BASIC ELECTRICAL ENGINEERING FOR CE

Transcription

1 EE24 BASIC ELECTRICAL ENGINEERING FOR CE LECTURE NO. B-2 Residential Motor Loads

2 Full Load Current of Motors 2

3 Example #1 Engr. Oliver Dy and Engr. Mechelle Perez bought an airconditioner for Engr. Marijo Pestano and it is rated 1.5Hp. Determine the full load current (FLC) of the airconditioner. Answer: Look at the table, FULL LOAD CURRENT, SINGLE PHASE (if the aircon is single phase) FLC is 10 Amperes. 3

4 Air-conditioning/Refrigeration Short Circuit and Ground Fault Protection PEC (a) Rating or Setting for Individual Motor Compressor. The motor compressor branch circuit and ground fault protective device shall be capable of carrying the starting current of the motor. A protective device having a rating or setting not exceeding 175% percent of the motorcompressor load current or branch circuit selection current, whichever is greater, shall be permitted, provided that, where the protection specified is not sufficient for the starting current, the rating or setting shall be permitted to be increased but shall not exceed 225%... 4

5 What is Branch Circuit Selection Current? FLA OR FULL LOAD AMPERE FLC or FULL LOAD CURRENT Branch Circuit Selection Current Motor Current FOUND in PEC/NEC Table Nameplate Rating 5

6 Air-conditioning/Refrigeration Conductor Sizing PEC Single Motor Compressor. Branch-circuit conductors supplying a single motor compressor shall have an ampacity not less than 125% of either the motor compressor rated load current or the branch circuit selection current, whichever is greater. PEC Motor-Compressor(s) With or Without Additional Motor Loads. Conductors supplying one or more motor compressors with or without an additional load(s) shall have an ampacity not less than the sum of the rated load or branch circuit selection current ratings whichever is larger, of all the motor compressors plus the full load currents of the other motors, plus 25 percent of the highest motor or motor compressor rating in the group. 6

7 Example #2 Engr. Marijo Pestano needs to install the airconditioner that Oliver and Mechelle bought. Rating is 1.5Hp, 230V Single Phase. a) Determine the branch circuit conductor that she needs to use b) Determine the short circuit protection/device that she needs to install 7

8 Solution A. Conductor Selection Aircon is 1.5 Hp, FLC = 10Amperes 10 A x 1.25 = 12.5 A minimum ampacity for cable Use 2.0 mm2 THHN. B. Short Circuit Protection 10 A x 1.75 = 17.5 A (Choose NEXT LOWER standard Circuit Breaker) Use 15AT 2P MCCB ALWAYS USE NEXT LOWER STANDARD CIRCUIT BREAKER RATING FOR MOTORS 8

9 Example #2 Engr. JB Co received a lot of airconditioner coming from a lot of girl-friends and boy-friends. He received from the following: One (1) 1.5HP 230V Aircon One (1) 2.0HP 230V Aircon One (1) 1.0HP 230V Aircon However, he has only one open circuit breaker space in his panelboard. How will he wire the three airconditioners? 9

10 Several Motors & Other Loads Feeder Calculation PEC Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity at least equal to the sum of the full load current rating as determined by Section (a)(1) of all the motors, plus 25 percent of the highest rated motor in the group, plus the ampere rating of other loads. 10

11 Solution 11

12 Air-conditioning/Refrigeration Overload Protection Each motor compressor shall be protected against overload and failure to start by one of the following means: 1) Overload Relay 2) Thermal Protector integral to the equipment 3) Fuse or inverse time breaker not more than 125% of rated load current 4) A protective system that will prevent overheating 12

13 Other Dwelling Motors/Pumps (Squirrel Cage / Wound Rotor) 1) Branch Circuit Conductor shall be based from 1.25 x Motor FLC, and then selecting the appropriate ampacity from table (with application of correction factors. 2) Branch Circuit protective device shall not be greater than 250% of Motor FLC for Circuit Breakers or 300% for Non-Time Delay Fuses with Across the Line (Direct Voltage Connection). 3) Motor Feeder Size calculation shall be the same as Airconditioning, such as (Sum of FLC of Each Motor x FLC of Largest Motor of the Group) 4) Motor Feeder Circuit Breaker Calculation shall be based on PEC (a), such as, Highest Rating/Setting of CB of Largest Motor + Sum of Full Load Current of the Remaining Motors 13

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