[Question] Issuing of CoC

[siphom_3]

Quite new around the block and need clarity around few item in simple way

• Is there any test/way I can conduct to make a distinction between a TN-S and TN-C-S systems
• What is the acceptable/min/max reading for Loop Impedance
• What is the acceptable/min/max reading for PSCC.

Will appreciate if you put it in simple terms.

[murdock]

what is your intention? hopefully not signing over COC...because if you cannot answer these simple question you are not suitable qualified to be issuing
COCs not as a single phase tester...installation electrician...ever tried reading the SANS green or now grey book.

[siphom_3]

You're right not to sign off the CoC but to gather as much info as I can in preparation to installation, inspection and testing of installation. Guess accreditation is not for sale, having said that I'm accredited translates to having read the green/grey book. You've been around for some times and thought that there are approaches. Specifically around earthing systems, I know exactly what it stands for but my challenge is still distinguishing between the abovementioned. Thanks for the welcoming statement.

[bergie]

dont mind murdock,the loop impedance and short circuit current is basically the same thing,you just uses ohms law to go from ohms to amps and back.
we cant change the readings if we do find it high or low,but the switchgear we install must be rated above the short circuit current (psc) if you read 1000 amps psc then a 3 ka breaker is ample.

[murdock]

You're right not to sign off the CoC but to gather as much info as I can in preparation to installation, inspection and testing of installation. Guess accreditation is not for sale, having said that I'm accredited translates to having read the green/grey book. You've been around for some times and thought that there are approaches. Specifically around earthing systems, I know exactly what it stands for but my challenge is still distinguishing between the abovementioned. Thanks for the welcoming statement.

the heading of this thread and the other concern is in your profile you indicate private jobs...mmm...no comment

[Dave A]

the other concern is in your profile you indicate private jobs...

I hear where you're coming from, but that's a different issue really. I can't see knowing or not knowing the technical answers is going to make any difference when it comes to privateering. If the person is that way inclined it's going to happen anyway.

At least knowing the answers means safety gets a better shot.

[murdock]

Quite new around the block and need clarity around few item in simple way

• Is there any test/way I can conduct to make a distinction between a TN-S and TN-C-S systems
  
  its not a test it is a visual identification of the type of earthing system...can be found in the sans book or you can request it from the supplier if you are not sure
  
• What is the acceptable/min/max reading for Loop Impedance
  
  this is a calculation which is done to determine the impedance (Resistance) from the main DB back to the transformer...dependng on the installation you will need to do a calculation and the result of the calculation will determine if the reading is correct by the size of the cuircuit breaker installed
  
  
• What is the acceptable/min/max reading for PSCC.

this is the short circuit current...thie is determined by a calculation which includes the distance from the supply transfomer...size of cable...bussbars...type of protective devise etc...

Will appreciate if you put it in simple terms.

so no there are no simple terms/short cuts...if it is to be done properly...if you would like me to post the calculations and the page number of the sans book...let me know but before i post the answer i would like to see at least some sort of effort from your side...other wise keep googling i am sure someone will answer your question .

[siphom_3]

Much appreciated Murdock, let me revisit my green/grey book and will revert for clarity or advice.