test referencing

dandanspark · Aug 11, 2011

Hello every 1 what is the easiest way\book to cross reference my test results, ie which book and page numbers Many thanks

telectrix · Aug 11, 2011

for reference look in osg. there's not that many pages to look at. i'd look it up but i'm also lazy.

tony mc · Aug 11, 2011

Is it ZS test results you are wanting to check?

dandanspark · Aug 11, 2011

yes ZS readings, but basically all readings such as R1, R2 R1+R2, is there somewhere specific i can check my readings out to make sure they are all ok. i am pretty new to testing as you can tell. Thankyou

telectrix · Aug 11, 2011

R1+R2 values can be calculated for any length of cable from table 9A. OSG. page 166.
max. Zs values are given in table 2D, page103. ( this is abbreviated just for MCBs, for fuses and fuller info., refer to the BRB.

topquark · Aug 11, 2011

Not that lazy then

telectrix · Aug 11, 2011

had to go to van for me smokes anyway, so picked up osg while i was there.

JUD · Aug 11, 2011

As Tel said, R1+R2 readings will need to be calculated to verify cable length is ok.

Divide the R1+R2 result by the resistance/meter of the line and cpc of your cable from Table 9A. This will give you the length of the cable.

Maximum cable length for Zs can be worked out as below:

Radial
L = (Z[SUB]41 [/SUB]- Z[SUB]e[/SUB]) ÷ (mΩ/m x 1.2)

Ring
L = 4(Z[SUB]41[/SUB] - Z[SUB]e[/SUB]) ÷ (mΩ/m x 1.2)

L = Maximum length of cable
Z[SUB]41[/SUB] = Max Zs value for the particular protective device from BS 7671
Z[SUB]e[/SUB] = External earth loop impedance
mΩ/m = Resistance per meter of the line and cpc conductors

However, maximum cable length is more likely to be limited by voltage drop. This can be worked out as follows:

Radial
L = (MaxVD x 1000) ÷ mV/A/m ÷ Ib

Ring
L = 4(MaxVD x 1000) ÷ mV/A/m ÷ Ib

L = Maximum length of cable
MaxVD = Maximum voltage drop (6.9V for lighting or 11.5V for power)
mV/A/m = Millivolts per amp per meter for the size of the cable from BS 7671
Ib = Design current of the circuit