prospective fault current

Jake1579 · Mar 26, 2015

i understand what pfc is - the maximum current that flows under fault conditions until protective device is operated.... and i know the difference between the 2 types
prospective earth fault current
prospective short circuit fault current

My question is what (path) would prospective short circuit fault current follow under fault conditions because i know with pefc its going to follow the earth fault loop path ZS so its going to have a low zs value so it trips quick. But what about if there was short on l and n i know if there was the breaker or what ever it would trip but i dont get how i know it will have a low resistance so it does trip quick but what path does it take if it is the earth fault loop path i imagine it will have a low zs but theres no earth involved if its on l and n is there??

Marvo · Mar 26, 2015

The PSC fault current path varies depending on the supply arrangement ie TNCS, TNS etc.

Jake1579 · Mar 26, 2015

could you elaborate on what you mean are you talking like tncs the earth neutral combined ect.. ?

davesparks · Mar 26, 2015

Prospective short circuit current is the current which will flow through a short circuit of negligable impedance at the incoming supply terminals.

What exactly are you trying to ask here ?

Jake1579 · Mar 26, 2015

say theres a short on live and neutral and you have that fault current flowing through it does that fault current on a short circuit between l and n just go into the protective device and detects that fault current and it just disconnects ??

davesparks · Mar 26, 2015

Jake1579 said:
say theres a short on live and neutral and you have that fault current flowing through it does that fault current on a short circuit between l and n just go into the protective device and detects that fault current and it just disconnects ??

The fault current will flow through every protective device upstream of it. One of these devices will clear the fault.

Silly Sausage · Mar 26, 2015

A Line to Neutral or Earth fault will create an overcurrent on that Line which the OCPD will see and operate.

PEG · Mar 27, 2015

Hi dude,if you get out the generic fault path diagrams,which simplify the path from generation to fault,you can imagine,or draw your fault,L to N,and see the path of that fault current,and the protective devices it flows through.

There are some excellent drawings on some of the help threads regarding 2391,2394/5.

There is no shame in a picture,i have used these to learn,to teach,and to explain. Even drawing out suppositions i may have,regarding problems,can confirm things,when expensive components are going to be ordered.

...The Bayeau tapestry isn't on a memory stick......get yer pencil out! :icon12: