Battery to Inverter Wiring

[xguard]

Looking at a 3000 Watt inverter that's to be installed in a home, not hardwired to receptacles or power panels. Just to run a few fans, tv, maybe coffee maker, etc. when power is out. What wire type is typically used between the battery and inverter? Or better yet what is required? I see many of these kits are sold with what looks like a automotive battery cable, not something typically installed in a building.

Question Deux. The instructions say to size the conductors from the battery to the inverter based on the inverter size, efficiency, and voltage. Using the example they provided I'd have:

(3000 W / (12 V x 0.9 eff)) x 1.25 = 347 amps.

That's a really big wire using the charts I typically use (310.15(B)(16). Since this isn't in conduit is the conductor allowed to be smaller than those installed in conduit (is this a free air situation?)?

One manufacturer sells 4/0 cable, and says it's "Typically used between the battery bank and a 2000 W or larger inverter." That doesn't make sense to me. They don't state the wire type or provide an ampacity..

Thanks for any help.

 

[tortuga]

Looking at a 3000 Watt inverter that's to be installed in a home, not hardwired to receptacles or power panels. Just to run a few fans, tv, maybe coffee maker, etc. when power is out. What wire type is typically used between the battery and inverter? Or better yet what is required?

Any chapter 3 wiring method , if your on the 2020 NEC see 480.12 for battery interconnects

I see many of these kits are sold with what looks like a automotive battery cable, not something typically installed in a building.

Question Deux. The instructions say to size the conductors from the battery to the inverter based on the inverter size, efficiency, and voltage. Using the example they provided I'd have:

(3000 W / (12 V x 0.9 eff)) x 1.25 = 347 amps.

How many kwh is the battery bank? What type of batteries will be used? If its over 1 kwh article 706 applies, requiring it to be a listed system.
That 1kwh seems really low,
if say you say a typical lead acid 'deep cycle' battery over 83 Amp hour, and an inverter it needs to be a listed ESS system.

Now as soon as this is not attached permanently to the house the NEC/AHJ has limited if no say.


That being said many years ago, in the days of modified sinewave, I had two 6 volt lead acid batteries connected to a used Trace 3kw inverter/charger on a cart in my shop for use in power outages, the 12 volt battery pack had a capacity of 110 Amp hour
I took the 1/3 C rate of the battery to size the conductor from the battery to the inverter, or about 40 amps.

That's a really big wire using the charts I typically use (310.15(B)(16). Since this isn't in conduit is the conductor allowed to be smaller than those installed in conduit (is this a free air situation?)?

One manufacturer sells 4/0 cable, and says it's "Typically used between the battery bank and a 2000 W or larger inverter." That doesn't make sense to me. They don't state the wire type or provide an ampacity..

The for better or worse the NFPA is trying to put the kabbash on electrician designed energy storage systems by requiring a blanket listing 706.5.

Thanks for any help.

 

[FionaZuppa]

3kw is a peak value of the inverter, or is that a rms value?
Peak or rms, will dictate the wire size.
You also have a diversity factor to consider.

I would opt to get 24v or 48v inverter (48 being preferable).

 

[xguard]

Any chapter 3 wiring method , if your on the 2020 NEC see 480.12 for battery interconnects


How many kwh is the battery bank? What type of batteries will be used? If its over 1 kwh article 706 applies, requiring it to be a listed system.
That 1kwh seems really low,
if say you say a typical lead acid 'deep cycle' battery over 83 Amp hour, and an inverter it needs to be a listed ESS system.

Now as soon as this is not attached permanently to the house the NEC/AHJ has limited if no say.


That being said many years ago, in the days of modified sinewave, I had two 6 volt lead acid batteries connected to a used Trace 3kw inverter/charger on a cart in my shop for use in power outages, the 12 volt battery pack had a capacity of 110 Amp hour
I took the 1/3 C rate of the battery to size the conductor from the battery to the inverter, or about 40 amps.



The for better or worse the NFPA is trying to put the kabbash on electrician designed energy storage systems by requiring a blanket listing 706.5.

Right now it's just one battery. 12 volt sealed acid battery. 200 amp hour.

 

[LarryFine]

What's the maximum foreseeable load and conductor length?

