Are you looking for a temporary troubleshooting tool or permanently installed monitoring? How much do you want to spend? Do you want to physically go to the device to get the data or be able to remotely access it?
Originally Posted by streets
It sounds like you might be looking for transients as opposed to long-term trending of voltage. Before you look for a product, you need to know what you want to observe. There are a lot of good Power Quality articles available at the Fluke web site including one on Electrical Noise and Transients.
The MMU is usually pretty good at identifying the sourse of a problem, but the last incident happened so fast (nano seconds) it could not record it.
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The World Needs More Electricians & Fewer Electrical Installers