Firestop for Electrical Boxes: Putty Pads & Box Inserts
Electrical boxes are the most common membrane penetration in a fire-rated wall — and the building code limits how big they can be, how close together, and how they have to be protected. When a box breaks the rating, a putty pad or a listed box insert restores it.
When electrical boxes need firestopping
In a fire-rated gypsum wall, protection is generally required when any of these are true:
- Metallic boxes exceed 16 sq in per 100 sq ft of wall area.
- Boxes on opposite sides of the wall are within 24 inches horizontally.
- The specific wall listing calls for box protection.
A listed putty pad or box insert restores the wall's rating — and often lets you reduce that 24-inch separation, which is a lifesaver in tight layouts.
Three ways to protect a box
- Putty pads — self-adhesive intumescent pads that wrap the outside of the box. Fast and familiar, but you need an open wall.
- Box Guard — a friction-fit intumescent insert that drops inside the box cavity. No wall-side access needed — ideal for retrofit.
- Cover Guard — installs invisibly behind the cover plate. Perfect for finished walls where opening the drywall isn't an option.
See all of them on the putty pads & box protection page. Box Guard and Cover Guard are Metacaulk exclusives — there's no Hilti/3M/STI equivalent.
New construction vs. retrofit
If the walls are open, putty pads are the quickest fix — peel, wrap, close up. If the wall is already finished or an inspector flagged boxes after the fact, Box Guard (inside the box) or Cover Guard (behind the plate) fixes it without demolition. Tell us how the inspector wrote it up and we'll match the product to the citation.
Frequently asked questions
Send your penetration schedule and we'll pull the UL system and quote it — distributor pricing, same-day shipping, free submittal support.