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How many lights/watts can I put on a 15 Amp service?

Smokin Moose

Fallen Cannabis Warrior
The rule of thumb is to only load a breaker up to 80% of its capacity. On a 15-amp service with 14/2 gauge wire one should only load it up to 12 Amps MAX. Since most lights will draw 1 amp per 100 watts a 15-amp breaker can handle one 1K light each. This brings up another point in home growing. That it is always good practice to have the fans and the light that they cool on the same breaker. That way if the breaker is somehow tripped (Murphy's Law) then both the light and its cooling system are down. Instead of the cooling system for the light going down and the light still blazes away because it was on another breaker.

Note: above figures are estimated based on 110V supply.
Nietzsche recommends purchasing a CAT III meter before doing any electrical work. It will allow for safe testing of the circuit before commencing work. A clamp meter is also handy for testing how many amps the circuit is drawing without having to break the circuit to do so, great to see if you get a peak when your lights first come on or just how many amps a given device is using.
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Member of the Month: May 2009, Oct 2010, Sept 2017
Keep in mind that many light setups draw significantly more power during startup than they do after they've been running - especially with traditional C&C (magnetic) ballasts. A setup that is (barely) within the tolerable range during operation can be well above it when the light(s) is(/are) firing.


New Member
Yes initial extra draw at firing up of bulbs considered. Thank you
With 2 ballasts that can run both standard house voltages and a switch on 220 I think the breaker will be okay. Two 1000w lamps on 220 with a wired 220 switch from dedicated breaker on a 30amp line should be plenty for everything. There are a few other circuits to borrow from and all on sub breakers.


New Member
If I measured the diameter of the wires that supply the box I should be able to tell how much they can handle between panels right? It's a short distance and the wires are newer. It's the rest of the place... All reversed polarity at receptacles and the gfcis blow out night lights. Any ideas?
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