In 2002 Underwriters Laboratories issued six revisions to strengthen its GFCI standard, among them a more stringent voltage surge test and a reverse line-load miswire test. Yet for some safety watchdogs the changes weren't good enough. A year earlier, NEMA released the results of a study that found that as many as 12% of GFCIs were non-operational in some parts of the country. A formal survey of end-users had yet to be undertaken to determine how often they tested their GFCIs — and still hasn't — but anecdotal evidence suggested it wasn't often, causing the Consumer Product Safety Commission (CPSC) to call for a product that would factor out the consumer altogether. In particular, they wanted a GFCI that could test itself.
Glenn Murphy, a senior product manager at Hubbell Wiring Device-Kellems, heard the CPSC's call and started working. Now, three years — and several design configurations — later, he's ready to introduce his team's response to the CPSC's challenge. The Autoguard GFCI, which simulates a ground fault 1,440 times per day (that's once a minute) and immediately indicates if the unit doesn't respond properly, does just what the CPSC asked for by accounting for those who don't manually test their GFCIs. “The big key here is that it's known that folks aren't testing their units at home,” Murphy says. “If you asked anyone who had a GFCI at home when the last time was that they tested it, their response is typically, ‘Was I supposed to test it?’ not ‘Oh, I did it three days ago.’”
Naturally, the hardest part of designing a GFCI that tests itself is dreaming up the test process itself. Every 60 seconds a simulated ground fault current is applied to the receptacle's printed circuit board. If the unit detects a problem, the current will then be allowed to continue on to an electronic switch, which will fire a solenoid that opens the activation circuit. And because the test is software-based, Murphy says, there's no concern it will one day stop working.
When a receptacle does detect a problem and shuts down, a red LED on its face begins to flash to indicate end-of-life. The end-of-life indicator will be required when the latest revisions to UL 943 take effect in July 2006.
The self-test feature unit goes well beyond anything included in previous GFCIs Hubbell has developed, but it's actually not what the company had first envisioned when it started the project in 2002. Murphy says early iterations of the receptacle would physically open and close the contacts in order to test its trip function. When he surveyed customers and engineers, however, they pointed out that in some situations such a temporary loss of power — no matter how brief — could cause major problems for sensitive electronic equipment, including costly restarts. “The more we went out and spoke to utility providers and end-users, the more we heard people say, ‘You're going to give us a problem that we didn't have.’”
Because the self-test GFCI costs more than a standard unit, Murphy says the company is initiating the launch by targeting facilities where safety is a conscious, ongoing effort, such as institutions, hospitals, and prisons. Reaching the homeowner market where the manual test function is so infrequently used, on the other hand, will require a different approach, one that Murphy says will involve partnering with contractors to educate the public.
Higher surge-withstand — Current UL requirements call for a GFCI to shut down if it can't meet a 6kV, 3kA surge test. However, a series of heavy-duty MOVs in the Autoguard allow it to meet those requirements without shutting down.
Reverse-wire safety — In the event that the line and load to the GFCI are reversed, it won't provide power. In addition, it will not be able to be reset in such a situation.
Test and reset buttons — If the unit tests itself, why bother with the test and reset buttons at all? For one, UL requires them, and, Murphy says, they provide an added level of assurance for the end-user. “If you're walking by and want to know right on the spot, you can,” he says. “You could wait 60 seconds, but you don't have to.”