I recently had an engineer ask me about AIC rating on a standard low voltage relay panel used for switching fixtures on & off. My understanding of the code is the relay is not considered a circuit protection device, like the circuit breaker, but a component of the circuit such as a toggle switch or time clock. I also was told by the factory I rep there really is no UL requirement or guidlines for switching relays to have an AIC rating. Does anyone have any insight into this?
Low Voltage lighting relay panels AIC Rating
- Thread starter sesco
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- Wisconsin
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- PE (Retired) - Power Systems
Re: Low Voltage lighting relay panels AIC Rating
In essence 110.9 says all devices must be rated for the maximum current which they are intended to interrupt/break.
An overcurrent device is intended to open on fault currents so it carries an AIC/AIR rating.
Motor starter and contactors are intended to break starting currents and low level short circuits so they also have an AIC rating.
Switches and relays not intended to break fault currents (in fact they often cannot even break their full load amps) so they do not carry AIC ratings. These devices are intended to stay closed during a fault so larger ones actually carry a withstand rating instead.
note: code article quoted from memory, which ain't what it used to be.
In essence 110.9 says all devices must be rated for the maximum current which they are intended to interrupt/break.
An overcurrent device is intended to open on fault currents so it carries an AIC/AIR rating.
Motor starter and contactors are intended to break starting currents and low level short circuits so they also have an AIC rating.
Switches and relays not intended to break fault currents (in fact they often cannot even break their full load amps) so they do not carry AIC ratings. These devices are intended to stay closed during a fault so larger ones actually carry a withstand rating instead.
note: code article quoted from memory, which ain't what it used to be.
Re: Low Voltage lighting relay panels AIC Rating
sesco,
What was the engineer's question? Was it about the relays or the size of the branch circuit conductors from the c.b. to the relay? I would think that he/she would know about relays.
On a few jobs with high AIC c.b.'s I had to run #6/#4cu. off a 20 amp. c.b. to the line side of the relay.
note-not for voltage drop.
frank
sesco,
What was the engineer's question? Was it about the relays or the size of the branch circuit conductors from the c.b. to the relay? I would think that he/she would know about relays.
On a few jobs with high AIC c.b.'s I had to run #6/#4cu. off a 20 amp. c.b. to the line side of the relay.
note-not for voltage drop.
frank
charlie
Senior Member
- Location
- Indianapolis
Re: Low Voltage lighting relay panels AIC Rating
The engineer was probably meaning withstand rating instead of interrupting rating.
110.10 Circuit Impedance and Other Characteristics. The overcurrent protective devices, the total impedance, the component 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 components of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the grounding conductor or enclosing metal raceway. Listed products applied in accordance with their listing shall be considered to meet the requirements of this section.
The engineer was probably meaning withstand rating instead of interrupting rating.
110.10 Circuit Impedance and Other Characteristics. The overcurrent protective devices, the total impedance, the component 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 components of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the grounding conductor or enclosing metal raceway. Listed products applied in accordance with their listing shall be considered to meet the requirements of this section.
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