When residential walls are retrofitted with “foamed-in” urea-formaldehyde or“blown-in” cellulose thermal insulations, the insulation may enter electrical outlet and switch boxes. The effects of these thermal insulations on electrical components such as outlet and switch boxes were studied.

Electrical outlet and switch boxes were filled with thermal insulation, and exposed to 44, 75, or 96 percent relative humidities for periods of 1 to 12 months. The amounts and rates of corrosion which took place were determined by measuring weight loss, corrosion current, and by visual inspection. Effects of the insulations on the performances of the electrical components also were investigated.

Results of this study indicate that shock hazards may exist if metal wall plates are used with ungrounded systems when they are in contact with moist thermal insulation. Therefore, it is recommended that thermal insulations should be removed from outlet and switch boxes.