Robert Lamoureux | Wire size, amps must be coordinated

Robert Lamoureux
Robert Lamoureux

Question No. 1  


We have just purchased an electric vehicle, which I am not yet prepared to charge at home, so I am in need of resolving this but would like your guidance, please. I am somewhat knowledgeable in electrical so I’m hoping with some assistance from you I’ll be able to set this up without calling in a professional.  

In my panel I have a 30-amp breaker that is not being utilized and I need to know if I can switch that out for a 50 amp that is needed for the car, and it will all work and be safe. Is this something that can be done?  

— A.  

Answer No. 1  

A. ,  

Unfortunately, this cannot be done. A 30-amp breaker runs off of a No. 10 wire and, if you then put a 50-amp breaker in, what happens is that, theoretically, the wire will burn before the breaker would trip.  

The wire size/breaker amperage is coordinated so that the breaker trips when overloaded, for safety. An undersized wire/oversized breaker together then can allow an extremely dangerous situation. This is called, “overrating” a wire.  

This job does require a licensed and insured electrical contractor, as there are many factors to be considered plus techniques to be used in order to prevent injury or life loss. Please do not attempt this on your own, it is too risky. Best of luck to you. 

— Robert 

Robert Lamoureux has more than 40 years of experience as a general contractor, with separate licenses in electrical and plumbing contracting. He owns IMS Construction Inc. in Valencia. His opinions are his own, not necessarily those of The Signal. Opinions expressed in this column are not meant to replace the recommendations of a qualified contractor after that contractor has made a thorough visual inspection. Email questions to Robert at [email protected]. 

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