Problem Grounding a Generator

[Tony Sivori]

I recently acquired a small portable back up generator for nuisance
outages. Only paid $200 new. It is 2500 watts continuous, 3250 surge rated
and no 220 volt outlet, so I won't be hooking it up to a transfer switch.

Even though I'm going the extension cord method, I decided to properly
ground it, and use an inline GFI and surge protector. I'm willing to risk
using a back up computer with it, and I am hopeful that a surge protector
might clean up the "dirty" generator power.

Now the problem. I drove an 8 foot ground rod into typical soil, used a
correct copper clamp (nothing improvised), and connected the rod to the
generator ground lug with a single strand 12 gauge copper wire.

Trouble is, the generator outlets still tests as ungrounded.

I immediately suspected miswired outlets on the generator. So I tried
checking the resistance from the power receptacle outlet ground to both
the generator frame and the generator ground lug. Both tests resulted in
zero ohms of resistance. I'm thinking that would eliminate miswiring on
the generator as the cause.

I then removed both ends of the ground wire connection, checked and
reconnected them.

Same result, tests as open ground with a three prong plug in tester. I
also tested the tester, and it shows grounded outlets in my house as
properly grounded.

I checked the resistance from the generator end of the ground wire to the
ground rod itself. It was also zero ohms.

So it seems to be a case of it has to work, but it doesn't work. Any
suggestions are welcome.

 

[PeterD]

I recently acquired a small portable back up generator for nuisance
outages. Only paid $200 new. It is 2500 watts continuous, 3250 surge rated
and no 220 volt outlet, so I won't be hooking it up to a transfer switch.

Even though I'm going the extension cord method, I decided to properly
ground it, and use an inline GFI and surge protector. I'm willing to risk
using a back up computer with it, and I am hopeful that a surge protector
might clean up the "dirty" generator power.

Now the problem. I drove an 8 foot ground rod into typical soil, used a
correct copper clamp (nothing improvised), and connected the rod to the
generator ground lug with a single strand 12 gauge copper wire.

Trouble is, the generator outlets still tests as ungrounded.

I immediately suspected miswired outlets on the generator. So I tried
checking the resistance from the power receptacle outlet ground to both
the generator frame and the generator ground lug. Both tests resulted in
zero ohms of resistance. I'm thinking that would eliminate miswiring on
the generator as the cause.

I then removed both ends of the ground wire connection, checked and
reconnected them.

Same result, tests as open ground with a three prong plug in tester. I
also tested the tester, and it shows grounded outlets in my house as
properly grounded.

I checked the resistance from the generator end of the ground wire to the
ground rod itself. It was also zero ohms.

So it seems to be a case of it has to work, but it doesn't work. Any
suggestions are welcome.

You may have high resistance soil, and need more than one ground rod.
Code typically calls for three, wired together.

 

[Tony Sivori]

You may have high resistance soil, and need more than one ground rod.
Code typically calls for three, wired together.

I think you are probably right.

A quick Google shows that multiple ground rods are often necessary.
Although I found the NEC calls for multiple rods only when a single rod
installation exceeds it says 25 ohms. And it seems that every other
possible reason has been eliminated.

 

[Shaun]

I think you are probably right.

A quick Google shows that multiple ground rods are often necessary.
Although I found the NEC calls for multiple rods only when a single rod
installation exceeds it says 25 ohms. And it seems that every other
possible reason has been eliminated.

I think I know what the problem is. In a house, at the electrical panel,
the neutral wire is connected to the ground. Your tester maybe assuming
this and that is why it is not showing a ground connection. Your generator
probably has a floating output (neutral not connected to the frame ground).
Which is why the tested shows no ground. This will not pose a problem when
using the generator, it is still grounded, it's just that the neutral is not
connected to ground.

Shaun

 

[Tony Sivori]

It sounds as though the generator's neutral leg is not tied to ground at
the generator. The outlet tester isn't actually testing that the ground
prong is anywhere near ground, merely that current can flow between the
hot and the ground leg.

I wasn't aware of that. Thanks.

(In a standard residential setup, the neutral leg is tied to ground at
the main breaker box, and all neutral and ground wires go to the common
neutral/ground bar.

That much I did know. I even knew that the only place the neutral can be
grounded is at the junction box.

The outlet tester would still show the outlet is wired properly even if
the ground leg were not actually connected to ground.)

A test with the outlet tester and an ungrounded outlet confirms that
you're right.

By the way, the surge suppressor will do pretty much nothing to clean up
the generator output power. It's also rather likely that the output is
reasonably clean to begin with; certainly far better than a typical
"modified sine wave" inverter output, which is a combination of a couple
of square waves. A typical computer, with a switching power supply, is
not picky at all about power quality, as the first stage in the power
supply is a rectifier and reservoir capacitor, changing whatever the
input is into (unregulated) high voltage DC power. They run just fine
from the above mentioned modified sine wave inverters, potentially even
a bit more efficiently than from sinusoidal inputs.

I've heard a few anecdotes of generator power damaging televisions and DVD
players. I thought a pair (one on each outlet) of cheap surge protectors
might help.

Anyhow, you could tie the "neutral" leg of the generator output to
ground at the generator, which would be safe provided the generator
frame is actually grounded, and which would make the outlet tester
happier.

