BPoindexter
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- Location
- MT Vernon, WA
I came across something I have not seen before. I have installed many HRG systems from 34.5kV to 480V and this is a first for me. We installed a Post Glover ground system on a 480/277 Wye. While looking at the unit we realized that they have the system grounded conductor coming into the main disconnect where it is connected to switched terminal on the unit disconnect along with the 3 phase conductors. This then goes to a fuse and then goes to the grounding resistor. What this means if someone turns off the detector unit or the single fuse blows in the grounding circuit then we lose our ground and this becomes an ungrounded system. Looking at the NEC there is no prohibition for the switch in 250.36 but one would infer that it should run from the X0 of the transformer to the resistor with out a switch and certainly without a fuse in the circuit. As is if someone were to open the disconnect or the one fuse were to blow then you have an ungrounded wye.
This does not seem logically correct to me given the purpose of such a system. This is the first time i have seen the grounded system conductor that is switched and fused? Typically they are run directly to the HRG CT then to the Resistor. Anyone seen this have any experience with this.
This does not seem logically correct to me given the purpose of such a system. This is the first time i have seen the grounded system conductor that is switched and fused? Typically they are run directly to the HRG CT then to the Resistor. Anyone seen this have any experience with this.