Safety grounding shack equipment

[OkieBoyKJ5JFG]

I hope I don't seem obtuse, but the more I read about grounding, the more confused I become. I think I understand grounding for lightning protection well enough, and I'll deal with grounding for RF interference later, but I have questions about grounding the equipment inside the shack for safety purposes.

Most things I read say I need to ground each piece of equipment to a common bus, then run a strap from that bus outside the house to a ground rod which is then bonded to the house's ground system. I understand bonding the equipment to avoid developing a difference in potential, but because the equipment is already connected to the house's ground system via its 3-prong plugs, is it really necessary to run the strap to a ground rod outside and thence back to the house ground? From a safety perspective, it seems to me that grounding via the plugs should be sufficient. Wouldn't it be enough to bond all the various pieces of equipment to a common bus and call it good? Am I missing something?

 

[mmckenna]

I understand bonding the equipment to avoid developing a difference in potential, but because the equipment is already connected to the house's ground system via its 3-prong plugs, is it really necessary to run the strap to a ground rod outside and thence back to the house ground? From a safety perspective, it seems to me that grounding via the plugs should be sufficient. Wouldn't it be enough to bond all the various pieces of equipment to a common bus and call it good? Am I missing something?

That third wire in all the outlets is often connected to a 14 gauge wire that takes a very long path back to the panel, often through more than one panel, to make it back to the ground rod. Along the way, that wire passes through lots of other outlet boxes.

That meets the code for a safety ground. It's not great for meeting the RF needs of a low impedance path to ground for your radios.

 

[OkieBoyKJ5JFG]

That third wire in all the outlets is often connected to a 14 gauge wire that takes a very long path back to the panel, often through more than one panel, to make it back to the ground rod. Along the way, that wire passes through lots of other outlet boxes.

That meets the code for a safety ground. It's not great for meeting the RF needs of a low impedance path to ground for your radios.

Ah, okay. Yes, I understand that RF grounding has different requirements, but most guides for grounding don't really differentiate. At the moment, I'm only installing UHF/VHF which (if I understand correctly) usually doesn't have issues with RF fluctuations. So, from a safety standpoint (again, if I understand you correctly) I should be fine to just bond my equipment to a common bus to avoid static buildup and not run the additional ground strap outside.

Thank you very much.

 

[mmckenna]

Well, one way to look at it is to give that energy a better path to ground that doesn't pass through your entire home and all the appliances.

But code/safety, you'd be covered. What you may want to look out for is devices that don't have a grounded cord. Those you'd probably want to ground separately, like SWR meter, antenna tuner, etc.

Remember that the code is the floor, not the ceiling. Code is the minimum you should do, and it's not hard to do better.

 

[prcguy]

An outdoor antenna should be grounded per NEC, otherwise most inside radio equipment is adequately grounded through the AC outlet third prong. An exception to this might be when using a single long wire antenna fed with a wire tuner. Something like a classic 135ft wire right to the tuner can tune ok on some bands and not have RF currents flowing on equipment but on other bands it can light up the ground paths with lots of RF. In this case a ground rod bonded to the tuner with a copper strap can route some of the RF currents away from the internal house grounding and calms things down.

Also, RFI does not know its supposed to go to ground and grounding equipment to an outside ground rod may or may not do anything for noise. I personally have not seen any decrease in RFI from grounding equipment to an outside ground rod.

NEC is for human safety for electrocution and not necessarily for lightning protection. I would consider protecting from a direct lightning hit impractical for most existing homes so build to NEC and disconnect antennas when lightning is possible.

 

[UTE-GE]

Tuned into the barometric pressure

 

[OkieBoyKJ5JFG]

Remember that the code is the floor, not the ceiling. Code is the minimum you should do, and it's not hard to do better.

I understand and I completely agree. I'm just not in a position to do everything at once. I figured I'd start with the stuff that potentially would keep me from accidentally frying my fingerprints off. I'll approach the rest in a stepwise fashion.

An outdoor antenna should be grounded per NEC, otherwise most inside radio equipment is adequately grounded through the AC outlet third prong.



NEC is for human safety for electrocution and not necessarily for lightning protection. I would consider protecting from a direct lightning hit impractical for most existing homes so build to NEC and disconnect antennas when lightning is possible.

I think I have the antenna and coax properly grounded against lightning. Everything I've read said that in the event of a direct lightning strike, your equipment is going to be toast, and I believe that. However, I've done all the "right stuff" to mitigate that as much as possible.

Yeah, my highest priority is human safety -- namely this human, since I live alone.

 

[AK9R]

From a safety perspective, it seems to me that grounding via the plugs should be sufficient.

Let's say you are running the typical 100 watt HF base radio or the typical 50 watt VHF/UHF mobile radio being used as a base. Power requirements for both are 13.8 volts DC. So, you get a power supply that takes 120 volts AC and converts it to 13.8 volts DC.

Let's assume that your power supply has a typical (for North America) 3-wire plug. Yay, your power supply is grounded to the electrical safety ground for the house through the wall outlet.

