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Joined: Aug 2004
Posts: 15
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Q 1) What is the purpose of ungrounded system. Is it not to trip the circuit breaker when

the first fault occurs? (for more controlled deactivation?)

Q 2) In a grounded system, having one conductor connected to earth provides the reference

for steady voltages supplied to loads. How is stable voltage accomplished in an ungrounded

system?

Q 3) Actually, there is no such thing as an ungrounded system, right? (Because an ungrounded

system is capacitively grounded.. whatever that means)


Thanks for your answers

Sung

Joined: Jul 2002
Posts: 8,432
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Sung,
Welcome to ECN, [Linked Image]
Most Electrical systems throughout the world have a reference to Earth.
This is mainly for Safety reasons.
It is so that there is a limit on the Line to Ground voltage.

Joined: Jan 2005
Posts: 354
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pdh Offline
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I wouldn't trust an ungrounded system where the primary has a higher voltage than the secondary to be very stable. Impedance grounding is generally adequate for a one fault tolerant system. And you'd need that grounding point to set an alarm to know where there is a fault.

I wouldn't even trust an article 411 system (411.5(A) requiring it to be ungrounded) unless it is isolated with a grounded electrostatic shield between primary and secondary, or has 2 transformers with an intermediate grounded loop at the final secondary voltage.


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