As 1,024 x 4 dual bus 1-pole matrix supplied in 1U full rack width enclosure, 60-553 supports high relay closure counts to optimize use with digital multimeter (DMM) or source meter for checking for insulation problems between single contact and all other contacts in unit under test (UUT) requiring closure of up to 1,024 crosspoint relays. Dual bus arrangement allows matrix to be divided into 2 smaller independent matrices and features isolation relays.