Ground Fault Detection 1

[ukgraduate]

Hello,

Everywhere I read on the net it says that Ground Fault Detection is not required on Low Resistance Grounding Systems only it is required on High Resistance <25A

However NEC 250.187 implies differently.


Can anyone help? What is the NEC requirement for Ground Fault Detection on low resistance grounded systems

 

[krisys]

I would like to draw distinction between the ground fault detection and ground fault protection.

a) The ground fault detection implies, it detects a ground fault in the system. Now you have a choice whether to sound an alarm to alert the operator (if one is available)or to trip and isolate the ground fault automatically. This is a generic term and normally used for a high resistance grounded system (HRGS).

b) Ground fault protection means the system is protected from the ground fault, by tripping/operating the closest protective device to the fault causing minimum supply disruption. For the low resistance grounded system and for the solidly grounded systems, this type of ground fault protection will be provided.

Due to the inherent nature of the ground fault detection system, the high resistance grounded system cannot be selectively tripped. Also due to the low current for the first, immediate isolation of fault is not essential.

Note:
Of late, I understand that the HRGS can also be selectively coordinated. But so far it is not the industry practice to coordinate the ground faults in HRGS.

Hope this clarifies your queries.

 

[ukgraduate]

Hi Krisys,

250.187 - states:

250.187 Impedance Grounded Neutral Systems. Impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current shall be permitted where all of the following conditions are met:
(1) The conditions of maintenance and supervision ensure
that only qualified persons service the installation.
(2) Ground detectors are installed on the system.

Consequently I see this as a requirement not only for HRGS but also LRGS?

 

[waross]

The Authority Having Jurisdiction may be more guided by the NEC than by free information available on the internet. But then what do I know, this is just more free information on the internet.

Bill
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"Why not the best?"
Jimmy Carter