Grounding your generator while transmitting up in the mountains.

[Kerensky97]

Grounding a portable generator is one of a few subjects that incite constant debate on RV and generator forums.
They usually split into the groups of:

"I don't and I'm still alive so don't ground them."
"OSHA/NEC doesn't have a specific regulation so you don't have to."
and "The manual says to do it so yes."

The thing is I don't care as much about regulations or the fact that it's safe to run without a ground. My main concern is signal noise on the radio so here's the scenario:

I'm up in the mountains or somewhere away from civilization boondocking in a travel trailer and I have a pair of Honda EU2000i generators powering the rig.
I have my radio base station connected to the trailer for communications in the area.
Would you ground the generator?
What will help keep signal cleanest?

When I was in the Army we always went through a rigorous grounding regimen but we usually had more complex power distribution setups, much higher power generators, one or more OE-254 antennas hooked to SINCGARS, etc.
I want to know if a simple consumer generator and radio setup will have as much need for it.

Here's the old pamphlet we used for info in the army. Like I said, it's very through.
www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA311375

 

[dwh]

Actually, the NEC does have rules for grounding generators. Search for "separately derived system".

The bottom line is that "grounding" is only for safety. Under non-fault conditions, it does nothing. It's only there to provide a path to ground if something goes wrong.

However, connecting a portable generator to the planet won't actually DO anything even if there is a fault, if the fault is isolated from the planet by some insulator, like truck tires.

Say you have a generator sitting on the ground, and some hot wire comes into contact with truck metal and now the whole truck is hot. If the generator is grounded, nothing happens because the truck isn't grounded. If you touch the truck and the planet, you might get a shock because the gen is grounded and you have become a path from the truck, through you, through the planet, and back to the generator.

So for safety, you normally only ground the generator to the electrical system that you are feeding and NOT to the planet.

If it's a truck mounted system, nothing is connected to the planet. If a building, then the building electrical system is connected to the planet, and the gen is connected to that, so no need to connect the gen to the planet.

By connecting a portable gen to the planet, you create a dangerous situation where a human, or dog or whatever, could become a conductor if some fault develops in the electrical system.

In certain situations you might have to do it to prevent a dangerous situation, but mostly, no, you don't ground portable generators to the planet.

Not a radioman, so I can't speak to that. On a phone so I didn't read the .mil manual you linked, but if they require connecting to the planet, I'm sure there is good reason for it. Ground mounted antennae maybe?

 

[DaveInDenver]

NEC Article 250.34 specifically handles portable generators. Floating them is the safest thing to do. It's not a separately derived situation unless you connect a generator to premise wiring through a transfer switch or otherwise. As long as you stick to the NEC recommendation of using only receptacles with cords and plugs and don't permanently wire to anything fixed then you can float the generator and the vehicle it's possibly mount on.

The reason the military does it (and why it maybe a good idea for hams) is probably lightning. If this is a concern and the decision is to Earth ground then you need to be very careful.

You don't need to Earth anything for RFI, that's not what is going to make a system EMI/EMC quiet or not. Unbalanced circuits, insufficient bypass or chokes, ground (current return, not Earth) loops are what you need to address.


Note: This is non-professional opinion, if considering design or installation please consult an engineer or electrician to verify you are adhering to all applicable codes and regulations.

 

[Kerensky97]

You guys all addressed the parts of grounding I'm well versed in and don't care about, and barely touched what I'm looking for.
Like I said I'm interested in radio signal noise or degradation, buzzing feedback, etc with commercial gear. My computer speakers pick up generator buzz so I want to see what I can do to keep the radio isolated from that same interference.

Has anybody ran a base station out of their trailer in the mountains while it was powered by a portable generator rather than battery?
When you did, did you notice any difference or interference when grounded vs. un-grounded? Less static or noise one way or the other?
What radios and power equipment were you using for clean power and signal?
What type of antenna and mount (to chassis, frame, suspended)?

Things like that.
I want to know what I can do to clean/normalize/isolate the power so I don't have a radio picking up the same clicking my my speakers get while playing movies off the computer.

 

[DaveInDenver]

You need to make sure you have balanced power, low impedance bypassing, high impedance chokes, eliminating current return loops, transformers. Earth ground may work to shield things but it doesn't fix the underlying issue.

Can't answer your generator question, don't have one and no budget for one. Sorry. I'd be more concerned with dirty generator/inverter design in the unit than whether it's grounded or not. I would think that a badly designed generator making quasi-sinusoidal 120VAC would be a lot bigger problem generating harmonics.

But you already can tell one thing, the computer speaker buzz is present on a grid supplied system with (presumably) a good Earth ground so it's not the magic solution. It's only there for safety and any shielding or reduction it's providing is incidental.

