Question: My church is looking to cut energy costs by regular bulbs with CFLs. One circuit controls fixtures for 30 light bulbs. Is there limit on the number of CFLs that can run on a circuit? — Tom, a Smart Choices reader
Mr. Tight Watt asked Rob Kirkpatrick, Service Concepts, and Paul Erickson, Gen~Sys, to answer Tom’s question.
Rob’s Answer: Tom, this is an excellent question. It is an electrical question more than a lighting question. First, if there are thirty 100-watt bulbs on that circuit, I’m assuming it is a 25–30 amp circuit. The off-the-top answer is that your church should have no problem with this at all, as long as the circuit doesn't have a dimmer or photo control. We're talking a max of 700-800 watts.
However, it does raise a secondary question that needs a deeper answer: What effect would that many lamps with a power factor of .5 (and THD of 150%) have on the overall environment inside of the meter? (Those 800 watts could mean as much as 1600 volt-amps, or 13+ very dirty amps.) I don't know the answer, and am not sure that we have that answer anywhere in the utility world right now. We know that most opinions, and the small amount of actual testing that has taken place, suggest that loading up a home with “normal” power factor CFLs doesn’t have enough affect to matter outside of the meter. But a more commercial environment, with bigger electrical and electronic loads, might be another question.
To be safe, at this point, without further testing, the best I can recommend is that you deploy high power CFLs. It will cost twice as much up front, but still save the 75% in power cost, and be the conservative route to go without further study.
Sorry an easy question doesn't have an easy answer!
Paul’s Answer: Tom, I don’t believe that 30 CFLs will have any major effect. The blower on their air handler should off set any power factor increase. We have installed over 400 CFLs per barn in laying facilities and had no problem.
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