Three EE thumb rules to follow:
Continued from part 7: Electrical Thumb Rules You MUST Follow (Part 7)
Accuracy Class of Metering CT
| Metering Class CT | |
| Class | Applications |
| 0.1 To 0.2 | Precision measurements |
| 0.5 | High grade kilowatt hour meters for commercial grade kilowatt hour meters |
| 3 | General industrial measurements |
| 3 OR 5 | Approximate measurements |
Accuracy Class Letter of CT
| Metering Class CT | |
| Accuracy Class | Applications |
| B | Metering Purpose |
| Protection Class CT | |
| C | CT has low leakage flux. |
| T | CT can have significant leakage flux. |
| H | CT accuracy is applicable within the entire range of secondary currents from 5 to 20 times the nominal CT rating. (Typically wound CTs.) |
| L | CT accuracy applies at the maximum rated secondary burden at 20 time rated only. The ratio accuracy can be up to four times greater than the listed value, depending on connected burden and fault current. (Typically window, busing, or bar-type CTs.) |
Accuracy Class of Protection CT
| Class | Applications |
| 10P5 | Instantaneous over current relays & trip coils: 2.5VA |
| 10P10 | Thermal inverse time relays: 7.5VA |
| 10P10 | Low consumption Relay: 2.5VA |
| 10P10/5 | Inverse definite min. time relays (IDMT) overcurrent |
| 10P10 | IDMT Earth fault relays with approximate time grading:15VA |
| 5P10 | IDMT Earth fault relays with phase fault stability or accurate time grading: 15VA |
Related electrical guides & articles
Jignesh Parmar
Electrical Middle management professional having more than 22 years rich and dynamic experience in Project Execution / Project Management / Designing / Maintenance diversifies from Electrical Power Transmission (400KV/220KV/66KV)- Distribution(11KV/220V) to Lifts-HVAC-Ventilation-Fire Fighting-Fire Alarm-Lifts-CCTV-Stack Parking Works (High Rise Buildings, Townships, Shopping Complex, Commercial Complex, School, Temple).Profile: Jignesh Parmar
THANKS SIR,
VERY NICE MATERIAL FOR PRACTICAL KNOWLEDGE IMPROVEMENT
How to prepare ELECTRICAL BOQ ? Can you pls help ? Do you have some study material or book on that. URGENT !
thanks sir, your articles helping me to boost my kowledge.
Thank you for providing such important information which will help to update my knowledge.
Thanks Jungesh ..Keep it up.
Good stuff ..
thanks Jignesh sir, for giving us the information about electric thumb rules.
i want help from you,
can you give me a thumb rules for the use of estimation and costing of electrical project work ?
Great electric engineering.
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Dear Jigu Sir,
Good and Thank you so much. It is use full for us.
I wanted to query the last part of your article regarding the accuracy class of protection CT’s. What was the intention of this part of the article?
Is it to give one an idea as to how to select CT’s?
To my knowledge, the CT ratings are dependent on the fault level of the application, this is one of the determining factors for the CT sizing.
If you have some time, please look into writing an article on this topic as well.
Thanks once again.
Your materials are very useful. How do I download them? Keep doing the great job.
You can find “Get PDF” Tag on middle left og the webpage,by clicking on that you can have pdf copy of what u want…have a great day