LT Electrical Service: Electrical Cable Sizing Selection

Cable size is important factor that determine how many amp or electrical load that cable can carry on. If the cable size that we select is lower than amp or electrical load that it can carried or under design, it will cause the DB to trip or even the cable melt down due to heat generated. However, if over design the cable size, it will cause additional cost to the client which is not recommended. Therefore, proper sizing the electrical cable is very important in term of safety and budget concern. Above is the table showing the recommended cable size for different level of load that need to be carried.

There are other factors that need to be considering when we select or design the electrical cable size. One of the factors that need to be considered is the travel distance of the cable. The longer the travel distance or the length of the cable the higher it is the voltage drop. Voltage drop might damage the connected equipment. Therefore, bigger sizes of cable need to be selected in order to overcome the voltage drop. The type of connected equipment also is one of the factors that need to be considered during the design especially motor load. Motor starting amp is very high, it might up to 3 time of it normal operation amp. Example, if the motor operation amp is 60A, it starting amp might up to 180A! some of the DB might trip due to this high starting amp. Therefore we cannot select the 16mm2 cable, we need to use at least 25mm2 cable to cater the high starting amp.