Square D load center surge protective devices, SDSA2040, are easy to install plug-in units that install as quickly as a standard circuit breaker. The surge suppressors use two pole spaces in a QO or Homeline load center, or NQ panelboard. US and Canadian UL Listed as Type 2 SPD to the UL 1449 standard. Complies with requirements of NEC Article 285, CSA 233.1-87, and CSA C22.2 No. 8- M1986 as appropriate. Meter Socket has no By-pass. This listing is for Each.