LOST B HYDRAULIC SYSTEM WHEN CAPT INADVERTENTLY TURNED OFF B ELECTRIC SWITCHES WHEN HE WAS ATTEMPTING TO DEACTIVATE ENGINE ANTI ICE SYSTEM.

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DURING CLB THROUGH 26800' IN MODERATE TURB AND ICING CONDITIONS; I WAS ON THE P/A ADVISING PAX OF TURB. AS I RETURNED FROM THE P/A I FIRST NOTICED THE ANNUNCIATOR FLT CONTROL LIGHT ILLUMINATED FOLLOWED BY LOW HYD SYS B PRESSURE. I ADVISED THE CAPT AND SUGGESTED THE CHKLIST. HE REPLIED 'REQUEST 26000';' AND ACCOMPLISHED THE APPROPRIATE CHKLIST. AS I WAS ACCOMPLISHING THE CHKLIST I HEARD THE ALT HORN AND OBSERVED THAT OUR ALT APPEARED TO BE 200-300' LOW AND ADVISED THE CAPT. HE CORRECTED AND FLT RESUMED. THE CAPT HAD DETERMINED DURING THE COURSE HE HAD TURNED OFF THE HYD B PUMPS (ELECTRIC) INSTEAD OF THE ENG ANTI-ICE VALVE CTL SWITCHES; WHICH ARE LOCATED DIRECTLY ABOVE THE B PUMPS AND ARE THE SAME TYPE SWITCHES. I RECOMMEND THE SWITCH KNOBS ON EITHER SYS BE REPLACED WITH A DIFFERENT SHAPE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR ADVISED TYPE OF ACFT AND THAT ON THE LATER MODELS PRESENTLY BEING BUILT; THE PROB HAS BEEN RESOLVED. IS NOT A GENERAL PROB AS FAR AS HE KNOWS; BUT HAS HEARD OTHER FLT CREW HAVE DONE THE SAME THING. SUGGESTS A GUARD BE PLACED OVER THE B PUMPS IN THE ON POS. FEELS STRONGLY THE CONDITION COULD BE CORRECTED RELATIVELY EASILY.