"never use more than 25 CFLs per 20A branch circuit" ?

Status
Not open for further replies.
Electric-Light

Electric-Light

Senior Member
Some CFLs say it on the package, some don't.

FEIT brand shows the same count-limit regardless of size. Both the 13W and 26W version warns:

"Never use more than 25 lamps per 20A branch circuit".

These use bulk-storage rectifier front-end and look the same as switching power supply to the line. Measured power factor is 0.55 and I'm guessing THD is between 100 and 130%, pretty typical for bulk storage rectifier front end load.

so, the 13W version uses 24VA, which basically means 5A/600VA limit per 20A circuit, which doesn't make sense, because higher power switching power supplies, such as LCD TVs and computers can exceed that amount in single device.

What is the basis for this limitation? Is there anything in the code about this?
 
SG-1

SG-1

Senior Member
Location
Ware Shoals, South Carolina
The inrush current is most likely the limiting factor. CFLs have a huge inrush at start-up, & a large number of them could trip the breaker. I think there was thread a while back where someone measured the start-up current with several bulbs in the circuit. The results were very interesting.

There could also be something else I am not yet aware of.
 
B

broadgage

Senior Member
Location
London, England
I suspect that the problem is not the running current, but the inrush current when the lamps are switched on.
If 25 lamps were switched together by the same switch or contactor, the combined inrush current would be substantial. Presumably the suppliers have calculated that more than 25 lamps switched together might trip a 20 amp breaker.

In a home rather than a business, the lamps would normally be switched singly or in small groups, and I believe that the only limit would then be that the total running current must not exceed 16 amps continually, or 20 amps for up to 3 hours.
If the lighting was corrctly designed, not serving an excessive floor area, it should be fine. If intended for incandescent lamps, then replacing these with CFLs of similar light output , will use about 25% of the watts, and about 50% of the current. Even replacing 60 watt incandescents with 23 watt CFLs wont increase the current, but will roughly double the light output.
The circuit breaker might trip on power restoration following an outage, but that should be a rare event.
 
Electric-Light

Electric-Light

Senior Member
I was able to get measured result of 27A inrush on a 26W CFL.

I don't expect front-end to be different between 13W and 26W CFLs and inrush causing a magnetic trip if they're turned on simultaneously does make sense.

i do remember an older power supply rated at something like 1kW. It was for some kind of telecom equipment. It had six D cell battery sized capacitors for bulk-storage. To mitigate the inrush current issue, there was a series high power cement resistor and a shunt solid state relay.

When initially powered, the inrush current is limited by resistor and either by timer or DC bus voltage, the solid state relay closed across the resistor to limit loss.

Older electronic ballasts used reactors to smooth out the current waveform and the reactors had natural inrush limiting capability, but I do recall, earlier all solid state(no iron core line frequency components) ballasts had very high inrush current just like CFLs.

Newer ones utilize series resistor and a bypass solid state relay to reduce pitting on contacts, improve reliability and prevent nuisance trips. It improves reliability as the uncontrolled inrush places a lot of stress on front-end bridge and capacitors.

Lutron has an article explaining it.
http://europe.lutron.com/product_technical/pdf/362-649.pdf
 
Electric-Light

Electric-Light

Senior Member
wankster said:
Why dont HID ballasts have a similar large inrush current?
Click to expand...

HIDs commonly use magnetic ballast. It is inductive, which inherently limits current.
Electronic ones do exist, but they're fairly recent and they are probably already built with in-rush issues in mind and have limiting front-end.
 
Status
Not open for further replies.
Top