One of the biggest advanced-instrument performance problems in all labs (and it is a serious problem) is circulating ground currents on conductive structures (i.e., metal pipes, steel rebar, steel beams, HVAC ducts, conduits, etc.) and net currents on electrical feeders due to N.E.C. violations (i.e., grounded neutrals, wiring errors, etc.) in the electrical distribution system that generate spurious magnetic fields causing electromagnetic interference (EMI) in high resolution imaging tools.

- From Tradeline's 2006 Summit on Facilities for the Emerging Sciences.

What is electromagnetic interference?