It is currently Sat Sep 23, 2017 6:31 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Allowable LOTO service disconnect
PostPosted: Tue Jul 10, 2012 4:51 am 
Offline
Sparks Level

Joined: Mon Jul 26, 2010 10:55 am
Posts: 56
Excuse my ignorance but I need some feedback on this question. In the end we are going to install 3 pole switches but I want some input on this.

We currently have people doing simple preventative maintenance on small fans. Some of these fans are very small 3ph motors with 2 pole disconnect switches. Their work would only be to replace a belt or sheave. They would never actually work on the motor or touch/troubleshoot the electrical components.

The question is would this 2 pole switch be code compliant strictly as a service disconnect?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Jul 10, 2012 9:50 am 
Offline
Sparks Level
User avatar

Joined: Sat Jun 07, 2008 5:11 pm
Posts: 143
Location: Connecticut
No... not compliant under a bunch of NEC & NFPA 70E rules. For LOTO all sources of energy must be removed. A two pole disconnect switch on a 3 phase motor will still leave one leg with the possibility of being energized. I'm not sure why a 3 phase motor has a 2 pole disconnect?? I've seen older starters with two overloads... but never with 2 pole disconnects.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 16, 2012 10:16 am 
Offline

Joined: Sun Jul 25, 2010 10:56 am
Posts: 3
geh7752 wrote:
No... not compliant under a bunch of NEC & NFPA 70E rules. For LOTO all sources of energy must be removed. A two pole disconnect switch on a 3 phase motor will still leave one leg with the possibility of being energized. I'm not sure why a 3 phase motor has a 2 pole disconnect?? I've seen older starters with two overloads... but never with 2 pole disconnects.


I disagree. The workers in question will only be doing tasks that expose them to MECHANICAL energy hazards (replacing belt / sheaves). The 2-pole disconnect switch does effectively remove the source of this hazard since a 3 phase motor cannot run with only one phase leg connected. On the other hand, if the workers were going to expose any wiring, thus exposing themselves to an electrical shock / arc hazard, all 3 phases would need to be opened and locked out.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 16, 2012 12:12 pm 
Offline

Joined: Mon Mar 29, 2010 8:31 am
Posts: 24
Location: Jonesboro, AR
NEC 430.103

Disconnecting means shall open all ungrounded supply conductors and shall be designed so that no pole can be operated independently.

Since the belt may be changed (which means work around the shaft) all poles have to be accounted for in safe discconect means.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 16, 2012 1:00 pm 
Offline

Joined: Thu Feb 04, 2010 5:00 pm
Posts: 36
Location: Camp hill Pa
Wormfood wrote:
NEC 430.103

Disconnecting means shall open all ungrounded supply conductors and shall be designed so that no pole can be operated independently.

Since the belt may be changed (which means work around the shaft) all poles have to be accounted for in safe discconect means.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 16, 2012 1:15 pm 
Offline

Joined: Thu Feb 04, 2010 5:00 pm
Posts: 36
Location: Camp hill Pa
240 volt single-phase motors connected to a 120/240 volt system will have 2-pole diconnects.

There were and maybe still are some old, older then me, 3-phase delta systems with an one leg grounded. Note this is not your usuall 120/240 high leg delata with the center of the one phase grounded that is used to supply single phase 120/240 volt and 3-phase 240 volt. In this case a two-pole disconnect works, since one phase is grounded. I suggest replacing this kind of a system with a more common system. This systyem was sometimes used for crane feeders, but I never heard of it supply other factory equipment, but it could. Square D amongothers in the 60's listed circuit breakers for use on such a sysstem.

