| M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|
| « Jun | ||||||
| 1 | ||||||
| 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 23 | 24 | 25 | 26 | 27 | 28 | 29 |
| 30 | ||||||
Richard Cummins
Electrical Manager
Lectrus Corporation
(832) 295-1200
Richard Cummins is Electrical Manager for Lectrus Corporation (formerly Metal Systems), a Chattanooga-based industry leader that engineers and builds fully-integrated, electrical equipment centers, operator centers and custom enclosures for the power, oil & gas...more»»
Motor Starting
Posted by Rem from Los Angeles, CA, US on June 30, 2009
What is the starting current of a 200 horsepower motor operating at 480V, 60Hz?
The starting current as per IEC or BS should be 6 times the rated current with tolerance. There is a 20% tolerance on Starting current. So maximum can be 7.2 times. Many manufacturers face problems in limiting starting current particularly in 2 pole machines. In such cases the published figure in the catalogue subject to 20% is the max value of starting current. The published values in some cases may be high and when referred to rated current may workout to 6 times rated current value plus or minus 20%. Inrush current = starting current = lock rotor current = 1000*hp*(kVA/hp)...
...where kVA/hp is Locked Rotor Code Letter refer to NEMA table 430-7(b) which is attached on the motor name plate as KVA Code for Siemens motors. Hope this helps!
VFD Protection
Posted by avdhut from verna, IN, IN on June 26, 2009
How can I protect a VFD and all power supply cards if I have a Harmonics distoration in the plant power? Also, what is the basic schematic of power protection devices for VFD and servo drives?
An Isolation transformer is a device used to perform isolation from the noise you describe. It is a 1:1 transformer that will decouple the grounds between your existing power and the output power to your VFD's, power supply cards and servo drives. You will need some type of power distribution system (panelboard or fuses) to complete the power feeds to several devices.
Current Transformer
Posted by kashif from Multan, OT, PK on June 23, 2009
We have a 2MW load. How do we calculate the CT ratio for this load?
CT ratio is the ratio of primary current to maximum secondary current under full load conditions. 150/1 means 1 amp will flow in secondary when there is 150 amps in primary side. You should size you CT to be a percent of the full load and monitor your CT's for load protection. The CT ratio depends on the range your monitoring equipment requires. Please refer to the range of your load monitoring equipment then size your CT to output full load current inside of this range.
Wire Voltage Rating
Posted by David from Lavergne, TN, US on June 19, 2009
What is the voltage rating if #6 wire is used in a 480V circuit? The AC unit requires a 50A breaker. The size of the conductor is #6.
The ampacity will depend upon the type of insulation your wire has and its rating. If you have THHN insulation it has an ampacity of 65 amps from 0 - 2000 VAC at 75 degrees C. Please consult Table 310.16 in the NEC handbook.
Electrical Receptical Safety
Posted by Joan from Chagrin Falls, OH, VI on June 12, 2009
In a double gang box, is it code and safe to run a wire from one receptical to another off of the side screw, or should the supply wire be spliced and placed directly on each receptical? The recepticals are made by Leviton.
Assuming you have two 120VAC outlets in the double gang box (with one branch circuit in and a traveler out), having a "traveler" between the receptacles is safe and common practice. A "traveler" is the wiring that continues a branch circuit from receptacle to receptacle. In your case, the "traveler" would be a short jumper between the receptacles in the double gang box. Just remember to connect all three of the grounds together in the box. Connect the ground wire properly to each receptacle and to the double gang box if it is a metal box.
