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iwire said:
I was under the impression that many hams use 12 VDC to supply the equipment getting around the problems of grounding.
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iwire -

Most (if not all) USA "base" and "mobile/base" Ham radios use 13.8vdc (+-15%) as their power source. On a "base" (home) station this is done by using a power supply (Astron, Alinco, Daiwa, and others). If this Ham wants to run several power supplies, then that is why (I'm guessing) he wants a dedicated 20A circuit, so he can run the power supplies.
 
LarryFine said:
What if the receptacle itself was fed through an isolation transformer, creating a new SDS? Is there a way he could not have to bond the new electrode system to the house's?
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I believe that too is no go - all grounds must be part of the system.

See I wouldn't have said anything.... I would run this guy a new ground - a #4 or > solid insulated conductor from a solid 1/4"X4"x12" or larger isolated ground buss where his equipment is, down to 3 10' rods in a triangle formation 10' apart - take your ground to one corner - then back to his existing rod from another corner.... :rolleyes: Charge him (a lot) then leave....
yhst-18711434844524_1982_13022397


If he calls and asks about the #4 going over to the existing rod - just tell em that is required by code, and now he also has all the grounds in the whole neighborhood via the POCO and the water company.:grin: By which time you have deposited the check....:rolleyes: If he gets all quirky about "Isolated" tell him it is "Isolated" nothing else is grounded to it until it hits the earth...

Why even stop at #4 wire, do copper buss work all the way - to a new UFER.... Make the UFER out of copper buss work... And connect it to the water when he's not looking with a #6. The shear appearance of that much copper will have him feeling really smart - in a football/mahogany type of way.... :grin: Charge accordingly...
 
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skingusmc said:
iwire -

Most (if not all) USA "base" and "mobile/base" Ham radios use 13.8vdc (+-15%) as their power source. On a "base" (home) station this is done by using a power supply (Astron, Alinco, Daiwa, and others). If this Ham wants to run several power supplies, then that is why (I'm guessing) he wants a dedicated 20A circuit, so he can run the power supplies.
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Thanks, thats what I thought, which means the equipment is already supplied by a "Separately derived system" and the supply EGC should not affect his equipment.
 
1793 said:
Looked at a job this morning where the customer wants to install receptacles for his Ham Radio equipment. He is demanding an ?Isolated Ground? from a ?Ground Rod? driven by this part of the house and run directly to his equipment.

I would like to know what section of Article 250 I should study to find out if this is a violation or the correct thing to do. Now I know I?m not the smartest person in the world but my gut tells me this is a violation and it is not necessary.

I would be running a dedicated 20 amp circuit,(NM-B) to his Radio Room. I could install an Isolated Ground Receptacle but again from what I think I know it is not necessary.

I don?t know how to reply to these people who ?Know so much.?

As always, thanks in advance and I look forward to your input.
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I dont see a problem, just make sure to connect a #6 insulated green or bare from the new ground rod back to the existing ground rod. Electrically it would be the same. Even better would be to install a nice collector bar in his radio shack to connect all of his equipment to.
I think he read or heard something somewhere and doesnt know what he really wants or needs. Maybe something from some other country that has a different electrical system then ours in North America.
 
jrannis said:
I don't see a problem, just make sure to connect a #6 insulated green or bare from the new ground rod back to the existing ground rod. Electrically it would be the same.
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Still a NEC violation of 300.3(B).

And strictly speaking due to impedance it is not 'electrically the same'. :)
 
jrannis said:
Assuming the length of the conductor in the impedence calculation? How big is the property?
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It's not the length of the circuit.

The issue is that during a short the EGC run away from the circuit conductors in an AC circuit will exhibit a high impedance.

Don R could explain it better, I do not fully understand it myself.

I will shoot Don a PM and ask him to look in on this thread.
 
brian john said:
The advantage of this type of installation is if there is a lighting strike in the vicinity of the new electrode the current path can be through the electrode through the radio to the main electrode at the service frying his equipment and making his wife and neighbors some happy campers.
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this is why the rods must be bonded together
 
iwire said:
It's not the length of the circuit.
The issue is that during a short the EGC run away from the circuit conductors in an AC circuit will exhibit a high impedance.
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When grounding for high frequency you can use a 5:1 rule. That being for every 5 inches in length the conductor should be 1" wide. That is why so many installations that are concerned with high frequency events use braided cable. Braid used because of the skin effect at high frequencies, it is better to have a wide and thinner conductor than a round one.

People often want to isolate their local ground from the power system ground to lower noise levels. Often the desire to have low noise goes against the need to bound for electrical safety reasons.

As has been mentioned before an equipotential ground is what is desired.
In a nearly ideal world you could place a large sheet of metal (say 100ft x 100ft)under the entire yard and house. Then bond that to the ground rod system and equipment. Not practical but great in theory.
 
On a low current circuit like this 20 amp one the increase of the impedance as a result of a physical separation of the supply conductor and the fault clearing path would probably not prevent the OCPD from tripping. When you get to higher current circuits (more than a few hundred amps) the increase in impedance from the inductive reactance caused by the separation may move the trip out of the instantaneous trip part of the curve into the short time part at best and at worst may limit the fault current to the point that the OCPD does not even open.
Don
 
ELA said:
In a nearly ideal world you could place a large sheet of metal (say 100ft x 100ft)under the entire yard and house. Then bond that to the ground rod system and equipment. Not practical but great in theory.
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Why not? That's what they do under substations, with a mesh.
 
Yes Power stations do have a great grounding structure.
Still not as good as a solid sheet -at the highest of frequencies.
And most home owners would not want to invest in it.
That is what I meant by good theory but not practical.
 
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