upgrade service panel


Old 06-18-18, 04:39 PM
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upgrade service panel

I just bought an electric car and want to install a charging connector to what once was an electric dryer circuit. That circuit is a 20 amp circuit and the charger connector is a Siemens US2: VC30GRYU unit. Tech specs list 240V X 30A= 702kW. It states I need a 2-pole 40A circuit breaker.

Can that just be swapped out in the panel? Do I really need to go all the way up to 40Amps? Existing Main is a 70 amp 2 pole breaker. Only using lighting and TV in electrical framework with all lighting LED. No dryer or range in electrical service and probably never will be as we switched to gas 6 years ago. No central AC either.

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Old 06-18-18, 05:12 PM
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Good electrical practice (and the NEC) dictate that for a continuous load the number of amperes may be just 80% of the breaker and wiring rating. So a 30 amp draw needs the 40 amp circuit with 8 gauge wiring. Car charging, I take it, lasts several hours.

Upgrades of this kind (large increase in amps) usually require a load analysis (sample rules and formulas at the back of the NEC). The results of the load analysis may dictate the need for an upgraded panel and service. Usually the new panel and service need a separate permit from the new (car charging) circuit.

Last edited by AllanJ; 06-18-18 at 05:42 PM.
Old 06-18-18, 06:11 PM
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Thanks for your quick reply. Yes, charging takes a while. About 8-10 hours on 120 and around 4-5 at 240. Quick charges at 440 take about 1/2 hour to 80%.
Old 06-18-18, 07:08 PM
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That would be 480v nominal and three phase. That would be expensive if you could even get it at a residential location.
Old 06-18-18, 08:00 PM
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You stated that your main is 70 amps. That is unusual. Post a picture, please as you may have a larger panel or something else going on.

There are other car chargers that you can re-configure to use a smaller circuit but the one you mentioned is not one of them.

Most dryers are set up to use a 30 amp circuit. With that they can use a 20 amp car charger.
Old 06-18-18, 08:00 PM
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Your dryer circuit was too small for the dryer, less alone be adequate for the car charger. You will need to run a larger cable and charge the breaker.

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