technical article from Blue Sea Systems
The standard under which all reputable manufacturers of battery switches rate their products is UL Standard 1107. This standard rates switches for 5 minute and 1 hour time periods.
A problem with these ratings is that marine battery switches are commonly used in the engine starting circuit and neither the Continuous nor the Intermittent Rating represents the conditions a switch endures in the engine starting circuit, typically for 10 seconds or less, but at very high currents. The ABYC Standards have propagated the problem by requiring that a switch in the engine cranking circuit have an Intermittent Rating equal to, or greater than, the highest engine starting current. Peak starting currents can easily spike to 1500 amperes, yet there are almost no marine battery switches rated at this Intermittent Current.
When starting the engine there is a large current spike of approximately ¼ second duration required to begin the rotation of the engine. This phase of engine starting is called the Inrush Period. Once the engine is rotating, but before it starts there is another period averaging 9-3/4 seconds, called the Cranking Period. These two Periods combine to make the Engine Cranking Cycle.
Below is a screen capture from our test equipment showing the inrush spike and then the cranking current versus time from a diesel engine in one of our tests. Each square vertically represents 200 Amps and each square horizontally represents 0.2 seconds.
Blue Sea Systems made observations that the typical boater conducted from 1 to 3 repeats of the Engine Cranking Cycle in order to start their engine.
Based on this research, Blue Sea Systems established the Engine Starting Standard. This Standard consists of 10 Engine Cranking Cycles with each cycle consisting of an Inrush Current Spike of ¼ second duration, a Cranking period of 9-3/4 second's duration, and a 2 second rest period for a total of 120 seconds. This is representative of the load imposed on a battery switch in the starting circuit under very difficult starting conditions. Generally, battery capacity limits will not allow more than 10 repeats of the Engine Cranking Cycle.
Blue Sea Systems battery switches, in addition to being tested to UL 1107, are also tested to the Engine Starting Standard by a United States Coast Guard certified Nationally Recognized Testing Laboratory (NRTL).
As of this writing, Blue Sea Systems is the only battery switch manufacturer using the Engine Starting Standard, however, the Engine Starting Standard is being used as the basis for a revision of the ABYC Standards. Once this revision is published it will create a common standard for battery switch and engine manufacturers to reference so that boater's can select the correct battery switch for their needs.
Original article from Blue Sea Systems