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Electrical Inspection & Testing Forum
Zs on ring
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<blockquote data-quote="SparkJ" data-source="post: 64745" data-attributes="member: 1364"><p>I have added a spur to a ring main in a small 2 bed modernish (20 years old?) maisonette.</p><p></p><p>Earthing is TNC-S, water and gas bonding is in place.</p><p></p><p>Consumer unit is a Hager unit with 30ma RCD covering all circuits. The ring circuit has a B32 MCB to protect against overload.</p><p></p><p>My problem is Zs readings. According to the OSG table 2D max Zs value is 1.16 ohms for a 32A 60898 breaker.</p><p></p><p>The Zs readings for all of the sockets on the ring apart from the spur that I have installed range between 1.06 and 1.1 but the spur comes in at 1.19. I have checked all of the connections behind all of the sockets and they are tight. There are no FCUs on the ring or any other connections that I can find.</p><p></p><p>The RCD trips at 1 times rated current at 37.6ms at 0</p></blockquote><p></p>
[QUOTE="SparkJ, post: 64745, member: 1364"] I have added a spur to a ring main in a small 2 bed modernish (20 years old?) maisonette. Earthing is TNC-S, water and gas bonding is in place. Consumer unit is a Hager unit with 30ma RCD covering all circuits. The ring circuit has a B32 MCB to protect against overload. My problem is Zs readings. According to the OSG table 2D max Zs value is 1.16 ohms for a 32A 60898 breaker. The Zs readings for all of the sockets on the ring apart from the spur that I have installed range between 1.06 and 1.1 but the spur comes in at 1.19. I have checked all of the connections behind all of the sockets and they are tight. There are no FCUs on the ring or any other connections that I can find. The RCD trips at 1 times rated current at 37.6ms at 0 [/QUOTE]
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