On 12/6/20 2:52 PM, Peter VanDerWal via EV wrote:
Your area must be different from the rest of the USA. Everywhere I've lived if you want to (legally) install a 200 amp main breakers you are require to have 200 amp service, which includes a 200 amp transformer (50kva) These requirements are in both the NEC and in most cases local codes/laws. You can install a 200 amp service panel on less than 200 amp service, but the main breakers MUST be sized to match the service you have. I.e if you have 60 amp service, you can install a 200 amp panel with 60 amp main breakers.
I know from personal observation and experience that it is exceeding rare for any "200 amp" breaker box, with a 200 amp master breaker, to have a transformer as large as 50kva in this region. I have lived only in Texas.
Especially in the cases where a transformer is dedicated to each meter, utilities are extremely reluctant to provide 50kva transformers where 15-25kva satisfies expected load. The large transformers are quite expensive and require larger (more expensive) poles to support. Ask me how I know. I've recently paid to replace two 15kva transformers with 50kva in order to support PV generation.
An anecdote: I have a friend in Austin, 30 miles distant on another electric provider than mine, that did not buy a PowerWall a few years ago because he had the misconception that he had 350amp service and Tesla was unable at that time to provide a 350 amp combination. The Tesla sales person overlooked the fact that the transformer was 25kva. That is, he could easily have operated with a five battery PowerWall.
You seem to imply that having demands that might reach 200 amps could be safety hazard on any transformer of less than 50kva. Not the case. When demand starts to exceed transformer capacity, voltage to customer drops. Eventually to the point where electric devices stop operating. A "brown out". The opposite happens when generation exceeds transformer capacity. Voltages rise and inverters eventually shut down. Typically up around 260vac. Ask me how I know.
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