VFD's and MOTOR STARTERS

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I?ve been on the sending and receiving end of job specifications.

The army has a policy, ?keep it simple, the stupid can understand it.?

As site agent for the company time spent on the site arguing with the contracting firm is non-productive as far as I can see. It would be trivial things that shouldn?t have been in the specification at all. But our contracts department knew better.
 
Tony S said:
I?ve been on the sending and receiving end of job specifications.

The army has a policy, ?keep it simple, the stupid can understand it.?

As site agent for the company time spent on the site arguing with the contracting firm is non-productive as far as I can see. It would be trivial things that shouldn?t have been in the specification at all. But our contracts department knew better.
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Yes. The "kiss" principle.
There are different levels of specifications. That which tell the manufacturer how to do the job they have been contracted to do - compiled by consultants who have never done it.
Then there are user manuals. These should be simple but adequate for the purpose intended.

PS. I forgot that lived in Nottingham. We were there yesterday. My younger daughter lives in the Sherwood area and we had a family get together. You could have been invited!

Sorry mods. I have wandered off topic. Be kind.
 
Besoeker said:
I forgot that lived in Nottingham. We were there yesterday. My younger daughter lives in the Sherwood area and we had a family get together. You could have been invited!

Sorry mods. I have wandered off topic. Be kind.
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I?ve got Glennsparks staying with me at the moment. I enjoy meeting other electricians now I?m retired.

Sorry, even further off topic.
 
Tony S said:
I?ve got Glennsparks staying with me at the moment. I enjoy meeting other electricians now I?m retired.

Sorry, even further off topic.
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Glenn could have been invited too!

But back to VFDs and starters.
We wouldn't get by without at least a contactor to provide a hard wired disconnect between drive and motor. In many cases we also have to have a lock off isolator and E-stop button adjacent to the motor.
Most of our kit goes in industrial plants and, because of the potential hazards with moving machinery, safety is taken to a different level.
 
Besoeker said:
Glenn could have been invited too!

But back to VFDs and starters.
We wouldn't get by without at least a contactor to provide a hard wired disconnect between drive and motor. In many cases we also have to have a lock off isolator and E-stop button adjacent to the motor.
Most of our kit goes in industrial plants and, because of the potential hazards with moving machinery, safety is taken to a different level.
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you can't use the safe torque off functions? what PL are you designing to? it seems to me that by the time you get to a PL that requires contactors to back up a safe torque off function you are talking about something very serious and not any common industrial process.
 
petersonra said:
you can't use the safe torque off functions? what PL are you designing to? it seems to me that by the time you get to a PL that requires contactors to back up a safe torque off function you are talking about something very serious and not any common industrial process.
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We install local disconnects on most motors. I would never regard a motor as electrically safe to work on unless I have a hard disconnect either
at the panel or by the motor. Sometimes this is just a lockable overload/breaker to the drive or starter. This seems to be a common practice
from what I have seen. What's a PL by the way? I profess my ignorance on this one.
 
Aleman said:
We install local disconnects on most motors. I would never regard a motor as electrically safe to work on unless I have a hard disconnect either
at the panel or by the motor. Sometimes this is just a lockable overload/breaker to the drive or starter. This seems to be a common practice
from what I have seen. What's a PL by the way? I profess my ignorance on this one.
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PL = PLC = Programmable Logic Controller?

I might trust the Safe Torque Off for e-stop, but never as a maintenance disconnect.
 
petersonra said:
you can't use the safe torque off functions? what PL are you designing to? it seems to me that by the time you get to a PL that requires contactors to back up a safe torque off function you are talking about something very serious and not any common industrial process.
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Pretty much any application. Pumps, fans, paper machines, conveyors........
 
With some all purpose adhesive you can put a padlock on just about anything - not saying you will lock anything besides the lock hasp though:angel:
 
I was just pointing out that from a LO/TO perspective, the contactor alone is not considered "safe" either, so the argument for it being there to protect someone working on the equipment is spurious. You need that disconnecting mechanism that can be locked in the open condition. A crossed wire on a control circuit to a contactor can energize it and do harm. Classic case in point was a bridge in Seattle that went up suddenly in traffic during a test of the control system, because a screw had fallen out of a terminal block and jumped across a safety interlock circuit on the contactor feeding the lift mechanism. They did not have a LO/TO procedure in place at the time. People were killed and maimed, I knew one of the ones who was maimed, she lost her foot because they had to cut it off to get her out of the vehicle when it "folded" across the barrier.
 
petersonra said:
you can put a padlock on the supply to a VFD regardless of whether there is a contactor there or not.
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Indeed you could. But we always fit a contactor - that is invariably part of the requirements to get a physical disconnect in the event of an EM stop.
 
Besoeker said:
Indeed you could. But we always fit a contactor - that is invariably part of the requirements to get a physical disconnect in the event of an EM stop.
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Used to be common here too, but with the advent of safety rated inputs on drives to put them into a safe condition, it is much less common.
 
Besoeker said:
There's less to go wrong with a contactor.
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Actually, the numbers suggest the contactor is more likely to fail then the safe torque off input on the drive.

The only times I typically see contactors on drives is where there are two safety contactors in series, but that is not real common. I wonder how "safe" a combination of a contactor and a safe off function is. Got to be better than two contactors.
 
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