Box cover units for standard electrical boxes provide supplemental fuse protection for small motor circuits and other loads requiring overcurrent protection below that of the branch circuit overcurrent protective device. Versions are available for a fused outlet, switch or plain circuit that fit standard sized electrical boxes. See catalog numbers for available configurations by box type. Use with SA adapters and S or SL type fuses may prevent fuse cover from closing. Not recommended for use with MB-15 Edison base circuit breaker.