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High PFC issues

Former Community Member
Former Community Member

Hi all,

First post coming in…

I have a installation that we have been asked to Test, I conducted the usual tests for the Ze & Pfc.  I got 0.4 ohms & 11.7kA respectively.  Its a commercial block and the transformer is behind a locked door about 20m away, so probably reasonable to assume it’s accurate.  So here is my question given the absence of 15kA RCBO’s and the rarity 15kA MCB’s, what are my options?

Thanks in advance.

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    Where exactly are the existing MCBs and RCBOs and where exactly was the prospective fault current measured ?

    You will probably find that most of the installation is fine as the fault current declines with distance from the transformer.

    For those parts of the installation close to the transformer then providing back up protection by HRC fuses is one option. Note for example that domestic installations if close to the substation often have a fault current in excess of the breaking capacity of the installed MCBs or RCBOs, this is acceptable due to the back up protection provided by the DNO service fuse.

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  • 0

    Where exactly are the existing MCBs and RCBOs and where exactly was the prospective fault current measured ?

    You will probably find that most of the installation is fine as the fault current declines with distance from the transformer.

    For those parts of the installation close to the transformer then providing back up protection by HRC fuses is one option. Note for example that domestic installations if close to the substation often have a fault current in excess of the breaking capacity of the installed MCBs or RCBOs, this is acceptable due to the back up protection provided by the DNO service fuse.

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