Which code represents the normal switch operating relay?

• A. Nwr
• B. Nwz
• C. Nx
• D. Os

Answer: (A)

In signaling maintenance codes, each device is labeled with a concise mnemonic that conveys three things at a glance: the normal operating state, the type of device, and its function. For a relay that operates a switch, the intended three-letter code combines Normal, Switch, and Relay. The Normal condition indicates the default electrical state; the middle letter identifies that this is a switch-related device; the last letter marks it as a relay. Put together, Normal-Switch-Relay becomes Nwr. This exact combination clearly signals you’re dealing with the normal switch-operating relay, which is why it’s the best match. The other strings would imply a different device or omit the relay aspect, so they don’t correctly describe the unit in question.