Splitting up wiring to smaller guages
Splitting up wiring to smaller guages
(OP)
Feeding into a control box with a 208Y feed, using 6/5 SO cable, full load on the system is 43.846A/phase
[derived from having a power supply with a draw of 14.42A, so using two legs and three supplies split across, each phase will see a draw of 28.8A, and then a 15A single phase 120V load for each phase]
So, the main feed from the load side of the control box breaker will come to a terminal block using #10 wire (free air), and the other side feeds two power supplies AND the 115V outlet. So the PS see a draw of 28.8A and that requires #14. Tapping off this phase and the neutral, the 15A feed only needs #18. So is it 'legal' to take two different wire sizes off the terminal block, or the studs of the circuit breaker?
[derived from having a power supply with a draw of 14.42A, so using two legs and three supplies split across, each phase will see a draw of 28.8A, and then a 15A single phase 120V load for each phase]
So, the main feed from the load side of the control box breaker will come to a terminal block using #10 wire (free air), and the other side feeds two power supplies AND the 115V outlet. So the PS see a draw of 28.8A and that requires #14. Tapping off this phase and the neutral, the 15A feed only needs #18. So is it 'legal' to take two different wire sizes off the terminal block, or the studs of the circuit breaker?





RE: Splitting up wiring to smaller guages
There are "tap rule" exceptions in the NEC that might allow this under certain situation, but I don't think #18 could ever be used.
RE: Splitting up wiring to smaller guages
RE: Splitting up wiring to smaller guages
The first important condition to be noted is that these standard circuit breakers have an ultimate trip limit of 138%, which means that for some short period of time a 15A circuit breaker could allow up to 20.7A (15A X 1.38 = 20.7A) to flow through your wire.
The second condition (and most important to your application) is that these standard breakers have a lower trip limit of 115%, which means that the circuit breaker could allow 17.25A (15A X 1.15 = 17.25A) INDEFINITELY.
The circuit breakers you are contemplating may be qualified to a different spec, but the same principle applies when sizing a circuit breaker to protect wire. You have to know as a minimum (there are other factors) what trip limits your circuit breaker will have so that you can characterize accurately what your wire will experience.
Best regards,
Debodine
RE: Splitting up wiring to smaller guages
RE: Splitting up wiring to smaller guages
Molded case circuit breakers rely on the connected conductors as a heat sink to keep the breaker from overheating and tripping below its rating. UL testing for 15A (and smaller) breakers is done with #14 AWG. So, that is smallest size conductor that can be (legally) used for NEC compliance.
RE: Splitting up wiring to smaller guages