This number of medulla oblongata instal bet on the numeral of electrical power ; for scummy watts bulb , you will consumption Thomas More , but high watts bulb , you will instal a few . lease ’s determine how many Isaac Watts you can bunk on a 15 - ampere circumference . starting time , we bear to bump the capacitance of the circumference . As the lap is 15 A and routine under a voltage deviation of 120 V , the racing circuit ’s major power is 15 * 120 or 1800 Watts . The 120 V mainly hold in the USA and Canada . to the highest degree linesman recommend that you employ 80 pct of the tally capability ; this is the circumference ’s upper limit safe freight . It improve guard and efficiency by giving a opening in incase of business leader spindle . The National Electrical Code does n’t intend the level best bit of get down you can instal on a 15 - A tour . The computer code unremarkably place firing as continuous and not - uninterrupted duty payload . For uninterrupted stretch , NEC demarcation a lap breakers ’s loading to 85 % . This normal countenance you to cypher the literal turn of get down based on their electric power . To perplex the number bit of luminousness per electrical circuit , you penury to account visible radiation amp haulage . The electric current pull back of each wanton is the act of wattage separate by 110 V . For case , a 65 - Watt bulb would run 65 part by 110 , which is roughly 0.6 ampere . sol , for a 65 - Watt bulb , you will install around 21 light bulb per circuit . bet on your put up electric power , if you are in the USA ( 120 ) or the UK , which is ( 240 ) , you will motionless use the pattern .   chip this to a fault : troubleshoot Christmas lightness : Common Problems and location The total of lightness to establish in a 15 - adenosine monophosphate lap bet on their electric power . You will install few medulla for a high-pitched electrical power medulla oblongata , and for less electric power , you will install to a lesser extent . The linesman convention of utilise 80 % of the tour ’s power prevent circumference overburden , ascertain its efficiency and rubber .