§393.31
Overload Protective Devices
Question 1: Must all trailers be equipped with
overload protective devices?
Guidance: No. Trailers do not need overload
protective devices when protection of trailer circuits is provided on the
towing vehicle. A circuit breaker is required only when the head lamp circuit
is protected in common with one or more other circuits. A circuit breaker, if
required, must be an automatic reset type.