Ze of 3rd , 4th db etc | on ElectriciansForums

Discuss Ze of 3rd , 4th db etc in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Jay Sparks

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Hi Guys

I know that if you have a main DB feeding a 2nd DB, then the Ze for the 2nd DB is:
Zdb = Ze from origin + (r1 +r2) of the cable supplying the 2nd DB. Or measured Zs at the second boards supply. But how do you then get Ze for, say a 3rd DB fed from the 2nd and then Ze for a 4th DB fed from the 3rd etc? :confused:

Any advice would be appriciated:)
 
2nd DB - Zdb = Ze (Origin) + (R1 + R2) of cable supplying 2nd DB

3rd DB - Zdb = Ze (Origin) + (R1 + R2) of cable supplying 2nd DB + (R1 + R2) of cable supplying 3rd DB

4th DB - Zdb = Ze (Origin) + (R1 + R2) of cable supplying 2nd DB + (R1 + R2) of cable supplying 3rd DB + (R1 + R2) of cable supplying 4th DB

.....and so on ;)
 
Last edited by a moderator:
Cheers Guys,

So basically after the first board your Ze at the others is actually the Zs reading of the cable supplying that particular board. Nice one.
 
Yep on a periodic report,you will find ZS reading and pfc for that db,so zs at that point would be the sum of ze at origin plus R1 & R2 of the sub main circuit to next db and so on,but ze is only taken at origin.
 

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