Why do you use a differnt voltage when calculating PSCC for a mains cable? i.e 230/Ze or 400/Ze?
Answer:
We use different voltage supplies for domestic and industrial uses and of course Ohm's Law applies. Because the protective devices in an installation have different characteristics we need the know the PSCC that will flow through then.
In power installations in European countries (230 V 50 Hz AC single phase power) the short circuit current available on the electrical outlets needs to be taken into account when designing all electrical power wiring. The short circuit current should not be too high or too low. The effect of too high short circuit current will be that the protective devises won't be able to handle the current flow, where as too low a short circuit current would mean that the protective devises will not operate in a short circuit situation it should be of the order of around 200 A or higher for normal 13 A or 16 A outlet to guarantee that the normal wire protecting fuse or breaker will quickly disconnect the supply in case of short circuit. So you can see that Zs is more important than Ze.
Quick disconnecting is needed, because in live-ground short circuit the grounding pin potential on the power outlet can rise compared to the local earth (water pipe etc.) during short circuit to a dangerous voltage, which needs to be shut down quickly for safety. If the short circuit current is lower than this figure, special precautions needs to be taken to make sure that the system is safe; these usually include using a RCD for extra protection.
The current through the conductors causes heat and the cross-sectional area of the conductors must be sufficiently high to carry the current continuously. The insulation used on cables also limits the operating temperature. Excessive heat will melt the insulation. The dielectric stress on the cable depends on the voltage. 230V is the Line to Neutral voltage and 400volts is the line voltage of the three-phase distribution system.
I am sure you can find more information on the Internet. Just search for 'Cable Current Ratings'
Or more simply
The two voltages represent:
230 = single phase voltage - between a phase and neutral L1 -N 03 L2 - N or L3 - N
400 = Across two Phases on a Three phase system. L1 - L2 L1 - L3. or L2 - L3
The answers post by the user, for information only, FunQA.com does not guarantee the right.
More Questions and Answers: