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Direct wiring DRO to lathe?

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by BFHammer, Jun 8, 2017.

  1. BFHammer

    BFHammer United States H-M Supporter - Premium Content H-M Supporter-Premium

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    I am planning the installation of a DRO (Sino SDS6-2V) on my lathe (PM1236). The literature indicates that the input voltage is 85V-250V and it appears that the power supply is internal (i.e. no black box plug).

    Any reason why I shouldn't be able to direct wire to the lathe. I have seen this mentioned on other threads but wondered if there are any considerations that I should be aware of.

    Thanks in advance for any input.

    Mark

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  2. mksj

    mksj Active User H-M Supporter-Premium

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    I have my DRO hardwired into my lathe control box running 240VAC. The only concern is that the lathe might be on a 30A or bigger breaker, the electrical cord gauge is usually rated for much lower current, so the wire could potentially burn up if there was a short in the DRO unit. In most control systems, there is usually a breaker or a fuse inline provide ancillary power to other machine equipment. II will often use a supplemental breaker or DIN mounted/board mounted fuse holder for branch circuits at the machine.

    If I recall the PM1236 does have two double breakers in the control box, I would pull DRO power off the smaller amperage rated one.
     
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  3. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    I believe the PM-1236 has a double breaker for the 220vac and a single for the 24vac.

    If you brought in a neutral line with your hookup wire you can tap one leg of the 220vac and the neutral to power the DRO. If you only brought in a 3-wire 220vac (no neutral) then use both legs of the 220vac. In either case, as mksj said, install a separate fuse(s) or breaker(s). I have a 3 amp breaker on mine.
     
  4. BFHammer

    BFHammer United States H-M Supporter - Premium Content H-M Supporter-Premium

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    This may be a dumb question, but since I don't have a neutral could I simply put one 3amp breaker between the 220v tap from the lathe - something like this?

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  5. JimDawson

    JimDawson Global Moderator Staff Member Director

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    That would work, but normally you want to break both lines on a 220V circuit. A 2 pole breaker would be the best.
     
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  6. BFHammer

    BFHammer United States H-M Supporter - Premium Content H-M Supporter-Premium

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    So locate my taps, install one of these and i should be good to go?
    Would 14ga wire be appropriate?
    Thanks for your patience with the basic questions - I'm learning!:mechanic:

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  7. JimDawson

    JimDawson Global Moderator Staff Member Director

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    14ga would be perfect. Looks like you're good to go. :encourage:
     
  8. markba633csi

    markba633csi United States Active Member Active Member

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    Circuit breakers often don't react fast enough to protect solid state circuits- there's probably a fuse in your DRO but you can certainly add a breaker outside too
    if only as an additional master switch.
    Mark S.
     
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  9. darkzero

    darkzero Global Moderator Staff Member H-M Supporter-Premium

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    I posted in this thread earlier asking a question but I deleted cause I was wrong about what I posted.

    Originally I thought I had my DROs wired directly to the input line which is on a 30A breaker. On my PM1236 there are 2 breakers, a 15A for 220V & a 2A for 24V. I have the DRO wired to the 15A breaker. I have to check my mill but I'm sure I did it the same way.

    Both of my DROs have fuses on the back. So that 220V 15A breaker probably won't protect the DRO's power cord from burning if it got shorted but I don't see how that could happen. The cords are cut to length, probably only 1-1.5ft long & not exposed to any possible physical damage. Should I still be concerned about installing a dedicated breaker like talked about in this thread?
     
  10. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    I tapped off my control transformer and mounted a fuse block for a fast blow fuse, then cut a hole for a handybox wired to it. With a proper cover, it looks like it belongs there. I just have to remember it's low amperage capacity and only can run the DRO. Can't use it for any high current items. The transformer has a 220 VAC input, as well as a 110 VAC input, and it was unused on my machine (well this one anyway) so I decided it made sense to use it for the low power Mit DRO. And of course, it is chassis grounded, and the DRO has a 3 prong grounded cord.
     
  11. mksj

    mksj Active User H-M Supporter-Premium

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    Circuit breakers are more to protect against shots and with some breakers arcs, not necessarily to protect equipment. Breakers also come in a number of different trip curves (like B, C and D) which have different amperage vs. time trip curves, so when using electrical equipment with high start up current you often use D curve breaker but for a DRO you might use a B or C curve. Wire can sustain much higher current for short periods, so if you look at a 15A wall socket, often the cords you plug into it would be 16 or 18AWG wire. The electrical device itself will have a fuse/breaker that limits the power at/in the device. So in this case you are protecting the power wire from a dead short. As wire ages or becomes damaged, this is can happen. If you use a dual pole 3A supplemental breaker, then you could run power to the DRO or light with 18-20AWG wire cord. Also since it is 240VAC, you are pulling half the amps that you would at 120VAC. If you where to use a 15A breaker going to sockets, you would want to use 14-16 AWG wire.There are a number of factors that determine a wire/cord ampacity or current load over time.

    Conductor amps.jpg

    It is common practice in 240VAC (single and three phase) machines with a transformer to have a 110 or 120VAC tap off the transformer to power ancillary low current equipment. These are often fused or have a breaker sized to the load that it can deliver. The wiring after the fuse/breaker only needs to be sized based on the fuse/breaker size. In many machines there will be separate breakers to provide power to ancillary electrical devices. Below is a system build I did for a PM1236, power to the machine is a 30A dual breaker on the control board, a branch circuit goes to a dual 6A breaker which is used to power the coolant and other 240VAC low power electrical equipment. Wire to both breakers is 12AWG, wire from the 30A is 12AWG, wire from the 6A is 16AWG. A standard circuit breaker does not protect a motor from overload, there is often specific motor breakers, or thermal overload contator relay that is used. So if the motor locked up the thermal relay would trip before the motor insulation burned up and shorted.

    PM1236 VFD Control System.jpg

    So the 3A dual breaker you have chosen will work fine. I clip the plug off of the stock cord and connect the wires (white and black or brown and blue, green is ground) to the 3A breaker. Most DRO's have a separate grounding stud on the housing, which is suppose to be grounded to the machine. I normally do not use this is the DRO is hard mounted to the machine via metal to metal bond. Thecord ground may be an electrical ground relative to the electrical board and electronics, but a chassis ground may be separate and dissipate surface charge.
     
    Last edited: Jun 9, 2017
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