I presently have A mill and a lathe in my shop, both wired directly into the system without a plug that can be pulled. The circuit breakers are just out side the shop door in the garage so are close at hand. Does this sound like it might be a dangerous practice, to have machinery wired in such a manner? I will be moving the new Hardinge TM into the shop and adding it to the same circuit, however, only one machine is run at a time.
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Is this a good idea?
- Thread starter rogee
- Start date
- Joined
- Nov 13, 2012
- Messages
- 175
I don't know the code on this, but as long as you remember to turn off the power before any maintenance, you should be OK. I have a table saw that's direct wired, except that I have a large knife switch under the extension table so that I can turn the power off to change the blade. My 2 mills and lathe are direct wired. The CNC is also, except that it also has a breaker on it.
- Joined
- Nov 13, 2012
- Messages
- 165
Another thing to think about is motor protection.
The circuit breaker is there to protect the wiring and to prevent a fire if the wire becomes overloaded.
The CB can also partly protect the motor if the FLA (full load amps) rating on the motor is close to the breaker trip point - but not too close.
Some smaller fractional HP motors have internal protection to shut down the motor before it overheats the internal insulation.
Most larger motors do not have this feature, but instead rely on an external current monitoring device such as a fuse or a motor starter. (Some machines have an on-board fuse box to protect the motor).
If the CB rating is far greater (say 2X) than the motor FLA, it is possible to overheat the motor and have a motor fire with the CB failing to trip.
In this case, a secondary form of motor protection might be a good idea.
One fairly low cost way to do this is to install a fused disconnect near the machine. You can still direct wire from the disconnect to the machine.
You can use the local disconnect as a safety disconnect when working on the machine - or when you don't want it to be started.
You can select from a number of fuse types which will protect the motor FLA and still allow it a short high-amp burst for starting.
You can find a name-brand, single phase, indoor rated, fused disconnect box at a typical home improvement store for $30 or $40. Another $20 or so for two fuses.
Ideally, there would be a fused disconnect for each of the machines, with the appropriately sized fuse for each motor. (I think a code expert would say is a requirement - I'm not an expert).
Congratulations on the new Hardinge.
Terry S.
The circuit breaker is there to protect the wiring and to prevent a fire if the wire becomes overloaded.
The CB can also partly protect the motor if the FLA (full load amps) rating on the motor is close to the breaker trip point - but not too close.
Some smaller fractional HP motors have internal protection to shut down the motor before it overheats the internal insulation.
Most larger motors do not have this feature, but instead rely on an external current monitoring device such as a fuse or a motor starter. (Some machines have an on-board fuse box to protect the motor).
If the CB rating is far greater (say 2X) than the motor FLA, it is possible to overheat the motor and have a motor fire with the CB failing to trip.
In this case, a secondary form of motor protection might be a good idea.
One fairly low cost way to do this is to install a fused disconnect near the machine. You can still direct wire from the disconnect to the machine.
You can use the local disconnect as a safety disconnect when working on the machine - or when you don't want it to be started.
You can select from a number of fuse types which will protect the motor FLA and still allow it a short high-amp burst for starting.
You can find a name-brand, single phase, indoor rated, fused disconnect box at a typical home improvement store for $30 or $40. Another $20 or so for two fuses.
Ideally, there would be a fused disconnect for each of the machines, with the appropriately sized fuse for each motor. (I think a code expert would say is a requirement - I'm not an expert).
Congratulations on the new Hardinge.
Terry S.
- Joined
- Nov 16, 2012
- Messages
- 5,596
The cost of a switch and outlet is 25 bucks -which is nothing compared to what we spend on supplies on a weekly basis. I have all machines on an outlet box that has a switch for that outlet and it's right next to the machine. Every night, I flip the switches. The op-rod to turn on a lathe is right at thigh height and I've bumped it myself and blipped it on. If a family member made the same mistake while I wasn't around, they might not know how to disengage the op-rod but they sure as heck know to turn-off a switch. -Extreme thinking but in-line with the machinist mindset. Aside from that, circuit breaker switches are best not cycled on a regular basis in case you're in the habit of shutting-off power to them at the breaker box.
I do believe that in real workshop environments, it's code to have each machine with a nearby accessible lock-out box.
Ray
EDIT: I will admit that I'm guilty of forgetting to put the switch cover on one of my outlet boxes. I keep forgetting to get one.
I do believe that in real workshop environments, it's code to have each machine with a nearby accessible lock-out box.
Ray
EDIT: I will admit that I'm guilty of forgetting to put the switch cover on one of my outlet boxes. I keep forgetting to get one.
- Joined
- Sep 3, 2012
- Messages
- 53
No, not good practice, code calls for some means of disconnect, be it a fused disconnect, a safety switch, or a receptacle and cord . My mill and my lathe have separate 2 pole( 220v ) 20 amp circuits and both have cord / receptacles as means of disconnect. I always unplug the cord when doing any sort of work on either machine ( especially changing the belts ), also each machine should be on it's own circuit, not shared. The only way you can be hard wired is if the breaker was in line of sight of the motor ( with in 50 feet ) and lockable , even then I still would put some sort means of disconnect adjacent to your machines. The advice given is based on motors of 2 HP / 300 volts or less.
- Al
- Al