[RE-wrenches] Utility transformer limitations

drake.chamberlin at redwoodalliance.org drake.chamberlin at redwoodalliance.org
Mon Dec 26 09:06:40 PST 2022


I ran into this once on an old transformer, which fortunately they
changed at no cost. It was a 10 kW transformer on a 200 A (48 kW)
service. They had some dimming of lights on heavy loads, and the
transformer was changed out on that basis, at no charge. 

My questions for the utility would be? 

	* Are there any other PV systems feeding the transformer? 

 	* If so, what is their maximum production.

 	* What size is the transformer?
 	* What percentage of transformer capacity is allowed to be back-fed.

If the math comes out in your favor, you will have a good case to
escalate to the next level. 

Good Luck, 


Drake Chamberlin 

Athens Electric LLC 

Ohio Electrical Contractor's License 44810 

CO Master Electrician's License 4526 

NABCEP Certified PV Installation Professional 


On 2022-12-25 13:58, William Miller via RE-wrenches wrote:

> Wrenched: 
> Merry Christmas to those of you that observe such traditions, or substitute the winter festivity of your choice. 
> I helped a previous employee install an Enphase IQ8 system on his home.  He applied for the utility approval concurrently with his building permit  The day he got his final inspection the utility contacted him and claimed "The aggregate generation exceeds the identified transformer rating" and refused him a Permission to Operate letter. 
> Adding up the service ratings of the homes on his secondary we get about 336 kW of potential consumption.  Adding the grid-tied systems on his secondary we get about 16.5 kW.  How is it that the back-feed exceeds the transformer rating? 
> I would appreciate any insight on how to consider this situation and how to fight it. 
> Sincerely, 
> William Miller 
> Miller Solar 
> 17395 Oak Road, Atascadero, CA 93422 
> 805-438-5600 
> www.millersolar.com [1] 
> CA Lic. 773985 
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[1] http://www.millersolar.com/
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