One common question we are asked is "What size circuit breaker do I need?" and in turn that follows with "What size wire do I need?"
The following table from the NEC (National Electrical Code via the NFPA) is used for finding the proper size wiring based on the circuit needs. In most cases, "continuous load" is never even a thought when planning the circuit to be installed, but Electric Vehicles that are charging must take this into consideration, per the NEC.
625.41 which states:
Overcurrent protection for feeders and branch circuits supplying electric vehicle supply
equipment shall be sized for continuous duty and shall have a rating of not less than 125 percent
of the maximum load of the electric vehicle supply equipment. Where noncontinuous loads are
supplied from the same feeder or branch circuit, the overcurrent device shall have a rating of not
less than the sum of the noncontinuous loads plus 125 percent of the continuous loads.
Please see our article on Load sharing if you plan to take advantage of this feature.
You will see based on the above chart and code, that we strongly urge the use of#6 copper wire for a 50A circuit in all applications as a minimum. This is especially true for installations that use residential (Romex or non-metallic sheathed cable) wiring. You can always go larger in wire if heat or distance will be an issue.
Please note that the NEC is a minimum requirement, and some jurisdictions will adopt their own code in conjunction with the NEC which may be different than that stated above. Always check with your local Authority Having Jurisdiction for local codes.
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