View Full Version : What is the formula to get the size of wire and size of breaker for 400watts lamp
omarromy
May 21, 2011, 04:40 AM
Electrical load
cdad
May 21, 2011, 05:58 AM
Watts / voltage = amps
sinnadurai
May 22, 2011, 04:30 PM
For lamps incorporating ballasts like fluorescent lamps multiply by 1.6
ballengerb1
May 22, 2011, 04:46 PM
Can you claarify that, multiply what by 1.6? Omarromy can you tell use what you are doing and where you live. If this is a single fixture in a residence we use 14/2 wire with a 15 amp breaker pretty much standard.
sinnadurai
May 22, 2011, 05:22 PM
In BS7671 it is mentioned to multiply the current by 1.6 to select the wire size.Breaker size depends on quantity of lamps connected or load. Normally in homes and offices 6A mcb is used. In factories where many fittings are connected to a single switch the engineer should calculate or consultant should specify in drawings
ballengerb1
May 22, 2011, 06:37 PM
Not sure what "BS7671" is but, in the USA, lets look at a typical residential circuit. 14 gauge wire is rated to carry 15 amps at 120 vac. There is no number in this sequence of 14, 15 and 120 that you can multiply by 1.6 and get 14 gauge wire.
sinnadurai
May 23, 2011, 03:05 AM
in BS practicing countries,lighting circuits are fed at 240V 50Hz and it is the normal practice to use 1mm^2 pvc insulated cables or sometimes 1.5mm^2 depending on the load
sinnadurai
Jun 5, 2011, 05:34 AM
The load in a lamp circuit incorporating a ballast(fluorescent) is the lamp watts plus the loss in the ballast. That's why a multiplying factor of 1.6 is recommended by the Institution of electrical engineers,UK.