On Tue, Mar 18, 2014 at 07:09:49PM -0400, David Hubbard wrote:
I've had to do that before; provider gave me a 208v/30a circuit and I already had a power strip I wanted to re-use that had a corded L6-20P connector on it. I purchased a L6-30P plug / L6-20R receptacle adapter from http://www.stayonline.com/nema-locking-6-30-amp-adapters.aspx They're only $25 and they ship overnight if needed. They have one foot cabled versions of the same thing too if you have tight working space and there's not enough room for both connectors back to back; works as a strain relief too so maybe that option is better regardless.
This is not really a safe thing to do unless the "adapter" has a 20A circuit breaker as part of it, or if you change out the upstream circuit breaker from 30A to 20A (and hopefully clearly mark the outlet as such).
If you're trying to go the other direction, plugging an L6-30P into an L6-20R 20 amp circuit, that I'd recommend against because it never fails that someone says hey, 30 amp power strip, let me plug some more stuff into it not realizing it's on a 20 amp breakered circuit, then all your stuff goes down while you try to find the facility staff to reset the breaker.
Going this way is safe, but as you say, you can only draw 20A (actually, you can usually only draw a derated 80% of that, so 16A).