Home UPS: grounding, isolating, connecting to panel

[arthurm]

I'd like to deploy a UPS system as shown below. My primary need is the setup shown in black, a simple setup feeding directly to my equipment. The transfer switch is 15A which is more than I need.


Considering the black setup:


1. At point "A", what can I use to isolate the batteries? I assume I need this to prevent inter-battery current fllow?

2. Also at point "A" or after, what breaker(s) can I use to limit amps and damage to the inverter? On page 11 of its manual, it states a 250A ANL fuse but I'd rather use a breaker.

3. How do I ground the charger and inverter (G1, G2)? The manuals only speak of DC ground, as in a vehicle. Can I just use the AC ground? Wire size?


My optional need is to feed three 15A circuits from the main panel through this setup. Note that the total amp load of all three of these curcuits is only 10A, if that. The blue setup shows one feed off the UPS APC transfer switch. The APC has several female outputs, again, 15A total output. My desire here is to have a switch to select between the UPS setup and the main panel. This will allow me to switch to the main if I need to service the UPS:


4. What should I use for the select switch(es)?
5. If a subpanel is more appropriate here, feeding off one APC output, please advise on how to wire that up.


Some information on the equipment:

Charger is Xantrex TC 4012: owner's manual
Inverter is Xantrex ProWatt SW 2000: owner's manual
Batteries are Lifeline GPL-31XT AGM: data sheet

Although I can probably use an all-in-one unit charger/inverter, I already have this equipment so would like to put it in use.

If I am overthinking this solution, please advise.

 

[BentleyJ]

1. At point "A", what can I use to isolate the batteries? I assume I need this to prevent inter-battery current fllow?

Batteries connected in parallel do not need to be isolated. They should be connected together with bus bars or large, low resistance cables so they can self balance and reach voltage equilibrium as a set.
There is something odd with your charger, battery, inverter wiring diagram. The charger has 2 wires, + and -, there are 3 batteries each with a + and - terminal and the inverter has 2 DC input terminals + and -. You should use 1 Pos and 1 Neg bus bar to make ALL the connections.

2. Also at point "A" or after, what breaker(s) can I use to limit amps and damage to the inverter? On page 11 of its manual, it states a 250A ANL fuse but I'd rather use a breaker.

Each battery should have its own breaker sized at the lowest value based on either the maximum discharge current for that model of battery OR 40% of the total current the inverter is expected to draw.

3. How do I ground the charger and inverter (G1, G2)? The manuals only speak of DC ground, as in a vehicle. Can I just use the AC ground? Wire size?

In a stationary system all the metalic components (inverter enclosure, APC enclosure, charger, metal conduit and battery cabinet if its metalic) must be connected to ground. If the charger and APC have 3 prong cords then they are grounded when plugged in. You may have to run a separate ground wire to the inverter enclosure/chassis. Keep in mind this is not an automotive system so there is no frame that is part of the circuit and the negative side of the battery is NOT connected to ground.

5. If a subpanel is more appropriate here, feeding off one APC output, please advise on how to wire that up.

A small subpanel may be an option but since the stated amperage required is only 10A is overkill. I would consider getting something like a 12" x 12" x 6" junction box and installing a 3 position selector switch along with a couple of duplex receptacles.
Run the inverter input into position 1 and utility into position 2 of the selector switch and plug in all 3 devices.

 

[arthurm]

Thanks for the quick reply. To clarify:

1. The charger has 3 + outputs and one - output. I agree on a neg bus bar but not for positive, as they are independently controlled by the charger.

2. The inverter max input for fuse is 250A, Class T. So, 100A for each battery?

3. Charger has AC ground input but still has a DC ground screw. APC has two AC standard plugs as inputs. Inverter only has DC ground screw. According to info below I should attach both ground screws to the AC ground at the main?

Please review these from the manuals:

 

[BentleyJ]

Having the entire Neg DC battery bus tied to earth ground is somewhat unusual from my experience and it does seem to be optional based on geographic location and codes.

As far as the Pos side of the batteries being separated, it makes no sense because the 3 terminals must be combined together and attached to the single inverter positive which by definition is a parallel connection. Not sure what else to offer here.

 

[arthurm]

Yes, the three pos terminals are connected going to the inverter. That's why I asked if I should isolate them with...what, rectifier diodes? If so, I'm afraid the voltage drop from the diode may be too much.

Perhaps I should abandon all of this and go with an all-in-one charger/inverter...MPP Solar model?