But, what about your equipment? Does the black wire on the 13.8 volt DC supply to your radios connect to the chassis of your radios? Does the black terminal on the 13.8 volt DC output of your power supply connect to the U-ground on the cable going to the wall outlet?

 

[OkieBoyKJ5JFG]

Let's say you are running the typical 100 watt HF base radio or the typical 50 watt VHF/UHF mobile radio being used as a base. Power requirements for both are 13.8 volts DC. So, you get a power supply that takes 120 volts AC and converts it to 13.8 volts DC.

Let's assume that your power supply has a typical (for North America) 3-wire plug. Yay, your power supply is grounded to the electrical safety ground for the house through the wall outlet.

But, what about your equipment? Does the black wire on the 13.8 volt DC supply to your radios connect to the chassis of your radios? Does the black terminal on the 13.8 volt DC output of your power supply connect to the U-ground on the cable going to the wall outlet?

I understand your point, but I've run various types of equipment on a power supply for literally years without any problem. From the standpoint of safety, the objective is to prevent a power surge from zapping me and I would think a fuse on the hot wire from the power supply to the radio would do that. That's how we set it up in a vehicle, after all, and nobody seems to think it's unsafe.

 

[N5ZKK]

I hope I don't seem obtuse, but the more I read about grounding, the more confused I become. I think I understand grounding for lightning protection well enough, and I'll deal with grounding for RF interference later, but I have questions about grounding the equipment inside the shack for safety purposes.

Most things I read say I need to ground each piece of equipment to a common bus, then run a strap from that bus outside the house to a ground rod which is then bonded to the house's ground system. I understand bonding the equipment to avoid developing a difference in potential, but because the equipment is already connected to the house's ground system via its 3-prong plugs, is it really necessary to run the strap to a ground rod outside and thence back to the house ground? From a safety perspective, it seems to me that grounding via the plugs should be sufficient. Wouldn't it be enough to bond all the various pieces of equipment to a common bus and call it good? Am I missing something?

If your shack has antennas outside then just the basic NEC250 does not cover your situation. For example when the lightning strike comes it is important that everything stays at the same potential as to prevent fires and equipment damage.

 

[prcguy]

If your shack has antennas outside then just the basic NEC250 does not cover your situation. For example when the lightning strike comes it is important that everything stays at the same potential as to prevent fires and equipment damage.

NEC article 810 covers antenna and feedline grounding.

 

[mmckenna]

I understand your point, but I've run various types of equipment on a power supply for literally years without any problem.

It's not a problem until it is. Being lucky isn't the same as being skilled.

From the standpoint of safety, the objective is to prevent a power surge from zapping me

That surge can come from many places.
A nearby lightning strike can induce enough energy into your antenna to be an issue, even without a direct strike.
That lightning strike might hit the power lines somewhere on the way to your house, that's a risk.
An AC fault in your house can cause issues.
A fault in your power supply can cause issues.

The idea behind this is to protect you, others, and the home.

and I would think a fuse on the hot wire from the power supply to the radio would do that.

Fuses do not blow instantly. It takes current + time for that to happen. The amount of voltage/current may be low enough to take some time to pop the fuse. And the fuse only protects the DC power side of your radio, not anything else.

That's how we set it up in a vehicle, after all, and nobody seems to think it's unsafe.

National Electric Code does not apply to vehicles.
The fuse in the radio power feed on a 12 volt system is designed to blow when the current exceeds the capacity for a certain amount of time. That amount of current is usually based on the needs of the radio as well as the capacity of the wiring. In a car, the fuse is there to help reduce the chances of a fire if the + lead grounds out to the chassis.

 

[MUTNAV]

I agree, grounding can be complicated and there is a lot of bad info out there.


Here is a thought though... On your bench, with a 3 prong power supply plugged into a wall outlet, and a DC output to your equipment. What happens to you when you touch the case of the equipment and a ground, or the case of another piece of equipment? I think that is why it's sometimes recommended to tie the chassis of all of the different chassis-es together. Either by hooking them up to a bus bar tied to ground, or with a wire.

A chassis is supposed to be isolated from an equipment case, theoretically.

The reason I mention it is I watched someone touch the case of a 5 volt power supply (100+amps), and get shocked badly (no burns, just a bad shock).

Thanks
Joel

 

[OkieBoyKJ5JFG]

Thanks, guys! It's easier to understand your explanations using real-world examples than the technical stuff I find everywhere. It also seems that it's less complicated than I thought. All those diagrams that look like spaghetti...

 

[kayn1n32008]

I understand your point, but I've run various types of equipment on a power supply for literally years without any problem. From the standpoint of safety, the objective is to prevent a power surge from zapping me and I would think a fuse on the hot wire from the power supply to the radio would do that. That's how we set it up in a vehicle, after all, and nobody seems to think it's unsafe.

A WISP that has a 120' free standing tower across the road(less than 100' from my old house at a fire hall) took a direct strike to the tower. I'd estimate the strike caused somewhere close to $20k of damage to the WISP, took out power to the WISP, fire hall, and the water system pump house(power was fed from the pole, to the pump house, to the fire hall to the WISP)

Damage:

-They had to re-pull the power to the WISP.