Hey, go into any old shop, and anything can be found. I was very impressed with Lake Union Dry Dock, Machine Shop years ago. Asingle large motor drove all of the machine tools though a shaft and pulley system that run though the shop. Each machine had a drive bolt that was placed on a pulley on the shaft to turn the machine on, and slipped off to turn it off, using a hook stick. Evidently in times past a steam engine drove the system and it was removed and replaced by a motor.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 16, 2012 6:03 pm 
Offline

Joined: Sun Jul 25, 2010 10:56 am
Posts: 3
Just because it is an NEC violation does not make it a 29CFR1910.147 OSHA violation. The energy hazard in this specific example is that of a rotating shaft, belts, etc. If the disconnecting means is effective in positively isolating the hazardous energy and preventing the energy from being restarted, it meets the requirements of the Standard. By opening and locking out 2 of the 3 phases, the rotational energy has been controlled. The remaining hot wire is not an energy hazard to the mechanic who is not exposed to any uninsulated conductors.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Jul 17, 2012 7:10 am 
Offline
Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 438
Location: Wisconsin
JayWes38 wrote:
There were and maybe still are some old, older then me, 3-phase delta systems with an one leg grounded. Note this is not your usuall 120/240 high leg delata with the center of the one phase grounded that is used to supply single phase 120/240 volt and 3-phase 240 volt. In this case a two-pole disconnect works, since one phase is grounded. I suggest replacing this kind of a system with a more common system. This systyem was sometimes used for crane feeders, but I never heard of it supply other factory equipment, but it could. Square D amongothers in the 60's listed circuit breakers for use on such a sysstem.


FYI.
You are describing a 'corner-grounded' delta system (oftentimes called grounded-B phase). These are not old and outdated nor limited in scope to cranes. Systems like this are frequently installed today, particularly when locations have 208V or 240V services that need to be stepped up to 480V for a few pieces of equipment.. Granted, they are not as common as 480Y/277V, but they definitely exist. In fact most panel manufacturers have this system as part of their normal UL Listing, however not every breaker is rated for corner-grounded systems.

The delta-breaker you referred to was a special 3-pole breaker that would mount into a single-phase panel. It had nothing to do with, and was not even rated for corner-grounded systems.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Jul 17, 2012 12:07 pm 
Offline

Joined: Fri Aug 26, 2011 7:38 am
Posts: 29
Location: Baltimore, MD
Unless the unswitched phase conductor is intentionally grounded (a grounded delta system) then the installation violates the NEC. Should any worker be accidentally injured, and it comes to light that the company knowingly allowed a NEC violation to persist, the company could face a major liability. Furthermore, eventually someone will need to do electrical work on the motors, at which point the disconnect will be ineffective even if one considered it effective for LOTO for shaft and pulley work. Even were there no regulations or legal liability, morally I think the company is obligated to correct an unsafe condition as soon as possible.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 23, 2012 8:00 am 
Offline

Joined: Mon Mar 29, 2010 8:31 am
Posts: 24
Location: Jonesboro, AR
Couple of other reasons not to have 2-pole disconnects.

Establishment of a Electrically Safe Work Condition - NFPA 70E
(3) Wherever possible, visually verifty that all blades of the disconnecting device are fully open or that the drawout-type circuit breakers are withdrawn to the fully disconnected position. (Opening and inspecting the disconnect requires proper PPE)
(5) Use an adequately rated voltage detector to test EACH phase conductor or circuit or circuit part to verify that they are de-energized. (In the 2-pole senario on 3-phase motor this would always fail.)

Per 29CFR1910.147
Energy isolating device. A mechanical device that physically prevents the transmission or release of energy, including but not limited to the following: A manually operated electrical circuit breaker; a disconnect switch; a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors, and, in addition, no pole can be operated independently; a line valve; a block; and any similar device used to block or isolate energy. Push buttons, selector switches and other control circuit type devices are not energy isolating devices.

