TT PFC question

[pevvers]

L to N 0.47 kA acceptable
L to E 93 A is this acceptable and normal?

Surely it would be PSCC that is the highest, at 470A, not the PEFC at 93A? Or have I missed something silly....

 

[electricAl]

Surely it would be PSCC that is the highest, at 470A, not the PEFC at 93A? Or have I missed something silly....

No, i don`t think you have

You`re quite correct if you`re saying that the PSCC will be filed as the PFC.

The OPs confusion was due (i`m assuming) to the very low PEFC values TT installs throw up. Hence the discussion

or atleast i thought thats what we were discussing

 

[pevvers]

Oh, it was only because he was asking which one to put down as the PFC value a couple of posts back, and you both said the PEFC.... Didn't want him to get a cross against something in his inspection by putting down the 93A value on his paperwork. Although with a Ra of 120 ohms it's gonna be a lot lot smaller than 93A.

I'm think I'm confused by the whole discussion, if I am please just ignore me and I'll go sit in the corner.

 

[electricAl]

Oh, it was only because he was asking which one to put down as the PFC value a couple of posts back, and you both said the PEFC....
I'm think I'm confused by the whole discussion, if I am please just ignore me and I'll go sit in the corner.

Umm... don`t think anyone did actually

Maybe i`m confused -think i`ll join you in the corner

 

[pevvers]

Ah bugger it....

 

[scotsparky]

I said the Phase earth fault which is the PEFC but dont worry about it.

 

[matt456]

i was looking for which value to put in the pfc box on the IET websites EIC certificate
0.47 ka was the reading L-N and 93A was the reading L- E
im a little confused as its been a while since i tested a tt system so hence a little confusion over the readings!!

 

[pevvers]

Then you would put the higher of the two, which would be the 0.47kA.

 

[scotsparky]

on the Zs and PFc boxes i put in the Higher Ze and Lower PFC as that is the "worst case sinario" as such if that complys all others do.

 

[pevvers]

Ah, so that's where the confusion has come into the discussion... On my part anyway.

I was always taught to put the highest of the PFC's into the box!

Would the worst case scenario not be the higher of the two?

 

[scotsparky]

Worse case woulf =ld be High ZE and low PFC remamber you want a high fault current for your disconnection times. so if its lower then slower disconnection times.

 

[pevvers]

I understand what you're saying completely, but I am going by what is written in GN3. I only have the 16th edition copy with me at the mo, but it states that "Prospective fault current (PFC) - The value recorded is the greater of either the short-circuit current or the earth fault current. Preferably determined by enquiry of the distributor"

Damn, I sound really arsey for a new poster on here but I don't mean to be. But like I said, I don't want the fella to get marked down on his NIC assessment.

 

[Lou7]

Record the highest reading, double for 3-phase,or x1.74 as I was told by NICEIC.

 

[electricAl]

Actually its 1.732 - the root of 3

 

[scotsparky]

yes fair play no worries Its just thats what i do i do stant to be corrected though. Mind you i also douple the PFc for 3 phase.