Testing a Smoke Detector Circuit In this video I demonstrate using a Megger MFT how to carryout the continuity of the cpc, polarity and insulation resistance tests for this smoke detector circuit (likewise this could be a CO detector). This circuit is wired in FP200 and MICC cable (Pyro or MI Cable) via a fuse connection unit. This circuit is similar to one in unit 107 of the City and Guild 5357. The same testing procedure will be required when testing a CO detector during AM2, AM2S and AM2E end