The Person operating the discconect is responsible for establishing the condition regardless of any other work being performed.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 23, 2012 9:32 am 
Offline
Sparks Level

Joined: Mon Jul 26, 2010 10:55 am
Posts: 56
First off - Thanks for all the input. This is not a grounded delta it is just an old existing installation. I know the correct long term thing to do is replace the 2 pole switch with a 3 pole and that has been done. With that said I still have this feeling that in this task specific application the 2 pole switch would serve the desired level of protection UNLESS we take safety to a point of "don't get in your car". On a side note if this does not serve as a proper safety disconnect why are 1 pole and 2 pole contactors allowed to be installed on equipment?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 23, 2012 9:40 am 
Offline
Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 438
Location: Wisconsin
100questions wrote:
On a side note if this does not serve as a proper safety disconnect why are 1 pole and 2 pole contactors allowed to be installed on equipment?

Controllers do not have to 'open' all ungrounded conductors, but disconnects do.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 23, 2012 1:02 pm 
Offline

Joined: Mon Mar 29, 2010 8:31 am
Posts: 24
Location: Jonesboro, AR
I'm going on remembered information here, so if I'm off please don't hold it against me.

I do not believe lock out/tag out was harped upon unitl @ 1990. Thus with older installations a disconnect to only break the power to keep things from running may have been acceptable. I know that NFPA 70E was around in the late 70s, but I don't have access to an old revision.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Jul 27, 2012 11:44 am 
Offline
Sparks Level
User avatar

Joined: Tue Apr 17, 2012 8:19 am
Posts: 240
Location: Charlotte, NC
100questions wrote:
On a side note if this does not serve as a proper safety disconnect why are 1 pole and 2 pole contactors allowed to be installed on equipment?


Different applications COULD use 1 pole and 2 pole contactors. Single pole contactors can be used on single-phase systems there there is a power and a neutral (like 120 VAC).

2-pole contactors are used on single-phase systems there there is a L1, and a L2 (like 240VAC).

Single-pole or 2-pole contactors are also used on DC systems where you are disconnecting an armature.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jul 30, 2012 3:09 pm 
Offline

Joined: Mon Jul 30, 2012 2:56 pm
Posts: 1
Doesn't NFPA 70E Handbook 120.2(B)(1) explained that even indirect electrical hazards, such as the mechanical motion of a motor, require the LOTO to be in accordance with NFPA 70E requiring a test of all phases for an absence of voltage? If this is true, a two pole breaker would fail the test.

Situational Example: An operator opens and locks a local disconnect, verifies the disconnect open through a viewing window, tries to operate the equipment, and then goes to work on the coupling or belt of a conveyor. How did the operator verify an absance of voltage and the removal of the indirect electrical hazard? If this is acceptable, why can't an electrician use the same method of verification?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Jul 31, 2012 5:03 am 
Offline
Sparks Level

Joined: Wed Oct 29, 2008 6:06 am
Posts: 136
Location: Michigan
[font=Tahoma]NFPA-70E 120.(B)(1) requires everyone exposed to electrical energy either indirectly (operator) or directly (electrician) to be involved in lockout/tagout. However, the operator is not exposed to the hazards of electric shock or arc flash and therefore different standards apply.[/font]

[SIZE=3][font=Times New Roman][color=#000000][font=Tahoma]OSHA 29 CFR - 1910 General Industry[/font][/color][/font][/size]
[font=Tahoma]Subpart J: General Environmental Controls - 1910.147 Control of Hazardous Energy (lockout/tagout)[/font]
1910.147 (d)(6) requires verification of isolation. A simple sample lockout program example is provided in appendix A where verification is done by attempting to operate the equipment.

Subpart S: Electrical - 1910.333 Selection and use of Work Practices
1910.333(b)(2)(iv)(B) requires a qualified person to use test equipment to verify the conductors and components to which they will be exposed are de-energized.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sat Aug 04, 2012 6:59 pm 
Offline
Sparks Level
User avatar

Joined: Sat Jun 07, 2008 5:11 pm
Posts: 143
Location: Connecticut
lblahj wrote:
I disagree. The workers in question will only be doing tasks that expose them to MECHANICAL energy hazards (replacing belt / sheaves). The 2-pole disconnect switch does effectively remove the source of this hazard since a 3 phase motor cannot run with only one phase leg connected. On the other hand, if the workers were going to expose any wiring, thus exposing themselves to an electrical shock / arc hazard, all 3 phases would need to be opened and locked out.


