Commercial Scale ESS Conductor Sizing & 2023 NEC

JimmysLimeade

JimmysLimeade

EE Student & PV Design
Location
Utah
Occupation
PV Design
I am designing a commercial ESS plan set, and I am somewhat confused by contradicting information on the topic of conductor sizing. Here is the general information that is important to my question:
  • 2023 NEC
  • ESS only & using the grid power to charge the ESS. (utility allows this type of connection)
  • ESS with a capacity 286.72kWh connected to the PCS (storage inverter) with an output of 125kW AC (Nameplate current rating: 151A)
  • 200A fusible AC disconnect in between the PCS and a gutterbox that will use a polaris block to intercept the service feeders in between the CT cabinet and main distribution panel
  • Service is 3p/4w 277/480V 800A
  • AC terminals are rated 75C
Here are the code sections and contradicting information I am confused about:
  • NEC 706.30(A)(1) says that the circuit current shall be the rated current indicated on the ESS nameplate or system listing
  • 706.30(B) says that output circuit conductors of the ESS connected to the wiring system serving the loads to be serviced by the system shall not be less than the greater of 706.30(A)(1) [151A] or the rating of the ESS OCPD [200A]
  • This is somewhat contradicted by this newsletter post (https://www.mikeholt.com/newsletters.php?action=display&letterID=2756) which mentions article 705 for ESS conductor sizing, even though there is no mention of article 705 in 706.30, and I dont think it is applicable
Here are my questions:
  1. Do I need to refer to article 705 for ESS conductor sizing?
  2. If I can use 706.30, do I need to take adjustment factors (conduit fill and temp) or can I just use the rating at 75C from 310.16?
    1. With an OCPD of 200A, this would mean I could either use 3/0 without adjustment factors or 300kcmil with adjustment factors (0.96 Temp Correction & 0.8 Current Carrying Conductors) (Assumed neutral as a current carrying conductor)
    2. The wording of 706.30(B) makes it seem like I wouldnt need adjustment factors for the conductor size, but I might be missing something there.
  3. Is there any scenario where you would use the nameplate rating instead of the OCPD because the OCPD has to be sized according to 705.31 which is 125% of the currents calculated in 706.30(A) meaning that the OCPD will always be higher than the nameplate rating.
I would love to get some feedback/help on this
 
Last edited:
don_resqcapt19 said:
If the ESS can operate in parallel with the utility, the rules in 705 would apply as that would be an interconnected power production source
Click to expand...
Ah that makes sense. I was assuming that since it isnt really producing power, just storing power from the utility, that 705 wouldnt apply. If the ESS was only standby, and only supplied power when the grid was down, 705 wouldnt apply right?
 
JimmysLimeade said:
Ah that makes sense. I was assuming that since it isnt really producing power, just storing power from the utility, that 705 wouldnt apply. ..
Click to expand...

It doesn't produce (net) energy, but it definitely produces *power* when outputting. It thus brings up all the same issues any other type of interconnected power source. In fact it needs to be considered as both source and load to the extent it will operate as such, and requirements must be met for both.
 
JimmysLimeade said:
Ah that makes sense. I was assuming that since it isnt really producing power, just storing power from the utility, that 705 wouldnt apply. If the ESS was only standby, and only supplied power when the grid was down, 705 wouldnt apply right?
Click to expand...
But then 702 would apply.
 
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