how to determine the size of ampere frame of a circuit breaker. for ex... 20 AT. is there any calculations for that to determine? or it is based on tables and standards?
please help..
2007-05-21 18:46:22 · 2 answers · asked by Rodz 1 in Science & Mathematics ➔ Engineering
A circuit breaker frame size and AIC (Amp Interrupting Capacity) must be determined by the short-circuit current made available by the local transformer. This is determined when the circuit breaker panel is selected.
The ampacity (trip rating) of a breaker must be no larger than the ampacity of the branch circuit wire. I read 20 AT as 20 Amp, twin-sized breaker, or a breaker thin enough that two such can fit in the space required by a normal breaker. Many codes prohibit the use of this type breaker.
The permissible ampacities of branch circuit conductors are given in tables in the NEC.These will vary according to the insulation of the wire, and how many wires are run together in a conduit. In designing branch circuits you calculate the maximum expected current the circuit is expected to carry, multiply this by 1.25, and go to your look-up tables. Again, as stated above, the breaker must have the same or less ampacity as the wire. Choosing a smaller breaker, though, will usually result in "nuisance trips".
2007-05-22 22:38:27 · answer #1 · answered by Helmut 7 · 0⤊ 0⤋
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2016-12-17 19:43:43 · answer #2 · answered by ? 4 · 0⤊ 0⤋