draw stuff that is used by a signal generator ( alternator, Msd box (inputs and power) , and stereos . and I have no buzzing or hissing or missfires .
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Old 02-18-2010, 01:18 PM
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I wish docvette was still alive as he could explain it like my dad could

( I wasn't around when he was here, but I have read some of his stuff talked just like my dad )
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Old 02-18-2010, 01:38 PM
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Wires are twisted usually to make them less susceptible to interference. Having the ground wrapped around the signal wire shields it to a point and lessens the effects of EMI and RFI. It lessens the natural antenna effect that all wire has.
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