Electrical wiring consultation

[Sshire]

I need an electrical consultation.
New 240v line for the "as soon as I find one I like" Bridgeport.

My plan is to run from the shop sub panel. 10awg 3 conductor wire (I don't need 4 since I have plenty of 120v outlets in the shop) from a new, 2 pole 30A breaker. The basement shop is dry, has AC and heat and has finished walls. No runs are on bare exterior walls.
It's about a 25 foot run to the new junction box.
Either a twist lock connector on the box or a rotary disconnect.
If a rotary disconnect, the SJOOW cable from the VFD on the mill would be permanently connected to the junction box. Otherwise, a twist lock plug on the cable from the VFD. The purpose here is to provide some way of removing power from the mill for maintenance rather than flipping the breakers.

Is all of the above correct?
Is there a better way?
Is there any advantage of the rotary disconnect switch over using a twist lock plug or vice-versa?
What did I miss?

 

[moya034]

I would say use a standard fused disconnect at the machine location with fuses rated based on the machine specifications. There's no reason to use a twist lock (what a great connector!) because you wont be moving the bridgeport around the shop. In fact the "code" would tell you to use a fused disconnect with permanent wiring for this instance.

The 30 amp breaker and 10 gauge is over kill, especially at 25 ft, unless you plan on running other equipment off this circuit.

I would wait until you have the machine and have the exact motor specifications before deciding on any fuse, breaker, or wire sizes. Also, you may or may not need to get a magnetic contactor motor starter, as well.

 

[moya034]

When I made my last post I forgot you are running a VFD. The VFD specifications may very well call for a 20 or 30 amp circuit, even though the motor will only use a fraction of it. The motor's amp specifications need to be configured in the VFD and it'll provide the over current protection to the motor.

Obviously, if you have the VFD you dont need the contactor.

 

[Sshire]

Thanks for *the info. I did get a fused disconnect box per your suggestion. I spoke with the VFD folks at Automation Direct. They said 20A double breaker.
I already have about 50 feet of 10awg wire so iom going to use that. Also I have enough 10awg SJOOW cable on the shelf and since I've pretty much exhausted the mill money, that's what it will be. Bigger can't hurt.*
A number of people have suggested an AC Line Reactor on the output side if you're not using an inverter class motor (which the 1967 Bridgeport is definitely not.)

"Line reactors used on the output side of a drive (load reactors) protect the motor insulation against AC drive short circuits and IGBT reflective wave damage, and also allow the motor to run cooler by "smoothing" the motor current waveform. Output reactors are recommended for operating "non-inverter-duty" motors and for any motors when the length of wiring between the AC drive and motor exceeds 75 feet."

 

[moya034]

Nothing wrong with using 10 guage in place of 12... Just say you did it for less voltage drop. Tho, me being me, I'd say if you have any future cabling projects planned it might be worth saving. You didn't specifically say romex, but I'm assuming that's what you are using between the fused disconnect and sub-panel?

As far as the AC Line Reactor goes, I can't give you good advice on that one. Never heard of such a thing, I'll have to research it a bit.

I will admit I'm somewhat dubious as to the benefit realized as most people run just about any kind of 3 phase old machine tool motor off the VFD directly, and have been doing so for years without issues.

That being said, if it eliminates the "whining" sound that comes from most motors running on an inverter have vs an RPC, I'd be all for it!

 

[Noitoen]

To eliminate/reduce the whining sound from VFD motors, the switching frequency of the inverter can be increased. It´s a good practice to disconnect the power from the inverter when not in use for a long period. It saves energy and protects the inverter in case of unexpected voltage spikes on the grid.

Do not touch the motor connections while the inverter is powered up and disconnecting a motor from an inverter while it´s running, can ruin an inverter also.

 

[kvom]

I'm using a GS2 VFD from Automation Direct (excellent unit BTW). I removed the power switch from the mill and wired the VFD directly to the motor leads, so all control of the motor is via the VFD control panel.

 

[Sshire]

The line reactor probably falls into the "it can't hurt" category.
I'm using NM wire from the basement sub-panel. Not running on an outside or unfinished wall so it's OK with code.
I hadn't even considered using the original Bridgeport switch. All will be controlled from the VFD and it will be powered off when I'm not in the shop. That's how I've been working with the lathe VFD.

