Discuss Table 41.3 Max earth fault loop impedence (Zs) in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Reaction score
5
The heading of table 41.3 says it shows " max earth fault loop impedance Zs for Circuits Breakers..... giving compliance with 0.4s disconnnect time of 411.3.2.2 and 5s disconnnect time of 411.3.2.3."
411.3.2.2 is for final circuits not exceeding 32A. 411.3.2.3 is for distribution circuits and final circuits 40A and above. But something doesnt add up here.. There's a 12-fold difference between 0.4 seconds and 5 seconds. But the table (look at part a for type B circuit breakers) is linear and gradually decreasing between 32A and 40A. Somethings not right here, or I just dont understand. Can someone please explain ???
 
Re: Tabvvle 41.3 Max earth fault loop impedence (Zs)

Circuit breakers reach a certain current and will then trip "instantaneously"; before a circuit breaker reaches that current the minimum disconnection time is about 12s for a type B MCB so does not meet the minimum disconnection time for either option, once the MCB reaches the instantaneous tripping point then the disconnection time complies with both 0.4s and 5s so the value of EFLI is the same for both disconnection times.
have a look at the time current graphs in appendix 3, e.g 3A4 for type B MCBs, and it should all become clear.
 
followup:
if anyone compares the values in table 41.3 with the calculation results from the formula in 411.4.5 you will find that the table is much too conservative, and will give loop dimensions much smaller than that from the the formula. so the formula is much preferred. compare it yourself !!!
 

Reply to Table 41.3 Max earth fault loop impedence (Zs) in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock