BUZZ-Fuel cell makers: Plug Power signs contract worth $20 mln
** Fuel cell makers' shares rise premarket after Plug Power signs a $20-mln contract
** Plug Power Inc up 10.6 pct; Ballard Power System Inc up 3 pct; FuelCell Energy Inc up 2 pct
** Plug Power signs multi-year contract with North American telecoms company for fuel cell systems and hydrogen services
** Plug Power says its fuel cell systems will power about 500 sites under contract
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