Generally speaking, the EMF produced by electrical cabling will not be sufficient to damage or cause data corruption on a hard drive. Electrical cabling can cause interference with network cables, if they run parallel for a long distance; over a long distance the interference adds up, and signals on a network cable are quite weak and thus relatively easily corrupted.
However, in a hard drive, there are several factors acting to reduce the impact of power cable EMF:
- Traces on a hard drive are very short, and thus don't pick up much energy from the power cables.
- The hard drive's platter and magnetic read heads are encased in shielding typically made of iron or some other ferromagnetic metal; this shields it from external magnetic fields.
- Although a SATA or USB cable is similar in some ways to a network cable, the relatively short run length reduces the chance that power cable interference will be significant, and error-correction codes will repair any corruption that does occur.
In short, don't worry about it, unless you're working with some kind of industrial equipment with VERY high currents on that cable (the amount of interference emitted from a power cable is proportional to the current on it). Household currents are unlikely to be a problem.