Cables for NGR Neutral Grounding Resistance

...."Neutral Earthing Resistors are typically rated 400 amps for 10 seconds,"...

https://www.postglover.com/neutral-earthing-resistor/

https://www.cressall.com/ner-standards/#:~:text=The%20only%20industry%20standard%20specifically%20covering%20Neutral%20Earthing%20Resistors%20is%20IEEE%20C57.

..."The Resistor is generally rated for 10 seconds with a maximum temperature rise of 760 °C....

..."Short time rating: typically, 10 seconds or 60 seconds. Continuous rating: normally 5% to 10 % of full load current. Maximum current when the resistor is cold."...

https://i-gard.com/site/assets/files/1097/ask_the_experts_lm_distribution_systems.pdf

Thanks

but I am looking for the cross-section of cables that are used to connect the NGR to the transformer and to the earthing network

The size of the cable will depend on the current carrying requirement of the design...I think the minimum would be 3.264mm

C57.32a-2020 - IEEE Standard for Requirements, Terminology, and Test Procedure for Neutral Grounding Devices

https://megaresistors.com/products/neutral-grounding-resistor/ngr-calculation/

Hi

could you please share with me where you found this I think the minimum would be 3.264mm

That's a very short cable.

Chat GPT says the rating of the cable should be 150% of the full load current.

it would be better to mention the standard

The cable rating is calculated according to the load, just like any current carrying conductor. There is a current transformer and overcurrent relay, the purpose of the relay is to protect the resistor by disconnecting the power to the transformer, in the event that downstream protection does not clear the ground fault. The conductor is sized to be protected by the ground resistor overcurrent relay as well, the cable damage curve being plotted on the coordination curve as well as the resistor damage and the down stream ground fault protection.

Hi Thanks

but in that case, which load is used?

It is the ampere rating of the resistor, ie 200 amperes, for 10 seconds, which is plenty of time to provide selectivity, while limiting iron damage in equipment lamentations, the primary reason to limit ground fault current. Modern zero sequence or doughnut current transformers are sensitive enough to reliably detect a 200A ground fault and trip the motor starter.

Laminations, that is

It is calculable using the electrical standard applicable at the location of the installation. Were it in the UK, for example, then BS7671 is applicable.

If in doubt, consult a local qualified Electrician.