[alan_3301]

Hi I have 2.2kw spindle run by chinese vfd.
2200 watts / 220v = 10 amps.
also have a 48v psu, rated 10 amp @ 220v. for stepper motors.
I also want to run a computer (350w) and monitor (84w)
4834 / 220 = 21.9 amps right?
This is okay to run through a 50 foot extension cord to a 30 amp circuit right?
just want to make sure. thanks

[neilw20]

1. The cord is rated for the job.
2. Make sure the cord is not rolled up in any way. No loops.
3. The vfd will rarely if ever run at full power.

[alan_3301]

thanks for the quick reply!
I've heard the no loops suggestion before.
why is that?
Say I only need 35 feet. but only 25 and 50 foot cords are available.
Do i run past the machine and U turn back, or have the cord in a s shape going to the machine.

[neilw20]

If you lay a wound up power cable with lots of current going through it you have an air cored transformer with shorted turns!

Get a 25 or 50' cable, and run a 2KW house hold heater for a few minutes and note the temperature rise!!

Many a caravan owner with a rolled up power cable (especially on original metal drum the cable came on) and running an airconditioner has ended up with a roll of molten PVC.

If you need the cable to be left long, lay it backwards and forwards, so as not to form a continuous loop.

Many power appliances have instructions to unroll power cable before use.

[Al_The_Man]

I think you are pushing it at that distance with 50ft extension cord, they usually only come in 12g max.
I would go to H.D. or your nearest electrical supplier and buy the right length in 10g SOW.
This will avoid any volt drop on spindle starts etc.
Al.

[alan_3301]

thanks for the replies.

Im looking at this extension cord
50 Foot 220 Volt Extension Cable w/ Outlet and Plug | eBay

It is listed as Type 8/3 STW - 40 amp - 250 volt

Another question is anyone has an answer. I am going to have fuses for the separate circuits inside my control box. Should i just go for 10 amp fuses on the inverter and motor power supply? Im not sure if you should exceed the max expected draw by a little bit?

Also, 1 more question. (sorry!) I will have the ground of the outlet grounding my control box, spindle housing, vfd, and 48v power supply.
The power supply has dc 48v and ground output terminals. Should I connect my DC ground to my main ground at the control box? Im not sure what procedure is when you have ac and dc circuits in the same box. Im thinking it is ok, and recommended? As long as ground loops are avoided. Correct?

[alan_3301]

on second thought, having the power supply grounded on the ac and dc side sounds like a ground loop to me.

any input?
thanks alot!

[neilw20]

Grounds, commons.
http://www.cnczone.com/forums/1066859-post10.html

[Al_The_Man]

Grounding supply commons or complete isolation?
There are two schools of though and either are valid if done correctly.
I tend to use the all-commoned method, the important thing in machine grounding is bonding all metallic parts of the machine and motor frames so that everything is electrically 'Neutral', which includes the important part of setting up a common earth ground point where all grounds and bonding conductors go to.
For many years there was a stress on grounding one end only of shielded cables It is now suggested that the preferred method is to ensure correct bonding and connecting both ends of shields, see section 6 of the PDF.
http://www.automation.siemens.com/do.../emv_r.pdf?p=1
And
Ground Practices
Also
http://www.cnczone.com/forums/phase_...se_issues.html
A good reference for N.A. is the NFPA79 document for wiring electrical machinery.
Al.

[mactec54]

alan_3301

Why buy this when you can, buy the cable from HD the right length & put Twist-lock plugs on it, it would be a better price & with better plugs do it yourself

[JD68]

Hi I have 2.2kw spindle run by Chinese vfd.
2200 watts / 220v = 10 amps.
also have a 48v psu, rated 10 amp @ 220v. for stepper motors.
I also want to run a computer (350w) and monitor (84w)
4834 / 220 = 21.9 amps right?
This is okay to run through a 50 foot extension cord to a 30 amp circuit right?
just want to make sure. thanks

Don't forget to take into account the gauge of the wire in the extension cord.

