The Omron D4SL-N4HDA-D is a guard lock safety-door switch — a mechanical lock that holds a guard closed until the solenoid releases it. It's the part that keeps a machine from cycling open or an operator from opening a door mid-cycle. The built-in switch configuration is 3NC + 2NC, meaning five contacts total, all normally-closed for fail-safe monitoring of the guard position and lock status. The solenoid releases on 24 VDC, and an orange LED indicator confirms power is present at the coil. The metal head and M20 conduit outlet suit industrial environments where the switch sees physical impact and needs a standard metric gland entry. Connection is via terminal block inside the housing.
No official successor has been designated for the D4SL-N4HDA-D. If you are holding this on a BOM for an existing machine, the current part is the right one to order. There is no pin-compatible replacement to evaluate — the mature status means Omron intends to keep supplying this exact configuration.
What the contact count means for your safety circuit
Five normally-closed contacts (3NC + 2NC) give you flexibility in wiring the safety chain. Typically, one set monitors the guard position, another confirms the lock bolt is engaged, and the remaining contacts can feed back to a safety PLC or relay for diagnostics. All NC means the circuit fails safe — if a wire breaks or the switch loses power, the contacts open and the machine stops. The mechanical lock / 24 VDC solenoid release (code A) means the door stays locked when power is removed. You apply voltage to release the lock. That is the standard fail-safe arrangement for access guarding — the guard cannot be opened in a power-loss situation unless you manually override the release key.