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Thread: Fused vs. Non-Fused

  1. #21
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    oh
    CircuitRyder --- Unfortunately not all good ideas are code enforceable.

  2. #22
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    Quote Originally Posted by mwm1752 View Post
    actually I got off on the wrong track as pv systems supply electricity & I would think the disconnect for pv fault currents would be rated per pv input power not utility -- so what is the max fault current on< 1 meg system???
    now I have to look in the book
    Fault current still comes from the utility

  3. #23
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    Quote Originally Posted by jaggedben View Post
    Fault current still comes from the utility
    Agreed. PV systems are a bit strange in that respect; under normal operating conditions the power flow is through the switch into the grid and/or local loads, but under fault conditions the current goes the other way. That is why we place our OCPD at the point of interconnection rather than at the inverter; in a properly designed PV system the inverter is incapable of endangering the conductors.

    I know you know all that, jaggedben.

  4. #24
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    I dunno if I should start a new topic for this, but since we're already sort of on it... how important are SCCR and AIC values when designing a PV system? What aspects of these values are important to me when regularly designing? I looked at the spec sheets for the SolarEdge inverters, and could not find an SCCR value. Am I misunderstanding something here?

    Regards,
    Andy

  5. #25
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    Quote Originally Posted by andrew.tkelly View Post
    I looked at the spec sheets for the SolarEdge inverters, and could not find an SCCR value. Am I misunderstanding something here?
    Well, yes. A grid tied inverter cannot feed a short circuit. Its nameplate maximum output current is just what it says - the most current it can produce - but unless it sees AC line voltage within its parameter window, it cannot produce anything.

  6. #26
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    Quote Originally Posted by ggunn View Post
    Well, yes. A grid tied inverter cannot feed a short circuit. Its nameplate maximum output current is just what it says - the most current it can produce - but unless it sees AC line voltage within its parameter window, it cannot produce anything.
    Most significant, IMHO, is that it is not located between a potential source of fault current and a *downstream* potential fault location. There is nothing "on the other side" of it in terms of an AC load.
    It is not required to survive an internal fault while waiting for OCPD to open.
    Nor is it itself an OCPD with an AIC rating.

    Sent from my XT1585 using Tapatalk

  7. #27
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    Quote Originally Posted by ggunn View Post
    Well, yes. A grid tied inverter cannot feed a short circuit. Its nameplate maximum output current is just what it says - the most current it can produce - but unless it sees AC line voltage within its parameter window, it cannot produce anything.
    Ok, I think I'm understanding this, at least in terms of an inverter. However, doesn't an AC panelboard have an SCCR rating in kA at a defined voltage ...but like an inverter, it is not a source that can feed a short circuit, yet it still has a rating. Or am I still missing something here?

    -Andy

  8. #28
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    Quote Originally Posted by andrew.tkelly View Post
    Ok, I think I'm understanding this, at least in terms of an inverter. However, doesn't an AC panelboard have an SCCR rating in kA at a defined voltage ...but like an inverter, it is not a source that can feed a short circuit, yet it still has a rating. Or am I still missing something here?

    -Andy
    The panelboard has a source upstream, usually POCO, which can supply very large currents into a bolted fault.
    And it has loads and associated wiring downstream where a bolted fault can exist.
    There will be OCPD upstream or downstream which can (hopefully) interrupt that current. That is characterized as AIC.
    But until the OCPD can complete its job that fault current has to pass safely through the panelboard bus. That capability is characterized as SCCR.
    An interrupting device has an AIC, a pass through device has an SCCR.
    A load or a grid tie inverter will be destroyed by an internal fault regardless, so neither AIC nor SCCR have any useful application.

    Sent from my XT1585 using Tapatalk

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