Thanks again for the replies.
1) If the lights and the fan are the only loads that are connected to the circuit, I recommend to tap into the existing circuit and extend the new light from there.
2) This really depends upon the total amps or wattage on the existing circuit. For example, the average attic fan is a 3 amp motor
and will "in-rush" to 6 or 7 amps upon initial start-up and then go back down to 3 amps or so. If the total light bulb wattage is around 420 watts, that gives you approximately a total amperage of 3.5 amps for the lights and another 7 amps for the fan (upon initial fan motor start-up). Therefore, the total amps required for these loads are well under a 15 or a 20 amp circuit breaker. All depends on whether all of the connected loads will ever be run simultaneously or not.
Whenever tap'ing into an existing circuit, electricians will typically use a clamp-on amp meter at the circuit breaker and then turn all connected loads to the ON position and obtain an amp measurement. Once the existing amps are known, then the determination can be made to tap into that circuit or install a new circuit. If no clamp-on amp meter available, then all of the wattage and/or amps on all of the connected loads must be calculated to make sure the breaker won't overload and trip.
Watts Law is used to calculate the total wattage or amps on a circuit as shown below:
P = I x E, where P = Watts, I = Amps and E = volts
or I = P/E. Once the total wattage is known, then the total amps can be calculated.
3) $1,600 is a reasonable price to perform a panel upgrade as well as installing a new sub-panel. However, I always recommend when hiring a local electrician to perform such work, that they be licensed, bonded and insured. All major electrical work should also be inspected by a local electrical inspector. Yes, I would also be cautious. Any major electrical work such as panel upgrades, etc. require that the electrician pulls an electrical permit and not the homeowner. Once the electrician pulls the permit, any liability is on the electrician.
4) Even though the main panel is maxed out, a sub-panel can still be installed. A sub-panel requires a double pole breaker to act as the feeder circuit. Two of the existing single pole breakers can be relocated and swung over to a sub-panel. The main panel will still be maxed out, but due to the feeder circuit, you now have the capability for future circuits inside the new sub-panel.
Hope this helps………If you have any additional questions, let me know and I’ll be glad to answer them for you.
Otherwise, don’t forget to rate me before you log Off.
The next time you have an electrical question, you can also request for me at: http://www.justanswer.com/home-improvement/expert-your-electrician ……….Thanks…………..Kevin!