1. TekScopes@groups.io
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Scope grounding and generators

Robert Simpson
 

Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my house. In use that won't be a problem as I will only be hooking appliances to the generator with extension cords separate from house power . However, since I don't want to initially power the scope from the generator until I check the generator output, I am worried about working with two different ground connections.

Bob
Chuck Harris
 

Probably the safest way would be to use a filament transformer. It will
affect the fidelity of the signal somewhat, but is way better than you
might think.

-Chuck Harris

Robert Simpson via groups.io wrote:

Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my house. In use that won't be a problem as I will only be hooking appliances to the generator with extension cords separate from house power . However, since I don't want to initially power the scope from the generator until I check the generator output, I am worried about working with two different ground connections.

Bob
Mike Dinolfo
 

Robert:

I don't see any reason why you can't check the generator output by
connecting it to a scope (to monitor the waveform and/or voltage),
subject to the following (in the US, at least).  I assume that your
generator is producing single phase power, either 120 VAC single phase
or 120/240 VAC single phase:

1.  To begin with, there's no reason why you can't connect the
generator's ground to your house ground.  But do not make any other
connections from generator wiring to house wiring.  The ground (the
National Electrical Code "grounding conductor") will generally be
identified as a bare, or green insulated, or green with yellow stripe
insulated, conductor.  Generator (and house) current carrying conductors
will be either neutral conductors (National Electrical Code "grounded
conductor"), which are generally colored white or grey, or phase
conductors (colored differently from the assigned colors for grounded
and grounding conductors.)

2.  Power up the scope from "house" power, using a probe with a
sufficient voltage rating (many 10x probes are rated to 600 V).  You
will need to make a grounding connection from the scope ground (scope
chassis) to the generator ground; this can be either an individual
"stand alone" conductor, or the shield/braid of the scope probe.  I
recommend a separate conductor rather than the scope probe shield; an
alligator clip jumper cable should be sufficient.  (Note: beware of
cheap alligator clip jumper cables with crimped connections at the
alligator clips; the connections should be soldered.)

The US standard NEMA 5-15R (15 amp) and 5-20R (20 amp) 3-terminal
outlets have the grounding terminal sized to accept a 3/16" diameter
metal rod; I've successfully used pieces of round copper or brass rod to
provide a good grounding stud, and then used alligator clip leads to
extend the ground connection.

3. Provided that you've got the ground jumper in place, you should be
able to probe the generator's output connector individual pins with the
scope probe's tip.  And you won't need to connect the scope probe's
grounding clip to the generator's frame (as this connection will be
accomplished by the alligator clip jumper cable described above.  If
probing a 120 VAC outlet (3 terminal), you should wind up reading 0.0
volts when probing the ground pin, and 0.0 volts when probing the
neutral pin, and ~170 VAC peak (340 volts peak-to-peak) when probing the
"hot" terminal of the 120 VAC outlet.  Of course, make sure that you've
got the scope set up with a "less sensitive" vertical deflection; 5
V/div should be adequate if you are using a 10X probe.

I know that there have been quite a few threads on TekScopes dealing
with possible safety issues when using isolation transformers, or
autotransformers (e.g. Variacs) that "carry thru" a ground connection
when testing switch mode power supplies, but I don't see any of these
issues applying for what you are describing.  But I've been wrong
before, so I hope others will correct me if I'm wrong on this issue.

Mike Dinolfo N4MWP

On 10/24/20 3:59 PM, Robert Simpson via groups.io wrote:
Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my house. In use that won't be a problem as I will only be hooking appliances to the generator with extension cords separate from house power . However, since I don't want to initially power the scope from the generator until I check the generator output, I am worried about working with two different ground connections.

Bob
stevenhorii
 

Would you check the outlet the scope is plugged into to be sure hot and
neutral have not been switched?

On Sat, Oct 24, 2020, 17:54 Mike Dinolfo <mdinolfo@erols.com> wrote:

Robert:

I don't see any reason why you can't check the generator output by
connecting it to a scope (to monitor the waveform and/or voltage),
subject to the following (in the US, at least). I assume that your
generator is producing single phase power, either 120 VAC single phase
or 120/240 VAC single phase:

1. To begin with, there's no reason why you can't connect the
generator's ground to your house ground. But do not make any other
connections from generator wiring to house wiring. The ground (the
National Electrical Code "grounding conductor") will generally be
identified as a bare, or green insulated, or green with yellow stripe
insulated, conductor. Generator (and house) current carrying conductors
will be either neutral conductors (National Electrical Code "grounded
conductor"), which are generally colored white or grey, or phase
conductors (colored differently from the assigned colors for grounded
and grounding conductors.)

