What's the difference between a System Sensor B401 and a B401B?

What’s the difference between a System Sensor B401 and a B401B? I’m looking at the documentation and they say that the B401 is compatible with the 2151 and 2451, but the B401B is not compatible with the 2151. I’m looking at the electrical ratings and they are the same on both bases. What’s the difference? Can I use a 2151 on a B401B?

The B401 is compatible with heat detectors, and has a higher standby voltage rating when used with heat detectors. So maybe it’s made to withstand higher voltages???

Which is better to use B401 or a B401B System Sensor?

It depends on what head you intend to use. I have found that the B401B and B110LP are identical other than the trim ring, and the trim rings are interchangeable. So, if you have a 2151 and a 2451, you can hot-swap them and swap the trim rings without issue. As for the B401 vs the B401B, please read the above posts.