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IndustryArena Forum > CNC Electronics > General CNC Machine Related Electronics > Powering CNC from two different outlets?
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  1. #1

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    Powering CNC from two different outlets?

    Since I live in the United States, my wall outlets are at 120V. I rent my home, and I am pretty sure the only 240V source is for my oven, which I cant really even move to get to. I have read some bad things about 110/120V VFDs and spindles, and want to go with a 220V +/- 15% VFD that powers a 220V 2.2kW spindle. To do this, I am thinking of using a hefty 120 to 240 volt transformer, but since the largest fuse available to me is 20A, I would need to have the transformer on a separate outlet than the rest of my hardware (motors, etc.). I have found a few forums that talk a little bit about this and mention something called a ground loop. I am not quite sure what this is, and I do not understand how connecting a VFD to one outlet and all other hardware to a different outlet would cause problems if everything is grounded?

    Is it unwise to power my CNC with two different outlets?

    240V outlets really isn't an option since my landlord likely will not allow me to change the outlets.

  2. #2
    Community Moderator Al_The_Man's Avatar
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    Is it unwise to power my CNC with two different outlets?
    .
    Not good practice at all.
    Do you have a 240v dryer outlet that could serve as double duty, as long as it was 4 wire, some were three wire(no neutral).
    If you do use two outlets, ensure that the E-stop control circuit also enables the VFD power.
    BTW, when using an isolation transformer, the earth GND has to be re-referenced by assigning one secondary conductor as a grounded Neutral due to galvanic isolation..
    NFPA79 shows the method diagrammatically.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    Since I live in the United States, my wall outlets are at 120V. I rent my home, and I am pretty sure the only 240V source is for my oven, which I cant really even move to get to. I have read some bad things about 110/120V VFDs and spindles, and want to go with a 220V +/- 15% VFD that powers a 220V 2.2kW spindle. To do this, I am thinking of using a hefty 120 to 240 volt transformer, but since the largest fuse available to me is 20A, I would need to have the transformer on a separate outlet than the rest of my hardware (motors, etc.). I have found a few forums that talk a little bit about this and mention something called a ground loop. I am not quite sure what this is, and I do not understand how connecting a VFD to one outlet and all other hardware to a different outlet would cause problems if everything is grounded?

    Is it unwise to power my CNC with two different outlets?

    240V outlets really isn't an option since my landlord likely will not allow me to change the outlets.
    You would not have enough Amps to run the 2.2Kw 220v with the 120v to 240v Transformer the spindle is 8.5A the VFD requires double that when using single phase at the input supply to the 220v / 240v VFD Drive so a minimum of 20 Amps with the safety factor, then you have the step down /step up from to 120v to 240v you would need more than a 30A 120v supply

    Most machines that use a 240v supply for a 220v / 2.2Kw spindle have a 30A Plus supply for there machine

    Is it wise to use 2 different outlets ( No it is not a good idea to use separate outlets to supply power to a machine ) you only ever want ( 1 ) Ground source

    Even in a rented place you should be able to wire up 30A 240v circuit that could be a temporary install, this could be like a dryer plug mounted in the wall some where and a correctly sized cable to your machine electrical cabinet

    You can just run a 1.5Kw spindle on 120v 20A, ( 25A supply is better, ) so you are short of Amps without doing some change to your electrical supply, need to get creative
    Mactec54

  4. #4
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    Re: Powering CNC from two different outlets?

    Friend , with a transformer it will work ok , the spindle doesn't draw that much current , only when it starts get a peak , after stay under 300w , depending on rpu u use , if u go lower it consume much more , mine at 3000 rpm go to about 700w consumption , this is from outlet .
    This is a real measurement with a powermetter .
    The spindle get about 5 amps when it starts , after go to about 1- 3 amps .

  5. #5
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by Andreiir View Post
    Friend , with a transformer it will work ok , the spindle doesn't draw that much current , only when it starts get a peak , after stay under 300w , depending on rpu u use , if u go lower it consume much more , mine at 3000 rpm go to about 700w consumption , this is from outlet .
    This is a real measurement with a powermetter .
    The spindle get about 5 amps when it starts , after go to about 1- 3 amps .
    And you are using 230v /240v if your spindle is only using up to 5A it is not 2.2Kw spindle the OP only has 120v
    Mactec54

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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by mactec54 View Post

    Is it wise to use 2 different outlets ( No it is not a good idea to use separate outlets to supply power to a machine ) you only ever want ( 1 ) Ground source
    Is there a reason I only want one ground source? I thought the point of a ground was that everything is common there for a reference voltage?

  7. #7

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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by Al_The_Man View Post
    Not good practice at all.
    Do you have a 240v dryer outlet that could serve as double duty, as long as it was 4 wire, some were three wire(no neutral).
    If you do use two outlets, ensure that the E-stop control circuit also enables the VFD power.
    BTW, when using an isolation transformer, the earth GND has to be re-referenced by assigning one secondary conductor as a grounded Neutral due to galvanic isolation..
    NFPA79 shows the method diagrammatically.
    Al.
    I only saw 3 prongs for my dryer outlet and checked this morning to verify - only 120V .