 

[tortuga]

Right now it's just one battery. 12 volt sealed acid battery. 200 amp hour

Then using Peukert's law I think thats a 1.9kW battery pack
12 * 200 = 2400 /1000 * .8 = 1.9

https://en.wikipedia.org/wiki/Peukert%27s_law

I'd go with #4 copper, you could fuse the DC feeder at 70A.
If you were pulling 35 amps at 12V you'd get about 3 hours per charge.

Peukert’s Law – how long an amp hour battery will last under a given load – BatteryGuy.com Knowledge Base

 

[xguard]

What's the maximum foreseeable load and conductor length?

1500 Watts. 3 feet one way distance.

 

[LarryFine]

That's only (1500/12) 125 amps and a short distance, so I'd probably use #1 or 1/0 copper.

You could probably use pre-assembles battery cables from an auto-parts store.

 

[tortuga]

1500 Watts. 3 feet one way distance.

For a single lead acid battery 200AH they will be lucky to get an hour with a 1500W load.
But if they have mostly LED lighting and an newer fridge, they might do pretty good for a day.

 

[FionaZuppa]

200AH 12v AGM for 3kW inverter, seems a bit undersized to me. At best you get minutes of run time at 3kW.

 

[xguard]

For a single lead acid battery 200AH they will be lucky to get an hour with a 1500W load.
But if they have mostly LED lighting and an newer fridge, they might do pretty good for a day.

1500 W is a coffee maker, conservative estimate. Won't need to run long. A couple fans, small tv, maybe fridge would be the typical loads.

 

[xguard]

My I guess general question is whether inverter or batteries should drive the wire size.

 

[tortuga]

My I guess general question is whether inverter or batteries should drive the wire size.

I'd say the battery, as thats the source. If as you said its not going to be connected to any permanent wiring of the structure, take Larrys suggestion and use a automotive battery cable. I'd make a plywood box for the battery and incorporate a DC fuse or breaker.

 

[retirede]

My I guess general question is whether inverter or batteries should drive the wire size.

I’d say the inverter.
Don’t we always size conductors based on the load?

A 100 AH battery could deliver 1000A under short circuit conditions. It would
Make no sense to size conductors for that.

 

[ggunn]

I’d say the inverter.
Don’t we always size conductors based on the load?

A 100 AH battery could deliver 1000A under short circuit conditions. It would
Make no sense to size conductors for that.

I think I would put an inline fuse at the battery sized to the max input current of the inverter and size the wire to the fuse.

 

[tortuga]

Normally i'd agree but this is a tiny tiny system, that battery could not sustain a 3000 watt load for more than a half hour.
That inverter is more likely to damage the battery by overloading it than the other way around.
I'd do some more research on the battery manufacturer specs, but I'd typically protect a lead acid battery at some fraction of its 'C' rate.

 

[retirede]

Normally i'd agree but this is a tiny tiny system, that battery could not sustain a 3000 watt load for more than a half hour.
That inverter is more likely to damage the battery by overloading it than the other way around.
I'd do some more research on the battery manufacturer specs, but I'd typically protect a lead acid battery at some fraction of its 'C' rate.

The system design should dictate that the battery be capable of powering the inverter at full output. If it can’t, the battery selection was incorrect.

Given that, the conductors should be sized based on the converter load, and the OCPD sized to protect the conductors.

Beyond that, some type of BMS may be in order to prevent battery damage once its charge level drops, but that should not be the job of the OCPD.

 

[LarryFine]

Normally i'd agree but this is a tiny tiny system, that battery could not sustain a 3000 watt load for more than a half hour.

But we must size conductors for short-duration currents.

 

[tortuga]

The system design should dictate that the battery be capable of powering the inverter at full output. If it can’t, the battery selection was incorrect.

Agreed and the battery easily can power full output for a brief time.

Given that, the conductors should be sized based on the converter load, and the OCPD sized to protect the conductors.

OK, thats pretty much what 710.15(B) in my 2020 NEC says, size the conductor to 100% of the nameplate.

So he could probably use 310.17 free air and a 2/0 CU battery/welding cable.

Beyond that, some type of BMS may be in order to prevent battery damage once its charge level drops, but that should not be the job of the OCPD.

I never thought of a BMS for old lead acid nor seen one, but not a bad idea.