pfc 4.6?

[sparknorfolk]

pfc on a domestic tn-s setup has come in at 4.6ka is this to high? its the highest ive ever had.

 

[Doc Hudson]

What sort of breakers have you got, aren't most MCB's 6Ka?

Doc H.

 

[NozSpark]

Nothing wrong with that...

most MCB's are at least 6kA rated

You can have over the rating of the MCB so long as you have a BS1361 type II which has a 16.5kA rating

 

[sparknorfolk]

type b breakers rated at 6k yes just thought reading was high but as long as under 6k this is always a pass is it?

 

[sparkytim]

Hi

As said before BACK UP protection is provided by the incoming service fuse and will cover this

BS 1361 TYPE II FUSE 33 KA

BS 88 80 KA

So no need to worry, the nearer you are to supply transformer the higher it will be and lower the Ze will be, What was the Ze by the way?

 

[NozSpark]

As my earlier post.. it can be higher and still be ok

 

[SPECIAL LOCATION]

pfc on a domestic tn-s setup has come in at 4.6ka is this to high? its the highest ive ever had.

The PFC will be inversely proportional to the Ze..

i.e. When Ze is lower and better then PFC gets higher.

so your (4.6ka )4600amp PFC would imply a Ze approx 230v/4600a = 0.05ohms

This would typically imply a TN-C-S rather than TN-S

unless you do have a real good earth and close to transformer?

What reading were you getting for Ze?

Either way 4.6ka in itself shouldn't be a problem providing your breakers are upto the job..

you can check this on pages 56 & 57 of On-Site-Guide,

Read from about half way down page 56.

bullet point i Prospective fault current

and ref table 7.4 on page 57.

:coffee

 

[Voltimax]

SparkNorfolk, I've asked before, but you've never answered. Where in Norfolk are you? I only ask because you're obviously new to the trade and I may be able to help you out with some of the things you ask here, I'm in Norfolk too, drop me a PM.

 

[sellers]

4.6 is fine, You may have seen my thread the other day, I got 20ka which made me think.

 

[Doc Hudson]

4.6 is fine, You may have seen my thread the other day, I got 20ka which made me think.

That is food for thought indeed sellers.

Doc H.

 

[muffin]

happy for someone to correct me but...

i have a terrible memory for figures but i think its "Its" and "Itn" are the ratings of ka for an mcb

one is the maximum a mcb can handle but will not be any good afterwards

one is the amount it can handle but will still work afterwards.

shown normally on the mcb 6in a box and then 3000 afterwards.

as stated in the nic book on testing.

so yes the mcb will handle it, but in my eyes an mcb is a resettable device and should be capable of doing so after a short circuit.

regards andy

 

[sparkytim]

See post 5

 

[sparkytim]

The PFC will be inversely proportional to the Ze..i.e. When Ze is lower and better then PFC gets higher.

so your (4.6ka )4600amp PFC would imply a Ze approx 230v/4600a = 0.05ohms

This would typically imply a TN-C-S rather than TN-S

unless you do have a real good earth and close to transformer?

What reading were you getting for Ze?

Either way 4.6ka in itself shouldn't be a problem providing your breakers are upto the job..

you can check this on pages 56 & 57 of On-Site-Guide,

Read from about half way down page 56.

bullet point i Prospective fault current

and ref table 7.4 on page 57.

:coffee

BRB Pg 76

434.3 (iv)

OSG pG 19

3.3

AND pG 56 7.2.7. Last paragraph.

 

[R&M]

Not a problem, i had 12.1 kA yesterday (in St Helena ) and with Ze= 0.04 Ohm and 1361 type II. Its ok.

 

[septiclecky]

Not a problem, i had 12.1 kA yesterday (in St Helena ) and with Ze= 0.04 Ohm and 1361 type II. Its ok.

Whats it like down in the South Atlantic this time of year?

 

[Andy™]

so yes the mcb will handle it, but in my eyes an mcb is a resettable device and should be capable of doing so after a short circuit.

regards andy

er... MCB's are designed to break a fault current. an advantage or an MCB is it can be reset, if its not damaged by breaking the fault. even if it does break and need replaced after breaking its rated current, its done its job.

 

[muffin]

yes but my point was you should fit an mcb rated to be resettable after fault. not have to replace it. yes it would have done its job and broken the circuit but why not design it properly and fit the right one for the job.

 

[kme]

Taking the last point first:

MCB lifespan is generally taken, by mfrs, to be 3 tripping cycles. More than that, and it is classed as U/S.

As for PFC; I`ve just had a number of boards (approx 40) in one building, with a PFC of at least 100KA

How would you deal with that, if you were the installer??