Samlex Inverter connection to e-panel

Rybren

I know that we've sort of discussed this before, but I'm still somewhat confused.

I have a Samlex PST-1500-24 inverter that I plan on using with my e-panel. The Inverter has both a GFCI and hard-wire output and both have a neutral-ground bond internally.

I'm a tad (okay, a lot) confused regarding the AC connection from the Inverter to the e-panel and subsequent AC out from the panel.

I know that with this configuration, I don't want to make a N-G bond inside the panel. Do I connect the AC ground from the inverter to the e-panel's ground busbar (which has the ground from the classic connected to it)? Would the ground wire on the AC out lines from the panel also connect to the same ground busbar?

What about the chassis ground from the Inverter? Would it go directly to the ground rod or can I also connect it to the busbar in the panel.

Thanks and sorry for all of the noob questions.

-Jerry

BB.

Re: Samlex Inverter connection to e-panel

First, assuming I have the correct manual (PDF download), this is a pure (or true) sine wave inverter and it has a GFI outlet and a Neutral to Chassis bond inside the unit:

Neutral “N” (16) is bonded to the metal chassis of the inverter through a loop of wire connecting the “N” terminal on the Line side of the GFCI to the chassis of the inverter.

So, you are correct, you will have to address the Neutral Bonding + AC GFI outlet questions.

First is the GFI outlet question. Personally, if this was a cabin or RV type installation and you are wiring up a permanent installation with the inverter. I would remove the GFI outlet on the output of the inverter and I would hard-wire the AC power system directly.

Having a GFI outlet on your "main power source" is a bit of a pain. If you have (for example) a GFI trip (using 120 VAC mixer near sink), the GFI trip will not only kill the power to the mixer (a good thing), but it will also kill the power everywhere--Leaving in the dark. It is better to have the GFI outlets where needed (near sinks/water, outside) so that they do not trip and kill power everywhere at once (also easier to find the offending short to earth).

With a GFI outlet in the inverter, the only place you can Neutral+Earth bond is inside the inverter before the GFI outlet. If you Neutral+Ground bond after the outlet, it is very likely the output will trip.

Without the GFI outlet on the inverter, you can leave the Neutral+chassis bond inside the inverter. Or disconnect the bond and use the Neutral+safety bond inside the E-panel. Or you could leave the AC "Neutral" completely floating (almost everything will work OK--But Neutral+Safety bonding in a cabin/home/RV "somewhere" is usually the best thing--But does raise issues with RV's and shore power--Another post if needed).

Where to connect all the grounds...

The Battery Negative to Safety Ground is made inside the E-panel (it should be--I think). If so, then the inverter chassis ground should be connected at the same place/ground bus bar. All green wire grounds should use the same ground bus. If you leave the Neutral-Chassis ground inside the inverter, then do not use the Neutral-Chassis bond inside the E-panel. If you disconnect the Neutral-Chassis bond inside the inverter, then make Neutral-Safety bond in the E-panel. Either is fine and depends on what is easiest for you.

Then connect a (typically) 6 AWG wire from the same E-panel ground bus directly to the 8-10 foot ground rod near the outside wall/foundation (assuming the E-panel is mounted on/very near to an outside wall).

Is there a DC-GFI ground setup in the E-panel (typically a ~60-80 amp breaker ganged with a 1 amp breaker on the PV solar panel input wiring to the charge controller).

Do you have lightning strike issues to be concerned about? If so, then you need to pay more attention to system grounding, surge protection, etc.

-Bill

Photowhit

Re: Samlex Inverter connection to e-panel

Bill, I think I asked Jerry about this before, I think this unit has both a GFI outlet and a hardwire. So would you suggest removing the neutral to chassis ground or just the whole unit, but look for an earlier connection/bond? ....Hoping that it will be a clear connection, likely opening the unit should have a wire connecting the chassis to the electronics.

BB.

Re: Samlex Inverter connection to e-panel

As long as you ground the inverter chassis to your "green wire" ground--You really do not need to lift the Neutral+Chassis bond inside the inverter.

Having multiple neutral to earth/green wire bonds can be an issue if you have a genset and/or shore power connection--And can cause GFI outlets to trip, or other possible issues (MSW inverters are the ones that can "smoke" with Neutral to Green Wire/Battery grounding).

Usually, my recommendation is to remove the GFI outlet from the TSW inverter--But that is my choice--It is up to you (and if you can safely remove the GFI and hardware in your distribution wiring).

-Bill

Rybren

Re: Samlex Inverter connection to e-panel

I did discuss this issue somewhat, but now that I'm getting close to installing the inverter, I was getting confused.

I can hook the hardwire output directly to the epanel and leave the GFCI on the inverter, they supposedly won't interfere with one another. It sounds like I had the grounding correct in my peabrain, but to confirm, the ac out lines also connect to the panel's ground bar?

Bill, I don't have a GFCI breaker in the panel.

Thanks for the help.

