DC Ground Fault detection without breaking the earth bond?


  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: DC Ground Fault detection without breaking the earth bond?

    It's probably just fine but I think it costs way more money that the other methods ?

    Arc Fault is most likely a better over all solution for stopping fires than ground fault IMHO.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,401 admin
    Re: DC Ground Fault detection without breaking the earth bond?

    There are a couple of threads that go into way too much detail about DC GFI issues:


    The MorningStar unit is certainly a huge improvement over the NEC DC GFI (see above threads for details).

    And if you were doing high voltage DC power distribution (such as the 380 VDC distribution consortium for computer data centers)--A DC GFI system for branch circuit protection would seem to me to add a huge amount of fault isolation/detection vs the standard methods of DC wiring (safety ground referenced, or floating both Hot and Return):


    AC power systems have an inherent fault isolation (galvanic isolation) and ultimate current limit (saturation) that transformers provide and DC circuits lack. The DC GFI detection (300 mamp differential trips the MorningStar device) gives us a level of fault isolation/detection that has been missing from DC power distribution systems and branch circuit protection.

    To address what the NEC wants to "fix" (arc fault)--It is a start--But probably not the complete solution at this time. A distributed arc fault detection system with disconnects at the solar array per string level--I think that is what the regulatory folks really need/should be looking for. If you are looking for detecting/quenching a high percentage of arc faults, adding arc fault detection to a DC GFI CPD like the MorningStar system would probably required.

    The problem is, without active monitoring and comparing against a standard (such as a reference solar sensor that monitors both sun and actual array output)--Trying to figure out faults and protecting against dangerous failures (vs just remote sensing of open and shorted wiring/connections/panels) is not a trivial task.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset