I tagged this question onto an older post, but got no response, so thought I would try again.

The question involves the high startup inrush current of CFL's, which according to my research can be anywhere from 50-100 times the steady state current (depending on manufacturer)! My particular problem all started when I designed and outdoor lighting system using 24 - 23 watt CFL PAR 38 floods on a 20 amp MCB. I planned to use a 16 amp rated manual residential switch and some motion sensor switches. Only 552 watts, no problem, right?

Then I started looking at motions sensors and saw things like 2000 watt, but only 300 watts for CFL's. or 3,000 watts, but only 500 watts for CFL's. <deleted>?

I did some research and learned that while a 60 watt incandescent bulb draws a steady 0.27 amps of power (on a 220VAC system), a 23 watt CFL draws its steady state power in repeated short spikes of ~0.6 amps. Thus, though its overall power consumption is lower, it mimics a higher draw for purposes of system design. Okay, so I can only use 1/6 as many "watts" of CFL's as I can incandescents on a single circuit without throwing the breaker. In addition, there is the danger of burning up a switch. If i use 24 - 23 wat CFL's, through they consume current of 0.10 amps, I will be switching the equivalent of 13.8 amps. Okay, so far so good.

But then there is start-up inrush current headache. For incandescents, it is 12-15 times the steady state load, or 3.2-4.1 amps for 60 watts. But for CFL's it can be anywhere from 50-100 times the steady state load and manufacturers do not tell you what the inrush current ratings are for their products! That means a single 23 watt CFL could pose a potential start up load of 10.5 amps! Twenty-four of these babies give a potential startup inrush current of 250 amps!

According to my research a typical MCB will handle 8-12 times its rating for startup inrush (or for a 20 amp MCB, 160-240 amps) and a typical household light switch will handle 10 times its rating (or for a 16 amp switch, 106 amps).

If I put 24 - 23 wat CFL's on a single lighting circuit (0.105 amps each), that comes to 2.51 amps of steady state consumption, but a whopping potential 250 amps of startup inrush current, which would throw the MCB and weld my switch contacts in the "on" position. So after putting together my well thought out "552 watt" system, I would have destroyed the motion sensors and the regular switch the first time I turned it on -- UNLESS I was lucky enough to get CFL's with a startup inrush current of only 50x. In that case, this system will scrape by.

This seems to be ditto for LED's

Does ANYBODY know of a supplier of CFL's and/or LED's in Thailand that discloses the startup inrush current of its products? If you are "close to the wire" (so to speak), this information is essential to system design.

This is a nightmare. I may be forced to use incandescent lights in the system which will cost four to five time more to operate. Of course I could split the system into two circuits, but that would defeat the purpose of the system as a security lighting system designed to light the whole place up instantly.

Another solution would be to put an inrush current limiting device into the circuit such as an NTC thermistor. The problem is, I am not an electrical engineer, and I have no idea how to do the calculations to determine the right specs for my system.

Further research of Schneider technical sheets suggest that using a CT Contactor will reduce the inrush current to an acceptable level with these CFL lighting systems. After studying both Schneider technical sheets and products catalogues, I have limited my choices to either a 16 amp single pole (NO) (Cat. No. A9C22511) or a 16 amp 2 pole (2 NO) (Cat. No. A9C22512) (no manual operation) CT Contactor. I have single phase service. What is the difference and which is most appropriate?

With a 2 pole, would both the line and the neutral go through the contactor? Is this a benefit or even appropriate?

Will a CT Contactor solve the problem?

Does anybody know?

Note: Many of the numbers shown above may not be perfect, but the principles are the concern. It is all very complicated, and well beyond the comprehension of the average Thai electrician.

Any help would be appreciated.

Data Sheet A9C22511.pdf

Data Sheet A9C22512.pdf

Edited December 8, 201312 yr by Ticketmaster

Start currents of electronic lighting (and other kit with switching PSUs) can be an issue, an office full of PCs which normally draws 10A will easily open a 50A breaker when the power comes back after an outage.

