How are safety functions lost in a circuit?
Note: Safety functions will be lost by a single failure, such as a short-circuit failure in the input wiring. <Fully Proven Parts and Safety Principles> (Refer to safety category 1.)
When to use safety relays and safety circuits?
By using safety relays as examples, I will show you when you should apply safety to your machine. A safety relay is a great and simple illustration of a safety circuit and how it works. It is very important to understand that safety relays are here for a reason. And that reason is to eliminate or reduce risks.
When to use supplementary devices in circuit protection?
In general, branch circuit-rated devices protect the wires, and supplementary devices provide additional protection, but they are not sufficient to protect the equipment or load exclusively. Supplementary devices often are used for lower load equipment, internal loads, or as a simple additional disconnecting means.
Which is safety circuit design is required in control engineering?
Quite often, when a “B” level standard makes a significant change (like NFPA 79, 2002 adopting safety PLC technology), “C” level standards may or may not be reconciled and/or in sync regarding how safety circuits “shall” be designed. So, the question is asked: Which safety circuit design is required?
By using safety relays as examples, I will show you when you should apply safety to your machine. A safety relay is a great and simple illustration of a safety circuit and how it works. It is very important to understand that safety relays are here for a reason. And that reason is to eliminate or reduce risks.
What are the NEC rules on industrial controls?
The Code also implies in 430.72 (A) that motor control circuits tapped from a motor branch-circuit, short-circuit, and ground-fault protective device (usually fuses or a breaker) need not be protected per the requirements of 725.23 because these circuits aren’t considered to be Class 1 circuits and the requirements of Art. 725 don’t apply ( Fig 1.
How are overcurrent protective devices used in control engineering?
“The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit.”
What does Category 1 have to do with safety relays?
Machinery Safety 101 has written a great series of articles about interlock architectures and the five control categories. You might ask what this standard has to do with safety relays. The reason for this is that, first of all when using category 1 you have to use “well-tried components and well-tried safety principles”.