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High PFC

Pete Murphy over 4 years ago

Hello,
I’m looking for help interpreting readings at a single-phase domestic CU, TNC-S. V= 241.6
Ze = 0.06Ω, main switch open, main earth disconnected.
I’ve taken the PFC readings twice now.

PEFC = 2.2kA, PSC =4.0kA

PEFC = 2.7kA, PSC =6.0kA

These readings were from the supply side of the closed main switch with main and supp. earth connected. I took one set of PSC readings direct from the (6kA) RCBO’s of which the highest was 5.9kA.
Seems a large difference for a combined earth and neutral.
Main fuse is BS1361 type 2 so no problems there but before I spend £300 plus for 10kA breakers am I missing something here?
Thanks for any comments,

Pete

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0 wallywombat over 4 years ago

Bear in mind the difference between the 2.2k and 6.0k readings corresponds to a difference in resistance of only 70 mOhm, so depending on how well your probes are making contact with terminals etc, you could easily see such variations.

Also, a domestic CU to 61439-3 annex ZB with 6kA breakers should be able to break 16kA when backed by a <=100A 1361 fuse.
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0 wallywombat over 4 years ago

Bear in mind the difference between the 2.2k and 6.0k readings corresponds to a difference in resistance of only 70 mOhm, so depending on how well your probes are making contact with terminals etc, you could easily see such variations.

Also, a domestic CU to 61439-3 annex ZB with 6kA breakers should be able to break 16kA when backed by a <=100A 1361 fuse.
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