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Author Topic: Field Operation: generator ground or not?  (Read 10947 times)

WB4SPT

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RE: Field Operation: generator ground or not?
« Reply #15 on: July 31, 2018, 12:03:18 PM »

As far as I understand, a generator in a typical field scenario does not need to be grounded. But I do see ground used often. So what is common practice?
If not required by code for safety, wouldn't  a ground on a generator have other advantages, as in regard to static, lightning, QRM? Or could it even introduce problems?

73 de Marc DL1MRD



actually, a two part question and answer.

Part 1:   should I ground the genset chassis to a local ground rod?

Part 2:  should I attach the 120V output neutral to chassis?  ie:  what to do with the neutral strap.


Any condition of the above will still result in correct delivery of power to the load. 

my answer to part 1:  Locally grounding a genset makes it unlikely to receive a static shock from touching the metal frame; although this is not usually a problem.
my answer to part 2:   This gets more interesting.  Hazardous voltages derived from even higher voltage is normally ground based.  This has two purposes;  first, if lightning hits, there is a path to earth.  You don't want 100kV pulse at your toaster!  Two, if certain faults occur, like a primary to secondary step down transformer short develops, or a open primary/secondary ground occurs, OR, if a high(er) voltage line falls or otherwise makes contact with the 120V occurs, some measure of safety exists.  Here, you don't want 9kV rms on your toaster!  Those events should activate upstream overcurrent protection devices.

BUT, a portable genset has an output that is not likely to get hit by a lightning bolt, and has no proximity to other, higher voltage sources.   Plus, an ungrounded output, L and N, become safer, since a grounded human contact can occur with either, and not result in a dangerous shock.

So, the "general" rule says to attach genset neutral to earth in "large installations", but not in "small installations".  A setting like a carnival should be considered a large install, and grounding provides some measure of protection when the ferris wheel gets hit by a bolt of lightning; attempting to keep the surge headed to ground and not appear in force everywhere. 

For a couple of tables of ham equipment in the field, I would suggest no ground contact.  For RFI, not so clear.  Depending on frequency, grounding at one end can still result in high RF at other points, depending on freq and cable length.  On the other hand, if a AM BC station is nearby, then grounding the N side might tend to settle down the entire AC system from RF. 

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K6AER

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RE: Field Operation: generator ground or not?
« Reply #16 on: August 19, 2018, 06:10:10 PM »

What about the general distribution system with multiple stations when one get a lightning strike. The whole distribution grid can rise to lethal voltages with out a general ground. The antennas are the lightning conduit and the radios generally get fried.

I have operated field day in the Rockies and we have had lightning issues during field day. No place to hide. A single 10 foot rod can yield a ground impedance of under 7 ohms. We leave the rod in place for next year. Never bring your best radio for field day in the Rockies.
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AA4PB

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RE: Field Operation: generator ground or not?
« Reply #17 on: August 19, 2018, 06:22:27 PM »

Wouldn't it be better to provide a ground rod near each antenna, connected to the coax shield rather than depending on the electrical safety ground for lightning protection?
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Bob  AA4PB
Garrisonville, VA

K6AER

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RE: Field Operation: generator ground or not?
« Reply #18 on: August 19, 2018, 08:18:42 PM »

Yes it would but have you ever seen old guys pound in a ground rod for field day for each station?

Better chance winning the lottery.
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W8JX

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RE: Field Operation: generator ground or not?
« Reply #19 on: August 20, 2018, 04:21:54 AM »

What about the general distribution system with multiple stations when one get a lightning strike. The whole distribution grid can rise to lethal voltages with out a general ground. The antennas are the lightning conduit and the radios generally get fried.

In a storm you should not be operating and equipment/rigs should be disconnected too

I have operated field day in the Rockies and we have had lightning issues during field day. No place to hide. A single 10 foot rod can yield a ground impedance of under 7 ohms. We leave the rod in place for next year. Never bring your best radio for field day in the Rockies.

Disconnect rigs and head for cars or SUV's.
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KC4ZGP

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RE: Field Operation: generator ground or not?
« Reply #20 on: August 20, 2018, 07:33:57 AM »


Why would you not ground it?

Kraus
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W8JX

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RE: Field Operation: generator ground or not?
« Reply #21 on: August 20, 2018, 08:04:32 AM »


Why would you not ground it?