2. Power up the scope from "house" power, using a probe with a
sufficient voltage rating (many 10x probes are rated to 600 V). You
will need to make a grounding connection from the scope ground (scope
chassis) to the generator ground; this can be either an individual
"stand alone" conductor, or the shield/braid of the scope probe. I
recommend a separate conductor rather than the scope probe shield; an
alligator clip jumper cable should be sufficient. (Note: beware of
cheap alligator clip jumper cables with crimped connections at the
alligator clips; the connections should be soldered.)

The US standard NEMA 5-15R (15 amp) and 5-20R (20 amp) 3-terminal
outlets have the grounding terminal sized to accept a 3/16" diameter
metal rod; I've successfully used pieces of round copper or brass rod to
provide a good grounding stud, and then used alligator clip leads to
extend the ground connection.

3. Provided that you've got the ground jumper in place, you should be
able to probe the generator's output connector individual pins with the
scope probe's tip. And you won't need to connect the scope probe's
grounding clip to the generator's frame (as this connection will be
accomplished by the alligator clip jumper cable described above. If
probing a 120 VAC outlet (3 terminal), you should wind up reading 0.0
volts when probing the ground pin, and 0.0 volts when probing the
neutral pin, and ~170 VAC peak (340 volts peak-to-peak) when probing the
"hot" terminal of the 120 VAC outlet. Of course, make sure that you've
got the scope set up with a "less sensitive" vertical deflection; 5
V/div should be adequate if you are using a 10X probe.

I know that there have been quite a few threads on TekScopes dealing
with possible safety issues when using isolation transformers, or
autotransformers (e.g. Variacs) that "carry thru" a ground connection
when testing switch mode power supplies, but I don't see any of these
issues applying for what you are describing. But I've been wrong
before, so I hope others will correct me if I'm wrong on this issue.

Mike Dinolfo N4MWP

On 10/24/20 3:59 PM, Robert Simpson via groups.io wrote:
Is there a safe way to use my 465M to look at my generator output? The
generator I recently acquired will have its own ground separate from my
house. In use that won't be a problem as I will only be hooking appliances
to the generator with extension cords separate from house power . However,
since I don't want to initially power the scope from the generator until I
check the generator output, I am worried about working with two different
ground connections.

Bob
Mike Dinolfo
 

Yes, I would check the outlet to be certain that the neutral and "hot"
connections are not swapped. But I would probably do this with a
commercial grade plug-in tester (available at most hardware stores;
typically under 15 USD, I believe); such devices typically have three
neon lamps; two of which are supposed to glow, and one of which is
supposed to stay dark with a properly wired outlet.  Although an
oscilloscope could also be used for this; I just think the
special-purpose tester unit is the way to go.  Or a multimeter can be
used for the same purpose by measuring the voltage from the "hot" outlet
terminal to ground, and from the outlet "neutral" terminal to ground. 
This applies to both the house wiring and the generator wiring.

In the several decades during which I've been a homeowner, every one of
the several homes that I've owned has had at least one outlet that was
miswired when I bought it.  So it's a worthwhile thing to check.  I've
never owned a generator; I suspect that the manufacturers generally know
what they are doing, but it's a simple thing to check.

Mike Dinolfo N4MWP

On 10/24/20 6:37 PM, stevenhorii wrote:
Would you check the outlet the scope is plugged into to be sure hot and
neutral have not been switched?

On Sat, Oct 24, 2020, 17:54 Mike Dinolfo <mdinolfo@erols.com> wrote:

Robert:

I don't see any reason why you can't check the generator output by
connecting it to a scope (to monitor the waveform and/or voltage),
subject to the following (in the US, at least). I assume that your
generator is producing single phase power, either 120 VAC single phase
or 120/240 VAC single phase:

1. To begin with, there's no reason why you can't connect the
generator's ground to your house ground. But do not make any other
connections from generator wiring to house wiring. The ground (the
National Electrical Code "grounding conductor") will generally be
identified as a bare, or green insulated, or green with yellow stripe
insulated, conductor. Generator (and house) current carrying conductors
will be either neutral conductors (National Electrical Code "grounded
conductor"), which are generally colored white or grey, or phase
conductors (colored differently from the assigned colors for grounded
and grounding conductors.)

2. Power up the scope from "house" power, using a probe with a
sufficient voltage rating (many 10x probes are rated to 600 V). You
will need to make a grounding connection from the scope ground (scope
chassis) to the generator ground; this can be either an individual
"stand alone" conductor, or the shield/braid of the scope probe. I
recommend a separate conductor rather than the scope probe shield; an
alligator clip jumper cable should be sufficient. (Note: beware of
cheap alligator clip jumper cables with crimped connections at the
alligator clips; the connections should be soldered.)

The US standard NEMA 5-15R (15 amp) and 5-20R (20 amp) 3-terminal
outlets have the grounding terminal sized to accept a 3/16" diameter
metal rod; I've successfully used pieces of round copper or brass rod to
provide a good grounding stud, and then used alligator clip leads to
extend the ground connection.

3. Provided that you've got the ground jumper in place, you should be
able to probe the generator's output connector individual pins with the
scope probe's tip. And you won't need to connect the scope probe's
grounding clip to the generator's frame (as this connection will be
accomplished by the alligator clip jumper cable described above. If
probing a 120 VAC outlet (3 terminal), you should wind up reading 0.0
volts when probing the ground pin, and 0.0 volts when probing the
neutral pin, and ~170 VAC peak (340 volts peak-to-peak) when probing the
"hot" terminal of the 120 VAC outlet. Of course, make sure that you've
got the scope set up with a "less sensitive" vertical deflection; 5
V/div should be adequate if you are using a 10X probe.

I know that there have been quite a few threads on TekScopes dealing
with possible safety issues when using isolation transformers, or
autotransformers (e.g. Variacs) that "carry thru" a ground connection
when testing switch mode power supplies, but I don't see any of these
issues applying for what you are describing. But I've been wrong
before, so I hope others will correct me if I'm wrong on this issue.

Mike Dinolfo N4MWP

On 10/24/20 3:59 PM, Robert Simpson via groups.io wrote:
Is there a safe way to use my 465M to look at my generator output? The
generator I recently acquired will have its own ground separate from my
house. In use that won't be a problem as I will only be hooking appliances
to the generator with extension cords separate from house power . However,
since I don't want to initially power the scope from the generator until I
check the generator output, I am worried about working with two different
ground connections.
Bob
Robert Simpson
 

Since I will not be connecting the generator to house power, I should be safe connecting house ground for my scope test. I want to see the shape of the power, the frequency and peak voltage. I think a scope will be my best tool for that. Besides, why have a scope if I don't use it whenever possible?
Robert Simpson
 

Also, I just checked the main breaker panel and the ground and neutral are on the same bus bar.
My extension cord for the scope will have a triple tap on the end. So I can use one of the ground hole sockets to connect to the generator frame lug for this test . That way the scope ground and generator ground will be connected electrically close.
Bob
Mike Dinolfo
 

Bob, I am reproducing your email with a few response comments...  and it
might also be helpful if you indicate what type of generator you have
(KW rating, voltage/phases output, etc).  Also, whether you plan to
monitor the generator's output with the scope receiving AC power from
the house, or the generator itself:

On 10/24/20 9:59 PM, Robert Simpson via groups.io wrote:
Also, I just checked the main breaker panel and the ground and neutral are on the same bus bar.
US National Electrical Code requirements call for the neutral (grounded
conductor) to be bonded to the ground (grounding conductor) at the
"service entrance" of any building service (but nowhere else); this is
in accordance with "code".
My extension cord for the scope will have a triple tap on the end. So I can use one of the ground hole sockets to connect to the generator frame lug for this test . That way the scope ground and generator ground will be connected electrically close.
Yes, this will serve as an interconnection between the house ground
system and any other loads (such as a scope plugged into the extension
cord), or the generator's ground system.  However: make sure that the
wiring from the house to the scope (or generator) has not been
compromised (insofar as maintaining the correct continuity of
identification/wiring of neutral, ground, and "hot" wire) all the way
from the service entrance, through intermediate outlets and the
extension cord, to destination load(s) or generator.