    Is the referencing for the isolation transformer just so I dont shock and kill myself on accident?

  8. #8
    Community Moderator Al_The_Man's Avatar
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    Is there a reason I only want one ground source? I thought the point of a ground was that everything is common there for a reference voltage?
    You do not create a new ground point, you reference one side of the secondary transformer 240v to the service earth ground conductor, this transformer terminal then has two conductors, one is earth ground, the other is termed neutral, so in effect you will create a 240v supply similar to that of countries such as UK and Australia etc, your VFD will not know any difference.
    Once you use a transformer for a separate supply, you lose the GND reference, hence the connection shown in the example, see 1T transformer terminal X2.

    Here is one example as shown in NFPA79.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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  9. #9
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    Re: Powering CNC from two different outlets?

    ...this may help understand how NA 240v Single Phase works
    https://www.google.com/search?q=240v..._frB_nF_uxD3aM

  10. #10
    Community Moderator Al_The_Man's Avatar
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by machinehop5 View Post
    ...this may help understand how 240v Single Phase works
    [
    One issue with the link, it portrays the normal N.A. 240v 1ph, which of course references the earth GND at the transformer C.T. point.
    In the single secondary 240v version, one side of the 240v becomes the neutral.
    i.e. N - 240v. instead of 120v - N - 120v.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  11. #11
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    Is there a reason I only want one ground source? I thought the point of a ground was that everything is common there for a reference voltage?
    You create a Ground loop by using to separate outlets this will cause EMI noise in your system much more than normal

    A ground loop is caused by the interconnection of electrical equipment that results in there being multiple paths to ground, so a closed conductive loop is formed.
    A common example is two pieces of electrical equipment, A and B, each connected to a utility outlet by a 3 conductor cable and plug, containing a protective ground conductor,
    in accordance with normal safety regulations and practice. that is why you don't want to do this
    Mactec54

  12. #12
    Community Moderator Al_The_Man's Avatar
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    .
    The method I have described, ground loops will not be an issue as it is done this way in all the electrical enclosure I have maintained, worked on and also Built.
    NFPA79 & NEC agrees.
    CNC machine enclosures often have a transformer for the L.V. control and another for the heavier motor systems, whether they be spindle for other motorized items.

    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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  13. #13

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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by mactec54 View Post
    You can just run a 1.5Kw spindle on 120v 20A, ( 25A supply is better, ) so you are short of Amps without doing some change to your electrical supply, need to get creative
    I read that 1.5kW 120V spindles should be thrown in the trash and stayed away from at all cost?

  14. #14

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    Re: Powering CNC from two different outlets?

    From a little reading and mactec's link, it seems like it is relatively simple to turn a 120V outlet into a 240V outlet? Is that true?

  15. #15
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    I read that 1.5kW 120V spindles should be thrown in the trash and stayed away from at all cost?
    No 2.2Kw and run with 120v is the problem setup, the 1.5Kw 120v just get by, not ideal but do run ok on a 20A circuit, you can get them also 1.5Kw 220v and run them with a Transformer 120v to 240v which is the best option so when you are able to get a 240v power supply you are set to go
    Mactec54

  16. #16
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    From a little reading and mactec's link, it seems like it is relatively simple to turn a 120V outlet into a 240V outlet? Is that true?
    I did not post a link in this Thread

    Only if it has L1 and L2 supply is that posable or you run a new 4 wire cable so it can have either 120v or 240v at the same outlet, the only other way is with a Transformer 120v to 240v

    Something Like this Transformer will get you going with a 1.5Kw 220v spindle you need the Transformer to be twice the size as you max amps most use a 3000w Transformers like the one in the snip there are many to chose from on Amazon if you go this way get one that has the circuit breaker built in
    Mactec54

  17. #17
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    I only saw 3 prongs for my dryer outlet and checked this morning to verify - only 120V .

    Is the referencing for the isolation transformer just so I dont shock and kill myself on accident?
    When you checked this plug was this with a meter, can you take a photo of this plug most likely it is 240v wired plug 240v can still be a 3 prong plug
    Mactec54

  18. #18

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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by mactec54 View Post

    Something Like this Transformer will get you going with a 1.5Kw 220v spindle you need the Transformer to be twice the size as you max amps most use a 3000w Transformers
    Wouldnt that pretty much immediately trip my circuit breaker, if the max fuse I have is 20A?

  19. #19
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    Re: Powering CNC from two different outlets?

    Quote Originally Posted by PrestonH View Post
    Wouldnt that pretty much immediately trip my circuit breaker, if the max fuse I have is 20A?
    A lot are using them in the same situation that you are in, yes they will trip the breaker if you over load them you don't have any other choice other then getting a 30A 240v supply put in, it is on the border line if you want to get going the go even smaller spindle 800w which a lot are using also
    Mactec54

  20. #20

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    Re: Powering CNC from two different outlets?

    Interesting. Also, I was thinking about ground loops (and reading forums from years ago that you, Mactec, were a main contributor for!) and I was wondering, couldn't I just ground everything to my CNC frame? It is all made of steel, and so it would be like a car where things are grounded to the chassis. I could then run the ground back to the outlet. Would that work, or is the principal different with AC systems?

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