Mike Dolt Enterprises
Mike Dolt Enterprises
User: [email protected], Location: 3 Hr 2 Min from Winged Horses
Asked on: Sunday, April 17, 2011 at 1:14 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:17 am EDT
Question: Do tables 310.16, 310.17, ... regarding current/wire size apply to AC and DC current? Is it permissable to use standard 20 amp AC circuit breakers for DC as well?
Tables 310.16, 310.17, ... regarding current/wire size apply to AC current only.
These tables are based on the heating effects of current flowing through conductors and the ability of the conductors to dissipate heat. The heating effects depend on the magnitude, duration, and frequency of the current. AC current constantly changes direction, causing the heating effects to be more evenly distributed throughout the conductor.
DC current, on the other hand, flows in a constant direction, causing the heating effects to be concentrated at certain points in the conductor. This can lead to overheating and damage if the conductor is not sized appropriately.
Therefore, the current/wire size tables in the NEC are not applicable to DC current.Standard 20 amp AC circuit breakers should not be used for DC circuits.
The interrupting capacity of a circuit breaker is based on the amount of fault current it can safely interrupt. AC fault currents are typically lower than DC fault currents, so an AC circuit breaker may not be able to safely interrupt a DC fault.
For DC circuits, specialized DC circuit breakers must be used. Flag for review