Power Plant + Generator

I live in New Jersey and we just got hit with a tropical storm and it very quickly wiped out power for most people. I’m still without power from the utility company, but I am running on a whole house natural gas generator.

I’ve always known that the generator’s electrical signal is very noisy, but I never knew how bad it was. My P20 will not even operate as its telling me there’s a short on the line. There’s no short but the oscilloscope is showing the ugliest sine wave I’ve ever seen. Output scope is not better. THD reported at 15%.

Obviously, the P20 is protecting itself and the components, so I’ve shut it off completely.

Just thought I’d post this info for what it’s worth.


The low voltage is an issue too. Perhaps your generator needs an adjustment to bring the voltage up or risk damaging other devices.

Plus or minus 6% at 120v is standard.

Wow, this is really cool! Very interesting as well! I’ve never seen it display such an ugly waveform. Thanks for sharing! Hope all is well out there.

I’ve asked every service guy to try and fix that frequency and you cleanliness of the power, but they never do. I think the unit’s just too old and lacks the newer technology. I have ordered the Tesla powerwalls. Now that I work from home full time and there’s so much highly sensitive electronics in my house it just make sense to have the whole house backed up with clean electricity.

1 Like

That’s interesting… we got hit in NH as well and my natural gas generator kicked in. The P12 showed short on all outputs, so I figured that I’d unplug it all and restart it in the morning. No issue at all after restart. I bet this is what happens when you have a sudden power drop and another incoming (and dirty for sure) power.

Good news is that now I know and I don’t have to panic when I see “short”

If you want to experiment, adjusting the phase tuning on the P20 will probably result in a better looking output waveform.

It also puts out a pretty gnarly waveform if you put an isolation transformer in front of it.


What a horror!

I’m investigating whole house generators and found the Generac guarantees less than or equal to 5% THD. What unit do you have? I’m looking at 15-20KW models running on nat gas.

For us it would not be for outages caused by weather rather something else that may destabilize the grid for an extended period of time.

Mine is very old (2007). The spec sheet for my model doesn’t mention THD. I don’t believe it was something generac cared about until a few years later. 2010 models have mentioned less than 5% THD.

I’m getting an upgraded generator soon and plan on running some tests. But it will be a few weeks before it’s in stock and installed.

Hope to learn from your experience.

I’ve got 5kw grid connected solar and might as well include provisions for a battery system in the future.