How safe are your surge suppression devices?

According to UL, maybe not very safe

Back in the day, when I was first working on SCADA systems, we put LPXes on the telephone line connections (yep, leased lines...long time ago). LPX was phonespeak for Lightning (or Line) Protection Devices, and they were usually big gas discharge tubes that would direct the surge from a lightning strike to ground. They didn't work all that well. In fact, several wags I knew used to say that the purpose of the circuit board in the RTU was to protect the LPX and keep it from failing. Wryly true, we often found perfectly good LPX units with slagged, burned and melted RTU circuit boards behind them. So I was very interested when I heard that a company called Raycap, who makes a set of SSDs, wanted to come in and give Control a briefing. We were joined by Dr. Kostas Samaras and Ted Arbuckle, from Raycap. The Raycap logo looks a lot like the old Raychem logo, before the Tyco buyout, and it should. Raycap grew from being the local distributor in Greece for Raychem products to buying the surge suppression technology that Raychem made, in 2002. Raycap is a $50 million per year company, and the Electrical Protection Systems part of the business is worth $10 million of that. Surge suppression, or transient voltage surge suppression (TVSS) devices have been around for years, and come in three basic flavors: spark gaps, which handle huge voltages and currents, but have horrible let-through, silicon avalanche diodes, or SADs, which also have bad let-through, and the more common MOV, the metal oxide varistor. MOVs, commonly made of ZnO, are referred to, again waggishly, as a "planned point of failure." Like my LPX example from the 1970s, MOVs often exist to be protected by the circuit board that explodes instead. Many MOV devices consist of large numbers of parallel MOVs-- often referred to as "varistor math." If one varistor will handle n kA, 20 varistors in parallel will handle 20n kA. Not. What actually happens is that the failure rate from aging and stressing is enough of a variable that one or more of those "parallel" varistors will fail before others, causing big smoke and flames. In fact, MOV devices are often protected by fuses. Dr. Samaras showed us a sample parallel varistor assembly which was rated for 100 kA, and protected by a 30A fast blow fuse. I dunno about you, tovarisch, but there's something wrong with that picture, I think. SSDs and TVSSes have had to comply, in the United States at least, with UL 1449. UL 1449 was revised in February of this year, and the 2nd Edition is substantially more stringent than the previous version. There are dozens of TVSS devices that could be sold as "UL Listed" until February 8th, 2007, which are now sold without the UL fig leaf. In fact, it is illegal to install a non-UL Listed device in a high voltage installation in the United States, but, when I asked Ted Arbuckle if his competitors were telling their customers that the products "used to be UL Listed" but now are not, he just laughed at me. So what did Raycap do? Samaras said, "We decided to develop a new kind of SSD, one that would not produce fire or flame, never expose the load to the transient, and have a life expectancy and reliability greater than the equipment it is protecting. We wanted a device that would protect the load at all times."Strikesorb modules Arbuckle said, "We wanted to exceed UL1449, 2nd edition, and IEC 61643-1 as well. We wanted to make an MOV as good as gas discharge tubes and SADs. We wanted a device that would absorb 1000A for 7 hours, at a maximum temperature of 45 degrees C. That would exceed the requirements of UL1449." "We call it Strikesorb," Arbuckle said. Here's how they did it: instead of ganging multiple varistors, Raycap designed single, huge MOVs that are thick and wide (80 mm diameter, for example, and approximately 5 mm thick) and designed a straight through path to ground or neutral. "Lightning likes straight paths," Samaras said, "and a typical MOV has three 90-degree bends. We wanted a straight path."cutaway He went on, "and we designed for an MTBF of 25 years in a harsh electrical environment. After developing data from the more than 250,000 units installed to date, Samaras said, "we are pleased to find that our design MTBF has stood the test."Samaras said that the module can even be installed directly behind a main breaker. So what does this mean to the end user? First, you better check to see how many spare MOVs of the old type you have in stock, because when they're gone you may not be able to buy new ones. Second, I'd recommend taking a look at equivalent specs between the SSDs you presently (I almost said currently, but that would have been a very bad pun, now wouldn't it?) use and the requirements of UL1449 2nd Edition. While you're at it, compare what you're using now with Raycap's product. You may find something interesting. Why, I asked, didn't their customer list include more petrochemical, oilfield, SCADA and water/wastewater customers? "I came out of the telecomms industry," Arbuckle said, ruefully, "and I started by going to the companies I knew. That's why we have major installations at ATT/Cingular, Rogers-Canada, and others, and why we have 80% of the FAA's business, too." Samaras said, "We're hoping you'll show this product to those other markets so we can get more coverage and more interest from them as well." Okay, show me a very interesting and novel product, and I'll do just that. Done.