Unless it would add safety, I'm not at all worried about bonding the
neutral to ground.

Safer, IMHO, is just using the GFI and not worrying about it
more. Indeed, code permits GFIs to be used on existing ungrounded
circuits to allow three-pronged devices to be plugged in despite the
lack of a safety ground conductor (albeit with certain cautionary
labeling required).

I may do that. One of the reasons I was dead set on proper grounding is
that I knew that the surge protectors can't work without a ground. If the
surge protectors are useless and unneeded, I could leave the ground
connected as is, and just use the inline GFI.

 

[Tony Sivori]

I think I know what the problem is. In a house, at the electrical
panel, the neutral wire is connected to the ground. Your tester maybe
assuming this and that is why it is not showing a ground connection.
Your generator probably has a floating output (neutral not connected to
the frame ground). Which is why the tested shows no ground. This will
not pose a problem when using the generator, it is still grounded, it's
just that the neutral is not connected to ground.

You're right about the floating neutral.

I found a couple of OSHA pages discussing portable generator grounding and
neutral bonding.

http://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

although it seems to contradict this one:

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=20448

 

[David Nebenzahl]

That much I did know. I even knew that the only place the neutral can be
grounded is at the junction box.

Don't say "junction box", as that statement will make all electricians
wince. You meant to say "breaker panel" or "distribution panel", right?

 

[Tony Sivori]

Don't say "junction box", as that statement will make all electricians
wince. You meant to say "breaker panel" or "distribution panel", right?

A slip of the tongue, or fingers, if you prefer.

I've found some more pages on the pros and cons of bonding a
portable generator floating neutral to ground.

http://blog.rv.net/2009/10/generator-bonding-and-grounding/

http://blog.rv.net/2009/10/portable-generator-grounding/

 

[Baron]

I may do that. One of the reasons I was dead set on proper grounding
is that I knew that the surge protectors can't work without a ground.
If the surge protectors are useless and unneeded, I could leave the
ground connected as is, and just use the inline GFI.

No relation to "wtom" ?

 

[Fred McKenzie]

My generator is 2500/3250 surge like
yours. And it is brushless. But there was nothing I could do to filter
the output well enough where my two 1000va APC UPS units would come
back off battery.

I've read elsewhere that the problem with generators and UPS units, is
that the generator doesn't hold an exact 60 Hz. You might find a
generator's frequency will range as much as 63 Hz to 59 Hz from no load
to full load. The UPS likely depends on a crystal controlled oscillator
to determine if 60 Hz power is present.

I wonder if inverter generators like the little Honda EU1000i, will work
with a UPS?

Fred

 

[PeterD]

I've read elsewhere that the problem with generators and UPS units, is
that the generator doesn't hold an exact 60 Hz. You might find a
generator's frequency will range as much as 63 Hz to 59 Hz from no load
to full load. The UPS likely depends on a crystal controlled oscillator
to determine if 60 Hz power is present.

I wonder if inverter generators like the little Honda EU1000i, will work
with a UPS?

Probably would work better. My UPS, a high end high power one, tells
me the line frequency on it's statistics page. Interesting watching
the statistics, and seeing line voltage variations, etc.

 

[Tony Sivori]

And good luck trying to clean up the generator output if you intend on
using a UPS in the circuit. My generator is 2500/3250 surge like yours.

Mine is a KingCraft from Aldi. Would you happen to have the same one?

And it is brushless. But there was nothing I could do to filter the
output well enough where my two 1000va APC UPS units would come back off
battery. Both are used in my A/V gear after a about with nuisance
outages of short duration but short enough to need to reset a lot of
things. Also I had two 9 foot copper ground rods, one on either side of
the house connected inside to my ham radio stuff. When hooked to an APC
multi outlet filter with a wiring fault indicator, the indicator did not
light while on generator power. So I guess in my case the two rods were
enough. And they sure reduced my noise level on the HF bands, the main
reason for their installation.

I'd guess that I'm grounded with the one 8 foot rod. I just didn't realize
how limited the cheap three prong outlet testers are. Live and learn.

 

[Tony Sivori]

No relation to "wtom" ?

wtom? Is that a nym?

 

[Tony Sivori]

I'd suggest checking your generator manual, to see if you can determine
whether it's designed to have a "floating neutral". I suspect that it
is.
If so, don't modify it.

Not much in the manual. No mention of the floating neutral, just a
statement not to connect it directly to any structure's electrical system.

 

[Baron]

wtom? Is that a nym?

A troll that jumped on anybody that mentioned surge protectors.

 

[Mike Tomlinson]

And good luck trying to clean up the generator output if you intend on
using a UPS in the circuit. My generator is 2500/3250 surge like
yours. And it is brushless. But there was nothing I could do to filter
the output well enough where my two 1000va APC UPS units would come
back off battery.

There was a recent discussion in demon.tech.pc by someone with a very
similar problem. (If you're aware of w_tom, you'll not be surprised he
featured in that thread.) We managed to establish that some APC UPSes
are specified by APC as generator-compatible and also have a button on
the back which can be used to reduce the UPS's sensitivity to poor mains
voltage.

I told the OP in that thread that his problems may be due to the lack of
a ground reference, but not being au fait with the subject had to bow
out there. Bear in mind this was a 240V (UK) installation, so I wasn't
comfortable with discussing tying one side of the output to ground.