Thanks for your response, this is consistent with my thinking. All of the motor applications where I've seen this design have been older (50+ year) installations and it was not clear to me that it was still a prudent design approach. Loads will not be stopped / started frequently, and 125 VDC...
We are looking at project specs which are specifying new 480 VAC switchgear that will control several larger HP (125 - 300 HP) motors directly across the line using the switchgear breakers and not via an MCC with motor starters/contactors. I am more familiar with motor starter construction -...
Is there an IEEE or similar standard for recommended max voltage drop on a 480 V distribution system during a motor start? I'm evaluating options for reduced voltage/soft start/VFD start for an existing installation - we can figure out what the transient voltage is, but I'm not sure of what...
In the one primary metered configuration that I did a preliminary design for - I included gang-operated switch w/cutouts at the service point to comply with 230.205. The contractor disagreed that it was needed since most secondary metered services do not have that. Someone else ended up doing...
Is the existing installation actually a service? Doesn't 250.24(C) require grounded conductor (neutral) pulled to service equipment?
The Green wires accomplish this, but I'd think they would be 'white' wires up to the service equipment. If its a service.
From the tagnames and configuration shown on the one-line I am pretty sure I know the plant this work is being performed at and agree that a grounding study requirement would be unusual for that size/type of plant, but there are many things unusual about that plant.
Hopefully MCC upgrades are...
Our approach would be as mentioned by xnuke - keep vendor drawings as vendor drawings, and create interconnect/installation drawings for the field installation that reference the vendor drawings.
In some instances the client may want loop termination drawings that end up duplicating information...
Can anyone point to a good reference to evaluate life expectancy of diesel engine-driven generator in an industrial, standby application?
We have a 750 kW unit. I have seen some reference suggesting 10000 - 20000 hours, depending on quality of maintenance, frequency of operation, loading...
Thanks Jraef -
Are the safety contactors you describe the starters? Or interposing relays in the control circuit - i'm trying to determine the bounds of the SIL system - whether it stops at the control circuit, or at the motor contactor. I am used to seeing SIL applied to valves/solenoids...
We have an application which requires SIL2 motor interlocks - to prevent 2 pumps running simultaneously. My experience with SIL systems is limited to process instruments, not necessarily motor starters - is there such a thing as SIL-rated motor contactors/starters?
in the context of an arc flash study, how does the arc-shield MCC affect the IE levels? Does it allow you to credit the main circuit breaker? Does it allow for reduced IE levels at the bucket due to its construction? While it is likely safer, does it buy you anything when performing an...
We have a standby generator - 480/277 V.
The vendor has provided p.u. reactance data for a 139/240 configuration.
I should be able to convert the p.u. to ohms and back to 480, correct? I am uncertain as to how the windings are reconfigured in the 480 application - is it as simple as doubling...
You might look in the standards associated with the propane installation rather than the electrical standards. For instance NFPA 58 in the USA says that a LPG container cannot be located within 6' of the vertical plane beneath overhead electric power lines that are over 600V.
