The most common item associated with electrical safety is the Ground Fault Interrupter (GFI) found on electrical outlets in bathrooms and areas where water is present. These GFIs designed for terrestrial use may not be adequate for use with electrical equipment used by the divers. There are two types of electrical safety devices specifically designed for diver applications. They are the 2.5-kVA Ground Fault Detector (Standard and Arctic versions) and the Underwater Electric Field Detector (UEFD).
• 2.5-kVA GFD (Standard and Arctic Version)
A GFD and shutdown system is available to protect divers from electric shock hazards. Shown in Figure D-6, the GFD monitors the insulation resistance of the load circuit being used by the diver. When the ground fault resistance drops to a predetermined level, a trip signal within the unit is sent from the control unit to a circuit breaker and all power to the output is shut off from the load in 10 msec or less. This same signal is delayed a few milliseconds and then fires an electrical circuit that places a short circuit across the output. This delay allows the circuit breaker to open under normal current loads. When the triacs fire, they provide a short circuit path to dissipate any stored energy in the load circuit, such as energy stored in a long cable due to cable capacitance.
There are two versions of the GFD available, the standard and the arctic version. The following is a brief specification of the GFDs:
Standard Version Arctic Version
2.5-kVA output power Same
115 VAC, 60 Hz Same
20 amperes max Same output current
Shutdown time in Same
10 msec or less Weight (pounds):
78 43 Dimensions (inches): 10.9x7.6x14.4 10.6x8.0x14.3
Both units incorporate the same design. The arctic version uses components that can operate at a temperature range of -40 to + 140°F. The standard version operates in a temperature range of +30 to +95°F. The arctic version is also lighter because it uses a lightweight isolation transformer. Both units meet the AODC safety standard for allowed fault currents and shutdown times and are approved for Navy use.
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