JD

[Al_The_Man]

thanks for the replies.

Im looking at this extension cord

It is listed as Type 8/3 STW - 40 amp - 250 volt

If you want to take a neutral over you will need 4 conductor, the one you link to is 3 cond.
Also on fusing, for a VFD you can usually use the 150% load rating of non-motor loads as you do not have the inrush of a normal across the line start of an induction motor.
Al.

[hub]

Grounding supply commons or complete isolation?
There are two schools of though and either are valid if done correctly.
I tend to use the all-commoned method, the important thing in machine grounding is bonding all metallic parts of the machine and motor frames so that everything is electrically 'Neutral', which includes the important part of setting up a common earth ground point where all grounds and bonding conductors go to.
For many years there was a stress on grounding one end only of shielded cables It is now suggested that the preferred method is to ensure correct bonding and connecting both ends of shields, see section 6 of the PDF.
http://www.automation.siemens.com/do.../emv_r.pdf?p=1
And
Ground Practices
Also
http://www.cnczone.com/forums/phase_...se_issues.html
A good reference for N.A. is the NFPA79 document for wiring electrical machinery.
Al.

That's interesting. I have always, and still do connect shields only on one end. However, at least here, shielding is not the same as grounding. Say a motor wire from VFD to a 3 phase motor has 4 conductors + shield: ph1, ph2, p3, PE + shield. The PE (common or GND) is connected at both ends, but the shield is connected at one end only to prevent noise (out/in).
Would I benefit to connect both ends on the shield? I've never seen that done.

Hub

[Al_The_Man]

However, at least here, shielding is not the same as grounding.
Hub

The same applies in N.A.
----------------
The probable reason it was done in the past is because although grounding was normal practice, their was a fear that different potentials may exist in separate sections of a machine and ground loops could exist and be conducted through a shield if both ends were grounded.
Now the stress is in common earth ground bonding of the relevant machinery and if this is done effectively there should be little to no chance of any ground loops existing.
IMO, poor grounding/bonding is the reason for many DIY projects that suffer from false triggering of inputs etc,
Al.

[hub]

That makes sense, but why is it better to connect the shield in both ends? Both ends are still connected to GND, all metallic parts are at the same potential.

I have struggled with ElectroMagneticCompability(EMC)/noise etc in various machines in CE/UL approval laboratories. Nobody ever suggested to connect the shield at both ends and I never tried it. Everyone seems to think the opposite. Would be interesting for sure to try and see the results in a lab.
Hub

[mactec54]

hub

Yes connect the shield at both ends only for the motor to VFD type wiring, all other shielded wires, the shield should only be grounded one end at the source

[hub]

hub

Yes connect the shield at both ends only for the motor to VFD type wiring, all other shielded wires, the shield should only be grounded one end at the source

Just to make sure (sorry), connect both ground AND shield at both ends?

Hub

[hub]

This is the VFD -> motor wire I use.

[Al_The_Man]

Just to make sure (sorry), connect both ground AND shield at both ends?

Hub

Well of course you are free to adopt which method you see fit, if you follow section 6. of the Siemens PDF it is recommended that all shields are connected at both ends now.
The single end grounding was a recommendation from before the common bonding came in to practice.
I was one that had this impressed on me in my electrical education, but I am always open to changes in current practice if the reason sounds viable.
This also went hand in hand with the once recommended practice of ensuring complete isolation between systems, it has since been found unnecessary when common point earth grounding is carried out.
There is also a paper on the Kollmorgen motor site that recommends this practice also.
Al.

[hub]

No don't get me wrong.
I'm also very open minded and I will change my mind easily as long as I understand the theory/ reasons.
I have enough experience to know I'm not always right.

Just additional clarity; do you understand that I'm using grounding at both ends connected with the yellow/green wire? Both ends are connected and grounded together. But the shielding (outermost metallic layer of the cable) is only connected at one end.

So every ground is connected to a single point, but the shielding layer is not. Only at one end.

Hub