Yes, electrically the motor won't run... However, it's absolute stupidity to put a 2 pole disconnect on a 3 phase motor.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Aug 10, 2012 12:52 pm 
Offline
Sparks Level
User avatar

Joined: Tue Apr 17, 2012 8:19 am
Posts: 240
Location: Charlotte, NC
Especially if you get a phase-to ground short on a motor with a 2-pole disconnect. If the fault is on the non-disconnected phase and there is a problem with the motor ground, someone is going to get a nasty suprise - even if they are just doing mechanical work on the motor.

Though I once saw someone get shocked off a sink that had NO wires attached to it. It was on a farm and a power strip (which had an individual ground rod and wasn't tied to the main service ground) had failed. The 120 VAC was shorted to the power strip ground and feeding into the ground and coming back up through the plumbing.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Aug 15, 2012 4:03 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1761
Location: North Carolina
Wormfood wrote:
Couple of other reasons not to have 2-pole disconnects.

Establishment of a Electrically Safe Work Condition - NFPA 70E
(3) Wherever possible, visually verifty that all blades of the disconnecting device are fully open or that the drawout-type circuit breakers are withdrawn to the fully disconnected position. (Opening and inspecting the disconnect requires proper PPE)
(5) Use an adequately rated voltage detector to test EACH phase conductor or circuit or circuit part to verify that they are de-energized. (In the 2-pole senario on 3-phase motor this would always fail.)


Whoa, mistake. NFPA 70E refers to electrical lockouts. Under OSHA this is Subchapter S, or if it is generation/transmission/distribution, Subchapter R (or a mix of R & S if you've got some of both distribution and utilization). What is being described is either one of a general lockout (Subchapter J) or an operational lockout (Subchapter O). Under subchapter O, the rules are so "loose" that you don't need an energy isolation device at all. This is to encompass things like an operator opening an interlocked door on a hydraulic press to remove a part. So under Subchapter O, neither of the above are required. Under Subchapter J an energy isolation device is required but you don't have to test for absence of voltage. In fact, the requirement to "try" which is typically implemented in Subchapter J lockouts as far as I know is only present in Subchapter S of all places.

Quote:
Per 29CFR1910.147
Energy isolating device. A mechanical device that physically prevents the transmission or release of energy, including but not limited to the following: A manually operated electrical circuit breaker; a disconnect switch; a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors, and, in addition, no pole can be operated independently; a line valve; a block; and any similar device used to block or isolate energy. Push buttons, selector switches and other control circuit type devices are not energy isolating devices.


Again, you are mixing LOTO procedures. This is a quote from Subchapter J for general lockouts. We're getting somewhere because most likely this is what the original poster was asking about. However again, you read this section in isolation from Subchapter S. In fact Subchapter J (1910.147) makes it very clear that this is NOT intended for electrical lockouts and refers to Subchapter S.

What I didn't even touch yet is that it also depends on the type of industry. Electrical and general lockouts are also vastly different for construction especially. There is a whopping 2 paragraphs for construction electrical lockouts (Article 1926). The only thing new over there is that tags are always required whereas they are optional under 1910 rules in many cases. The rules change again if you are under MSHA. And this is just the sections I'm familiar with. I'm completely blind to what you do in maritime.

Long story short: read the ENTIRE section when quoting OSHA regulations. You CANNOT mix and match. That "introductory" material at the beginning is critical to understanding what regulations apply to what situations.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Aug 15, 2012 5:19 pm 
Offline
Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 415
Perhaps this might be useful to find the correct Subpart: http://www.osha.gov/dts/osta/oshasoft/lotoplus.html.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 20 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883