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Circuit breakers are more to protect against shots and with some breakers arcs, not necessarily to protect equipment. Breakers also come in a number of different trip curves (like B, C and D) which have different amperage vs. time trip curves, so when using electrical equipment with high start up current you often use D curve breaker but for a DRO you might use a B or C curve. Wire can sustain much higher current for short periods, so if you look at a 15A wall socket, often the cords you plug into it would be 16 or 18AWG wire. The electrical device itself will have a fuse/breaker that limits the power at/in the device. So in this case you are protecting the power wire from a dead short. As wire ages or becomes damaged, this is can happen. If you use a dual pole 3A supplemental breaker, then you could run power to the DRO or light with 18-20AWG wire cord. Also since it is 240VAC, you are pulling half the amps that you would at 120VAC. If you where to use a 15A breaker going to sockets, you would want to use 14-16 AWG wire.There are a number of factors that determine a wire/cord ampacity or current load over time.
It is common practice in 240VAC (single and three phase) machines with a transformer to have a 110 or 120VAC tap off the transformer to power ancillary low current equipment. These are often fused or have a breaker sized to the load that it can deliver. The wiring after the fuse/breaker only needs to be sized based on the fuse/breaker size. In many machines there will be separate breakers to provide power to ancillary electrical devices. Below is a system build I did for a PM1236, power to the machine is a 30A dual breaker on the control board, a branch circuit goes to a dual 6A breaker which is used to power the coolant and other 240VAC low power electrical equipment. Wire to both breakers is 12AWG, wire from the 30A is 12AWG, wire from the 6A is 16AWG. A standard circuit breaker does not protect a motor from overload, there is often specific motor breakers, or thermal overload contator relay that is used. So if the motor locked up the thermal relay would trip before the motor insulation burned up and shorted.
So the 3A dual breaker you have chosen will work fine. I clip the plug off of the stock cord and connect the wires (white and black or brown and blue, green is ground) to the 3A breaker. Most DRO's have a separate grounding stud on the housing, which is suppose to be grounded to the machine. I normally do not use this is the DRO is hard mounted to the machine via metal to metal bond. Thecord ground may be an electrical ground relative to the electrical board and electronics, but a chassis ground may be separate and dissipate surface charge.
It is common practice in 240VAC (single and three phase) machines with a transformer to have a 110 or 120VAC tap off the transformer to power ancillary low current equipment. These are often fused or have a breaker sized to the load that it can deliver. The wiring after the fuse/breaker only needs to be sized based on the fuse/breaker size. In many machines there will be separate breakers to provide power to ancillary electrical devices. Below is a system build I did for a PM1236, power to the machine is a 30A dual breaker on the control board, a branch circuit goes to a dual 6A breaker which is used to power the coolant and other 240VAC low power electrical equipment. Wire to both breakers is 12AWG, wire from the 30A is 12AWG, wire from the 6A is 16AWG. A standard circuit breaker does not protect a motor from overload, there is often specific motor breakers, or thermal overload contator relay that is used. So if the motor locked up the thermal relay would trip before the motor insulation burned up and shorted.
So the 3A dual breaker you have chosen will work fine. I clip the plug off of the stock cord and connect the wires (white and black or brown and blue, green is ground) to the 3A breaker. Most DRO's have a separate grounding stud on the housing, which is suppose to be grounded to the machine. I normally do not use this is the DRO is hard mounted to the machine via metal to metal bond. Thecord ground may be an electrical ground relative to the electrical board and electronics, but a chassis ground may be separate and dissipate surface charge.
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