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#129419 - 02/28/05 12:58 PM what really is an ungrounded system?
unsaint32 Offline
Member
Registered: 08/24/04
Posts: 15
Loc: eden prairie, MN, USA
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
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#129420 - 03/01/05 02:00 AM Re: what really is an ungrounded system?
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Sung,
Welcome to ECN,
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.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
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#129421 - 03/01/05 04:20 AM Re: what really is an ungrounded system?
pdh Offline
Member
Registered: 01/20/05
Posts: 354
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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