I posted the following information in an engineering inspection report, pertaining to a lighting retrofit project at a large hospital that was built in the mid-1960's:

"A majority of the interior areas on campus are primarily lit by T-8 fluorescent light fixtures using 32-Watt (W) fluorescent lamps of various color, temperatures, and standard efficiency electronic ballasts. Since much of the lighting is on for long periods of hours, the fluorescent lighting represents a significant portion of the entire campus lighting electrical consumption. Long burn hours produce quick lamp failure, making these fixtures disproportionately burdensome to maintenance staff. A retrofit to LED will provide the highest possible efficiency -- reducing lighting electrical load by 40-50%.

Since LED rated life greatly exceeds that of the existing fluorescents, the maintenance burden will also be significantly reduced. Patients and staff can expect less frequent disturbances to maintain these fixtures. Replacement of existing metal halide fixtures in the parking garages with new LED luminaries will likewise provide similar benefits, reducing that electrical load by up to 80%, along with extending maintenance intervals by a factor of ten.

But what we have here is a mid-20th century building – with mid-20th century electrical wiring – that's now had 21st century lighting installed.

While the lighting electrical contractor may be able to make some accommodations in some areas to adjust the lighting levels to meet the standards of ASHE (American Society of Healthcare Engineers) criteria, the hard fact is that much, if not most, of the lighting in this 50+ year old hospital may not be able to be properly adjusted to the proper luminescence level, simply because the facility and office spaces are not properly wired to do so.

Some areas clearly need double-pole light switches, so that only half, or all of the lights could be turned on and off (when the sunlight through the windows is bright), as it suits the occupant.

And as far as dimmers, some of the 1960's electrical wiring in these buildings could not accommodate the quickly rising and lowering amperage spreading across the distance of the wire, without possibly leading to a potential electrical fire hazard."

The hospital electrical engineer became livid, and replied via e-mail with: "This paragraph is not true. Installed LED lighting takes less wattage and amperage to operate. For dimmers installation, the dimmer requires two smaller size wires (14ga.) and uses Direct Current (DC) Voltage to operate in addition with the existing AC wiring (10 or 12ga.) to power the LED rectifier. The 1960’s electrical wiring has nothing to do with what you stated in the above paragraph and is not a potential electrical fire hazard."

My argument is that it is not only just the reduction in magnitude of current that we should be concerned with, but given the age of the wire itself, plus the rate of change in the current (dA/dt), still presents electrical/electronic friction, which could cause a rise in temperature, and thus subsequently, an electrical fire hazard.

I need to come back at the hospital engineer with cited NEC code that backs up my premise:

1) Age of wire is a factor. Even if all copper wire was used during hospital construction in ~1965, there could be aluminum components in the switches and junction boxes. Or unless the spacing of wires in the junction boxes has been inspected by the electrical contractor before reconfiguring with dimmer switches, all of these factors still present a hazard.

2) Rate of change is current (dA/dt), not just magnitude of current, could present a rise in temperature in electrical wiring. Unless current flow tests are conducted in the existing 50+ year old wiring at the hospital, or unless all of the lighting electrical wiring is replaced to meet 2017 NEC code, the electrical contractor should not reconfigure the old wiring with LED lights plus dimmer switches.

Thank you for your insight and feedback.