Review on BQD390 Panelboard Circuit Breakers SIEMENS by Bill Howard

Here is some information and specs from his own specs in plain English that might be helpful. BQD390 means it is a BQD type industrial circuit breaker for Siemens switchboards (large switchboard). They are commonly used in large commercial or industrial installations to drive large motors such as large AC motors from 30 to 50 hp. and equipment, depending on which circuit-breaker of the series you choose. 40, 50, 70, 90, 100 amps, etc. This is rarely used in consumer equipment as it is designed for larger devices. The 3 in the part number means these are 3 phase circuits (not just 1 or 2); Therefore it has 3 independent circuits that fire simultaneously if one (or more) of the 3 is overloaded. The 90 on this means it's designed to trip when the load goes over 90 amps/m, or much faster if the load is much higher. The current interrupting rating (how much it can interrupt at once under heavy load) is 14,000A at 480V, which is not very high compared to the large 600V Type J or T fuses, which are typically rated at 100kA Apply and blow faster; However, fuses cannot be reset or used to simply turn power on and off like a breaker. The break rating is not a rating of when it will trip, but a rating of how much current it can stop when needed. The breaking capacity of this switch is higher when used on 240V circuits than on 480V circuits, in which case it is rated for a breaking capacity of 65 kA (65,000 amperes). Due to the age of the product I have not been able to find a graph of its trip curve showing how quickly it will trip at 150A or 300A etc in the event of an overload. This is an older product so the price varies a lot. Lots of options and it's great for panel type S4 800A along with other BQD switches size 20, 50, 70, 100A etc. One side of this clip consists of 3 strong plastic clips already used in S4 (panel type BQD) and The other side attaches with 3 10-32 pan head screws that attach to the 3 power spade lugs shown in the product photo. Then the front panel is laid on its front part. If your panel comes with internal hardware, it may fit so well that only 3 screws are required to mount. However, if your existing panel does not have internal support hardware, you may need other parts to install it. Everything worked fine for us as the panel has physical and electrical mounts that can be installed behind the bezel.