jraef,
My state has had a NRTL excemption for "Industrial Electrical Equipment" in state law for many years. Should I find that the C&D switches will work and they'll ship to us directly, the lack of a NRTL label will not preclude their use in our plants.
Very nice jraef! You'll get a star from me, too! That was just what I was looking for. Because these are 3 HP motors, 12 t-leads in a box is really no big deal.
Thanks!
Thank you all for a very lively thread! To answer some of the questions raised:
We are still going to have traditional 30A NEMA disconnects for each motor for servicing. We will be fully compliant with NEC requirements.
All our disconnects have an aux contact back to the drive or PLC to...
Bill,
Our standard is to incorporate an Aux switch on our disconnects so that the drive "knows" that we are disconnecting the motor. Saves us from a lot of drive faults.
Lots of switches could be used for this with the conductor size and load, but as you point out, I haven't found any that...
We thought about using a safety relay to disable the PowerFlex output transistors but explaining how all this works to OSHA is assumed to be problematic. The operator would have a keyed switch with the key captured in the closed position. To use, the operator stops the line, opens the switch...
Terminations in MV motor boxes need to be very carefully made. Our plants use putty, cambric and lots of #88 tape. Failure to properly wrap the T-leads and motor leads can result in phase-to-phase or phase-to-ground faults through the wrap that could easily destroy a cast iron termination box...
I have an application where I need to disconnect and lock out four VFD motors (all are 3 HP) with one switch. But I have been unable to find a suitable switch. Does anyone know of a switch that might work?
This switch is to allow the operator to lock out four sections of belt drivs so that...
Check out Scribd for an upload of Olson's Dynamical Analogies - 1943 which describes several different mechanical systems compared to electrical systems.
http://www.scribd.com/doc/12914354/Olson-1943-Dynamical-Analogies
I advised against it for the reasons all of you mention. I never recommend running motor leads from multiple drives, DC or AC, in the same pipe. But that's the way they originally installed the DC drives and it has worked for fifteen years or so without incident. But parts for these drives...
One of our plants has DC motor conductors for several DC drives run in the same conduit. They want to replace one of the DC motors with a 3-phase induction motor and run the AC drive conductors in the same conduit as the DC motor conductors. I think this is a very bad idea but there is no Code...
"On power transformers, the industry standard is to assume the RMS inrush current is 25 times RMS full load current for .01 seconds and 12 times RMS full load current for .1 seconds. Control transformers can have peak inrush currents that are 100 times the full load RMS current for 1/2 cycle."...
I believe Oregon also allows two years experience credit for a Master's degree. Google "OSBEELS" for more info.
A PE license is good only for the state in which it is issued, however, you can be licensed in most states even if not a resident. In fact, you can take the PE exam in another...
