pscc pfc values

[Farmelectrics]

just done eicr on a 3 phase db LI= 1.33KA L2=1.44 L3=1.48 THESE ARE THE PSCC VALUES SO ADDED TOGETHER THEY GIVE ME 4.25 KA THE LAST TEST DONE 5 YEARS AGO WAS 5.5KA NO WHAT WOULD CAUSE THIS TO BE LOWER NOTHING HAS CHANGED IN DB AND I NO THE READINGS ARE ACCEPTABLE YOUR THOUGHTS PLEASE

 

[timbobelfast]

Are you using the same test kit as last time?

Would PFC not fluctuate at different times of the day with network load demand?

 

[Farmelectrics]

no tim diferent tester ok take your point that could have an affect thanks

 

[JUD]

Aren't you just supposed to double (or more accurately x 1.73) the highest of the readings to get PSCC on 3 phase.

So in your case PSCC would be 2.96kA (double your L3 value). I don't think you're supposed to just add them all together.

That's what I was taught anyway.

 

[rich.250]

As above^^^^
Double highest L-N reading.

Or if your tester is capable you can test between phases.

 

[SirKit Breaker]

Jud has got it, and it also looks like the bloke who did the last test did it wrong as well.

Cheers...........Howard

 

[Farmelectrics]

Well I thought you double it my self had a quick look in gn3 not had time to read properly yet but all I did see was your pscc will always be higher than your pfc on a 3phase system anyone find we're it's says it's doubled let me no what page my gn3 is at work cheers

 

[JUD]

Page 52 last paragraph

 

[Farmelectrics]

Thanks wiil look up in morning

 

[Farmelectrics]

Sir kit I've recorded reading as L1=1.33 L2 =1.44 L3 =1.48 I've not added them together on the test sheet but the previous test sheet just has one value of 5.5 ka

 

[Farmelectrics]

Ok will check in morning in gn3 but jud said you double them values so will alter test sheets in morning

 

[Silly Sausage]

........................

Your readings are line to earth measurements.
Line to line short circuit fault current is higher due to the higher voltage difference (as you know!)
V line = root3 x V phase.........hence record the highest reading x root3

 

[Farmelectrics]

So archly maybe what your saying is the previous tester has got the higher reading and times it by 1.73 maybe that's we're he's got his 5.5 ka reading

 

[trebor]

The line to line pscc will be the highest, the rule of thumb as others have said is single phase pscc x 2, this should be recorded as in your example as 1.48 x 2 to avoid any doubt by office persons verifying test sheets

The previous result is pretty close to x2 x2 of your measurements so maybe he was using twu thumbs!

 

[Farmelectrics]

strange on one of the 3 phase boards we tested over the weekend the pfc was highier than the pscc what could cause this