[José_Fuentes]

Hello. In catalogs I have seen medium voltage cable down to 2 AWG but no smaller. The ampacity for these cables is around 150 A. Do customers that are hooked to a underground primary distribution system, but with a relatively low load (Schools with lots of air conditioners, small industries, etc.), say –around 150 kVA– use these cables?. I'm asking because it seems a huge waste to do so, yet I haven't seen smaller medium voltage cables being sold, and some electrical power companies limit secondary distribution customers to ~30 kW. For instance, only 3.77 A are required to transfer 150 kVA from a 23 kV 3-phase system. Regards.

 

[Big John]

For reasons I can't answer a lot of power companies require a #2 minimum for direct burial, I would assume because it has a more limited overload capacity than free air and when it does fault it's much more expensive to repair. So you're probably gonna have trouble finding any URD smaller than #2.

That said, check out 5kV Okobond. I think their MV-90 is produced as small as #6 or #8.

 

[José_Fuentes]

Thanks for your reply. I was able to find cable down to 8 AWG and 6 AWG in Okonite's catalog for 2.4 kV and 5 kV (at 133% insulation level) respectively. I understand that these voltages are being quickly replaced for higher voltages for primary distribution systems. What do customers do in the case of underground distribution at the more common voltages like 23 kV (at least it's common in my country, along with 13.2 kV and 34.5 kV)?. Do they use (and pay for) 2 AWG cable with almost 2 complete orders of magnitude of unused capacity?. Does the power company requires customers to use at least 2 AWG cables in their own (customers') side?.

 

[Arc'n'Spark]

Per the NEC (not sure about the mexican/local electrical codes), the minimum conductor size for a 15kV conductor is 2 AWG, and 1 AWG for 25 kV nominal systems.

 

[José_Fuentes]

Thanks you. I will investigate about the relevant code in my jurisdiction.