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Subject - Plaster Ring
David Hyatt When adding a 1/2" deep single gang plaster ring to a 4x4 box, how many cubic inches does that add? Enough to add an extra #12?
JimmyDee The plaster ring is the same size as a 3" x 2" box but not as deep.
You would figure a single, 1/2" plaster is the same as 1/3 of a 3" x 2" x 1 1/2" box
That box is 1 1/2 " deep or equal to 3 x 1/2" deep plaster rings.
So I we have a ring that is 1/2" deep it is a 1/3 of 7.5 ci which is 2.5 ci.
2 gang is double or 5 ci for a 1/2 deep.
Easiest way I know how to do it.
Jim
Ryan_J
quote:
314.16(A) Box Volume Calculations. The volume of a wiring enclosure (box) shall be the total volume of the assembled sections, and, where used, the space provided by plaster rings, domed covers, extension rings, and so forth, that are marked with their volume or are made from boxes the dimensions of which are listed in Table 314.16(A).


Mathematics is not an option for plaster rings. The ring must be listed with its cubic inch capacity, otherwise it doesn't count for box fill.
ravengotu and u/l listed stamped as well..
Ryan_J Raven...the listing doesn't have to come from UL. It can come from many, many different sources, such as UL, CSA, MET, ETI, et cetera