I purchased the NTS in October but could not install until now.
While I was making the frame ground cable I connected a kill-a-watt and powered up the inverter.
KaW showed solid 120v output. I attached an APC outlet strip (for test loads) which showed ‘wiring fault’ (no ground).
Before connecting the FG cable I checked FG-to-building ground. I saw AC sweeping from 4 up to 11 VAC and back.
No AC ground, and voltage on FG, is this a bug or a feature?
Greetings,
The topic of grounding and bonding in alternative energy systems is an extremely messy one, to understate the matter.
It’s not necessarily an anomaly for a device of the type in question to show an open-circuit between the neutral and ground terminals of the output connector. Traditional utility power systems are predictably referenced to Earth, terra firma, the dirtball spaceship. That makes it easier to reason out the what-if-when sort of questions that arise when thinking about safety issues.
In the case of a device like this that’s designed to take a battery input and spit out something that looks like traditional utility power but isn’t, the manufacturer can’t reasonably make any assumptions about what the user might connect to what else. The basic answer to that problem is to build a device that does the essential function desired and leave the user to fret about the what-if-when sort of questions that apply during a tiny portion of collective use.
As for a voltage existing between the frame ground and output ground, that can’t decisively be called an anomaly either. The meter used to measure that almost certainly has an input impedance into the megaohm range, and only a small sniff of capacitive coupling between two nodes is needed in order to start measuring significant voltage between them. Such coupling is commonly put there on purpose for reasons of controlling radio emissions.
Long story short, your unit is most likely functioning as designed.
Feel free to ask further questions if desired.
rick_1976,
Thanks for your (exceptionally) fast response.
The meter I used for the 48v system is an older fluke (79 III) from my early network engineer days when I sometimes had to adjust voltages due to the number of cards in a device.
THIS ups system (meanwell 48v charger, 48v lifepo battery, meanwell 48v inverter) was intended for a collection of desktop-class computers (6) for vm hosts. (48v == way less amps)
Since PC power supplies are 3-prong, I’m somewhat concerned about grounding.
My network device ups configuration (iota 12charger, renogy 12v battery, renogy 12v inverter) does not show the same issues.
I may have used a different meter for that install, however, the APC does not complain about ground with the renogy inverter.
Should I look for a different inverter?
I’m pretty sure that Fluke is a >10 megaohms impedance AC voltmeter.
To make a low impedance voltmeter with the Fluke connect a low value resistor across the meter leads while making the measurement.
A 100K resistor should be low enough to dampen out RF suppression capacitor leakage voltage.
Honestly, that’s a choice that’s up to you and whatever regulatory entities involve themselves in your affairs.
In the use case as I understand it, the safety component of the end-equipment earth ground becomes redundant, due to the isolation provided by both the charger and inverter in your apparatus. In typical use, a single failure within the end equipment could potentially expose the user to AC line voltage, while in the double-conversion UPS scenario suggested, that hazard doesn’t exist until both devices upstream also develop similar faults, which is much less likely.
Because earth ground connections often serve secondary functions related to radio emissions control however, a chain of isolated switch-mode conversion devices might well cause problems from that standpoint if a chassis connection to earth is not provided.
Unfortunately, I’m not in a position to offer more conclusive comment than this on the issue.
@x3b_6k4 The product manager agrees with this statement.
They indicate, “It’s normal. The NTS-1200-148US outputs neutral and FG are floating that it has voltage.”
Thanks to all of you. Very helpful. Much appreciated!
Everything connected and working as expected. Could use a more ‘proportional’ fan speed controller on the charger though. 
