Nothing Trips Faster and More Securely Than the SEL-T400L The SEL-T400L Time-Domain Line Protection is the beginning of a revolution in the electric power industry. Using a combination of time-domain and traveling wave technologies, the SEL-T400L is the only relay that trips as fast as 1 ms without compromising security. With just a handful of simple settings, the SEL-T400L has initiated a new age in protective relay history. This is transmission line protection, redefined. Click here to preorder your SEL-T400L today. SEL-T400L Time-Domain Line Protection