Zs on 3 phase board.

[rEEl]

Hi ppl.  This is my 1st post but not last i hope! 

I'm testing a small site the location is on 5th floor. 

Its new installation but building is existing - so is the electrical source of all building. Down in basemant its 11 Kv and 3 step down transformers to 400. They have UPS and "dirty power"

My board is fed from sub - boar witch is fed from UPS source. There are 3 UPS sources and i tested 2 different boards from diferent UPS sources and for som reason  Zs  for L1  is very high on roof its 0.76 (one week) 0.66( next week) L2 and L3 (0.16 and 0.19 ).

Board on 5th floor is from other UPS source ( wich is fed directly from buss bar)L1  was 0.18 when i did the incoming cable only, and 0.30 when i connected 40 circuits) L2 and L3 was low 0.9 and 0.8 before adding circuits and went up by 0.05 ohms when installed them 40 circuits. 

Anyone have any good explenation why from bouth sources L1 is much higher than L2 and L3. 

 

[Sharpend]

Sorry I'm confused by your figures ? Isn't 0.18 lower than 0.9 & 0.8? 

 

[Manator]

Welcome to the forum rEEL, as Sharpend says in his post, 0.9 &0.8 are higher than 0.30. Its all in the decimal place. If you were to write 0.30 to one decimal place it would be 0.3

Zs tests should be carried out with all bonding in place, it is common for the Zs to be a lower measured figure, than one calculated. The Zs should be within a range across all three phases, your readings are a fair way out of what you would expect. I would always test the R1+R2 of each phase, this along with the Ze would give me a ball park figure to work from.

You will get variations during the day as with all tests as demand in the area and such like effect the results.

 

[rEEl]

My question is what would cause reading to L1   be much higher than to L2 and L3

Sharpend sorry i made mistake. 

On 5th floor board L2 and L3 are 0.09 and 0.08 ohms.