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Safety Relay Topic: Reason of Safety Relay is Required in Safety Circuit

FAQ No. FAQ02301

Question

Why are safety relays needed in safety circuits?

Answer

Safety Relays have forcibly guided contacts to prevent NO and NC contacts from operating at the same time during contact welding, which enables detection of contact welding in the Safety Relay itself. This can be used in building safety circuits. General-purpose Relays do not have forcibly guided contacts.

Sufficient care must be taken, however, because some circuits can be dangerous even with Safety Relays, depending on how the circuit is constructed. The circuit in Figure 1 below, for example, is dangerous because the power cannot be cut.

Build redundancy and a self-monitoring function that uses the welding detection function provided by the forcibly guided contacts into the circuit, as shown in Figure 2.

Fig.-1

Figure 2: Part of a G9S-301 Safety Relay Unit Circuit (Extract)

K1, K2, and K3: Safety Relays built into the G9S-301

Other Safety Relay FAQs

 What is the feedback circuit for in Safety Relay Units?

 What is the difference between an auto reset and manual reset?

 Why are two inputs required for Safety Relay Units?