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Solar PV DC earthing.

Jake Morgan

Hi all, I'm in the process of designing a solar install where the DC strings are going to have to be buried in the fabric of the building. I am planning to use PV ultra SWA cable or earthed steel conduit and make sure there are plans to record where it is, as per IET COP for Solar PV 5.10.3. 

It has got me thinking about what actually happens in a scenario where someone drills through it. With 230V AC systems the earthed containment would contact the Line and cause a short circuit that would hopefully trip an MCB/RCD. DC strings do not have a reference to earth nor is there any device to trip so what happens? Or is one of the poles earthed in the inverter?

Can anyone point me towards further reading on this?

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    If the first fault happen from positive to earth, usually nothing will happen yet, until the second fault occurs at the negative pole which result in short circuit scenario usually protected by fuse. This only prevent further escalation e.g. fire, etc. This short circuit current is high and human is not protected against this fault. Thus usually there are no human activity allowed nearby the solar panel in case isolation is not possible especially during day time to avoid safety incident and worse case, fatality. 

    alternatively, we can limit the voltage design of our system to below 120VDC as the lower voltage result in higher impedance required for the severe impacts towards human


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  • 0

    If the first fault happen from positive to earth, usually nothing will happen yet, until the second fault occurs at the negative pole which result in short circuit scenario usually protected by fuse. This only prevent further escalation e.g. fire, etc. This short circuit current is high and human is not protected against this fault. Thus usually there are no human activity allowed nearby the solar panel in case isolation is not possible especially during day time to avoid safety incident and worse case, fatality. 

    alternatively, we can limit the voltage design of our system to below 120VDC as the lower voltage result in higher impedance required for the severe impacts towards human


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