And you probably already know this, but I'll state it anyway- don't
under any circumstances interconnect the neutral and/or "hot" wires
between the house and the generator.

Mike D. N4MWP

Bob
Mac Perkins
 

Even if you have a dedicated ground rod for your generator, please bond (connect) that ground and your house ground (generally a bare wire coming from the ground rod to the electrical panel). Since a (three wire) extension cord from the generator to an appliance (eg refrigerator) will connect the generator's ground potential to the appliance, any difference between generator ground and house ground will present a shock hazard.

In general, all earth ground rods should be bonded together.

Using a small filament transformer or repurposed wall wart (older iron core transformer type with AC output) is an excellent idea for safely observing the power line. As noted, the distortion is minimal and having no direct ohmic connection to the power line gives protection against unpleasant surprises in the case of the wiring not being as it should be.
Chuck Harris
 

At issue is how the generator is internally connected, and
the possibilities of accidents.... and on whether or not you
are willing to bet your life that the generator is connected
the way you think it should be, and that it hasn't any faults.

For instance, you scope's ground wire is connected to earth
ground through the power cord.

Your generator should also be grounded, but if it isn't, an
accidental connection between the generator's hot lead and
the scope's ground, could cause the generator to be elevated
120V, or more, above the scope's front panel.

As I stated earlier, I use a filament transformer for such
measurements. Its fidelity is very good, and most are isolated
for several hundred volts... actually many of the older
filament transformers are good for 3000V.

-Chuck Harris

Robert Simpson via groups.io wrote:

Since I will not be connecting the generator to house power, I should be safe connecting house ground for my scope test. I want to see the shape of the power, the frequency and peak voltage. I think a scope will be my best tool for that. Besides, why have a scope if I don't use it whenever possible?
Simon
 

Be careful connecting appliances with a standby mode to a generator. On a couple of power cuts I connected my coffee maker to the generator and both times fried the standby circuit.
Simon
Jean-Paul
 

Robert: Most generators have a distorted sine output, depends on rating, and design.
Some have quite high THD. Other have terrible transients and EMI. Normally the mfg will have complete specs.

Rule of thumb: Larger size and high cost - (10..50 kVA) are closer to sinewave, low THD and transients
Cheaper consumer generators eg from Costco, under a few KVA, worse in every respect!

What is your intended use, and what power levels, make and model of generator?

I have used battery operated portables like TEK 212, rather than line powered scopes like 465M.

But you can float the 465 with an isolation trsf.

Good luck,

Jon
Glenn Little
 

For safety, the generator should be grounded to the single point utility ground for the building it will be providing power to.

The NEC probably requires this, I do not currently have access to a copy.
MIL-HDBK-419 (available on the web) addresses grounding.

Safety first.
Ensure all grounds are bonded together.

Glenn

On 10/24/2020 11:49 PM, Chuck Harris wrote:
At issue is how the generator is internally connected, and
the possibilities of accidents.... and on whether or not you
are willing to bet your life that the generator is connected
the way you think it should be, and that it hasn't any faults.

For instance, you scope's ground wire is connected to earth
ground through the power cord.

Your generator should also be grounded, but if it isn't, an
accidental connection between the generator's hot lead and
the scope's ground, could cause the generator to be elevated
120V, or more, above the scope's front panel.

As I stated earlier, I use a filament transformer for such
measurements. Its fidelity is very good, and most are isolated
for several hundred volts... actually many of the older
filament transformers are good for 3000V.

-Chuck Harris

Robert Simpson via groups.io wrote:
Since I will not be connecting the generator to house power, I should be safe connecting house ground for my scope test. I want to see the shape of the power, the frequency and peak voltage. I think a scope will be my best tool for that. Besides, why have a scope if I don't use it whenever possible?






--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
Chuck Harris
 

Isolating the scope may protect the scope from catastrophic
currents, but it does nothing to protect the scope's operator.

The front panel on most lab grade scopes is grounded to
the same ground as the BNC's, and as such the scope probes.

If you connect the scope probe's ground to a voltage that
is other than earth ground, the scope's front panel and
chassis will be elevated to the same voltage as the scope's
probe's ground clip lead.

