Wiring a CNC router electronic enclosure

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Old 08-11-16, 03:51 PM
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Wiring a CNC router electronic enclosure

Hello all,

I am working on a control box for my CNC router. Currently the router spindle and the the router electronics have two separate power sources, which I was told is not a favorable situation.
Recently I got my new router spindle and VFD which now needs 240V. To have only one power source, I will have to split the incoming 240V to get 120V for the router electronics. Basically the same situation like in a dryer, where 240V were split, to have 120V for the dryer electronics.
The 240V line (30amp breaker) and receptacle was installed by an electrician, the line is a 4 conductor line - two hot - neutral - ground.
I would think that can be done relatively easy using a terminal block, one "hot" and the "neutral" and you have 120V, ground will go the "enclosure ground" (not sure if that is the right term) where also the ground from the 240V line terminates.
I think/hope I got the principle correct, however since I am not an electrician I would like to get some input how this should be done correct and according to code. It would be nice to see a wiring diagram to get a better idea what is OK and what not.

I appreciate any input.

Thanks
Chris
 
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Old 08-11-16, 03:58 PM
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Welcome to the forums.

Technically what you are purposing will work but I'm not sure that's the best way to supply the electronics with 120v.

The couple of machines I worked on had a small sub panel nearby with two circuits... a 240v and a 120v feeding the machine.

Rather than elaborate any further.... I'll let my forums partners reply. A know Tolyn has a similar setup.
 
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Old 08-11-16, 05:26 PM
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As Pete said, your proposal is correct in that you can obtain 120 volt by using one leg of the 240 and neutral. Because your electronics will draw much less current than the drive, you should have a separate fuse or circuit breaker in the 120 volt section, with a rating a little higher than the maximum current draw of the 120 volt gear.

You may see some electrical noise from the VFD coupled into the 120 volt gear. Theoretically, running the electronics off a separate 120 circuit would minimize this, but as a practical matter in a residential environment, there probably won't be much difference. The VFD should have filtering built in to reduce electrical noise on the AC line anyway.

Good luck!
 
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Old 08-12-16, 12:52 PM
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Hello,

thank you for your input that is already a great help.

@CarbideTiped

"...you should have a separate fuse or circuit breaker in the 120 volt section.."

Do you have something special in mind. I was looking around to find something like terminal block equiped with a 15 amp fuse, but so far have not been successful. It is very likely that I am not looking in the right place, so it would be nice if somebody could point me to a website or a product.

Thanks
Chris
 
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Old 08-12-16, 01:26 PM
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What is the load on the 120 volt supply? In other words, how many amperes at 120 volts do you need?

I personally would use a 240 to 120 step-down transformer rather than connecting the 120 load to one line lead and neutral. This keeps the incoming line "balanced". You should have fuse or circuit breaker protection on both the primary and secondary transformer windings. This arrangement is common with machinery that uses a higher line voltage with 120 volt controls.
 
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Old 08-12-16, 02:01 PM
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There are many styles of fuse holders, here are two:

https://www.amazon.com/DIGITEN-5x20m...ne+fuse+holder

https://www.amazon.com/Bussmann-Pane...ds=fuse+holder

Those would use this style fuse (but you need to pick correct amp rating):

https://www.amazon.com/Bussmann-BP-A...words=agc+fuse

Do not use automotive type fuse as they are only rated for 24 volts.
 
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Old 08-13-16, 07:48 AM
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Hello all,

thank you for your comments on my little project and your advise.

@Furd
I am sure that you have a good reason to suggest a step-down transformer but is a step-down transformer required per code. If not would you be so kind and explain what the advantage of a step-down transformer will be.

So what will be in the 120V section:

- the power supply (24V DC) for the CNC electronics - 120V 10 amps
- submersible water pump for the spindle cooling
- dust extractor 10 amps
- work piece coolant

which means I need four power 120V (15amp) power outlets

In the 240V section is only the spindle

I understand that regardless of the transformer I would need a circuitbreaker for the 240 V section and 120V section?
In the 240V section I should have a 30 amp breaker and in the 120V section a 15 amp breaker, would that be correct? The spindle VFD is rated with almost 10 amps.

Thanks
Chris
 
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Old 08-13-16, 08:11 AM
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My familiarity is with industrial installations. To my knowledge a transformer is not required by any code but OSHA rules mandate that any machine that has multiple energy sources must be placarded detailing all the various energy sources. Having the transformer connected to the primary power means you have ONE source of electrical power and only ONE switch (circuit breaker) to move to disconnect all power to the machine.

The transformer is the safest but also the most expensive option.
 
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Old 08-13-16, 05:02 PM
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Hello,

I like the idea that there is only one power cable going to the machine and with one Switch everything is off.
However currently it appears to me that this is not such an easy task than just having 120V only. I am thinking to switch my VFD to the 110 Version, which was not available (for the 2.2KW spindle) at the time, when I decided to get 240V installed in my basement.
Anyhow I will make one attempt to get it right.
I like the transformer idea however I would not even know what transformer to choose. Clearly AC to AC 240 to 120V but what power output rating that is a little difficult to determine and they appear to be pretty expensive.

I made a picture from a very rough setup of the enclosure in case I wouldn't use a transformer. I would basically have to circuit braker pairs, one for the 240V and one for the 120V, then use terminal blocks to step-down the voltage and distribute the lines. There will be a neutral bar and a ground bar, I am wondering if such a setup is almost like a sub panel and neutral should not be bonded with ground.

Thanks
Chris


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Old 08-13-16, 08:19 PM
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Neutral and equipment ground are NEVER bonded (together) except at the SERVICE panel. The service panel is the first fuse or circuit breaker after the utility's kilowatt meter.

In your case I think that running a dedicated 240 volt circuit to the machine and then a separate 120 volt, 20 ampere circuit for the auxiliaries is the easiest. Use a heavy-duty plug strip (or two) to have multiple receptacles to plug in the auxiliary equipment. Use the appropriate 240 volt plug/receptacle for the amperage as the local disconnect for the VFD.
 
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Old 09-01-16, 08:21 AM
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Hello all,

I will try to continue this topic since I am still working on the electronics of my CNC router.

Meanwhile I decided to give the whole thing a little more structure and found a simple program that draws wiring diagrams.
So attached you will find the beginning of my wiring diagram, please keep in mind that I am not a professional, hence my wiring diagram might appear very unprofessional.

Currently I am using a simple treminal block to split the 240V into 120V, however, I still think about a transformer to use instead, because of the reasons described by Furd below.
Unfortunately I still have a problem to find out what transformer I would actually need to have enought power for the spindle and the rest. So the first part is easy, it should be 240V to 120V, an AC to AC transformer. The second part is where im struggling, what VA rating would I need here? I saw some information, that to figure this out you have to multiply the outgoing Volt with Amperage of the application. Which would be

VA = Volt x Amps

is that correct ?

Thanks
Chris

Name:  CNC enclosure wiring diagram.jpg
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Old 09-01-16, 08:25 AM
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OK ... attached as a picture, that is quite useless
Here is a PDF version, much better resolution.

TinyCAD panel wiring.pdf
 
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