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Author Topic: Question about copper braid for grounding  (Read 697 times)

KG4RUL

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Re: Question about copper braid for grounding
« Reply #15 on: October 10, 2020, 10:28:58 AM »

I like to use Grounding Braid 1/2″ Flat Tinned Copper with Grommets available from ABR Industries https://abrind.com/shop/grounding-braid-tinned-copper-flat/grounding-braid-12-flat-tinned-copper-with-grommets/ or order through Ham Radio Outlet https://www.hamradio.com/detail.cfm?pid=H0-014430.  It is much easier to neatly route than the flat, copper strip.
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KF5LJW

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Re: Question about copper braid for grounding
« Reply #16 on: October 13, 2020, 09:03:13 AM »

12v doesnt matter since the ground carries no current till lightning hits

Incorrect sir. At 12 volts takes a lot larger wire to induce enough fault current to operate breakers and fuses in the event there is a 12 volt fault. Lightning has nothing to do with it.
« Last Edit: October 13, 2020, 09:06:45 AM by KF5LJW »
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W9WQA

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Re: Question about copper braid for grounding
« Reply #17 on: October 13, 2020, 06:09:37 PM »

current in the 12v circuit doesnt go thru the outside ground circuit.
its like a radio connected to a battery floating till one side is grounded.
12v current is just inside the battery/power supply circuit.
assume the supply is not grounded as some suggest. the 12v current cant flow outside since its not attached...
but this will be argued...

matbe if you think of a flashlight in your hand, no current outside the case.

but this will be argued.
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KF5LJW

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Re: Question about copper braid for grounding
« Reply #18 on: October 19, 2020, 09:24:47 AM »

current in the 12v circuit doesnt go thru the outside ground circuit.

While that should be the case, certainly not true for most hams. Dc current does indeed flow on outside ground wires is a known fact. All you have to do is look at the circuit. 

The problem is the DC power supply and your car radio in the house.
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W9WQA

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Re: Question about copper braid for grounding
« Reply #19 on: October 19, 2020, 11:41:18 AM »

think about a flashlight sitting on a piece of plastic.
thats your radio on a floating p s.
you can ground it and the light bulb will be the same.'
no outside current.

but this will be argued
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KF5LJW

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Re: Question about copper braid for grounding
« Reply #20 on: October 19, 2020, 02:37:16 PM »

think about a flashlight sitting on a piece of plastic.
thats your radio on a floating p s.
you can ground it and the light bulb will be the same.'
no outside current.

but this will be argued

It would not be argued if it were true. That would be a true statement if your DC Power Supply were Floating. In other words neither polarity bonded to Ground. Fact is DC negative is bonded to ground, not once, but twice. For most, the first bond is inside the DC Power Supply itself where the Negative is bonded to the chassis. The second bond is your radio bonding DC negative to the chassis. Both are extremely easy to see electrically, and if you open your power supply can touch and remove the bonding jumper.

Given the fact DC Negative is bonded twice to ground puts DC negative in parallel with ground. That gives DC negative current two paths to your radio. One you know about, the intended conductor, the negative from the PS to the radio. The second path you have never noticed in your life is out on the AC power cord ground > AC Service Ground > Shack Ground > Coax Shield > Radio Chassis. No argument about it, most hams have DC on their outside grounds. Simple parallel circuit laws, Negative is in parallel with Ground.

Problem is stupid simple to fix. Figure it out.
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AA4PB

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Re: Question about copper braid for grounding
« Reply #21 on: October 19, 2020, 03:31:47 PM »

Yes, there is a parallel path for DC current from the power supply case through the AC ground lead to the panel box, to the AC ground rod, through the bonding wire to the radio ground rod, and back through the coax shield to the radio case. The question is: how much DC current is flowing in this parallel path? In my case I measured it. With the radio drawing 20A, the current in the loop is 1mA. That's hardly enough to cause any concern in my opinion. I do have a 1" wide copper braid about a foot long bonding the power supply case ground bolt to the radio case ground bolt, the center of which is bolted to the metal console in which everything is mounted.

