Electronic flash unit compatibilities?

Is the National PE-201M electronic flash unit compatible with the Nikon D3100?

Looking at this site
http://www.botzilla.com/photo/strobeVolts.html
I don't find the National PE-201M. However, they do list the PE-205. With a trigger voltage of 155V, that model could damage a DSLR. I would advise against it. It might still be able to provide some useful service as a remote flash with an optical slave unit.

I wouldn't risk it; if it does damage your Nikon camera it will void your warranty for using unapproved accessories. Get a Nikon flashgun; the SB-400 is quite cheap.