# Direct wiring DRO to lathe?



## BFHammer (Jun 8, 2017)

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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## mksj (Jun 8, 2017)

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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## jbolt (Jun 8, 2017)

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.


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## BFHammer (Jun 8, 2017)

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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## JimDawson (Jun 8, 2017)

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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## BFHammer (Jun 8, 2017)

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!


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## JimDawson (Jun 8, 2017)

14ga would be perfect.  Looks like you're good to go.


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## markba633csi (Jun 9, 2017)

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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## darkzero (Jun 9, 2017)

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?


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## Tony Wells (Jun 9, 2017)

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.


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## mksj (Jun 9, 2017)

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.




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.




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.


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## tomjaksa (Aug 13, 2017)

Hi Guys
Just a 2 cents worth. That breaker on ebay for sale....................hmm i had one burn up in on position which then proceeded to burn wiring down the line, Get a good brand name do not skimp on safety.


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## Doodle (Aug 13, 2017)

If your power to the lathe is 220/240 VAC and the DRO can operate at that voltage, then go ahead and connect it to the lathe power in. Check the DRO and if it has  a switch for selecting the voltage, be sure it is switched to the voltage you are connecting it to. The DRO in the picture has a power connector that is in general use and can be easily obtained if one did not come with the unit. Since you intend to wire it into the lathe power, turn off power, and open the wiring area and look to see if there is adequate room to connect the ground and two line and neutral connected wires. I would expect you have to cut the plug off the cord as you cannot use a 110VAC plug when connecting to 220/240VAC. The intent here is to wire it directly to lathe. So provided you have the room to wire, cut the cord plug off and take the cord with you to the store and find a cord grip fitting that fits the cord diameter. Use a connector for a 1/2" knockout sized hole.

A cord grip fitting is superior to a romex, bx style clamp for holding the cord. The screw connector clamps tend to crush the cable and eat through the insulation over time. A cord grip connector will hold the insulation without damage and keep dirt and crap out of the electrical box.

With the cord mechanically attached to the lathe power box, wire it. Connect the ground wire first. If you don't understand the colors of the wires look it up on the internet. It has stranded wire, use a ring terminal properly crimped  (never soldered) if mounted on a grounding stud. If there is a grounding lug available you may use it. Don't share grounding lugs on barrier strips with multiple ground wires, let it have its own place.

For 220/240 VAC in the USA, you don't need a breaker or fuse on the DRO line. The DRO is already protected from cord connected power as shown by the UL or CE label. For safety, identify the two power leads with black tape so no one will expect a grounded neutral is in use on your lathe.

The wire used must be rated at  300V and selected for the environment it is used in. So if you plan to wash down the lathe wiring area with chemicals the wire insulation must be selected for it. If the wires will be subjected to extreme heat, insulation must be selected for temperature.


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## mksj (Aug 13, 2017)

A few points to above, for 240V operation a neutral is usually not used in this type of equipment. Some DRO displays allow universal input voltage, so something like 100-240VAC is allowed (85-250V on the above DRO), since they usually have a detachable IEC socket at the DRO, one can change the cord for the appropriate voltage/current. The cord is only rated for a specified maximum current, and this is based on the wire gauge and plug that goes into the wall, the socket current rating is based on the breaker for that circuit. If you have a 30A breaker for your lathe, which is what I use, then the high voltage wiring in the machine has to be rated as such, unless you use a supplemental breaker/fuse for a branch circuit. This is suppose to protect the wiring, but as TO mentioned that buying a cheap breaker may not be the wisest choice. I use  UL listed breaker's that are specific to the application, but I think the general message here is that safety is the first priority.  On many machines that run 240VAC 3 phase, and some 240 single phase they use a separate transformer with a fused output to provide 110/120V single phase for subsystems, and this can be used for the DRO (which draws minimal current).


