Direct wiring DRO to lathe?

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
 
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.
 
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.
 
"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
 
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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