Pfc

[Carnegstar]

I think its sometimes difficult to recall experience from training when you need it most.
Like the lad said his lecturer didn`t dive into it the subject well and he wants to understand it more, thats why I joined this forum.
So when im asked a question by my apprentice i can atleast have some confidence about what i am explaining is correct.

 

[shagbite]

jeez, fellas; the lad only asked for a bit of clarification on pfc. i'm sure he could have referenced one of his old college text books for the answer, but people join these forums for a bit of social interaction and to pick the brains of knowledgeable folk like yourselves - sometimes it's better to get an answer in layman's terms. you can argue that he should know the answer, being a practising electrician, but if we all knew it all, then the iet wouldn't make any money from flogging the on-site-guide, which i'm pretty sure we've all used in the past. it's a long while since i was 22, but i'm pretty sure that when i was, i'd have come out swinging as well, if i felt i was being ridiculed. having said that, i also think it's difficult to read people when you're having a conversation through a keyboard (emoticons aside), and it's easy to take offence when non was intended.

 

[Octopus]

jeez, fellas; the lad only asked for a bit of clarification on pfc. i'm sure he could have referenced one of his old college text books for the answer, but people join these forums for a bit of social interaction and to pick the brains of knowledgeable folk like yourselves - sometimes it's better to get an answer in layman's terms. you can argue that he should know the answer, being a practising electrician, but if we all knew it all, then the iet wouldn't make any money from flogging the on-site-guide, which i'm pretty sure we've all used in the past. it's a long while since i was 22, but i'm pretty sure that when i was, i'd have come out swinging as well, if i felt i was being ridiculed. having said that, i also think it's difficult to read people when you're having a conversation through a keyboard (emoticons aside), and it's easy to take offence when non was intended.

It was going OK till he used the txxxxxx word and declined to use the "thanks" button.

What ever happened to "pleases" and "thank yous" - this may be a forum but theres no excuse for being rude.

 

[shagbite]

It was going OK till he used the txxxxxx word and declined to use the "thanks" button.

What ever happened to "pleases" and "thankyous" - this may be a forum but theres no excuse for being rude.

i take your point, but i feel the thread was getting a bit tetchy before the lad started swearing. also, i believe he thanked everyone in advance in his original question.

 

[Octopus]

i take your point, but i feel the thread was getting a bit tetchy before the lad started swearing. also, i believe he thanked everyone in advance in his original question.

He put "cheers guys in advance" in the OP .... which is quite different to using the "thanks" button at the bottom left of each response that you like and or appreciate!!

 

[shagbite]

He put "cheers guys in advance" in the OP .... which is quite different to using the "thanks" button at the bottom left of each response that you like and or appreciate!!

maybe he didn't "like and or appreciate" any of the posts. having looked at the all the people who've posted on this thread, non of them have a very good 'thanks to thanked' ratio.

 

[Octopus]

maybe he didn't "like and or appreciate" any of the posts. having looked at the all the people who've posted on this thread, non of them have a very good 'thanks to thanked' ratio.

So that means they aren't worth thanking??

Pleases and thank yous cost nothing.

 

[shagbite]

So that means they aren't worth thanking??

Pleases and thank yous cost nothing.

that's true. but if the lad thought he was being picked on, i'm sure thanking them was the last thing on his mind.

 

[Chr!s]

Hi guys would just like to understand PFC a little better, here goes....... I was at a job 2day and cut off had 400 fuses rated at 80ka, it then fed a section board with mccb rated at 25ka, it then went on to feed a d/b with mcb rated at 10ka, obviously I know that under a short circuit fault the 10ka is designed to blow 1st, so my question is when measuring the PFC at the d/b fed from the 25ka mccb I got 7.2ka x2 which gave me 14.4ka what does the result actually mean? Do I want this to be less than 25ka? but what if its not? If I had measured the PFC at the end of a lighting circuit rated at 10ka what is it I'm actually achieving by doing this test?

hope I understand this a little better soon and i don't sound like to much of an idiot but my lecturer never really dived into details about this

cheers guys in advance

Well what you seem to be asking is more to do with Discrimination and Back up/ Cascading protection.

You need to be careful in both instances, best to follow type tested where possible.

If you have Discrimination between protective devices then the upstream device will see the full PFC, the device itself may limit the let through dependent upon fault level.

So lets assume we have Discrimination between the 400 kA and the 25 kA.
You measure 14 Ka downstream of the 10 kA MCB, so we either fit a MCB with a Breaking capacity >14 or we look to see if we can rely upon the 25 kA MCCB to provide back up protection.

HTH

 

[Octopus]

that's true. but if the lad thought he was being picked on, i'm sure thanking them was the last thing on his mind.

Posts 4, 5, 6 & 7 are, in my humble opinion, worthy of "thanks"

 

[nicsin02]

Thank you every1 for your advice

 

[trev]

No bother pal

 

[Billythekid]

Thank you every1 for your advice

Apologies if my post read as an insult, that truly was not my intention. I was only asking to adjust my further responses. In any case i fell asleep (Bloody Codeine :sleep1, so i wasn't much help anyway.

Regards

Billy