Motor Control Level 1 Practice Test

In transformer protection, you want to isolate faults quickly on the supply side and still guard the downstream circuit without overcomplicating the protection scheme. Placing fuses on both primary lines provides solid protection for the high‑voltage side and the upstream supply; any short on the primary is interrupted by opening those fuses. On the secondary side, fusing only one line gives a practical level of protection for the downstream circuit while keeping wiring and fuse count reasonable. This arrangement is often used when the secondary consists of a single fused conductor feeding the load, with the other secondary conductor returning current, so a fault can be cleared by the secondary fuse without needing fuses on every secondary conductor. Putting fuses on all secondary lines or leaving the secondary unprotected would either add unnecessary cost and nuisance trips or fail to protect the secondary circuit adequately.