How is the primary connected to on a pole mounted transformer. Like a small 75kVA, with 240/120 secondary. I only ever see one squiggly line down to a high voltage bushing going in to case, which is also tapped to an arrestor, grounded to the case. The secondary has its three insulated terminals...
Does anyone know, in general what NEC section (table) best describes how to derate SOW type cable. I am unable to verify voltage drop calcs. The application is for (temporary) power disto from smaller portable generators (15kw). The cord reels are specified with 200' SOW cable, 3wire+G #10AWG...
A senior electrical designer is trying to convince me that on a 480 system voltage drop isn't really a consideration. Here's the situation. We have a feed to an 800A MCC with about 434 TCHP / 514 KVA of motor load. He insists that since the voltage drop over the feeder is on 1-2% that the...
I was intending to use LPS-RK fuses to replace FRS-R type, for some FVNR starters (10-40hp), vfd's (40hp), & SMC's (125-150hp) all 460V. According to NEC 430.52, size time-delay fuses at 175% of full load current. I have no nameplate information from the motors, so I assumed that FLA = FLC for...
I am curious about the history of Carbon Monoxide awareness (residential) in the USA. I am a young firefighter. We receive CO alarm activations year around, nearly all false alarms / malfunctioning detectors. The Red-Cross has distributed CO alarms free for about the last 7 years (literally like...
Is it appropriate to install both a line ractor and load reactor (dV/dt filter) to combat: harmonics on the source feeders, and IGBT effects on long motor leads, respectively. I am assuming our motors were not spec'd as inverter duty rated. The various drives range from 30, 45, 75, and 100 hp @...
We are working at a plant with 480/277V, and is distributed using 3 wires + ground. The incomming feeders are 13.2kv to a delta - wye transformer. I guess the wye secondary is grounded somewhere at the substation? Although I only see a delta-star diagram on the nameplate. Should / does the sec...
Opinions needed: What does this mean to you?
MCC Incomming Line Disconnect
Circuit Breaker
Frame - 800A MC
Trip - Non-Auto
The first three lines are obvious. What is the reference to Non-Auto (Trip). I was told it was a thermal-magnetic breaker, without the overload ("thermal"). It would...
What is the propper pressure to pump into the FDC sprinkler system. I thought it was constant, regardless of building size, assuming the inlet would be sized appropriately to maintain estimated flow rates. So if the building has a standpipe, what is the minimum working pressure that must be...
Any advice / opinions for a young engineer - would be helpfull. I am working with a designer on sizing feeders to a freezer / cooler room. The PDP requires a 3000A service (480v, 3ph, 4w), but has 75deg C terminations. The designer wants to run 10 sets of 500kcmil in seperate RMC. The run is...
Another engineer has told me that I need to locate my MCC closer to my motor loads " to limit IGBT effects on the system". I have a few medium loads between 30 and 60 hp. Could anyone provide a brief explanation about the determental effects of lengthy cables and how this is related to...
I would like someone to verify an engineers calculations:
I have a delta / Y-grounded 45 KVA-3phase 480-208/120V transformer.
I calculate the rated line current at I primary @ 54.12A and I secondary @ 125A. The individual phase current should be Ip = 54.12/sqrt(3) = 31.25A and Is = 125A. The...