Don't do it!

If your intention is to connect anything to *ANY* pin on
a running generator, the generator must have its grounding
point connected to a good earth ground.

If you do not ground the generator any single point fault
in the generator or load that shorts the hot lead to earth
ground will elevate the generator's case 120 or 240V above
ground.

If your intention is to use a 465M, it too must have its
chassis grounding point connected to a good earth ground.

The only valid exceptions involve a whole lot of thinking,
and isolating of the operator, scope, and generator from
dangerous contact.

Isolating grounds on test equipment and generators is a
very dangerous "rookie" mistake.

Read the "OPERATORS SAFETY SUMMARY" that is in some form
in every Tektronix scope's manual since Tektronix stopped
being rookies themselves.

Why do I harp on such stuff?

Because I made that rookie mistake when I was a teenager
working alone. I was tuning up a transmitter, and for
stability, I had the hand holding the diddle stick on the
chassis of the transmitter, when I smelled smoke. Wanting
to avert a catastrophe, I quickly reached over with my
other hand and flipped the metal bat handled power switch
on my intentionally ungrounded (for "safety" reasons) power
supply.

I woke up in a very battered state crumpled on the floor,
up against a cement block wall.

You don't have to repeat this experiment. It has already
been done too many times.

-Chuck Harris

Jean-Paul wrote:

Robert: Most generators have a distorted sine output, depends on rating, and design.
Some have quite high THD. Other have terrible transients and EMI. Normally the mfg will have complete specs.

Rule of thumb: Larger size and high cost - (10..50 kVA) are closer to sinewave, low THD and transients
Cheaper consumer generators eg from Costco, under a few KVA, worse in every respect!

What is your intended use, and what power levels, make and model of generator?

I have used battery operated portables like TEK 212, rather than line powered scopes like 465M.

But you can float the 465 with an isolation trsf.

Good luck,

Jon

-
 

I fried my refrigerator and the digital display board in my freezer when
I connected them to a generator during a hurricane. They worked for a while
but soon developed problems. Since then I've picked up a largish 440 or 220
to 220 or 110 volt transformer with dual primaries and dual secondaries
that I can strap for the necessary voltage and I will connect my devices to
the generator through it. Hopefully it will filter out some of the voltage
spikes and higher frequencies (> 60Hz). Large transformers like this are
frequently found in large commercial machinery and there's little demand
for used ones so they aren't hard to find. The one that I have weighs about
40 pounds and is rated at 10kW IIRC so it should be able to handle my 5kW
generator. A constant voltage transformer should work even better and they
show up on places like E-bay frequently and usually sell for next to
nothing because of their size and weight and the difficulty and cost of
shipping them. I have several 300 W sized ones and they're slightly larger
than a shoebox and weigh probably 20 pounds. I've been using them on my TV
and some other equipment and none of it has ever been damaged despite
nearby lightning strikes that took out a lot of unprotected equipment. The
trick to buying things like this is to watch E-bay and look for ones within
driving distance and to pick them up in person instead of shipping. Because
of the shipping costs, these items get few bids and typically sell for the
opening bid price. Also look for a dealer in surplus industrial and/or
electronics equipment in your area.

On Sun, Oct 25, 2020 at 12:39 AM <tenareze32@gmail.com> wrote:

Be careful connecting appliances with a standby mode to a generator. On a
couple of power cuts I connected my coffee maker to the generator and both
times fried the standby circuit.
Simon
Tony Fleming
 

Are the new digital scopes also grounded to the earth ground? Only when
plugged into 120V and not using the battery that is inside to usually power
my digital scopes.
I like this diagram:
https://images.search.yahoo.com/yhs/search;_ylt=AwrCmmD9e5VfhFgAbywPxQt.;_ylu=Y29sbwNiZjEEcG9zAzEEdnRpZAMEc2VjA3Nj?p=connect+isolation+transformer+AND+oscilloscope&fr=yhs-iba-syn&hspart=iba&hsimp=yhs-syn#id=9&iurl=https%3A%2F%2Fi.stack.imgur.com%2F3bwTC.png&action=click
I have a couple isolated transformers that I use when working on old stuff
like Radios and TV's....

