uHeat Banner - Forum Discount Available
This official sponsor may provide discounts for members
Advertisement - Content continues below
Advertisement - Content continues below

Discuss High PFC in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

andyb

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

I’ve just been to look at a job where the client wants to have a couple of extra sockets fitted.
The consumer unit is an old rewirable with no rcd protection, but there is a new garage rcd/mcb board fitted next to it with a spare way that was installed just 2 weeks ago by their landlords electrician when he installed an electric heater.
Ok, should be easy, just test the existing circuit that I’m going to extend and put it into the new board on a 32 amp mcb.
The electrician only installed 16mm tails and 10mm earth but I can easily up grade these, the problem I have is that I did a quick Ze and got a very low reading of 0.04 ohms. This prompted me to do PFC test and I got a result of 11Ka.
Now, the new garage has domestic 6K breakers fitted, I know I can get 10K mcbs but I do not know of anything with a greater breaking capacity.
Any ideas ?
 
Test Meter - Forum Sponsors since 2007!
This official sponsor may provide discounts for members
Advertisement - Content continues below
the 11ka is the reading you would get if a fault occured before the mcb if / when you do an eli at your new points or the exsisting ones it will be far lower than that
 

andyb

-
Arms
Esteemed
  • Thread Starter Thread Starter
  • #3
The 11 Ka is the maximum current that could flow in fault condition.
Therefore the breaking capacity of the mcb has to able to cope with this, this is why you note it on the certificate.
If the pfc was say 7Ka I would fit a 10Ka mcb, but as it's 11Ka even this would be inadequate.
 
D

DanBrown

I know this might be besides point now, but according to the OSG if you have a 11KA PFC, a 10KA breaker would be adequate, but would only be able to interupt a single fault before the breaker would be unusable. A 10KA would be able to keep in performance upto a 10KA fault, but after 10KA to 20KA should be able to perform once only.
Would like some confirmation on this, as this is something new ive learnt..:) or i think lol..
 
you wont get.04 or 11ka after the mcb your .04 reading is at the cu further down the installation it will drop quickly,
eli an outlet fed off that cu and see what you get
 

andyb

-
Arms
Esteemed
  • Thread Starter Thread Starter
  • #6
The rated short circuit current must be less than the pfc at the point where it is installed. OSG Pg 56.
The device is installed in the board, the pfc at the board is 11Ka.
 
yes but if there is a fault at the board the mcb is not protecting the board nor carrying the fault the device that protects the board (main cut outs) will do that and need to be 11ka or more if the fault is after the board the mcb will cover it but the pfc wont still be 11ka by this point

can anybody else confirm this is so.
 
S

Spudnik

Now chaps, i could be wrong but i calculate PFC at around 6ka?
 
G

Guest123

Hey.

In relation to your Ze, your PFC should be around 5.8KA.

Your reading is a bit high, is the installation right next to a transformer/sub-station??
 
S

Spudnik

I know thats probably the reason the Ze is low which, in turn, increases PFC but 11ka is nearly double what it should be!

Possible faulty tester or leads??

Would be interested to see the readings for PEFC or PSCC.
 

andyb

-
Arms
Esteemed
  • Thread Starter Thread Starter
  • #13
The house is close to the sub station,
The Ze was what made me do a pfc test because it is a t-n-s supply and the earth is just a bit of 10mm connected to a clamp on the lead sheath, (I think the last electrician fitted this, it's not right but i'm not going to touch it)
I did the pfc test across live & neutral.
 
G

Guest123

Hey Mark, I was trying to find the reg for you - 434.5.1, P76, I believe is the one.
 

andyb

-
Arms
Esteemed
  • Thread Starter Thread Starter
  • #15
Thanks Lenny.
Back to my op, what can I do about it? and does anyone know of an mcb with a higher breaking capacity?
 
Aico Carbon Monoxide Detectors
This official sponsor may provide discounts for members
Advertisement - Content continues below

Reply to High PFC in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Advertisement - Content continues below
Top Bottom