Maintenance Manager reported a brake failure during the taxi back from maintenance engine runs due to popped circuit breakers. The emergency brakes were used to stop the aircraft and it was towed back to the hangar.

Narrative

While taxiing back from engine runs; brakes failed. Emergency brake was used to stop aircraft. Root cause was the PWR Brake System CB popped/disengaged. Vendor had the aircraft out on the taxiway for Engine 5 point-capped runs due to RH engine change. When returning to the company hangar in ZZZ; they were following Operations. While getting ready to turn off the taxiway; the low brake pressure annunciator light came on. The Technician checked the brakes and found no brakes were present. They then turned the aircraft back to the taxi with Operations and slowly stopped the aircraft with the emergency brake. No aircraft damage; no one hurt; and stopped a slow rate using the TR (Thrust Reverser) system to not flat-spot the tires with a sudden stop.Operations went to the aircraft and stopped aircraft movement until Vendor got the tug on site and pulled the aircraft to the hangar. Once inside the hangar; the nose area was inspected due to the statements that there was fluid coming out of the nose area. After reviewing; it was the fluid in the lines that was blown out when the emergency brake was pulled and was coming out of the drain only. Inspected the LH and RH gear; no leaks were noted. Opened the MCD (Mode Control Display) and noticed the PWR BRKS CB was not engaged and the anti-skid was in the off position. Technician did not know the CB was popped.