 

[4x4junkie]

I think the only thing you'd have to worry about with running a generator is pulse-type noise from the engine ignition, which a radio's noise blanker circuits are generally quite good at eliminating. Maybe it's possible to use a resistor or RFI-suppressor type plug and/or ignition cable on the genset engine too. However if you are speaking of inverter-type generators, the inverter part of it might introduce it's own mix of noises which I cannot comment on, not having used one, I do know the RFI from typical DC to AC inverters can make communications on HF frequencies essentially impossible, even affecting the receiver sensitivity of VHF units.

Dealing with the type of noise created by an inverter usually means adding bypass capacitors and/or common-mode chokes to every wire entering and exiting the device's enclosure (and if it's enclosure is non-metallic, you likely will need to line the inside of it with foil tape or something similar to act as shielding as well). Grounds of the type used for electrical safety do little to nothing for RFI, especially at the mid-upper HF frequencies & higher.

I went through this myself with my MPPT solar controller which has similar high-speed DC-switching circuits as an inverter, the harmonics of which are what create RFI.

 

[FlyFishermen]

What 4x4junkie states pretty much sums it up. You can get RFI from a lot of sources and shielding is the main thing. Any kind of electronic switching circuit can cause RFI (switching power supplies, inverters, etc). Ignition systems on motors can cause RFI.


On a side note related to safety grounding of generators - I was hooking up the antennas to a comms trailer with the SAR team I was on for a few years one day. The outlets in the trailer were all grounded to the trailer. There was a box on the outside that had the hook ups for the generator and bulkhead coax connectors. The generator was running at the time. Lets just say I got a lesson in the importance of grounding. I would think that if nothing else, the generator and trailer grounds should have been connected together.

 

[dwh]

And the OP is running two *inverter* generators. I've run non-inverter gens for years and never heard any noise in any of my computer's speakers.

 

[IdaSHO]

If you are concerned with RFI, then by all means make sure your grounds are good.

Otherwise, I see zero reason to ground a generator to the earth.

 

[DaveInDenver]

Make sure you're not confusing Earth ground, power ground, signal ground and circuit returns into one lumped "ground" term.

All currents want an easy way to get home, back the source that initially forced them. Sending them to Earth might make sense if their original source was also Earth referenced. But most likely not. The main reason we like Mother Earth for a ground is that it's got essentially an infinite ability to accept electrons and when you have no idea how large a fault might be that's good. Other than that it's not really all that practical. It's difficult to achieve very low impedance (NEC actually only requires 25 ohms) so it's not really a great reference point.

Your first step is to consider safety, which most of the NEC considers getting to Earth while interrupting the flow. With a portable generator this is fuzzy because it's also very easy to make a poorly constructed grounding system that puts a person, animal or alternate object into the circuit with a lower impedance and is thus dangerous or potentially a fire hazard. Your highest responsibility is make a safe system. But just realize that floating does't mean unsafe. It's all relative. Just because there's a voltage above ground doesn't mean it's not safe. If everything is at the same potential no current that can flow. A bird on a power line is at 240V from your perspective on ground but he's not cooking because there's no potential from his frame of reference. If he touches another line or ground, he's done, well done.

So EMI is all about giving power and signals good, controlled return paths and not giving them multiple options. So you often actually do NOT want to Earth ground RF circuits and if you do you want that bond to be very, very low impedance so that interfering voltages are not created and reference points do not fluctuate.

If you want more explanation please say, but suffice to say remember the fundamentals of EMI, you need low impedance bypassing and high impedance chokes for both common mode and differential noise. I don't want to talk down, we're all hams here so the idea of RFI shouldn't be foreign. Do you want specific examples?

I'll mention this, that there are extremely good ways to provide low impedance, EM quiet systems without being on the Earth. Consider the example of aircraft. They are floating in the most obvious way and find a way to be both safe and low noise. It's about putting the noisy signals on paths that get them back to their source without being a problem to signals that have low tolerance for interference. They have very large inverters and generators, lots of RF sources (intentional and unintentional radiators) and critical sub-systems.

 

[Kerensky97]

You need to make sure you have balanced power, low impedance bypassing, high impedance chokes, eliminating current return loops, transformers. Earth ground may work to shield things but it doesn't fix the underlying issue.

Can't answer your generator question, don't have one and no budget for one. Sorry. I'd be more concerned with dirty generator/inverter design in the unit than whether it's grounded or not. I would think that a badly designed generator making quasi-sinusoidal 120VAC would be a lot bigger problem generating harmonics.

But you already can tell one thing, the computer speaker buzz is present on a grid supplied system with (presumably) a good Earth ground so it's not the magic solution. It's only there for safety and any shielding or reduction it's providing is incidental.

I should have been more clear about the 2 inverter solution. That's what I WANT to have setup but don't want to spend $2000 without knowing if that is the source of the noise.
The speaker buzzing wasn't coming from the grid it was coming from my friend's generator, I think it was a Dewalt or something. He told me he had a good electric system that cleans the power coming in from the gen which is why I was irritated it still had issues. But there is a good chance that it was a bad generator or power system.

That's why I want to know where the options are for keeping clean power; it's good to know there is other options to look into if the generators are good.

 

[dwh]

Isolation transformer.