Line-Loop Testing

[Bradley6969]

Hello all,

Just got a quick question for you all.

Recently noticed our engineers have been advised to start testing line-loops at every piece of equipment. They are recording the highest and noting this within the comments section on each circuit schedule of test results.

Other than systems conforming to TT and to verify the overcurrent device will operate for any short circuit faults. It seems they are also coding the results based on what results they get.

For example - B63 60898 distribution circuit has a maximum Zs = 0.72 Ohms. If they get higher than this on the line-loop they will also code as C2.

How would I cross reference the results they get?

I was always told if the cable size is adequately sized to the overcurrent device this would be sufficient for any short circuits.

Thanks all.

 

[littlespark]

I use the following guide, which I downloaded from the internet. The information is from the 18th edition of regulations.

Circuit breakers and fuses also have a “type” as well as current rating… which is related to their trip time characteristics.

Your example of a 63A 60898 circuit breaker is for a Type 1, not B… which is 0.58 ohms

Comparing the measured readings to this guide has been part of an EICR for years. They should have always been doing this… not just started recently.

 

[newfutile]

I think these are old values not taking into account cmin .