1 or 2 dedicated 120VAC circuits for my CNC?

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03 Dec 2022 06:23 #258397 by Sray69

You have to consider who the audience for your labeling is. It will generally be "future you" who will have forgotten much of what "current you" knows.

If you put the same labels on the wires as on the circuit diagram and put the diagram in the cabinet, then future-you will thank you.

Great points! Thanks

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05 Dec 2022 18:57 #258619 by Sray69
I am caught up on the wire gauge and shielding. In order to future proof (upgrading to inverter/spindle as well as other features) and minimize possible noise issues I am looking at shielded cables.

I have been told that all cables carrying any signals should use double shielded cable. Exactly which cables would this apply to, besides the driver/motor cables?

I found double shielded 18awg 4 lead cables for the motors but I am having a hard time finding an equivalent for 20awg 2 lead cables. I found 22awg but not sure that I can use 22awg for the rest of the low voltage wiring.

I'm thinking I could use 22awg for all wires to and from the Mesa board as they are 5-24V at fairly low amperage. Does this sound correct?

What about the power coming from the 60V 20A PSU to the drivers? The drivers will be providing 5A to the motors. I don't think 22awg would work for that. What gauge would work best and should that also be shielded?

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06 Dec 2022 02:00 #258656 by andypugh
I wouldn't bother with shielded cables for GPIO or power to the steppers inside the control cabinet, but for runs out to the limit switches etc it makes sense.

Have a look at "DMX" cable www.rapidonline.com/sommer-cable-520-005...-34mm-22-awg-59-1179
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06 Dec 2022 04:12 #258661 by Sray69
Yeah I have gone back and forth on this topic.

Others have told me the same thing.

Thanks for your input.

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07 Dec 2022 00:02 - 07 Dec 2022 00:06 #258769 by Sray69
As I am researching cable I need some help explaining why specs for cables use different amp ratings at different temps.

Here is an example.
Belden (1033A 0101000) - 2 Conductor (1 Pair Twisted) Multi-Conductor Cable Black 20 AWG Foil 100.0' (30.5m)
Operating Temperature: -30°C ~ 105°C
Amp Rating: 8 Amps per conductor @ 30°C

VS

Belden (5300FE 008500) - 2 Conductor Multi-Conductor Cable Gray 18 AWG Foil 100.0' (30.5m)
Operating Temperature: -20°C ~ 75°C
Amp Rating: 5 Amps per conductor @ 25°C

From what I have read, the amp rating of a wire/cable is based on the current it would take to reach a certain temperature within the conductor under standardized test conditions. That being 60°C, 75°C, 90°C, 105°C, etc.
With that said:
  1. I do not understand why they are being rated at the low end of their temperature range? Why wouldn't they be rated at their max temp range (75°C/105°C)?
  2. Why are they not rated at the same temp (standardized test conditions)? 
  3. Is that their max amp rating? If not, how do I find out what it is? Is there a calculation?
I am sure this can be very technical but hoping there is an easy way to explain it. 
Last edit: 07 Dec 2022 00:06 by Sray69.

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07 Dec 2022 14:27 #258810 by spumco
You'd have to contact Belden for exact answers, but here's my speculation...

The typical NEC-based ampacity chart covers single-conductor wires.  What you're looking at below are multi-conductor cables... and there are a bunch of specifications for multi-conductor cables.  And the max ampacity depends on numerous factors - insulation type, thickness, number/size of individual conductors, specifications to be met, etc.

The numbers you posted appear to be the manufacturer's ampacity rating for the environment in which the cable is operating.  In the first case Belden considers 30c to be the 'standard' environmental temp for that specification cable, and 25c for the other.  And the spec could be read as "this cable can handle up to 8 amps per conductor when operating at 30c"

Note that one of the cables is "PLTC" rated (power limited tray cable) and the other is not.  It may be that to meet PLTC specs the rating has to be given at 'xxx' temperature.

So addressing your questions:
1. Because each individual conductor should stay below the individual conductor max temp of 105c when the cable is operated at xxx amps at yyy temp.  To see if this is the case, look up other cables in the same Belden family and compare the 2-conductor to a 12 (or more) conductor of the same AWG.  I bet the high-conductor count cable has a lower amp-per-conductor rating than the 2-wire.

2. Because they're different cables, meeting different specifications and intended for different use-cases.

3. I would treat  the number given is their max rating, but you should contact Belden for clarification.
 
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07 Dec 2022 17:29 #258820 by scotth
Use MTW for current carrying applications.

MTW Wire - UL 1015

A type of hookup wire with a highly stranded bare copper conductor typically used in control cabinets, machine tool applications, and appliance wiring applications such as HVAC equipment. Wire & Cable Applications for MTW Wires are best for use in dry locations at 90°C, or not to exceed 60°C in wet locations or where exposed to oils or coolants.

The Beldon cable is best for signal applications. It is a bit of overkill for most switch inputs.

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07 Dec 2022 18:23 #258822 by Sray69

So addressing your questions:
1. Because each individual conductor should stay below the individual conductor max temp of 105c when the cable is operated at xxx amps at yyy temp.  To see if this is the case, look up other cables in the same Belden family and compare the 2-conductor to a 12 (or more) conductor of the same AWG.  I bet the high-conductor count cable has a lower amp-per-conductor rating than the 2-wire.

2. Because they're different cables, meeting different specifications and intended for different use-cases.

3. I would treat  the number given is their max rating, but you should contact Belden for clarification.

Thanks for your speculations. That kinda makes sense. 

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07 Dec 2022 20:57 - 07 Dec 2022 20:59 #258833 by Sray69

Use MTW for current carrying applications.

MTW Wire - UL 1015

A type of hookup wire with a highly stranded bare copper conductor typically used in control cabinets, machine tool applications, and appliance wiring applications such as HVAC equipment. Wire & Cable Applications for MTW Wires are best for use in dry locations at 90°C, or not to exceed 60°C in wet locations or where exposed to oils or coolants.

The Beldon cable is best for signal applications. It is a bit of overkill for most switch inputs.

Thanks. I was not aware of this classification. I will look into it.

Yeah I am still trying to determine sizing for the different circuits. Wire gets expensive these days especially when you have so many different sizes and ratings.
Last edit: 07 Dec 2022 20:59 by Sray69.

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07 Dec 2022 21:05 #258835 by scotth
MTW is a lot cheaper than Beldon. Beldon is a wonderful product and works well for intended applications.

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