Re: TVSS installation
Jason it has to do with the SVR rating. The Suppressed Voltage Rating (SVR) is a value that is assigned to an SPD by UL to indicate its protective characteristics. Each mode of the SPD is subjected to three impulses of a 1.2/50ms, 6kV voltage waveform and an 8/20ms, 500A current waveform. The resultant ?measured limiting voltage? is measured at the ends of 6? leads extending from the terminals of an integrated product or 6? extending from the enclosure of a wall-mounted SPD.
Well designed units will have a SVR rating of 330 volts (assuming a single phase service) with 6-inch leads. However once you go beyond the 6-inches the SVR value rises significantly there by nullifying the unit. As a rule of thumb you can add 100 volts to the SVR per every 1-inch of lead length. So if you were to have lets say about 1-foot lead length, you would raise the SVR to around 1000 volts, defeating the purpose of the device.
I think it becomes pretty clear that most wall mounted TVSS add-on units are rendered usless by the installation. The more efective method is to install panels with TVSS built-in the panel where the SPD's are bolted directly onto the bus.
[ December 28, 2005, 11:49 AM: Message edited by: dereckbc ]