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## Doodle (Aug 13, 2017)

Haven't looked at the code recently as I have retired from the trade. In the old days on motor controllers voltage for the control circuit was limited to 120VAC thus the reason controls had the step down transformer. Circuit breakers are sized to the load and must be rated to be capable of breaking the maximum instantaneous current supplied. In most residential USA that was 10000 Amps. Wire sizes in the USA when the National Electrical Code (NEC) is accepted by the Authority having jurisdiction are selected from tables in the code book. So for example a 12 gauge copper conductor is capable of 30 amps but is derated based on temperature, type of insulation, how the conductors are cooled as in open air, conduit fill, and length. Exceptions to the rule used to be load sharing and the tap rule. Keep in mind that the NEC is the minimum safety requirement. Doing above and beyond is allowed.


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## Cheeseking (Aug 14, 2017)

Honestly I don't see the benefit of doing this other than a tad less clutter.  If you have a 120v outlet reasonably close to the lathe I would use it and skip the integration with the lathe itself.   Just my .02


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## darkzero (Aug 14, 2017)

The benefit for me is that I don't have to bother switching the power on/off for the DRO separately. Just a convenience aside from less clutter. When I turn the power on/off for my mill or lathe, the DRO does as well just like the lights mounted on both machines. I don't have very many 110v outlets in my garage either. My power feed on the mill is plugged into to 110v, I forget to turn it off all the time.

I agree with the points made in this thread. I asked my electrician about it. He told me not to worry about it. I understand just the power cord may not be protected but he said the chances of the power cord getting shorted is pretty rare how I have mine set up. My power cords are cut short to length & are tucked away. Perhaps I may add some inline fuses to them someday anyway.


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## mksj (Aug 14, 2017)

Agree with Will, in fact on my my lathe I have the DRO as a direct power connection in the control box, but it is only 120V. When I get into the 240VAC range I get a bit more skittish, do not ask me how, but the wire can go up in flash quickly and violently. On my mill, I am bringing in 240VAC  power with 10G wire, 32A fuses. I bring in 4 wire power and have two duplex respectable each going to 15A supplemental breakers.  So different approaches, as long as the wire is in good shape, and terminated well, I do not think it is a big deal. I just like to erh on the conservative.
Mark


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## Doodle (Aug 15, 2017)

Watch your fuse holders for bad connections and fires, they are notorious for failures if the fuse holders are weak. Everyone should get the non contact temperature meter now that they can be bought for as little as $20 at HFT. Stand back about 2 feet and scan your electrical wiring, breakers, VFD, Motors, etcetera and note the temperatures. Bad connections will show spikes from ambient temperatures and other equipment will have nameplate operating temperatures. It is a great way to protect your investments.


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## Linghunt (Aug 19, 2017)

*One common practice:* After you do your wiring / upgrade and some time has gone by, say a few weeks. Go check your terminal blocks and snug them up again. This is more important on higher power level joints, but still a good practice.  Pop the cover off of your breaker panel ( POWER OFF and MEASURED) and check the lugs, you will see what I'm talking about.

*Don't oversize wire sizes.*  This is common error that is done by electrical types in the business as well.  Had a few arguments over this topic before.  The bigger the wire is all good when everything is working, *but when you have a failure....*

Let's say your breakers, fuses etc don't work. what is next to go?  If you got a 20 gauge wire compared to a 14 that has say 5 A running thru it.  That larger wire will be able to run longer with more power before it burns up.  I would rather have it burn fast breaking the circuit. 

*Example:*  I had a 14 AWG fuse link ( just a wire like 5 inches long. ) in my design.  Wire was used to tap power off of a 300A , 3 phase busbar leg to a small breaker.   Anyhow some E tech was in there adding an upgrade for something else and ended up running the wire from phase to phase.  Anyhow on power up *BOOM.*   The tech blamed my design and upgraded it to a 8 AWG, going around me to facility electrician post discussion.  All his fix would have been was a louder bang and surge.   I let it go and waited a while then had a different tech go back in and change it to 18 AWG.   Design had a flaw I learned from this this event.   I was 25 year old rookie engineer then and tech had some 30 year experience.  He wasn't going to listen some punk kid.   Years later I finally got him to see why.  He was going to go change the wire, and I told him I had it done years ago without him knowing.  LOL     

DON'T GO CRAZY ON TINY WIRES EITHER.   Practical aspects of them getting kicked around needs to be considered.  I try to stay at 20 AWG or larger when possible.


