3kw Powmr 48v inverter -> transfer switch general questions

Welcome to the forum Tremmert,

I looked through the manual and other information at your link to the hybrid inverter... It does not talk about system grounding anywhere.

What would I do? (this is your system--Verify my suggestions before doing anything--I have no special knowledge here)

First, take your Ohm meter and measure the resistance between Chassis ground (metal bonding screw on exterior of chassis) (note: no external wiring connected to AC in or AC out connectors--Don't want genset or main home panel to affect Neutral+Ground connections) and:

• On the AC Input power connector:
• Check left terminal (labeled as GND in manual) and see that you have near zero Ohm resistance (ground=>ground---Should be "the same gnd)
• Check right (#3 terminal) labeled as Neutral and you will have either near zero Ohm resistance (Neutral bonded to Chassis Ground) or you will have >>100's of Ohms of resistance (NO Neutral to Chassis ground bond).
• On the 120 VAC Output power connector:
• Check external Chassis Ground to right hand "Neutral" terminal (as labeled in manual). Either near zero Ohms or >>100's of Ohms of resistance (non-bonded N+G).

Are you using AC power from Genset or AC/Utility Mains?

Genset: In this setup, the genset should have "floating" Neutral (no N+G bond). Check with meter (or genset manual)--If there is a N+G bond, I would suggest to "lift" the N+G bond connection (larger gensets "assume" they are the only AC energy source and Bond N+G. Smaller gensets (and AC inverters) usually have Neutral floating (no N+G bond).

AC Utility Power: Technically we treat AC utility power as "floating" Neutral--Even though it is usually tied to ground rod at the pole transformer.

AC Main Panel for Home: Generally AC main panels have a screw that "bonds" Neutral Bus bar to Earth Ground (chassis or earth ground bus bar).

The NEC defines that all AC loads go through L1/L2/Neutral wiring. If you have tow or more N+G bonds (say in AC inverter and AC main panel), then you have parallel current paths (Neutral in parallel with Green wire/conduit safety ground). And we do not want that. Floating Genset and AC Inverter Neutral and having only one N+G bond in the AC main panel is the typical method to address this issue.

As a first pass--Multiple N+G system grounds in your home power system will not cause major problems.

Second pass A--If you have two or more N+G system ground (parallel current flow)--It can cause weird effects... Such as causing circulating current in the Main AC panel sheet metal (transformer coupling from 2 parallel current wires going into sheet metal between two separate holes--Can induce current in sheet metal and cause heating in chassis sheet metal.

Second pass B--If you have a N+G bond in the genset and N+G bond in the main AC panel, If there is a GFI (ground fault interrupte) outlet or similar--This looks like a "ground fault" and will trip the GFI on the genset.

Regarding the Transfer Switch:

I guess that your main AC panel is 120/240 VAC split phase power (standard North American home wiring).

This inverter (and genset, if used?), is a 120 VAC single phase inverter. So you will only wire 120 VAC circuits for backup power (yes, is usually obvious, but just want to be clear).

This transfer switch is a 120/240 VAC split phase type. You have two options--One is to only use 1/2 of the transfer switch and use 120 VAC wired to the "black" circuits (lose the "red" circuits).

Or wire AC inverter L1 / N as" L1 to both "black" and "red" circuits--And only support 120 VAC loads. And this is probably what you will plan on doing.

HOWEVER, this does run into an issue.

For 120/240 VAC split phase power... The neutral current is the "difference" between L1 an L2 (i.e., if you have 10 amps on L1 and 6 Amps on L2, you have 4 amps on Neutral).

Where this can be an issue... For example you can get 2 wire ROMEX (Black, White Neutral, and copper ground wire) or 3 wire Romex (Back, Red, White Neutral, and copper ground wire).

With 120 VAC power... The Neutral is only carry the max rated current (14 AWG @ 15 Amp rated). Since Neutral current is L1-L2=N, that is fine.

If you have 120 VAC single phase L/N from inverter tied to L1/L2/N, the current in the neutral is L1+L2=N ... So if you have 15 amps in L1 (black) and 15 amps in L2 (red), then the "return current" in the White Neutral is now 30 Amps. And 30 Amps exceeds the 15 amp rating of 14 AWG wiring.

Since both 2 wire and 3 wire ROMEX circuits (and older knob and tube) are common in homes--You have to check and see what circuits you plan on supporting for emergency backup to ensure you don't over current a common neutral in 3 Wire Romex. (2 wire ROMEX will not be an issue here).

-Bill

So far so good... Floating Neutral in AC inverter. If you have an backup genset--Need to confirm that it has floating Neutral (or figure out how to lift the N+G bond in genset--In theory, if you use the genset as a portable, you are supposed to reconnect N+G bond--Although, many smaller than ~3.5 kWatt gensets and AC inverters default to floating output).

For a 14-30 NEMA plug--30 Amp rating so you should use a 10 AWG "jumper" between L1 and L2--I do that on the male plug that goes into the 120 VAC genset outlet (as this will alway be 120 VAC and no danger of shorting a 120/240 VAC outlet (say a bigger genset with 120/240 VAC output).

To identify ROMEX... I believe that White ROMEX sheath is 14 AWG, and Yellow ROMEX sheath is 12 AWG (I am not an electrician). 2x wire with ground:

And 3x wire + gnd ROMEX looks like this:


Again, I am no Electrician... But from what little I have seen is BLK+White is 2 wire ROMEX, and BLK+RED+White is 3x ROMEX. And the B+R+W 3 wire having a common neutral being the "issue" with possible over current in the White/Neutral.

Make sure you match the 14 AWG @ 15 Amp wiring with your 15 amp Transfer Switch Circuits and 12 AWG @ 20 Amp wiring with 20 Amp TS circuits (If you can).

You have to trace back to the ROMEX sheaths to see which sets are Paired. And that L1/L2 pairing of B+R needs to trace back to your breakers too... You do not want two breakers on L1 to feed B+R+W sets in ROMEX (same issue, possible overheating of Nature).

The link to your photo has "expired", so I cannot confirm (the details) that the breakers are wired correctly for B+R pairs (L1+L2, not L1+L1 or L2+L2 breaker pairs).

You can post photos directly to the forum too.

All this make sense? I/We want you to be safe. Ask questions if not making 100% sense.

-Bill