Does a variac with no load dissipate power?

[ghub005-at-xtra.co.nz (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hello list

I feel a bit embarrased about asking this, but does a variac with no 
load consume a signnificant amout of power? I imagine it dissipates 
a little power through hysteresis + resistance etc - but I have no idea 
of the actual amount.

I'm asking because I've just finished my 11kVA three-phase PSU 
and I want to put a switch in that allows me to bypass the internal 
variac and inductive ballasts. The circuit I have in mind won't isolate 
the variac stack - it just switches between the variacs' output 
terminals and a bypass line.

Thanks in advance for your help,

Gavin Hubbard