You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old March 18th, 2003, 08:07 AM   #1
grey
Member
Canada

grey is offline
 
grey's Avatar
 
Join Date: Feb 2003
Location: Canada
Posts: 14
disconnect location

Is it normal or a good practice to locate an on/off switch disconnect between a VFD and the motor in a 3 phase application? example.. an on/off lockable switch located 3 feet from the motor and the source VFD many feet away . My concern is there is no way of really knowing if when the switch is turned on, whether there is instant live power to the motor, if all circuits are ready ?
  Reply With Quote
Old March 18th, 2003, 08:28 AM   #2
jrwb4gbm
Lifetime Supporting Member + Moderator
United States

jrwb4gbm is offline
 
Join Date: Apr 2002
Location: NC
Posts: 2,212
It is almost always a good practice from a safety standpoint. You should put an interlock contact in the disconnect operated by the on/off handle to disable the output of the VFD drive. This is to minimize risk to the drive and personnel. The only time I can think of to not have one is when a greater risk to personnel is created if the switch is operated inadvertently. By the way, you should always assume the live power is there in these types of applications.
  Reply With Quote
Old March 18th, 2003, 09:10 AM   #3
grey
Member
Canada

grey is offline
 
grey's Avatar
 
Join Date: Feb 2003
Location: Canada
Posts: 14
re ....when a greater risk to personnel is created if the switch is operated inadvertently.

This was my point. There is sometimes 2 or 3 operators and personnel around these machines who could turn it on. There is no interlock contact at present. It is just the power wires in the disconnect.

If a door switch was bypassed or held for troubleshooting for example and the on button engaged the machine would move instantly when this extra disconnect is turned on, possibly by another person. I will advise we put an interlock into the disconnect.
  Reply With Quote
Old March 18th, 2003, 09:18 AM   #4
Ed01
Member
Netherlands

Ed01 is offline
 
Ed01's Avatar
 
Join Date: Jul 2002
Location: Alphen aan den Rijn
Posts: 58
Hi there,

You should check the VFD documentation if switching in the output of the VFD is allowed, there are some brands that not allow you to switch in the output.
  Reply With Quote
Old March 18th, 2003, 09:27 AM   #5
RDay
Member
United States

RDay is offline
 
RDay's Avatar
 
Join Date: Apr 2002
Location: Evansville, Indiana.
Posts: 143
Unhappy

Would it not be safer to have one disconnect that provides power to the VFD and then lock that dissconnect out? If there is no power to the VFD then the motor will not be powered. If there are multiple disconnects through out the circuit it may cause confusion and end up getting some one hurt.
__________________
RDay

  Reply With Quote
Old March 18th, 2003, 10:29 AM   #6
Steve Etter
Lifetime Supporting Member + Moderator
United States

Steve Etter is offline
 
Steve Etter's Avatar
 
Join Date: Apr 2002
Location: Morristown, TN
Posts: 915
Hi Grey,

EdO1 and RDay are both right on track. Some VFD manufactures definitely tell you not to put a disconnect between the drive and the motor or risk damaging the VFD if there is no load on the VFD when told to operate.

The best solution is to locate your disconnect in front of the VFD. This solves the initial safety concern and prevents the potential damage to the drive.

The idea of installing an interlock in the disconnect is a good idea for monitoring purposes but may not really reduce your liability for the equipment (assuming that the manufacturer said "don't do it at all") and certainly does not put you in any better condition in terms of OSHA's "Lock-out, Tag-out" guidelines.

You made three statements that are cause for concern:
1) "There is sometimes 2 or 3 operators and personnel around these machines who could turn it on",
2) "If a door switch was bypassed", and
3) [If a door switch is] held for troubleshooting.

Each of these statements seem to indicate that your company needs to revisit its machine safety training and guidelines.

Any time a disconnect is turned off, the person who did so must lock it out. If they do not, they have no way of being certain it remains that way and, as a result, they must be the one to turn it back on. This is basic to OSHA's guidelines.

No door or safety switch should ever be bypassed or held open. Period.

