Inverter & Battery Cables

Make the Right Connections for Best System Performance
Intermediate

Inside this Article

Copper battery cable
Fine stranded, UL listed copper battery cable.
4/0 UL battery cable
This fine-stranded 4/0 AWG, UL-listed cable is designated as THW, making it appropriate for battery–inverter cabling.
Welding cable vs. battery cable
Welding cable (top) and UL cable (bottom) look very similar, but welding cable is not NEC-approved. Be sure to carefully inspect the markings before you make a purchase.
Copper cable lugn
A bare copper closed-end-type lug made for 4/0 cable.
Tin-plated battery cable
A tin-plated copper lug is crimped onto its cable, protected with heat-shrink tubing, and marked for polarity.
Tinned and crimped lug.
A crimped, open-ended lug.
Pulled out, poorly installed battery cable
A tug on this poorly crimped cable pulled it out of its lug. Good crimps are necessary for safety and low-resistance connections.
Heat shrinking
When heated, heat-shrink tubing with sealing glue inside will keep out corrosive fumes and support the fine wire strands.
Quality crimping tool
Using the right crimping tool for the cable size and lug type is crucial for making a good mechanical connection between the wire and lug.
Components & finished cable
The cable components before (top) and after (bottom) assembly, crimping, heating the shrink-tubing, and labeling with colored tape.
Copper battery cable
4/0 UL battery cable
Welding cable vs. battery cable
Copper cable lugn
Tin-plated battery cable
Tinned and crimped lug.
Pulled out, poorly installed battery cable
Heat shrinking
Quality crimping tool
Components & finished cable

Poor-quality and improperly installed battery and inverter cables can cause problems in the function and safety of a battery-based system. Here’s how to select the right cables and install them correctly, for optimal system performance.

There is a perception that battery and inverter cables are expensive—and it is a tempting place to cut costs—but buying cheap cables can result in significantly reduced performance of the battery bank and inverter(s). It’s a lot like putting cheap tires on a high-performance car—you save some money, but you don’t get the performance and safety you might need. The common problems seen with cabling in battery-based renewable energy (RE) systems are typically due to low-quality cables and hardware, in combination with poorly made crimps and connections.

You can purchase preassembled cables or have them made to order, but you can also build them yourself. The details are important—battery cables and their ring terminal connectors (also called “lugs”) carry high current and are used in harsh environments where they can be exposed to sulfuric acid, hydrogen gas, high temperatures, and dissimilar metals.

Cable Ampacity

For battery/inverter RE systems, the largest conductors in the system are usually the ones connecting all of the batteries together and then exiting the battery box to connect to the inverter. Since nearly all battery-based inverters operate at 48 VDC or lower, the cables need be large to handle high currents without significant losses. Sizing of these cables is based on the battery voltage, the inverter’s continuous amperage rating, and the length of the cable. Commonly, these cables are either 2/0 AWG (acceptable for use with a maximum of 175 A breaker or fuse) or 4/0 AWG (acceptable for use with a maximum of 250 amp breaker or fuse), but will need to be individually calculated. For example, the installation manual for OutBack Power Systems’ VFX3524 (3,500 watts; 24 VDC) inverter recommends 4/0 AWG for a battery-to-inverter cable length of 10 feet or less. This size cable would result in a voltage drop of less than 1% at full rated output of the inverter, resulting in 34 watts of losses in the 10-foot-long positive and negative conductors. Shorter cables would reduce the losses proportionally. 

Cable Types

High-quality battery/inverter cables are made of fine-strand copper conductors with a flexible insulation covering and are available from manufacturers such as Polar Wire Products or Cobra Wire & Cable. Although finely stranded cables are not required, they make installing and servicing the system easier and reduce stress on the battery and inverter terminals. All high-quality battery cables are made with UL-listed wire and include a National Electrical Code (NEC)-required designation, such as RHW, THW, or THHW.  

Lower-quality battery cables are often made from automotive or welding conductor cable. This type of cable is cheaper and easier to obtain—but is not acceptable by the NEC since it is not UL-listed or marked with the NEC wire type. While some types of welding cable have a UL listing, they have been approved using a different set of UL standards and tests, and are not marked with the required NEC wire-type designation.

Comments (6)

ideas2014's picture

nice article really but i wish to rasie question about the cable length from batter to inverter ,,this is any equation for that to calculate ,,i have project case that need longer cable more than 10 feet ,,,any suggestions pls share with me

Michael Welch's picture

Hi there. I can help you calculate cable size, but I need the following additional info:
1. The combined length of the positive and negative battery cables.
2. The DC system voltage
3. The size of the inverter in watts.

ideas2014's picture

thanx michael for your help
1- the combined length for + ,- is 20 meter
2- DC voltage 48
3- Inverter size is 10 kw
do u any recommendtion of reliabel inverter fro grid tie Battery based according yr experinces and practices
thanx

Michael Welch's picture

I am sorry, but that is not going to work out. You need to keep the inverter cable lengths to under 10 ft. Figure out a way to move the inverters closer to your battery.

There are some great battery-based inverters out there. Here's a good starting place for your research:
www.homepower.com/162.44

ideas2014's picture

thanx a lot and sorry for my reply i was travelling ,,,so u mean no possibility at al to tackle this problem ?

Michael Welch's picture

Not that I know of. The only answer is to move the inverter closer to the batteries.

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