Cariboocoot

Re: Samlex Inverter connection to e-panel

Something that should be checked is whether or not the hard wire option connects to the inverter before or after the GFCI circuitry. A standard GFCI outlet has connections for 'protecting' other outlets connected to it (downstream protection); they may have simply connected to that to provide the leads for the hard wire option.

Rybren

Re: Samlex Inverter connection to e-panel

'Coot,

When I had the hardwire cover open, it appeared that the terminal block was connected to the inverter before the GFCI, so it doesn't seem to be an issue.

Cariboocoot

Re: Samlex Inverter connection to e-panel

Rybren wrote: »

'Coot,

When I had the hardwire cover open, it appeared that the terminal block was connected to the inverter before the GFCI, so it doesn't seem to be an issue.

That's the best you could hope for.

Rybren

Re: Samlex Inverter connection to e-panel

Not to flog a dead horse but....

I'll be heading up to the camp tomorrow morning to wire up the inverter and this will be my last chance to clarify everything in that peabrain of mine.

I plan on leaving the N-G bond in the inverter. There will be no N-G bond in the e-panel.

Ground connections:

The inverter Chassis ground will connect to the e-panel ground bar.
The inverter AC out ground will connect to the e-panel ground bar.
The AC out lines from the e-panel will connect to the e-panel ground bar.
The Classic 150 ground will connect to the e-panel ground bar.
The e-panel ground bar will connect to the ground rod outside of the power shed.

Thoughts & thanks.

BB.

Re: Samlex Inverter connection to e-panel

I would also suggest that you connect Battery Return (usually negative bus) to your ground bar too.

If you have a cold water pipe/ground rod, you want a minimum of 6 AWG from the E-panel ground bar to the "earth ground"--You can connect that battery negative there too (ground rod/cold water pipe) instead instead of at the ground bar--either would be acceptable (If you go with larger inverter, you should use a heavier than 6 awg cable from battery to "common ground".

And if the "common ground point" for AC+DC is the ground rod, then a heavier than 6 awg from ground rod to ground bar in E-panel (remember, you want the ground return path to the battery to "safely and reliably" pop the heaviest fuse/breaker in the system--which is usually the Inverter protective device).

You could leave the battery negative floating-Or even use the DC GFI--But I believe that both of those options are not nearly as good as the solid Battery Return grounding, and "floating or DC GFI" can create way more safety/operational problems.

Even the E-panel ground bar does not "need" to be connected to an earth ground rod--But for a fixed installation (not RV), a ground rod is desirable and critical to your lightning control measures (and Battery Return grounded to ground rod too).

Make sense?

-Bill

Rybren

Re: Samlex Inverter connection to e-panel

Thanks Bill,

Why the battery return connection to ground? The e-panel instructions don't call for it and I must admit that I don't understand why you recommend it.

Having said that, you always give great advice, so I suspect that there is a very good reason for it.

BTW, this is a permanent installation at my off grid camp.

Thanks, Jerry

BB.

Re: Samlex Inverter connection to e-panel

Several reason for grounding your battery negative bus to the Epanel ground bar+ground rod.

First is safety, if there is a DC "Hot" to metal short (epanel sheet metal, inverter case, charge controller, case, etc.)--You want to pop the fuse/breaker and kill the power to the short. If you do not "hard ground" the DC battery side, you can get all sorts of issues that are "ugly" (I can give you a white paper on the problem if you want the details)... Just think of the issues if your car when from Negative Ground to Positive Ground if a positive cable became shorted to ground--Not good. Here is a long discussion about DC power system grounding:

• Ground Fault Protection

Quoting myself from that thread:

One other quick way to look at the DC GFP setup... Imagine you designed a Negative Ground system and put fuses/breakers on all positive wiring. No fuses/breakers on negative wiring, and one solid connection between the negative bus and earth ground (including grounding to water pipe, fixtures, wiring boxes, conduit).

If there is a fault from anywhere in the Positive circuit path, positive wire will be protected by an appropriate fuse/breaker which will be tripped by the excessive current flow.

If there is any negative/return wire to earth ground, virtually nothing will happen as both are very near the same voltage. (it is possible with ground loops to overheat return wiring, but for now, NEC does not address over current from ground loops other than recommending/requiring single point grounding).

Now, you replace that one Earth Ground with a 1-5 amp fuse. And now earth ground, randomly, anywhere in the Positive Wiring Path (PV wiring or Battery wiring). Pops the 1-5 amp fuse, and stops power flowing from solar panels to/through charge controller... Now you have a positive earth grounded system with fuses in the earthed positive paths.

No current limits on Negative Grounds. Items that were assumed to be "touch safe" (like lamp sockets) are now powered by battery or PV Array voltage/power. And the current limit available anywhere on the negative/return wiring is dependent on where, specifically, the Positive to Earth Fault was made.

The second is lightning control. The battery is actually a great surge suppressor (lots of capacitance, chemical action to keep batter at 12 volts (or what ever) and even a "spark gap" too). If you connect Battery Return to the ground rod, it will dramatically reduce the effects of nearby lightning strike.

-Bill

Rybren

Re: Samlex Inverter connection to e-panel

Thanks Bil

I knew there was a good explanation, I just couldn't see it.