if your meter is only single phase meter then test between phase and neutral phase and earth which ever is the highest times it by 2 to give the total never connect your single phase meter across two phase or you will damage it
i understand that i want to calculate it with numbers and not measure it directly i know for single phase it is supply voltage divided by the phase - neutral loop impedance, so what is it for three phase don't think is is 415/Zpn is it must be a correction factor ??
Ah, forgot to mention that bit Steve! :O I'm so use to 3 phase testing kit that you forget that there is still kit out there that'll go bang if you connect it to 400 volts! :O Never mind you could always get it fixed here!
yes that is what i will do just wanted to know the formula i know where the x2 comes from now it is the approximate sq root of 3 thanks for that mate.
Ah, forgot to mention that bit Steve! :O I'm so use to 3 phase testing kit that you forget that there is still kit out there that'll go bang if you connect it to 400 volts! :O Never mind you could always get it fixed here! :^O :-|
Never mind you could always get it fixed here! I was looking for the original post on that subject the other day to see what the outcome was. Have the mods deleted it?
You'd think it was the square root of 3, but it is x2. Forgotten exact reason. The question comes up on 2391 paper every now & then. Can't remember exact reason, but it is 2x. Have to dust the old notes down. Or even try to remeber where they might be.
Assuming that the phase and neutral conductors are of the same impedance (Z), the approximate single phase fault current is given by 240/2Z. The approximate three phase fault current is given 240/Z. Therefore to determine the three phase fault current from a single phase measurement we take the ratio of these two i.e. 240/Z divided by 240/2Z which equals 2. Apologies for using the “old” voltage levels!
Hello Phase conductor impedance Z plus neutral conductor impedance Z equals a loop of 2Z. The reasoning behind using just conductor impedance is to eliminate the complication of what to do with the “source” impedance. You can therefore assume this to be equal to zero or that it is included within the impedance of the conductors. Either way it is the ratio that we are after. As a further example, if we know the phase to phase impedance then again the three phase impedance can be determined through ratios but this time 240/Z divided by 415/2Z which is approximately 1.154 (2 divided by the square root of 3).