NEC 705.30(B) Over Current Device Ratings (Electric Power Production Sources)

[WA_Sparky]

Can someone confirm that this code applies to optional standby generators?
This is stating that the conductor and OCPD have to be sized for not less than 125% of max current rating of source.

If so, A 200A generators conductors and OCPD have to be sized to carry a minimum of 250A.

Lets walk down a hypothetical situation..
If someone oversizes the two to 400A, Loads are added later on, utility loses power, 400A rated ATS transfers 300A metered load to gen power. The conductors and OCPD wouldnt trip but...
Would the gen sense over 100% load is being pulled and turn off?
Would it essentially attempt to overload its self at 150% and heat up until it grenades it self?
Or would it essentially only output the designed 200A and something similar to a brownout would occur to the critical loads?

 

[wwhitney]

Can someone confirm that this code applies to optional standby generators?

See 705.1 Scope. Is your "optional standby generator" going to be "operating in parallel with a primary source of electricity"?

Cheers, Wayne

 

[WA_Sparky]

See 705.1 Scope. Is your "optional standby generator" going to be "operating in parallel with a primary source of electricity"?

Cheers, Wayne

Yes that answers my first question. It will be operating in parallel therefore it does apply.

 

[wwhitney]

Yes that answers my first question. It will be operating in parallel therefore it does apply.

Sorry, it's an "optional standby generator" but it will be operating while the grid is up? I understand parallel operation to be simultaneous. Installations with a transfer switch wouldn't be subject to Article 705.

Cheers, Wayne

 

[WA_Sparky]

Sorry, it's an "optional standby generator" but it will be operating while the grid is up? I understand parallel operation to be simultaneous. Installations with a transfer switch wouldn't be subject to Article 705.

Cheers, Wayne

Oh I misunderstood that then. I interpreted parallel as in Emergency parallel to Normal loads entering ATS. Didnt see the "does not cover sources that are connected by a transfer switch that permits operation of a single source".