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Thread: would I get away with this?

  1. #1
    Join Date
    May 2013
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    would I get away with this?

    my power supply for my shed is 63amp, our 3 phase is 400v here.

    at the moment the worse case loading for the workshop is:
    25hp sander, it draws 34.4 amp on full load, this is stated on the machine plate, sander is on VSD, the sander will not draw more than 34amp.
    10hp compressor, it draws 13.8 amp (plate value)
    5.5hp extractor, it draws 7 amp (plate value)
    that is 55amp all up.

    my extractor is a bit undersized. I would like to upgrade to a 10hp extractor, that means the amp draw will be around 14amp. this will bring the total amp draw to 62amp. just under the the supply of 63amp.

    I know the sander only draws 34amp when its a wide panel or when I try to sand too much in one hit.

    The question is:
    Would I be alright to upgrade the extractor to a 10hp unit and rely on the mains power? this means I will have to start my machine in various sequence and be real careful about the sanding and possibly have to put VSD on the compressor or/and the extractor.

    OR

    buy a generator and put the extractor or the compressor on the generator. this is less desirable because I really dont want to spend anymore than I have to.

    one of the option I have been told is to change the motor on the compressor so it runs on gas, I am reluctant to do this because I just bought the compressor new in 2014 and its in a quiet capsule. modifying it will cost too much.

  2. #2
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    at the least double the AMP for any motor for inrush current. What's the size of the wire are you running from the circuit board to the socket? if it's just to the limit the rule of thumb is not to START motors simultaneously it's ok to run them all at the same time, but not start.
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  3. #3
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    Without really understanding your equipment and how you work, it isn't easy for us to give you an exact answer. There are a lot of "well, it depends on how...." you understand.

    Frankly, I doubt that you will hit the full current draw of each piece of equipment but then again, I do not know your working situation.

    Perhaps there is a time where you are running a wide table top through your sander and going slow with the extractor (I assume this is the dust collector...DC as we call it around here) and the compressor kicks on. Unless you have other gates open sucking in sawdust (table saw?) at the same time, I kinda doubt the full 10 hp of that DC will be used. In fact, unless you upgrade your DC pipes to something LARGER, odds are decent that bumping up the DC power (and I assume impeller size), may not have the desired impact. Again, I don't know what you have in your shop.
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  4. #4
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    here is a bit more info on my equipment and how I work.

    I have a Robland Combination machine, Omga double mitre saw, SCM S400P band saw, a Masterwood OMB1V mortiser and a SCM 5RCS1100 sander.

    however I work alone so the worst case or the largest requirement for extraction is when I use the sander. The sander has 2 x 160mm(6 1/2 inch) hood and 2 x 120mm (5 inch) hood, the sander's manual says it needs a dust extractor/DC capabale of 6330m3/hr, or 3725CFM. the static loss through the machine is 2300pa or 9 inch of wg.

    The existing main DC pipe is 10 inch. but its a short run between the DC and the sander (about 9-12 ft of total duct run) therefore I can easily upgrade them to 12 inch or larger if required. the workshop is only 30 ft x 18ft.

    I would like to have the DC to stay inside because the noise.

    hope this clear things up.
    Last edited by Albert Lee; 02-29-2016 at 7:22 PM.

  5. #5

    Another opinion

    Quote Originally Posted by Yuriy Karpov View Post
    at the least double the AMP for any motor for inrush current. What's the size of the wire are you running from the circuit board to the socket? if it's just to the limit the rule of thumb is not to START motors simultaneously it's ok to run them all at the same time, but not start.
    An electrician's view-
    In the USA, which is where my training/experience is from, inrush is not a part of calculating feeder capacity. (We often call this type of circuit a feeder.) However, the first step is to take the nameplate amps (or Full Load Amps as the code refers to it) and multiply by 1.25. Here are the NEC references:
    From 430.24, you can see that conductors that supply several motors must have an ampacity not less than:

    • 125% of the highest-rated motor FLC [430.17], plus
    • The sum of the FLCs of the other motors (on the same phase), as determined by 430.6(A), plus
    • The ampacity required to supply the other loads on that feeder.

      So 34 x 1.25 = 43 amps; + 13.8 + 7 = 63.8 amps total load now.
      In the USA you are full up now.

      Question, how did you determine the 63 amps? The one determining factor (again, in the US) of a feeder would be the wire size and material, for example #4 Copper or #2 Aluminum. People tend to look at the circuit breaker to figure out capacity, how many amps they have, and it does not work that way.

  6. #6
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    Thanks for the input....

    The 63 amp was provided by the line company. on the drawing provided by my electrical engineer it states "16mm2 4C + E (6mm2) copper pvc circular tps" and this is what was installed from the street fuse to my main switch board.

  7. #7
    Can you clarify what you mean by 'get away with'? I suspect from the values you quote you are in New Zealand. If so, don't think you can conform to code with your proposed increase. In the US, that wire size is between #6 and #4 and would have an ampacity of about 85 amps, and it would work, just barely. In my mind you are pushing the envelope pretty hard, but could well operate for years without a problem. On the other hand, I don't want to imply this advice is as valid as your local professionals would provide.

    Best of luck, really.

    Quote Originally Posted by Albert Lee View Post
    Thanks for the input....

    The 63 amp was provided by the line company. on the drawing provided by my electrical engineer it states "16mm2 4C + E (6mm2) copper pvc circular tps" and this is what was installed from the street fuse to my main switch board.

  8. #8
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    What I meant with "get away with" means I dont have to buy a generator for one of the machines or upgrade the amps to 100amp..

    I think my cable is rated for 85 amps as well but need to check with the electrical engineer who did the design for me, hopefully he wont charge me too much

  9. #9
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    Is there any reason you have to have the compressor on when you've got the WBS and DC running? If not, then there's your solution. Just turn the compressor off and you've got 28 amps for your extractor. Other than spray finishing and sanding, I don't see where you'd be using so much air that you couldn't run off the tank for a while, but I am simply guessing about your set-up.
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  10. #10
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    I guess I can turn it off for a short time... the sander uses 30l/min for the tensioning and 700l/min for the blower(timer controlled). If I turn off the blower then I am all good.

    I think this is my solution for now. or sand very light with each pass.

  11. #11
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    I sure would not turn off my compressor while running a WBS.

    Do you have other service options from your power company? Call then ad get an engineer out there and discuss options. Seems like small service for the size shop you are trying to build/run?
    Glad its my shop I am responsible for - I only have to make me happy.

  12. #12
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    I am talking to the power company now. it it cost less than a stand alone generator then I will upgrade the mains.

  13. #13
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    just an update.

    Got a quote from the line company, it will cost about $350 USD to upgrade the mains from 63amp 3 phase to 100amp.

    I have instructed the line company to proceed with this.

  14. #14
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    Very good. Glad you called them. Be safe and good luck.
    Glad its my shop I am responsible for - I only have to make me happy.

  15. #15
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    East Rochester, NY
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    Wow....good luck :-)

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