Resistance unit set up in Nottingham house (3)
I believe the answer is:
ohm
'resistance unit' is the definition.
(ohm is a kind of resistance unit)
'set up in nottingham house' is the wordplay.
'set up' is a reversal indicator.
'in' indicates the answer is hidden within the clue.
'mho' is hidden within 'nottingham house'.
'mho' in reverse letter order is 'OHM'.
(Other definitions for ohm that I've seen before include "physical unit" , "measure of resistance" , "Physicist" , "SI unit of electrical resistance" , "lawmaker" .)