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Zs Readings vs Max allowable


Tony Way

Question

Hi

New to this game, and unsure about TT system I've just tested.

system setup has a 100A DP MCB between the Head and the DB.

DB has a 100 A main inclommer with split load 63A 30ma RCDs.

Ze on the system is 49ohms

PFC is 9A (0.0009kA)

BUT on the Zs tests, almost all outlets - sockets and lights are reading similar reading of between 35 and 42ohms and a PFC of 9A.

These readings are well above tables in 7671, but consistant with the calculation method of obtaining Zs

Would appreciate some guidance and or ideas on what is causing the high readings

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8 answers to this question

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on TT, earthing to gas/water (/other parallel paths) can reduce the Zs value to much lower than Ze. in some cases, as low as TNCS value's

dont forget, if using 30mA RCD, your Zs is 1667 ohms

and your PSC is the highest of L-E or L-N, fot TT, its almost guaranteed to be L-N

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Allo buddy.

Great to be back. Like going back to a pub you haven`t been to in years; and there`s still the same bunch of alco`s at the end of the bar............... :)

Seriously mate. Missed you all, and couldn`t wait to get back. Happy times ahead, what with an "exported thingy" thread an` all! Somebody must`ve started it just so me & steptoe`d come back..........:):)

Won't be able to do to many late ones, have been working in London for quite a few weeks so have to leave real early.

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Got it - you`re Theo in disguise?

Got cave???

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Of Course - 411.5 - Shows how much attention I paid to TT systems.Blushing

Many thanks

:D

Don't worry it confuses everyone :^O

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Just because I`m pedantic........

0.0009KA is equal to 0.9A

9A is equal to 0.009KA

(sorry)

KME

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Just because I`m pedantic........

0.0009KA is equal to 0.9A

9A is equal to 0.009KA

(sorry)

KME

Evening Martyn how have you been. Nice to see one of the old regulars back.

Batty

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Allo buddy.

Great to be back. Like going back to a pub you haven`t been to in years; and there`s still the same bunch of alco`s at the end of the bar............... :)

Seriously mate. Missed you all, and couldn`t wait to get back. Happy times ahead, what with an "exported thingy" thread an` all! Somebody must`ve started it just so me & steptoe`d come back..........:):)

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