What is the ampacity or current rating for my cable? What size copper conductors should I use for my application?
Ampacity and Heat
An insulated conductor's ampacity is the maximum current it can safely operate at without exceeding the temperature limitations of its materials of construction (such as insulation and jacketing materials). As current flowing through a conductor is increased, additional heat is created through the phenomena of Joule heating (also known as Ohmic heating) that is proportional to the conductor resistance and the square of the current. So if current is doubled, the Joule heating is quadrupled.
If this heat is not dissipated appropriately the wire or cable's rated temperature may be exceeded resulting in premature cable failure and a potential safety hazard.
Ampacity and Cable Sizing
Most cable is sized according to its ampacity needs based upon application requirements. Therefore every cable application and project needs to consider all relevant codes and considerations for optimum reliability and safety as well as the involvement of trained electrical professionals. This is where the National Electrical Code (NEC/NFPA) and the concept of Authority Having Jurisdiction (AHJ) factor in.
National Electrical Code (NEC) and NFPA
The National Electrical Code (NEC or NFPA) Allowable Copper Conductor Ampacities are one of several organizations and resources providing guidelines and requirements for safe electrical installations including wire and cable ampacity and conductor sizing.
The NEC methodologies factor in the role of ambient temperature, insulation/jacketing compound temperature ratings, the number of current-carrying conductors (in cabling applications) amongst other considerations. Additional background on ampacity and the NEC can be found in our resource titled "Ampacity: Choosing Cable When the Heat is On".
The Authority Having Jurisdiction (AHJ)
Due to the uniqueness of many applications LAPP Tannehill always recommends that our customers, installers, etc...contact their appropriate AHJ or "Authority Having Jurisdiction". Per the NFPA/NEC the AJH is defined as "An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation or a procedure". Depending upon the nature of your project the AJH may be the local governmental inspector (in the case of a city or state jurisdiction), or oftentimes for industrial projects the primary AHJ might be the owner company and its appointed professional engineering resources.
Only the AHJ has the qualifications and experience to provide detemerination concerning cabling end-use suitability and installation requirements. Manufacturers and distributors of cabling products such as LAPP Tannehill can only make recommendations on general application-use characteristics (e.g. temperature, environmental, etc...) and not detailed and prescriptive conductor sizing or other electrical details.