Control Box Question

[Rob Carnell]

I have my lathe running with Acorn quite well.

I followed the circuit shown on the website.

I have a main fuse on the 220 coming in to the box, that’s all.

I have seen pics of boxes with assorted contractors, circuit breakers, fuses and filters.

Is there a post or video explaining where these should be fitted?

I have a larger control box and will move to a larger case with more room for this stuff.

I am running Leadshine closed loop drives with a 48 volt supply, and no VFD.

Rob

[martyscncgarage]

Hi Rob,
Can you tell us more about your lathe? What size spindle motor, how many watt axis motors etc? Pictures of the machine?
That would be helpful.

Marty

[Rob Carnell]

Thanks Marty, I appreciate your assistance.

It is a 600mm lathe, I documented the build here, there are lots of pics:

http://www.cncprojects.net/lathe/base-lathe

Spindle is 1HP.

Leadshine Drives (clones from Stepperonline) are:
X axis : Stepper Kit 4.25Nm Nema 24 Closed Loop Stepper Motor ＆ Driver
Z axis : Stepper Kit 8.25Nm Nema 34 Closed Loop Stepper Motor & Driver

Rob.

[martyscncgarage]

Your 1hp spindle at 220V will draw about 3.125 amps running, FULL load. At start up it could draw over double that. That's why time delay fuses are usually used on an induction motor load.

I would guess your drives/motors would not draw much more than that either. I would likely fuse the entire cabinet with a pair of 10amp fuses.
Its not until I get into larger spindle motors 3hp and above and larger servo motors and drives where I would use a pair of fuses dedicated to the VFD and a pair of fuses for the control and axis motors. I like fuses. They are quick acting and inexpensive. I know there are breakers out there and they are more convenient to reset. That's just me. I use fuses you can typically get at the big box home centers so they are readily available. IF you use 10Amp fuses, you want to wire all your AC devices with the right size wire. You don't want to put an 18 gauge wire on a 30Amp fuse. The wire itself could burn up before a fuse or breaker trips.

You size fuses/breakers for the load. In a CNC machine, you have several loads, Spindle, Axis motors and the control itself which is generally negligible.
Your circuit breaker feeding your machine should be a 15amp two pole breaker.

Just my .02
Others may have differning opinions.

Marty

[Rob Carnell]

Thanks Marty.

I'm running the spindle manually from another socket, will move to VFD in a few months.

Looks like I am ok with the 10 amp fuses I have.

Rob.

[tblough]

If you fuse the entire cabinet with a 10 amp fuse, then ALL your power wiring in the cabinet should be 16ga or larger.

[Rob Carnell]

Thanks, no problem there.

Rob.

[Richards]

There are a lot of articles on the Internet about fusing industrial control cabinets. You'll find everything from a single circuit breaker to cabinets that have fuses on every signal. By reading the articles and understanding the principles involved, deciding what to do becomes easier.

In my case, I use a 15A circuit breaker (C-type) as the main fuse for my boxes (120VAC service). From there I use a Midget sized slo-blo fuse on the 120VAC side of each power supply. Each fuse is sized to handle the load to the power supply. I use slo-blo fuses to handle the high inrush current to the power supply. On the output side of each power supply, I have another Midget sized fuse to protect the power supply from a direct short in case I pinch some wires. That's all that I use in my latest cabinet.

On my testbench, I've used fuses in-line with each Teknic Clearpath motor power + line. Page 34 of their manual shows where to put the fuse (up to 10A, slo-blo). They also recommend a fuse going to the power supply if you use a non-Teknic power supply. I have used fuses on the power + lines of stepper drivers. Be aware that if you have several drives connected to a single power supply that the failure of one drive can cause a power surge to the other drives. Gecko recommends against using a fuse. Their drives have very fast acting fuses built it.

As far as input signals go (homing sensors, limit sensors, etc.), to me, using fuses depends on the build. If any cable can be pinched, walked on, or abraded outside the enclosure, then adding a fuse makes good sense. For lighter load circuits, I prefer to use fuse holders like the DN-F6 series from AutomationDirect. They cost about $4.25 each for the non-indicator type and about $6.00 each for the indicator type (12VDC, 24VDC and 120VAC). Those fuse holders and the Midget sized holders use a pull-down mechanism so that the load can be disconnected from its power source by simply pulling the handle on the terminal block holder. As long as the fuse is wired properly with the power going to the top of the holder, the load is isolated from the power source when the handle is open. The fuse can be removed/replaced without danger of getting shocked.