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Author Topic: Inverter generator strangeness  (Read 835 times)

Tim Hite

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Inverter generator strangeness
« on: April 07, 2019, 11:13:49 pm »

Had a wedding over the weekend and the groom provided an EU3000 Honda generator from our local (reliable) generator company. When I fired it up and ran a load tester on it, the CT70 was showing red and the H and N terminal lights were flipping back and forth. I've not sen anything like it.

Called the generator company tech and they said they've never had a problem powering stuff with the unit. I borrowed a small light from the photographer and plugged it in and nothing bad happened. I ran sound and some HID light fixtures for the evening and everything was fine.

Any guesses as to what was going on there?

CT70 was showing 127VAC with polarity swapping back and forth from H to N. H to G showed .7VAC, no GFCI to test in at the generator.
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Art Welter

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Re: Inverter generator strangeness
« Reply #1 on: April 08, 2019, 12:10:52 am »

When I fired it up and ran a load tester on it, the CT70 was showing red and the H and N terminal lights were flipping back and forth. I've not sen anything like it.

Any guesses as to what was going on there?

CT70 was showing 127VAC with polarity swapping back and forth from H to N. H to G showed .7VAC, no GFCI to test in at the generator.
Tim,

From your description and partial reading of the Extech CT 70 manual, sounds like no earth ground and a H/N reversal.
Someone may have wired the receptacle backwards after replacement.
H/N reversal does not cause a problem "powering stuff", but is a safety concern with certain gear configurations and should be corrected.

Art
« Last Edit: April 08, 2019, 12:27:29 am by Art Welter »
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TJ (Tom) Cornish

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Re: Inverter generator strangeness
« Reply #2 on: April 08, 2019, 08:10:45 am »

Had a wedding over the weekend and the groom provided an EU3000 Honda generator from our local (reliable) generator company. When I fired it up and ran a load tester on it, the CT70 was showing red and the H and N terminal lights were flipping back and forth. I've not sen anything like it.

Called the generator company tech and they said they've never had a problem powering stuff with the unit. I borrowed a small light from the photographer and plugged it in and nothing bad happened. I ran sound and some HID light fixtures for the evening and everything was fine.

Any guesses as to what was going on there?

CT70 was showing 127VAC with polarity swapping back and forth from H to N. H to G showed .7VAC, no GFCI to test in at the generator.
I believe this is normal behavior of the single-phase EU series generators.  They provide quasi-balanced power to the frame via capacitor coupling: 60v hot to frame and 60v frame to neutral .  There is no ground of any consequence on these generators - both hot and neutral are floating such that if you short either hot or neutral to the frame, there is no fault current path to trip a breaker.  You are supposed to ground the generator frame to the earth via a ground rod (rarely done in practice), but even if you do that, the CT-70 will not read a ground path, as it is trying to put a load between hot and ground for testing, which it sees as an open circuit (which it is other than the coupling capacitors).

We've discussed these generators extensively going back a few years.  In a building, shock prevention depends on ground -> neutral bonds, GFCIs, and over-current protection devices.  In single-phase isolated power scenarios like this, a different thought process is used - if the power source is totally floating, even if you have a single fault - i.e. hot to ground, in practice nothing happens as there is no fault current path unless you also contact the other current-carrying wire; which ultimately boils down to the same safety as a traditional wiring system - if you touch both hot and neutral even in a fully code-compliant electrical system, you're going to get shocked.

TLDR - your generator is fine; the CT-70 just doesn't know what to do with a different wiring and safety scheme.

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Tim Hite

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Re: Inverter generator strangeness
« Reply #3 on: April 08, 2019, 11:21:33 am »

Thanks Tom.

Art, this definitely wasn't a H/N reverse polarity situation. The indicator light was moving back and forth between hot and neutral. In an RP situation, the indicator lights for polarity would be unchanging.
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Mike Sokol

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Re: Inverter generator strangeness
« Reply #4 on: April 08, 2019, 04:53:26 pm »

Thanks Tom.

Art, this definitely wasn't a H/N reverse polarity situation. The indicator light was moving back and forth between hot and neutral. In an RP situation, the indicator lights for polarity would be unchanging.

I've written about this issue extensively for the RV industry, and even created a video showing how to correct it using a simple G-N generator bonding plug. Here's my latest article: https://www.rvtravel.com/rv-electricity-generator-neutral-bonding-basics/
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Tim Hite

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Re: Inverter generator strangeness
« Reply #5 on: April 09, 2019, 11:15:22 am »

Thanks Mike, figured you'd covered this already. Just didn't recognize the strange error condition.
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Jeff Robinson

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Re: Inverter generator strangeness
« Reply #6 on: April 22, 2019, 12:57:56 pm »

Had a wedding over the weekend and the groom provided an EU3000 Honda generator from our local (reliable) generator company. When I fired it up and ran a load tester on it, the CT70 was showing red and the H and N terminal lights were flipping back and forth. I've not sen anything like it.

Called the generator company tech and they said they've never had a problem powering stuff with the unit. I borrowed a small light from the photographer and plugged it in and nothing bad happened. I ran sound and some HID light fixtures for the evening and everything was fine.

Any guesses as to what was going on there?

CT70 was showing 127VAC with polarity swapping back and forth from H to N. H to G showed .7VAC, no GFCI to test in at the generator.

What we have here is a 'separately derived' source. See NFPA 70 (the code) 250.20(D), 250.30 and 250.104(D) per the index of my 2005 copy.

250.30(A)(1) states: System Bonding Jumper. An unspliced system bonding jumper … shall be used to connect the equipment grounding conductors of the separately derived system to the grounded conductor. …
See: https://www.ecmweb.com/code-basics/grounding-and-bonding-separately-derived-systems

Ths applies to both generators and transformers (necessary for OCDs to trip when a short circuit occurs). Bonding elsewhere (other than the service entrance) will cause GFCI/RCD devices to trip unnecessarily because of circulating currents due to voltage buildup in the current carrying neutral.

If the generator is the only source, also see articles 520, 525-IV, 525.30, 31 & 32

Two weeks ago I installed a transformer on a 240V circuit (no neutral was pulled to the convenient attic fan source that has not been used in decades) to power a 120V load and the other end of the MC line fed a duplex in a metal box (not installed by me) and the hot terminal touched the grounded metal box, causing the fuse I added to the transformer to blow, because I bonded the secondary, per code, preventing the box from becoming hot, I did ground the circuit as well.

HTH, FYI, ETC. (If you need the difference between grounded and grounding explained, you are not qualified.)

Edit: adding link about balanced (symmetrical) technical power (+/- 60V)
http://paul-lehrman.com/S2N/Articles/PowerGrounding.html
I use this to feed my home theater rack because it reduces both video and audio noise floors.

Jeff Robinson
« Last Edit: April 22, 2019, 01:45:07 pm by Jeff Robinson »
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Re: Inverter generator strangeness
« Reply #6 on: April 22, 2019, 12:57:56 pm »


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