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## Cheeseking (Aug 20, 2017)

I will respectfully disagree re wire size.   Fuses are VERY reliable and breakers while they can fail, I bet there's 100 situations to 1 where oversize conductors would be more desirable in the event of a short circuit on equipment.  
At that point the hope is the equipment itself has some sort of protection and becomes the next weakest link.   Rather have a motor or whatever let out the magic smoke than somewhere inside my walls


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## Linghunt (Aug 20, 2017)

Each situation is different.  That is why one does a PHA ( Process Hazard Analysis ) on the project. A PHA is basicly an organized way to ask *what if's* and the resulting $ cost to life and material.  This will allow you to fix the high risk items that are low cost to do.

I agree that fuses and breakers work pretty good.  That said I've seen knife switches fail where only 2 phase are disconnected. Seen many breakers fail closed, these bad boys do have a low life cycle ( 20K I think).  The boys using those for LOTO tend to wear them out.  You got non electrical folks using them and no clue that that break as they work on dangerous equipment.  Breakers are current limit device not a switch.  

Run a breaker towards its limit for years. then see if it trips.  Contacts can get welded together.  Perhaps one pole will open and the others don't.  You got a tech that doesn't measure, and assumes it's off will get smoked. 

As for fuses,  have you seen those conduit or copper tube fuses ?  We bought out a company and went to disconnect equipment and get it ready for transport.  Stick of conduit and a bandsaw is all that is needed to make fuses.  Unreal.  Not all fuses work good is the point.

Have you seen the techs that keep adding a larger fuses to see where the problem is via smoke/flame.  No smoke then he says fixed and has an overrated fuse in there.  The engineer had a lower fuse size for a reason.  Designing for future failure modes can be tough, having seen lots of crap, has alternate my design thought at times.   

Part of the "what if question" we all should ponder. 

Small gauge wire in a drywall type wall doesn't sound like a good idea.  Pretty sure that's a NEC Code violation as well.  

Wire size and  current capacity is part of design thought process.  Don't assume that larger wire is always better approach was my point.  

The fuse link example above was in a large steel enclosed electrical cabinet on a multi-million dollar machine.  

Switching neutral and grounds is one of my favorite soap box topics that puts the burrs under my saddle blanket.


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## Cheeseking (Aug 21, 2017)

Sorry to have gone off topic a bit but since its gone there, anyone interested in electrical safety may want to check out Mr NEC himself Mike Holt on YouTube.    Good stuff.   very knowledgeable group of individuals reviewing various code sections.    There are several on grounding and conductor sizing.


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## mksj (Aug 21, 2017)

"Each situation is different. That is why one does a PHA ( Process Hazard Analysis ) on the project. A PHA is basically an organized way to ask *what if's* and the resulting $ cost to life and material."  I could not agree more, there is a reason for how electrical/mechanical systems are designed and the materials/components used. There is also a risk/failure mode analysis vs. cost, and as we all well know that everything is built to a price point, so factor that in when you buy electrical components/equipment.

The comments in this posting bring up a lot of sage points that I think we should all take note of. I am not and electrician, but practicing medicine for many years it became clear that the answer is almost never clearly black or white, but shades of grades.  When it come to machinery and electrical safety, there is a lot of information to understand and even the experts will tend to disagree. Through the years, I have repeatedly gone back to the NEC guidelines and also local electrical requirements. On machinery I reviewed many accident reports, often very gruesome to understand what happened, and what the conclusion(s) and corrective procedure(s). Looked at countless factory schematics, specifications and electrical installations to better understand the does and don't, and the potential failure modes. Mike Holt's information is eye opening, and shocking about all the myths and misunderstandings of electrical code. With all that, I still feel dumb. The common notion that it won't happen to me, or I am smart enough to remember, well it only takes a moment of poor judgement or lost concentration and it happens in a blink of the eye.

