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Why are low voltage electrical cables earthed and high voltage cables not in an electrical system?
Wiki User
∙ 12y ago
The answer is more obvious if you use slightly different terminology to ask it. You could re-phrase the question as:
Why are the low-voltage wires in a building earthed , but high-voltage transmission lines not?
Wiring in a building or home that a person may come in contact with is earthed, or grounded for safety. If a live conductor in a grounded system comes in contact with an equipment frame or other metal object, fault current flows and trips the overcurrent device. If the building's wiring were not ground-referenced, you could have exposed live parts and not know it. Surprise!
On the other hand, high-voltage transmission lines are optimized to transport electrical power long distances. Power transmission typically uses 3-phase delta which does not need an earth connection. The grounded conductor, or neutral, is derived locally after the distribution transformer. Overcurrent protection is for the protection of the lines themselves, not for people that might accidentally come in contact with them! This is why there are such strict rules concerning keeping us separated from the transmission lines.
Keep in mind that the transmission towers themselves are grounded, and there is usually a grounded wire up top, but this does not form part of the transmission system, it is there for lightning protection.AnswerUnderground high-voltage cables are earthed.Wiki User
∙ 12y ago
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