Testing a 110v Industrial Socket System

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electelconnections

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Hi Guys,

We are completing a periodic inspection of a factory unit and have come across a transformer supplied from 1 of the DB's which in turn supplies 110v to a single phase DB which feeds 3 110v socket banks from D type DP mcb's.

We have been informed by NICEIC to test supply into transformer as a distribution circuit and test the 110v as a Db: Question is How do you perform zs test and will a megger MFT1552 perform a 110v zs test?

 
Aren't these centre earth tapped to its only 55V RMS to earth? I thought the Meggers only needed over 50V to perform a test but not sure if this will work or not.

Ian.

 
with it being centre tapped, it may show as wrong polarity and refuse to test. in which case you could test L1 to earth and L2 to earth and note the highest

 
thanks Andy,

we tested between phases and earth and could not get a reading but when we tested between the 2 phases we got a zs reading?

 
yes we got reading between phase & Earth when doing R1&R2 but we did not get a zs result between phase & Earth but we got a result when we tested between the 2 phases?

 
between phases we got 0.32 but I dont understand how we got a reading between phases as earth fault impedance surely needs to be tetsted between phase and earth?

 
just asked this question at my periodic. the answer was not many testers will do it so its down to calculation

 
On a lot of these systems, the earth has to be linked during installation.

If it hasn't been linked, then you will not get a Zs reading, as there will be no continuity.

 
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