Battery Conundrum - Powerwall

[timpollnow]

Hello All,

NEC 2014 states in 690.71(B)(1) that the largest battery in a dwelling can be 50 volts and yet Tesla powerwalls are nominally around 400 vdc. Am I misinterpreting a definition or missing an exception, how is the powerwall allowed indoors?

Is the 50 v limit for a specific type of battery?

Thanks in advance,

 

[gadfly56]

Hello All,

NEC 2014 states in 690.71(B)(1) that the largest battery in a dwelling can be 50 volts and yet Tesla powerwalls are nominally around 400 vdc. Am I misinterpreting a definition or missing an exception, how is the powerwall allowed indoors?

Is the 50 v limit for a specific type of battery?

Thanks in advance,

First, 690 is talking about PV systems. That aside, if the terminals are not readily accessible during routine battery maintenance, the exception allows you to go to 690.7 for further info. There, you might, kinda, infer that you can operate up to 600 volts. I'm guessing this is what they hang their hat on.

 

[SolarPro]

Exactly right. The Powerwall battery requires no maintenance and has no user serviceable parts. So defer to the exception for the time being.

In reality, the energy storage system is not a component of the PV power system. Rather you have two separate energy systems subject to different Code requirements. This gets clarified properly under NEC 2017, which strips all references to batteries out of Article 690 and adds a new article (Article 706) for energy storage systems.

 

[c_picard]

Hello All,

NEC 2014 states in 690.71(B)(1) that the largest battery in a dwelling can be 50 volts and yet Tesla powerwalls are nominally around 400 vdc. Am I misinterpreting a definition or missing an exception, how is the powerwall allowed indoors?

Is the 50 v limit for a specific type of battery?

Thanks in advance,

Another thing to consider is that the "battery" operates at ~48Vdc(nom), there is an onboard DC/DC Converter that ramps up voltage.