Forums
New posts
Search forums
What's new
New posts
New media
New media comments
Latest activity
Media
New media
New comments
Search media
Members
Current visitors
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Main Forums
Student & Learning Zone - City & Guilds
Type d mcb
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Help Support Talk Electrician Forum:
This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Message
<blockquote data-quote="apprentice87" data-source="post: 533279" data-attributes="member: 13534"><p>Here is how i do it without messing about with charts or culculators or any of that nonsense..</p><p></p><p>Firstly, yes, i know that they brought in an amendment that supposedly allows for the volt drop under fault conditions but i could alter my method to allow for that if i wanted.</p><p></p><p>Anyway, we know that to trip in the required time a "B" curve requires a fault current 5 times its rated current, a "C" curve 10 times and a "D" curve 20 times...</p><p></p><p>We also know that MEASURED Zs must not be more than 80% of its calculated value to allow for the increased cable resistance caused by the heating effect of the fault current. So the reciprocal of 0.8 is 1.25.. Ok????</p><p></p><p>Right then, an example..</p><p></p><p>i bimble about and i come across a final circuit, it is fed by a 32A "C" curve MCB Does this circuit comply?? Ok, so, 32A x 10 = 320A </p><p></p><p>320 x 1.25 = 400A </p><p></p><p>I test the PEFC with my meter, it is 475A [say] YES!! all is well!! If LESS than 400A umm, we have a problem...</p><p></p><p>Who needs charts or calculators????</p><p></p><p>john..</p></blockquote><p></p>
[QUOTE="apprentice87, post: 533279, member: 13534"] Here is how i do it without messing about with charts or culculators or any of that nonsense.. Firstly, yes, i know that they brought in an amendment that supposedly allows for the volt drop under fault conditions but i could alter my method to allow for that if i wanted. Anyway, we know that to trip in the required time a "B" curve requires a fault current 5 times its rated current, a "C" curve 10 times and a "D" curve 20 times... We also know that MEASURED Zs must not be more than 80% of its calculated value to allow for the increased cable resistance caused by the heating effect of the fault current. So the reciprocal of 0.8 is 1.25.. Ok???? Right then, an example.. i bimble about and i come across a final circuit, it is fed by a 32A "C" curve MCB Does this circuit comply?? Ok, so, 32A x 10 = 320A 320 x 1.25 = 400A I test the PEFC with my meter, it is 475A [say] YES!! all is well!! If LESS than 400A umm, we have a problem... Who needs charts or calculators???? john.. [/QUOTE]
Insert quotes…
Verification
Post reply
Main Forums
Student & Learning Zone - City & Guilds
Type d mcb
Top