If one is, as an accepted practice, then there are some bigger problems that needs to be addressed in management, personnel training, and safety device integration.

That's my humble opinion anyway.
Steve
  Reply With Quote
Old March 18th, 2003, 11:03 AM   #7
grey
Member
Canada

grey is offline
 
grey's Avatar
 
Join Date: Feb 2003
Location: Canada
Posts: 14
re the points 1, 2, 3 ...I know all these things are true.
It is because someone in the Company has authorized putting these disconnects in between the VFD and the motor. I dont think they are safe or needed and I am trying to figure out how to get them safe or have them removed .
To me a lockable E-stop could have been used on the main control panel if extra flexibility was wanted. These disconnects have been added in after years of safe operation as the system was originally designed and engineered. I am not convinced all safety aspects and machine concerns were looked at when they were added. So that is where I am at now.
  Reply With Quote
Old March 18th, 2003, 11:39 AM   #8
David_Emmerich
Lifetime Supporting Member
United States

David_Emmerich is offline
 
David_Emmerich's Avatar
 
Join Date: Sep 2002
Location: Smiths Grove, KY
Posts: 670
Per OSHA guidelines, you must have a lockable disconnect switch at remote motors, usualy interperted as being within 3 feet/arms reach of the motor pecker head. We use a 3 pole manual motor switch with an aux contact feed back to the VFD's run contact. The way we use it is to stop the motor using normal stop switch, then open and lock the remote motor sw. This way, you do not damage the VFD by removing its load while it is running, but it will not start until the motor is back in the circuit. It only takes two more wires to do it this way, and I have never blown a drive.

David
  Reply With Quote
Old March 18th, 2003, 11:51 AM   #9
grey
Member
Canada

grey is offline
 
grey's Avatar
 
Join Date: Feb 2003
Location: Canada
Posts: 14
Ok...this 2 more wires sounds like the best way to go.
Must be an American thing....I have never heard of a "motor pecker head" before ?
  Reply With Quote
Old March 18th, 2003, 12:06 PM   #10
rsdoran
Lifetime Supporting Member
United States

rsdoran is offline
 
rsdoran's Avatar
 
Join Date: Apr 2002
Location: Birmingham, AL
Posts: 7,372
its just the box on the motor where the wires are connected, is an old term.
__________________
http://www.patchn.com Industrial Electrical & Maintenance @ www.patchn.com "Tell me and I forget, show me and I remember, involve me and I understand."
  Reply With Quote
Old March 18th, 2003, 12:46 PM   #11
Tom Jenkins
Lifetime Supporting Member
United States

Tom Jenkins is offline
 
Tom Jenkins's Avatar
 
Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 5,879
"motor pecker head" is indeed the conduit box or motor lead termination box on the side of the motor. As Ron says, it is an obslolete term (and one I have to remember to avoid when I'm talking shop with my wife!)
  Reply With Quote
Old March 18th, 2003, 12:54 PM   #12
Steve Etter
Lifetime Supporting Member + Moderator
United States

Steve Etter is offline
 
Steve Etter's Avatar
 
Join Date: Apr 2002
Location: Morristown, TN
Posts: 915
David,

I may be wrong here, but I think you are refering to NEC regarding the location and distance requirements for your disconnects. I believe OSHA only addresses what constitutes an acceptable lockout device and how to use it. If I am wrong, I would appreciate a pointer to where I can find the guideline to which you are refering.

Also, while the NEC code is only meant as a minimum guideline, this is the first time I have heard your "3 feet / arms reach" interpretation. 2002 NEC Code, Article 430.102 reads:

Quote:
430.102 Location.
(A) Controller. An individual disconnecting means shall be provided for each controller and shall disconnect the controller. The disconnecting means shall be located in sight from the controller location.

Exception No. 1: For motor circuits over 600 volts, nominal, a controller disconnecting means capable of being locked in the open position shall be permitted to be out of sight of the controller, provided the controller is marked with a warning label giving the location of the disconnecting means.

Exception No. 2: A single disconnecting means shall be permitted for a group of coordinated controllers that drive several parts of a single machine or piece of apparatus. The disconnecting means shall be located in sight from the controllers, and both the disconnecting means and the controllers shall be located in sight from the machine or apparatus.


(B) Motor. A disconnecting means shall be located in sight from the motor location and the driven machinery location. The disconnecting means required in accordance with 430.102(A) shall be permitted to serve as the disconnecting means for the motor if it is located in sight from the motor location and the driven machinery location.

Exception: The disconnecting means shall not be required to be in sight from the motor and the driven machinery location under either condition (a) or (b), provided the disconnecting means required in accordance with 430.102(A) is individually capable of being locked in the open position. The provision for locking or adding a lock to the disconnecting means shall be permanently installed on or at the switch or circuit breaker used as the disconnecting means.

(a) Where such a location of the disconnecting means is impracticable or introduces additional or increased hazards to persons or property

(b) In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment
Now, obviously your rule of thumb certainly fits this definition, but I think it is important to note that it is a much tighter interpretation than "within sight".

I also think it is important to note that a VFD qualifies as a "Controller" in 430.102(A) and needs to have its own disconnect (or, as per Exception No. 1, at least one disconnect for a coordinated group of controllers).

Steve
  Reply With Quote
Old March 18th, 2003, 04:23 PM   #13
Vetteboy
Member
Canada

Vetteboy is offline
 
Vetteboy's Avatar
 
Join Date: Jul 2002
Posts: 380
Wink

Peckerhead isn't just an American term . As an apprentice here in Canada, I didn't know it had any other name. Once I was a journeyman and worked in a few different places, I actually heard someone call it a termination box. How boring! It would only be offensive to people who use that term for something else, indicating they have probably heard it before.
  Reply With Quote
Old March 18th, 2003, 04:23 PM   #14
jrwb4gbm
Lifetime Supporting Member + Moderator
United States

jrwb4gbm is offline
 
Join Date: Apr 2002
Location: NC
Posts: 2,212
Grey,
In reference to the lockable E-Stop you mentioned in post #7.
In recent years there have been some changes in the NEC in the US.
They can not be used for as a primary safety disconnecting means for protection of personnel or equiptment, but I think that they are allowed to remain as a supervisory type of device. That would let a machine operator keep the machine stopped and locked off for production changeovers to prevent product mix-ups or contamination.

In reference to my earlier post (#2), I mis-read it somewhat, I thought you had a disconnecting means for the motor and the VFD.The safe solution is to lock out both points.
  Reply With Quote
Old March 18th, 2003, 05:43 PM   #15
David_Emmerich
Lifetime Supporting Member
United States

David_Emmerich is offline
 
David_Emmerich's Avatar
 
Join Date: Sep 2002
Location: Smiths Grove, KY
Posts: 670
Hi Steve et al,
Yes 3 feet is much closer than required, but if I had my shirt get caught for what ever stupid action I was doing, don't you know I would try for that d@#@ sw!!!!! We always put a sw, and sometimes two, within EASY reach of a motor... it's an old habit that I have always insisted on. Most of the plants I have worked in have such a high noise level, a person 20 feet up would have a very hard time getting the attention of someone down below, and even if they could, that person would probibly just wave.
I think that you are correct about OSHA and the lock out...sorry, but you get my drift... Like someone said, the NEC is just a guide that should be met or exceded...most of the time it does not cost much to do better then expected, and it sure can pay off...just that one time it counts.

David
beerchug beerchug beerchug beerchug beerchug
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
programming PLC in remote location morzian LIVE PLC Questions And Answers 4 March 22nd, 2007 07:44 PM
Hazardous Location Phone. (OT) elevmike LIVE PLC Questions And Answers 4 December 27th, 2004 01:27 AM
I/P Location GregPLC LIVE PLC Questions And Answers 12 August 25th, 2004 04:50 AM
Disconnect sizing GregPLC LIVE PLC Questions And Answers 1 July 16th, 2004 04:56 PM
Disconnect or FUSE ??? Orn Jonsson LIVE PLC Questions And Answers 2 February 7th, 2003 11:23 PM


All times are GMT -5. The time now is 01:50 AM.


.