Harmonic currents are calculated for the odd harmonic frequencies not divisible by 3 up to the 49th, as is standard practice. The total connected load including the adjustable frequency drives is used to calculate the percentage distortion for each of these harmonic frequencies. The total connected load is based on the maximum demand load current. This current is calculated from the average of the maximum demand load currents over the previous 12 months. For new installations it is based on the predicted load profile. The total harmonic current distortion and voltage distortion percentages are also calculated. A comparison is then made between these calculated levels and those recommended for the system size vs the demand load ratio. This is determined by the ratio of the short circuit current available at the PCC and the demand load current for the user.