With some exceptions (see below), a permit shall be obtained before installing, altering, repairing, replacing or remodeling any building or structure. If you have mechanical, electrical and plumbing work, you will need separate permits for each of those categories. There is no single MEP permit that covers all three. However, if you are obtaining a construction permit for a house, addition, or new Accessory Dwelling Unit (ADU), then those the mechanical, plumbing and electrical work would be included together under a single Residential Building Combination (RBC) Permit. For example, if you are adding a bathroom, you can include all of the the related MEP work within the building itself under the scope of the Combination Permit.
The following types of work are exempt and do not require MEP permits: