An evaluation of creepage requirements for electric motors

While tremendous advances in dielectric materials for ground insulation and turn insulation have been made in recent years, little thought has been given to creepage requirements. Creepage "requirements" seemed adequately defined in 1913 when Gray stated: "To prevent breakdown of the end connection insulation due to this cause (ionization of the air over the slot insulation extension), the distance (from core to the end of the slot insulation) is made as large as possible without increasing the total length of the machine to an unreasonable extent, and the end connection insulation is made strong enough to withstand the full puncture voltage but with a lower factor of safety than that used for the slot insulation."¹