worried about psc at db

[theskid]

i have a query,im an inspection and testing engineer and its a new role for me
i have a Zs reading at a distribution board 3 phase of 0.02 and were that provides the highest psc which is 17.24 (after being doubled due to 3 phase).where the sub main feeding this db is a schneider 60947-3 set at 100amp and states 35 ka at 400v but does that reading count at the db board for all the 60898 and 61009 rcbos whic are rated at 10ka,do i have a problem?

 

[telectrix]

nope. because the MCBs/RCBOs are downstream . it's the equipment upstream that carries the 35kA, except in the rare occasion where you'd get a fault of negligible impedance close downstream of the MCBs. and while doubling the value for a L-L fault on 3 phase, the actual factor is 1.732, so that would ease the result somewhat.

 

[theskid]

thankyou, mind at rest , cant beleive they tell you in the 2391 to double the highest reading lol
will take that 1.732 figure into account

 

[Sintra]

Most modern meters will test fault current between phases. Saves doing sums.

 

[MDJ]

i have a query,im an inspection and testing engineer and its a new role for me
i have a Zs reading at a distribution board 3 phase of 0.02 and were that provides the highest psc which is 17.24 (after being doubled due to 3 phase).where the sub main feeding this db is a schneider 60947-3 set at 100amp and states 35 ka at 400v but does that reading count at the db board for all the 60898 and 61009 rcbos whic are rated at 10ka,do i have a problem?

you must be right next door to the main sub station with a reading of 0.02 ohms?

 

[theskid]

yes the place im a new q.s at ,and testing inspection engineer ,they have the old metrel testers which are not the most accurate testers although I have always used metrel ,but the latest range I don't rate them that well and not had experience with other brands which do you guys recommend the megger range?

 

[Engineer54]

yes the place im a new q.s at ,and testing inspection engineer ,they have the old metrel testers which are not the most accurate testers although I have always used metrel ,but the latest range I don't rate them that well and not had experience with other brands which do you guys recommend the megger range?

If your testing at or very close to a distribution TX, then you'll find that most, if not all MFT's and standard ELI testers do not have the resolution to accurately measure Ze/Zs and PFC values. Your company needs to purchase a made for purpose ELI meter with a high resolution.

Failing that, you can always use IQ's suggestion to give your present test equipment a fighting chance to give you a more meaningful/realistic value


From the Sticky's of this forum

Higher-accuracy low Ze test procedure

 

[Spark1979]

Had the same problem back in 2006, rang electrium about it, they said that their 6ka breakers in an appropriate bs board were rated at 15ka and their 10ka breakers were rated at around 25ka in a bs enclosure or board