If the wires are not long enough, can I pigtail additional wire on to them?

Hello Jack, We do not recommend you that please check with your local inspector, and just to let you know, to obtain the maximum system performance, locate the device as close to the circuit being addressed as possible to minimize the interconnecting wiring length. For every foot of wire length, approximately 160 Volts (6 kV / 3 kA, 8/20 microsecond) is added to the suppressed voltage. The Voltage Protection Rating (VPR) is located on the device nameplate and is measured six inches from the enclosure sidewall, according to UL® 1449 test standards. Regards, Schneider Electric Customer Care