Dual rated Magne-Blast breakers have much longer model numbers than most and can be very confusing to laymen and professionals alike. There are not a lot of these breakers on the market and finding an exact replacement with the same long model number is not only impractical but not necessary either.
Breaking Down a Magne-Blast Dual Rated Breaker
A typical dual rated breaker would be, for example, AM 2.4/4.16-150/250-3. What does that number indicate and do you have to find a breaker with the same model number to ensure it will work? In a nutshell, this breaker is rated for 150 mva at 2.4kv and 250 mva at 4.16 kv. The confusion tends to clear when you realize that all AM 4.16 250 breakers are rated for 150 mva if operating a 2.4kv line voltage and 250 mva on a 4160v line.
There is nothing inherently special about the breaker and any breaker rated 250 mva that follows all the other guidelines we discussed in other blog posts will also work. So, if you have an AM 4.16 250-4H will it work? Yes! How about an AM 4.16-250-7H? No, not without modifying it to fit in the older switchgear by converting it to a “C” breaker.
Care needs to be taken though because this AM 2.4/4.16-150-250 has a sneaky cousin, the AM 2.4/4.16-100/150. This breaker looks identical, but because it’s only rated 150mva at 4160 volts it should not be used in an application that calls for an AM 4.16 250 breaker. Of course, bigger is still better, so can you still use any 250 mva breaker in place of the 150 mva.