Kraus

If you are referring to antennas, I live in a rural area on 12 acres and have had about a dozen lightening hits on property ith 4 causing damage in house and two of those several thousand dollars worth. None of strikes that that cause damage hit antennas or damaged rigs but did destroy, TV a few TV's several computers, routers, switches, printers and few microwaves. (damage was from EMP or strike energy down power lines). I have always floated antennas (not grounded them) and switched rigs into a dummy load. Whether science s sound I cannot say but I can say that of strikes causing most damage,  one strike hit metal pole barn about 100 feet from house and one hit a tree between house and antenna but none has ever hit a antenna that were floated.
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WB4SPT

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RE: Field Operation: generator ground or not?
« Reply #22 on: August 20, 2018, 01:08:59 PM »

Yes it would but have you ever seen old guys pound in a ground rod for field day for each station?

Better chance winning the lottery.

Yep.   The odds might be a toss up between a heart attack risk and the two day lightning risk.  Part of the large vs small installation puzzle.  If one antenna/operator is taken out, do you want to limit the spread of damage?
If it truly demanded, for some perverted reason, operation near storms, you would want to be in a protected area.   As in, a ground grid to protect against step charge, plus an overhead wire to catch any bolts. But, that would compete with antennas, and so, its back to the van/SUV for cover.
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AA4PB

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RE: Field Operation: generator ground or not?
« Reply #23 on: August 20, 2018, 02:19:11 PM »

Have the club purchase a hammer drill with a ground rod bit  ;) It makes quick work of driving an 8-foot ground rod (unless you have rocky ground).
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Bob  AA4PB
Garrisonville, VA

KD0REQ

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RE: Field Operation: generator ground or not?
« Reply #24 on: September 12, 2018, 01:47:40 PM »

the book on my genset says drive a ground rod and ground the control panel, which grounds the genset. even if it's not code, it's a good idea. even if the genset book is Changlish.
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K5LXP

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RE: Field Operation: generator ground or not?
« Reply #25 on: September 12, 2018, 03:16:48 PM »


even if it's not code, it's a good idea. even if the genset book is Changlish.

What if it can be demonstrated that having a grounded genset can increase the shock hazard?  Is it a coincidence that per NEC gensets used for plug and cord devices are not grounded?  Why would you place more faith in a translated user manual over established practice?

Mark K5LXP
Albuquerque, NM
 
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W8JX

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RE: Field Operation: generator ground or not?
« Reply #26 on: September 13, 2018, 11:21:51 AM »

I think grounding it increases shock hazard. When not grounded it floats above ground and therefore ground is not part of circuit. Much like a lineman is insulated from ground when work on lines minimizes shock hazard. When you tie generator to ground you create a new return path for energy and therefore another path to get shocked thru and increase chance of being shocked.
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W9FIB

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RE: Field Operation: generator ground or not?
« Reply #27 on: September 16, 2018, 02:55:33 AM »

But can you be absolutely sure that the generator sitting on the ground is not making any contact with the earth (electrically) and therefore safe? The linemen use special insulated equipment (like a fiberglass bucket). Anything special being done to make sure the generator is totally insulated from ground?
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73, Stan
Travelling the world one signal at a time.

NK7Z

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RE: Field Operation: generator ground or not?
« Reply #28 on: September 16, 2018, 11:03:01 AM »

But can you be absolutely sure that the generator sitting on the ground is not making any contact with the earth (electrically) and therefore safe? The linemen use special insulated equipment (like a fiberglass bucket). Anything special being done to make sure the generator is totally insulated from ground?
Yes.  Set it on an insulated pad, where it is dry.
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Thanks,
Dave
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https://www.nk7z.net

W9FIB

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RE: Field Operation: generator ground or not?
« Reply #29 on: September 18, 2018, 02:14:19 AM »

But can you be absolutely sure that the generator sitting on the ground is not making any contact with the earth (electrically) and therefore safe? The linemen use special insulated equipment (like a fiberglass bucket). Anything special being done to make sure the generator is totally insulated from ground?
Yes.  Set it on an insulated pad, where it is dry.

And then it rains....
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73, Stan
Travelling the world one signal at a time.
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