*My understanding is that as long the path can't find the earth ground in
any combination, I should be safe.*

Excluding my Tektronix 2465 DMS that is grounded to earth ground and in
case I need to isolate my "path" I have isolation transformers for that.
Many experienced people make mistakes even today, despite knowing this
little problem that can cost $$$ or hurt you beyond repair.
Am I wrong or is there a "path" that can "bite me anyway" ?
Thanks.

On Sat, Oct 24, 2020 at 10:50 PM Chuck Harris <cfharris@erols.com> wrote:

At issue is how the generator is internally connected, and
the possibilities of accidents.... and on whether or not you
are willing to bet your life that the generator is connected
the way you think it should be, and that it hasn't any faults.

For instance, you scope's ground wire is connected to earth
ground through the power cord.

Your generator should also be grounded, but if it isn't, an
accidental connection between the generator's hot lead and
the scope's ground, could cause the generator to be elevated
120V, or more, above the scope's front panel.

As I stated earlier, I use a filament transformer for such
measurements. Its fidelity is very good, and most are isolated
for several hundred volts... actually many of the older
filament transformers are good for 3000V.

-Chuck Harris

Robert Simpson via groups.io wrote:
Since I will not be connecting the generator to house power, I should be
safe connecting house ground for my scope test. I want to see the shape of
the power, the frequency and peak voltage. I think a scope will be my best
tool for that. Besides, why have a scope if I don't use it whenever
possible?
Sean Turner
 

Chuck Harris makes a great point...don't repeat mistakes that have already been made. In his case, it might have cut his life short. It has cut short the lives of very experience engineers. If you're going to be making measurements on high energy sources, regular old lab scopes really aren't the thing. Get yourself a Fluke Scopemeter. These are designed to safely make floating measurements, and they have all the same protections that you get in a normal high quality multimeter (especially, nothing that might be live for you to accidentally touch).

Don't play Russian Roulette with your life.

Sean
Dave Voorhis
 

On 25 Oct 2020, at 17:31, sdturne@q.com wrote:

Chuck Harris makes a great point...don't repeat mistakes that have already been made. In his case, it might have cut his life short. It has cut short the lives of very experience engineers. If you're going to be making measurements on high energy sources, regular old lab scopes really aren't the thing. Get yourself a Fluke Scopemeter. These are designed to safely make floating measurements, and they have all the same protections that you get in a normal high quality multimeter (especially, nothing that might be live for you to accidentally touch).
Aren’t the venerable Tek 222, 222PS, and 224 also intended for that kind of use, up to about 400 or so volts on the probes?
Sean Turner
 

Sure, if you have one of those it is probably suitable as long as it's in good condition.

The point I was making was that the OP really should get the right tool, be it a scopemeter, a 222/222PS, etc. A laboratory oscilloscope is not the right tool for scoping high energy circuits. Just because you can doesn't mean you should!

Sean

On Sun, Oct 25, 2020 at 10:46 AM, Dave Voorhis wrote:


On 25 Oct 2020, at 17:31, sdturne@q.com wrote:


Chuck Harris makes a great point...don't repeat mistakes that have already
been made. In his case, it might have cut his life short. It has cut short
the lives of very experience engineers. If you're going to be making
measurements on high energy sources, regular old lab scopes really aren't
the thing. Get yourself a Fluke Scopemeter. These are designed to safely
make floating measurements, and they have all the same protections that
you get in a normal high quality multimeter (especially, nothing that
might be live for you to accidentally touch).
Aren’t the venerable Tek 222, 222PS, and 224 also intended for that kind of
use, up to about 400 or so volts on the probes?
Robert Simpson
 

First , thanks everyone for the feedback. I do want to be safe.
So, I haven't, don't and won't be floating the scope. Never have and don't see why I would. In the house if I need that type of measurement, I would use my 7A22.
For my generator test, the scope will be plugged in normally which means the scope frame will be at earth ground. By only temporarily connecting the generator frame to house earth ground, I don't see danger.
Again, my only use of the generator will be with extension cords. No plans on connecting the generator to house power.
The generator is a Briggs & Stratton Powermate 5000. Which is 5000 watts max continuous and 6250 surge. My use is planned at less than 4000 watts. (small freezer, refrigerator, one light and two small muffin fans in my heating wood stove.) as a side note for my motivation, you may have seen news articles about power shutdowns in California.
Bob
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