Frequent Questions: Wiring

What is a series/parallel connection? 
A series connection is when you connect the positive of one solar panel, battery, etc., to the negative of another, leaving you with one free positive and one free negative.  With series connections, the voltages of the items connected in series sum [18V + 18V + 18V = 54V], while the current averages [(5A + 5A + 8A)/3 = 6A]. 

A parallel connection is when you combine the positive leads of solar panels, or batteries, etc. to make one lead and combine the negative leads to make another lead.  With parallel connections, the current from each of the items sums, while the voltages average.

If you have two six volt batteries and want to make a 12V battery bank, you would connect the two batteries in series.

If you have four six volt batteries and want to make a 12V battery bank, you would connect the batteries in two parallel groups of two batteries in series.

When a solar panel gets shaded, its current drops and its voltage remains roughly the same.  This is why we recommend parallel connections for solar panels.  In a parallel connection, a drop in current without a drop in voltage from one source will not have an effect on the other sources connected to it.  In other words, with solar panels connected in parallel, partial shade on one panel will not bring down the other panels in your system.

What gauge wire should I use? 
All of our SunRunnerTM System Cores come with an appropriately sized wire harness to minimize line losses and maximize value.  We use 10 gauge cable from the solar panels to the combiner box.  Since the panels in our systems are always connected in parallel you can assume about 6 amps per 100 watts of solar panels.  For cable run lengths typical in RV applications, we recommend 10 gauge wire for 20 amp systems up to 4 gauge wire for 40 amps systems.  If your system calls for more than 40 amps of charging current you will use multiple wire harnesses to multiple charge controllers. 

The cables going from the battery bank to the inverter have to be much thicker because they have much more current flowing through them (up to 250A in some situations).  These cables are typically limited to 10 feet in length and a 2/0 cable is most commonly used.

How should I route wires from my roof? 
With the majority of our installations, cables go from the solar panels to a combiner box (or boxes) on the RV roof.  Depending on your rig, these combiner boxes may be installed near existing roof penetrations, like vents, or a new roof penetration will have to be made underneath the combiner box.  The placement of these combiner boxes and cable routes is always planned very carefully before any holes are made.  An installer will want to keep cables as short as possible while maintaining structural integrity and preserving the vehicle’s aesthetics.

Do I need fuses or breakers?  Where? 
You aren’t going to get a surge from solar panels (unless maybe there was a very unusual solar flare, in which case you have bigger issues to worry about.)  Because of that, our kits do not use fuses between the panels and the charge controller.

To protect the charge controller in the event of a short-circuit or some other unforeseen event, we recommend a fuse or breaker on the positive line between the charge controller and the battery bank rated at the maximum current of the charge controller.

We also recommend a fuse on the positive line between the battery bank and the inverter.  To determine the size of this fuse, take the wattage rating of the inverter, divide it by 12 and multiply it by 1.25.  For example, a 2000 watt inverter would have a rating of about 200A (2000 / 12 x 1.25 ≈ 200).

Do I need grounding? 
Since your RV moves down the road on rubber tires, a grounding rod obviously isn’t going to be a part of your system.  Our systems are designed in such a way that a lack of grounding will not affect performance.