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AssuredElectrical, Master Electrician
Category: Electrical
Satisfied Customers: 4241
Experience:  Contractor-42+ Years in the ElectricalTrade
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My question is about derating conductors. Let's say I have

Customer Question

My question is about derating conductors. Let's say I have 24 #10 THHN wires in a conduit. More than 20 wires thru 30 wires you are at 45%. That results at 18amps. Sence they don't make an 18amp breaker, can I put these wires on a 20 amp breaker or do I have to land them on a 15 amp breaker.
Submitted: 2 years ago.
Category: Electrical
Expert:  AssuredElectrical replied 2 years ago.
Welcome. My name is ***** ***** would be glad to assist.You can put the #10 on a 20 amp breaker in this case, IF the load meets the below requirements only. 240.4 Protection of Conductors Conductors, other than flexible cords, flexible cables,and fixture wires, shall be protected against overcurrent in accordance with theirampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).(B) Overcurrent Devices Rated 800 Amperes or Less. The next higher standard overcurrent devicerating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met: (1) The conductors being protected are not part of a branch circuit supplying more than onereceptacle for cord- and-plug-connected portable loads.(2) The ampacity of the conductors doesnot correspond with the standard ampere rating of a fuse or a circuit breaker without overloadtrip adjustments above its rat- ing (but that shall be permitted to have other trip or rat- ingadjustments).(3) The next higher standard rating selected does not ex- ceed 800 amperes. Let me know anything further needed,Thanks