I recently had a conversation with a customer who was insistent that 50A DC flowing from the roof mount combiner box to the charge controller was dangerous. But, that isn’t at all the case when you consider the low voltage.

The Physics:


Voltage is pressure, or the driving force behind electrons and Amperage is how many electrons pass through an area per second (1A = 6,241,000,000,000,000,000 electrons per second). While it is true that amperage is what kills you, in order to have high amperage passing through something with a high resistance (flesh) it needs to be driven by a high voltage.

Consider this equation: Voltage / Resistance = Amperage

In this 50A scenario with a combiner box through roof cables and a charge controller to a battery bank, you have 18V / 0.36Ω = 50A. If you get your body in the way, you add a huge resistance, lets say it is roughly 10,000Ω. This resistance causes the panels to operate at a higher point on the IV curve which drives their voltage near Vsc = 22V. Now the equation looks like 22V / (10,000Ω+0.36Ω) = 0.0022A. Suddenly we have a situation where the amperage is actually very low.

Now imagine you are getting shocked by a taser at 50,000V. Now you have 50,000V / 10,000Ω = 5A. This is dangerous.