 

[moya034]

You should be able to wire the bridgeport switches into the logic control of the VFD for start/stop.

 

[Sshire]

What are the reasons in favor of the original switch vs. VFD controls which give me Forward, Reverse, Stop.?

 

[kvom]

The mill's switch should not be used to switch power directly as that can harm the VFD. If you want to use the switch than it needs to be connected to the low-voltage control pins in the VFD. For me this was more trouble than it was worth. So I use the small panel on the VFD to control everything- on/off/reverse. I use the small knob as speed control, and program the LED display to show the spindle RPMs (multiple of VFD output frequency).

I removed the switch entirely and replaced its case with a small NEMA box to enclose the wire ties. You can leave the switch ON and connect the VFD to its input leads, then remove the knob for safety.

It is OK to overspeed the motor as long as it's not done for an extended period. Setting the max. frequency to 90 hz allows a 50% overspeed, useful for smaller drills. On my mill torque goes down quite a bit with spindle speed, so I use back gear below 600 RPM.

 

[idahoan]

Hi Stan,

Congratulations on your new (to you) mill; I'm sure that you will enjoy it.

Here is a picture of the temporary control box I made to control my VFD until I get my CNC project finished; eventually everything will be controlled by Mach 3. Although I will still probably retain the manual controls; at least for the spindle.

The VFD is tucked safely away in an enclosure on the side of the mill.

Dave

 

[idahoan]

One more thing; to me at least for me; the push buttons and speed pot are much easier to deal with than the membrane panel on the VFD. I power tap quite often and the push buttons work great for that.

Dave

PS. My VFD is a Hitachi SJ200 series FWIW.

 

[Sshire]

Dave
That looks great especially the E-stop label
Where did you get the cover plate ?

 

[Sshire]

I tried power tapping (3/8-16) on my BF20 but not enough torque. The BP in back gear should eliminate that issue. Can you tell me your power tapping procedure?

 

[kvom]

I've done power tapping on the BP, but only on through holes. You need a spiral flute tap that pushes the chips forward for that. For blind hole tapping I'd need a tapping head which I don't have.

 

[moya034]

What are the reasons in favor of the original switch vs. VFD controls which give me Forward, Reverse, Stop.?

The original switches are big industrial switches already mounted to the machine in a convenient spot. The VFD is ideally going to be mounted in a safe spot where oil, coolant, and swarf won't get to it. You don't need a pot since its vari speed.

Now if you don't like those switches you can get a myriad of replacements. The nice industrial ones aren't cheap, and I'm not about to stick a $3 radio shack switch on a machine tool.

To be clear, I'm talking about running the low voltage logic signals from the VFD, not switching power.

 

[idahoan]

Hi Stan

Like what kvom said; I usually only power tap through holes and only with spiral pointed or spiral fluted taps. My VFD is set up to dynamic brake so it stops plenty fast. What I do is to first make sure the quill stop is out of the way, start the spindle and then before I start tapping I push and hold in the start button; this way the only thing that can happen now is to let go and the spindle stops. This really helps if you panic and tend to hit the wrong button. Having the speed pot right there is nice so when you reverse the spindle you can speed it it up to back the tap out.

The control box is an off the shelf item; I made the aluminum plate to hold the switches as the box was use and already had holes in the cover. The label was drawn in Auto cad, printed full scale, covered with some self adhesive laminating film, then installed with double sided tape.

Once I decide what I want my permanent CNC control panel to contain and look like I will most likely engrave it.

Dave

 

[Sshire]

Since most of the holes I tap for engines fall into the 2-56 thru 10-32 range, I use my Tapmatic head with form taps. Gotta love those. No chips to clog anything. The tech people at Balax who make the form taps I'm using were very helpful considering my purchase probably didn't effect their bottom line.
My head goes up to 1/4". I don't bother to set it up for a few holes.
The PIA was hand tapping 48 3/8-16 holes for a rotary table mounting plate.

 

[vascon2196]

Hi Stan,

Congratulations on your new (to you) mill; I'm sure that you will enjoy it.

Here is a picture of the temporary control box I made to control my VFD until I get my CNC project finished; eventually everything will be controlled by Mach 3. Although I will still probably retain the manual controls; at least for the spindle.

The VFD is tucked safely away in an enclosure on the side of the mill.

Dave

I love the "oh ****" button...priceless.