There are extensive codes to specify what the minimum NEC electrical standards, they are there based on the accumulation and understanding engineering/electrical/material/device properties and  what went wrong in the past. Newer requirements for thing like GFIs and ARC fault breakers are a consequence of understanding the failure modes and how to minimize risk, this also goes for many machine control systems like E-Stop systems. To each application, there is a complex standard as to how to do proper electrical installations and a myriad of factors to take into account. There is a big difference in application, such as wiring in an electrical box vs. wiring in a wall. Two machines with the same functional specifications may have  totally different designs to achieve the same operational specifications, so there are different approaches to how to build them.

The flip side to the discussion, if one bypasses or ignores the safety devices, such a bypassing a fuse/breaker, then something else is going to fail and maybe with much more serious consequences.  This all leads back to understanding the safety devices, and reasonable electrical/mechanical implementation/safety.  On most of my machines, I use finger safe cartridge fuse holders/fuses, the fuse characteristics are specific to the application. Supplemental breakers/fuses are used for subsystems in accordance with the load characteristics and associated wiring and terminal ratings, the wiring associated equipment is to the same electrical ratings (temperature, installation specification, etc.). The wiring to the socket/electrical box is to the NEC code.  I am constantly reading commentaries by engineers and electricians specific to questions and there replies. As much as I do not care for forums like the Practical Machinist that can be very hostile to layman individuals, there is a lot of forum contributors that have extensive knowledge in electrical/code installations, and usually substantiate their comments. I always listen to those who have the education and experience in the field, but there opinions may not always agree between them.

So this all folds back to trying to do your installations properly with knowledge, and not necessarily with the thought that it won't happen to me. Seek out someone with the appropriate expertise in the field and ask. We are  hobbyist, each with very different backgrounds and experience. The purpose (at least for me) for these types of discussions is to learn and grow from each others knowledge and expertise.
Mark


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## Linghunt (Aug 21, 2017)

mksj , some very good points. 

I see NEC as a guideline for design in my OEM equipment and not a rule book unless my product will see an Inspector ( house or building type jobs ).  When that is the case you need a licensed electrician, not someone like me.   TUV, UL and the such add to the mix as well. 

I got a pdf copy of the 1897 NEC if you are interested. 

http://www.linghunt.com/101Spearfishing/Spearfishing101RefManuals.html#NEC

Mike Holt is a great source of info as well.  

EC & M is one of my favorite spots current events on this topic.  

http://www.ecmweb.com/  

To add to the mix the OSHA regulations make designing pretty tough.  Poorly written technical regulations by lawyers and other inside the beltway types.    

Go read section *1910.333 * which has some pretty good stuff, and my favorite *1910.147* for Lock out / Tag Out. 

I can walk into any company and shut you down for not being 100% compliance with this document.  

PHA documents and the such is the kinda stuff an inspector will want to a see if they are giving you an exam. Do diligence is very important.  I've had outside independent inspectors review some of my equipment and was told it was not in "complete" compliance.  That said I was also told it was one of the safest designs he had ever seen.  You can't win is the point for a design that is actually safe and in check with laws and regulations. 

I went to a paid OSHA class once through the local jr college, It was a joke for me, but boss sent me with a couple techs and our companies hygienist. The instructor couldn't answer my tough nosed questions on the gray areas, I keep them to a minimum and did more of it in 1 on 1 chat.  Class was for general introduction for Industrial Hygienist types to check off a box for knowledge base.      

I'm a huge fan of LOTO.  The biggest flaw in any LOTO program is "real" education of the end users.  Designing to protect electricians and technicians is one of my main concerns. This ties me back to floating neutrals and commons that tweaks me big time.

TUV and European compliance certificates has been a tough bar to jump for me.  EM noise emissions in general. What was interesting is their lack of LOTO requirements. 

One of my favorite accidents to illustrate LOTO safety. The Fortuna, CA tree debarker (1992).  Watch the FARGO movie (1996) and the brush shredder for a visual. 

https://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=170718944


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