Ground Fault Protection

What is ground fault protection and do you really need it?  A ground fault is an abnormal condition in which current is traveling along the ground wire, which is normally a non-current carrying conductor.  This means that something in the Solar Array is shorting out, causing the current to flow into the ground wire.  If the condition is left to remain, the point where the short is happening will eventually fail causing a fire.  This can be seen in two recent devastating fires caused by Solar Array Ground faults. (Bakersfield, CA and Delanco, New Jersey)

Now is where the question arises, doesn't a circuit breaker of fuse remove the ground fault?  In a ground fault, a circuit breaker of fuse may not open clearing the ground fault.  The reason behind this is that in order for a circuit breaker or fuse to trip, the current flowing through that device must be higher than the devices rating.  For example, a 20 ampere circuit breaker needs over 20 amperes to trip.  In a ground fault there may not be enough current flow to trip the breaker.

The problem with ground faults is that not all of the current is flowing into the ground wire.  There is always a certain amount of resistance that happens in a ground fault that reduces the amount of possible current.  This means that even though there is a fault, it is not high enough to trip the circuit breaker of fuse that is normally in the system.  Therefore, ground fault protection is added to the circuit.  In general, a ground fault protective device is set to trip as low as 1 ampere.

A ground fault protection device will disconnect any loads on the Solar Array.  By disconnecting the loads, there is no longer a flow of current stopping the short circuit from persisting.  Now the Solar Array is brought to a safer condition until the short can be removed from the system.

Now for the million dollar question, do you need one?  If you are planning on putting solar panels on your dwelling, the answer is yes.  A ground fault protective device will help prevent your house from catching fire due to a ground fault.  Remember, ground faults generally do not trip your normal circuit breakers or fuses.  On the other hand, if your solar panels are going to be ground mounted, this isn’t a requirement, but still a good idea.

Having a ground fault protection device installed in your Solar Array is like having insurance.

Car Fuses and Solar - Not a Good Mix

Car Fuses and Solar – Not a Good Mix

When it comes to protecting your solar investment, it couldn’t be easier than adding a fuse.  In the event that the current in your solar array goes too high, the fuse opens up.  This removes the current draw on the system and protects it from further damage.  The problem comes from the fact that not all fuses are right for this application.  In this article, we are going to discuss why using just any car fuse isn’t a good idea.

I’ve seen a lot of talk about using car fuses in solar applications.  Why wouldn’t you use them?  They’re rated for up to 32V of DC electricity.  Most small off-grid solar arrays are running at 12V to 24V of DC electricity.  All of our requirements are met so far, aren’t they?

Truth be told, our requirements are not met.  A key component to fuse sizing is the AIC or Amperage Interrupt Capacity.  During a short circuit event, a solar array may produce amperage in the thousands.  This is especially true when talking about the batteries.  It is not uncommon for batteries to have short circuits in the 5000 amp range.  To keep it simple, the AIC rating tells you how much current the fuse can withstand.  If the short circuit of the solar array exceeds the AIC rating of the fuse, the fuse will fail to operate properly, causing damage to the array.

A standard car fuse typically has an AIC rating around 1000 amps.  During a short circuit event, this fuse will fail.  This is why there are specific fuses created for solar arrays.  An example of this is the KLKD Series from Littlefuse.  The KLKD series fuse can handle up to 600V DC with an AIC rating of 100,000 amps.  If you still choose to use a car fuse, be sure to use an ANL type fuse.  An ANL fuse will generally have an AIC rating of at least 2,700 amps.

Protect your investment, use the right fuse.