www.maida.com
201 S. Mallory Street sales@maida.com
Hampton, Virginia 23663
Phone: (757) 723-0785
DEVELOPMENT COMPANY
Manufacturers of Ceramic Capacitors, Varistors and Thermistors
Established 1947
www.maida.com
There are advantages for using either epoxy or phenolic coatings. The use of either coating is
dependant on the end application:
Epoxy Advantages:
High Dielectric Withstand
Moderate to High Moisture Resistivity
Moderate to High Chemical Resistivity
High abrasion and wear resistance
Epoxy Disadvantages:
Less resistant to burning
Phenolic Advantages:
High Resistance to Flame
Moderate to High Thermal Conductivity (useful for Thermal Cut-Off devices)
Moderate Moisture Resistivity
Moderate Chemical Resistivity
Phenolic Disadvantages:
Low to Moderate Dielectric Withstand
Higher Cost
As listed above the main disadvantage for using an epoxy coating is that is burns under flame
test and will burn during out-of-specification overvoltage conditions if appropriate disconnects
are not installed in the application. The burnt epoxy can result in debris on printed circuit boards
causing additional complications in the circuit. The main disadvantage for using a phenolic
coating is its lower dielectric withstand voltage. Maida’s phenolic coating requires much thicker
coating, relative to the epoxy, to obtain the required dielectric withstand ratings.
The most important characteristic of the phenolic coating used by the Maida Development
Company is the high resistance to flame. As seen in Figure 2 the image on the left is the phenolic
coated varistor while the image on the right is the epoxy coated varistor. This is the result of a
Flame Test, which is the application of a propane torch blue flame for 60 seconds. The flames
continued to burn on the standard MOV even after the propane torch was removed. There were
no flames on the phenolic varistor even under the propane torch. Similar results are obtained
during limited current abnormal overvoltage testing (UL1449 3
rd
Edition).