Very high prospective fault currents.

[Achnabreck]

Ze 0.02 giving a PEFC reading of 12.4kA which equates correctly; high but acceptable with fitted 100A BS 1361 supply fuse.

However, PSC reading of >50kA. Instrument (Fluke1653B) checks out ok. Any ideas?

Will be contacting supplier when I discover who the supply company is.

 

[malcolmsanford]

You have a transfomer in the garden?

 

[telectrix]

not got a transformer, but i've got a dalek

 

[tony mc]

Have a look at this post by IQ Electrical.

Higher-accuracy low Ze test procedure

 

[Engineer54]

Megger and i'm sure other test equipment manufacturers can supply higher accuracy E Loop Testers for use in sub-stations and the like. If you don't do a lot of substation work, then use IQ'S method, ...much cheaper!!! ...lol!!!

 

[Chr!s]

Ze 0.02 giving a PEFC reading of 12.4kA which equates correctly; high but acceptable with fitted 100A BS 1361 supply fuse.

However, PSC reading of >50kA. Instrument (Fluke1653B) checks out ok. Any ideas?

Estimated fault levels.

Taken from a table in the Electrical Association Publication.

25 kA(0.23p.f) at the point of connection of the service line to the bus bars in the boards distribution substation.



Will be contacting supplier when I discover who the supply company is.


http://www.nationalgrid.com/uk/Electricity/AboutElectricity/DistributionCompanies/

Regards Chris

 

[Achnabreck]

Ze 0.02 giving a PEFC reading of 12.4kA which equates correctly; high but acceptable with fitted 100A BS 1361 supply fuse.

However, PSC reading of >50kA. Instrument (Fluke1653B) checks out ok. Any ideas?

Will be contacting supplier when I discover who the supply company is.

Appears the answer to this problem lies within the tolerance of the meter at very low impedance values; ie: it is just not sensitive enough. This seems to be common to most popular testers (Megger, Fluke etc.). As Engineer54 said above, sub-station testers required (thanks for that). Enquiry to the distribution company ensures a maximum of 16kA at cut out.

 

[IQ Electrical]

Appears the answer to this problem lies within the tolerance of the meter at very low impedance values; ie: it is just not sensitive enough. This seems to be common to most popular testers (Megger, Fluke etc.). As Engineer54 said above, sub-station testers required (thanks for that). Enquiry to the distribution company ensures a maximum of 16kA at cut out.

That was exactly the reason for my guide, the standard issue Meggers and Flukes etc. are absolutely hopeless at reading down to loop impedances sub 0.10 Ohms, and when you look at the difference 0.01/0.02 Ohms can make to PFC values, it is a problem.

After applying the procedure, in almost every case I've come across (probably >30) the Ze values have reduced by 0.01-0.05 Ohms, enough to make a massive difference to PFC.

 

[Achnabreck]

Thank you, I hadn't seen youre guide until now.