-Replace the power enclosure on the outside of their equipment cabinet. The door was blown open from the breaker and outlet blowing up, and the prongs/contacts vaporizing.

-Replace a 4" electrical junction cover where power exited the fire hall. It was found 40 or so feet away from the building. It probably would have been farther away had it not hit the pump house.

-Replace the 15A breaker(it was in pieces after blowing up).

-Replace the DIN rail 110v outlet(all contacts were vaporized.

-Replace the surge protector(prongs on the plug were vaporized).

-Replace 9 radios( 4 sectors per band, plus a 900MHz dual polarized omni).

-Replace 2 PtP microwave radios(back haul from other sites.

-Replace Cat6 cable on the tower.

-Replace all the CAT6 lightning protectors.

-Replace the fire departments satellite TV LNB and receiver. Lightning induced a current spike on the quad shield RG-6, that the power conduit crossed at 90⁰.

2 things of interest:

-Their fiber fed switch survived.

-The tower is on a screw pile base. Each pile is 8" in diameter, and it has a 3/4" plate steel base, with welded gussets. There are 3x grounds between each tower leg and pile. The equipment cabinet, and power enclosure are integrated on the tower base. I don't know if there was any other grounding done.

If you think fuses on your 13.8v leads and breakers in your power distribution panel are going to save your gear, or anything else in your house in the event of a strike, direct or close by, you are living in a fantasy world.

 

[kayn1n32008]

From the standpoint of safety, the objective is to prevent a power surge from zapping me...

Uhh. No. From the standpoint of safety, you want to keep a lightning lightning strike from entering your house, destroying all your gear, all your appliances and anything else that is plugged in, in your house. You also want to prevent a lightning strike from burning your house down and/or killing you.

If it enters your house, you want to make sure EVERYTHING is at the same ground potential. Tower, antennas, feedlines, radios, and anything that is plugged in in your house.

I would think a fuse on the hot wire from the power supply to the radio would do that.

Lmfao. Nope. Not even close.

That's how we set it up in a vehicle, after all, and nobody seems to think it's unsafe.

Your vehicle is an entirely self-contained system, operating on DC. Your house is part of an interconnected power grid.

I really recommend you search for, and download a copy of Motorola R-56. It's the gospel for communication site grounding and lightning protection. I'd also read the relevant NEC sections others have posted in this thread.

 

[prcguy]

I'll reiterate your not going to protect from a direct lightning hit without a complete redesign of the house electrical and major grounding costing a ton of $$. So just know you won't survive a direct hit and build to NEC with maybe some info from R-56 that makes economical sense. You can up the design some to protect from a nearby strike that can induce lots of voltage onto wire antennas, long runs of coax, etc. Then make provision to disconnect feedlines from entering the house during a storm or when your not home.

Its better to know you can't survive a direct hit over thinking you will and you wont.

 

[DLHeinz]

I have a end fed antenna with RG8x coax entering the house in a storage room above the garage, the room has no electrical outlets. The coax runs 25 feet across the storage room floor and into another room where the radio is located. When not in use and when a storm approaches, the coax is disconnected from the radio coiled up and stored 25 feet away from the radio in the storage room where it enters the house. Would this mitigate any potential damage from a lightning strike ? .. The antenna is not grounded .. Would this be any difference then coax wrapping around house with security cameras that are no longer in use ? ..

 

[AB4BF]

I have a end fed antenna with RG8x coax entering the house in a storage room above the garage, the room has no electrical outlets. The coax runs 25 feet across the storage room floor and into another room where the radio is located. When not in use and when a storm approaches, the coax is disconnected from the radio coiled up and stored 25 feet away from the radio in the storage room where it enters the house. Would this mitigate any potential damage from a lightning strike ? .. The antenna is not grounded .. Would this be any difference then coax wrapping around house with security cameras that are no longer in use ? ..

When not using my HF, I have a connector strip with several SO-239s that I have wired both the center and shield to ground, and the connector is routed through #2 copper wire straight to 3 ground rods which are in an "L" position 10 feet apart from each other. This will certainly not stop a direct hit from lightening but will drain the static that occurs during any storm and wind blowing across my dipole (hopefully).
I would not coil my coax inside without grounding both the center and shield connections straight to at least one 8 foot ground rod. However, if lightening decides to strike, all bets are off, but you may have saved your equipment by the antenna not being connected to the equipment...

 

[prcguy]

When not using my HF, I have a connector strip with several SO-239s that I have wired both the center and shield to ground, and the connector is routed through #2 copper wire straight to 3 ground rods which are in an "L" position 10 feet apart from each other. This will certainly not stop a direct hit from lightening but will drain the static that occurs during any storm and wind blowing across my dipole (hopefully).
I would not coil my coax inside without grounding both the center and shield connections straight to at least one 8 foot ground rod. However, if lightening decides to strike, all bets are off, but you may have saved your equipment by the antenna not being connected to the equipment...

If you ground an antenna to a ground rod not bonded to the house main entry panel ground per NEC you could have more damage from a direct hit than not grounding the antenna.