![]() ![]() Just shorting the aerial created a loud bang, and an arc flash big enough to be seen through the plastic switch plate before the MCB tripped. If you connect to L or phase, rather than Sx, you are defeating a safety fuse when the switch is closed. this is a multi-layer PCB, so you are seeing several traces together:įibaro fgd-212 pcb topsides 1174×740 302 KB The other side of the PCB (with the Sigma module) is very black due to the energy of the sudden failure. Here’s a picture of the topsides of the dead FGD-212 after stripping the board for parts - the blue disc is likely a polyfuse or similar protective component. The aerial cable chafed after having to reset and re-pair the FGD-212 several times when diagnosing what turned out to be firmware issues in pre-v3.5 software. The FGD uses a capacitive dropper power supply, so is still referenced to mains voltage, so if the aerial cable shorts to the CPC it lets the magic smoke out violently. I am an electrical engineer, but still managed to blow a FGD-212 when screwing the face plate on a 25mm UK metal back box, which is connected to the CPC. ![]() Should the dimmer develop a fault (like the power triac welding itself a dead short, or the single insulated aerial wire being chafed and connecting to the circuit protective conductor), connecting Sx directly to phase bypasses the FGD protective fuse and increases the risk of bad things happening. ![]() Measuring between the L and Sx terminals does indeed show a low resistance, but this is misleading. The protected L phase then connects to the Sx terminal. The reason is simple - the L phase connection connects directly to what looks like a polyfuse, or similar protection device which disconnects the dimmer should a fault occur. ![]()
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