Challenge: Detecting low level AC current without adding a physical connection and added burden to the circuit is relatively easy and quite common. In North America, all electrical outlets mounted in wet environments are required by codes to be protected with ground fault relays to save lives by cutting the power when a very small fault to earth is detected. If an AC current of 5 to 7mA passes to the ground, a circuit breaker or the contacts in the power receptacle open before electrocution can occur. Most electrical heating elements must also be protected to keep equipment from damage in the event of a ground fault.
Trying to detect the same fault condition in a DC circuit with a floating ground is not as simple. With the proliferation of photovoltaic panels and other alternative power sources, the need for ground fault relays in DC powered systems is critical. With solar panels or battery-operated systems, the positive and negative conductors are insulated to contain the voltage potential between each and also to earth. When connections get wet, this insulation becomes compromised and current can pass to earth. Water is the most common cause of DC fault current, while deteriorating insulation and contaminants on battery housings are additional factors. Since DC current leakage to earth presents a dangerous situation, detecting a fault before it causes harm is essential. Ground fault detection without adding impedance to the monitored circuit is the safest approach.
Solution: NK Technologies developed an innovative solution to DC ground faults that employs the same zero-sum principles as its AC offerings. The DG Series DC ground fault relay, used with loads drawing 50 amps or less, can be incorporated at a fraction of the cost of the typical and cumbersome hardwired installations.