The motor is 5 horsepower, 230 volts, single-phase, on a 240 volt circuit. It runs a shop air compressor.
The wire and the breaker are sized from Table 430.248, not from the nameplate, 430.6(A)(1). The table gives 28 A for this motor.
The overload relay is sized from the nameplate, 430.6(A)(2). The nameplate in the picture reads 22 A with a service factor of 1.15, so the relay may be set at 125 percent, 430.32(A)(1). Real 5 hp single-phase nameplates read about 19 to 23 A.
The breaker must carry the start current, 430.52(B). An inverse time breaker may be up to 250 percent of the table current, Table 430.52(C)(1). 70 A is a standard size, Table 240.6(A).
The wire must carry 125 percent of the table current, 430.22. 8 AWG copper carries 40 A in the 60 C column of Table 310.16. The ground wire is 8 AWG too, from Table 250.122 for a 70 A breaker.
A 70 A breaker on 8 AWG wire is allowed for a motor circuit, 240.4(G). The overload relay keeps the wire from running hot. The breaker only has to stop short circuits and ground faults.
The 35 A choice shows a breaker sized like an ordinary circuit, at 125 percent of the table current. It can trip on a hard start or on starts close together. The motor rules let the breaker be larger so it stays on.
The start current is 168 A, the highest locked-rotor current Table 430.251(A) allows for this motor. Real 5 hp motors draw about 97 to 145 A. Current drops as the motor speeds up.
The start lasts about 6 seconds, which is typical for a compressor starting under load.
Trip times come from a teaching model, not one product. The overload relay trips in under 10 seconds at six times its setting, like a Class 10 relay. The breakers trip near the fast end of a real breaker’s range, and the magnet trips at 10 times the rating in one cycle. The breakers use the same model as the visual on what trips a breaker.
The fault current counts only 50 feet of 8 AWG copper out and back, at 0.778 Ω per 1,000 feet, Chapter 9, Table 8. The rest of the system adds resistance, so a real fault draws somewhat less.
The relay in the picture is set to trip at 27.5 A. Many relays are dialed to the nameplate current instead and add the 125 percent themselves. Follow the maker’s instructions.
The overload relay is not built to stop a short circuit, and the contactor cannot safely break that much current. The breaker does that job.
The disconnect is ahead of the starter and in sight of it, so it cuts power to the starter too, 430.102(A). It is in sight of the motor, so it also serves as the motor disconnect, 430.102(B)(2).
On the short circuit tab, time runs 150 times slower so you can see the AC current swing back and forth. The clock shows real time.
Amber dots show how much current flows. Red diamonds show fault current. They do not show electron speed. Real electrons drift less than a millimeter a second.
The disconnect, the starter, and the motor terminal box are drawn cut open so you can see inside. Their covers stay on while the motor runs.
Parts turn red as they get hot. Real heaters and strips do not glow.