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Bob  AA4PB
Garrisonville, VA

W9WQA

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Re: Question about copper braid for grounding
« Reply #22 on: October 19, 2020, 03:35:19 PM »

imagine the flashlight case grounded to anything. the current inside goes nowhere but the light bulb. no escape.

but this will be argued....forever


oh and it could have the battery positive connected to the case, positive ground...
« Last Edit: October 19, 2020, 03:37:41 PM by W9WQA »
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AA4PB

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Re: Question about copper braid for grounding
« Reply #23 on: October 19, 2020, 04:44:19 PM »

Ah, but if the current flows through the case to get from the far end of the battery to the bulb then there will be current flowing in the case and some voltage drop (however small, depending on the resistance) across the case. If you were to connect a ground wire to each end of the case and connected them to a common point then there would be some current flowing in the ground wires. Typically the resistance of the case is very small and the resistance of the ground wire is much higher so the majority of the current flows in the case and very little in the ground wires.
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Bob  AA4PB
Garrisonville, VA

W9WQA

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Re: Question about copper braid for grounding
« Reply #24 on: October 19, 2020, 04:51:39 PM »

 If you were to connect a ground wire to each end of the case ...

now you are setting up a new situation having nothing to do with the case being grounded as described.
yes you could have two batteries with the center grounded. it never ends.
keep it simple
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W9WQA

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Re: Question about copper braid for grounding
« Reply #25 on: October 19, 2020, 07:55:06 PM »

i guess you guys are considering the tiny voltage drop across the very short black neg power supply cable.  that indeed might be readable but i dont consider it a problem.  have never experienced it causing trouble. milivolts have to travel a long way to get around and back...
in my case the power lead from supply to rig is about 2 feet of  #10. not much to measure
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W9FIB

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Re: Question about copper braid for grounding
« Reply #26 on: October 20, 2020, 03:27:32 AM »

After trying to read these last posts, I forgot what the real subject was.
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73, Stan
Travelling the world one signal at a time.

KF5LJW

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Re: Question about copper braid for grounding
« Reply #27 on: October 20, 2020, 09:01:01 AM »

The question is: how much DC current is flowing in this parallel path?

Any current is too much as it does not comply with any electrical codes. The real issue is you loose your isolation from the AC system.  No commercial or professional operator would ever allow any DC or AC current flowing in any ground conductors. So easy to fix.
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W9WQA

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Re: Question about copper braid for grounding
« Reply #28 on: October 20, 2020, 09:23:52 AM »

i consider it more dangerous to float the secondary and risk line voltage on the radio and coax. worry about 1 milliamp later
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KF5LJW

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Re: Question about copper braid for grounding
« Reply #29 on: October 20, 2020, 10:35:24 AM »

i consider it more dangerous to float the secondary and risk line voltage on the radio and coax. worry about 1 milliamp later
That is a Straw-man argument and absence of any facts. As a ham you should know and follow electrical codes as it pertains to the hobby. Code requires you to bond the coax and radio chassis to ground using a 6 AWG conductor all the way back to the AC Service Ground, the exact same place the #14 AWG green wire ground in the AC power cord and your house wiring go too. 

As I have said before, you prefer to use the 14 AWG in the AC power cord rather than a dedicated 6 AWG going to the exact same spot. Both work, however one is better than the other. 6 AWG is a much larger conductor with significantly lower power frequency impedance capable on conducting a lot more current than a 14 AWG. Using a dedicated #6 AWG also isolates you from the AC system which is exactly what you want to do. Two undeniable facts.

Here is another fact that has escaped your attention. A DC PS output would NOT BE FLOATING if you remove the bonding jumper inside the PS as you claim. Your 12-volt transceiver chassis is solidly bonded to the DC Negative circuit . When you bond the radio chassis to ground as required by code, the DC Negative is GROUNDED and not Floating. That is the crux of the problem you keep ignoring or do not know. If you bond DC Negative twice, you put Ground in parallel with DC Negative (the Neutral conductor in DC systems). Electrical codes do not permit you to bond a neutral circuit conductor twice because it defeats the purpose of having a ground conductor. You force normal load currents onto equipment grounds. You no longer have a Ground, you have two negative circuit conductors allowing voltage to be present on the radio chassis. Remove the jumper in the power supply and all that goes away. There is no code or equipment requirement for a 12-volt system to be a Grounded System. Code requires all chassis and enclosures to be Grounded, but not the System. A 12 volt system can Float or be Grounded.

Why do you think manufactures place a Ground Terminal on the back of the radio with a WARNING label, and instructions how to use it. Your radio equipment is Hard Wired rather than plug-n-cord with ground. Electrical codes see all your radio toys same as a light fixture, electric oven, cook-top, central air conditioning, or an electric water heater all being Hard Wired devices. Hard wired devices have more restrictions and requirements beyond plug-n-cord. They are to be installed and maintained by qualified personnel. One of the very fist requirements is for the device to be SOLIDLY GROUNDED by approved means. It requires the equipment ground to be securely fastened, and guarded against accidental disconnect. That is what the Ground Terminal is provided for. A coax is not Ground and cannot be used as such because it is considered a removable connection. Now look at the rest of your radio toys, especially the passive devices like a SWR Bridge, Antenna Tuner, and Coax Switch. Now you know what that Ground Terminal is for. It enables you to easily comply with electrical codes.
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