For your CFL lighting don't think too much, just drive either of those contactors with the residential / motion sensor / timer / daylight / other switching method and switch your lighting with the contactor.

Contactors are extremely robust as far as surge currents are concerned, use the two pole unit with both poles wired in parallel and you will never have an issue.

If you can easily split your lighting between two circuits on separate MCBs then do so running one circuit through each pole of the contactor (no need to switch the neutral), doing it that way will reduce the possibility of the MCB opening on start up if you happen to hit the peak of the mains cycle.

We have 250W of CFL floods being switched by a cheap and cheerful plug-in time switch, it's been switching on and off twice a day for two years with no issues, I expect the start surge is doing the relay no good whatever but when it finally fails I'll just get another timer.

Thanks a million, Crossy, you came to the rescue again. I do not know what we would do without you! Man, I've spent 12-18 hours researching this on the internet to learn what I have learned and to find the device.

Just to clarify, the contactor goes BETWEEN all the switches and the load? In other words, feed the Line from the panel through all the various switching devices, then through the contactor, then to the load?

Now the challenge is to source the contactor. I'll find it somewhere in the world.

The contactor is like a relay, it has a coil and contacts.

Feed the coil as if it were the load from your switch / timer etc.

The NO (normally open) contacts connect the load to the breaker.

If you need a diagram let me know.

Your local electrical wholesaler should have all the necessary bits.

Man, I would love to have a diagram if you have one.

I'll go to my electric supplier Wednesday. They are very good (one of my very favorite shops, actually). If i can get it in Thailand, they will find it.

Here you go, do it something like this:-

You can take the live supply to the switch / timer etc. from any convenient location (like your lighting circuit).

Thanks for that!

I used to run 296 watts of CFL lighting on a 10A breaker and never had a problem (all turned on simultaneously). Now replaced by 81w of LED's, also no problem.

For LED's forget buying in TH - buy direct from CN/HK. Just make sure you buy units with CREE or Edison LED's that clearly state the LED module and bin number used, so you can verify the lumens output..... Otherwise your new 5watt 800 Lumen LED turns out to be only 250-350LM - which is less efficient than CFL. The other upside of buying lights with quality chips is that they will also have proper driver circuits for current limiting.

Only the chips mentioned above are capable of 200LM/watt - anything else will be lucky to reach 100LM/watt. CFL varies from around 65-80LM/watt.

Edited December 8, 201312 yr by IMHO

IMHO, thanks for the info on the LED's. I am VERY interested in sourcing them.

As for my 552 watts of CFL, my primary concern was not the 20 amp MCB. My primary concern was that the high inrush current would fry the several 16A residential switches on the circuit. There will be both motion sensors and a 5-switch 4-way switch system on the circuit. With CFL lighting of 300 watts or less, none of this would have been an issue. But problem solved with the relay.

As for the relay, Crossy, I was thinking way, way too much. I got so far down the rabbit hole thinking (obsessing) about over-current suppression (with NTC thermistors, etc.), that when I stumbled across the Schneider CT Contactors, I kept that frame of mind, not even understanding what they were. Still thinking in terms of suppression, I did not even realize the 2 pole unit had 6 terminals until I saw your drawing, which initially made no sense to me, and I thought might even be wrong.

Then, as I kept looking at your diagram and wondering why the hell you would have a neutral lead going into the contactor, I suddenly had a forehead-slapping epiphany: "It's not a suppression device, STUPID, it's a relay; a protection device!"

I actually understand these devices perfectly. In fact many years ago, I put together a system using an electromagnetic relay to switch a 2 KW bank of metal halide lights from a small low wattage timer switch. It's just that I had read so many data sheets and articles and obsessed over suppression so much that by the time I stumbled into the Schneider device, my head was so far up my ass that I couldn't see the forest for the trees. Thanks for helping me pull it out. Once again, Crossy, you "turned on the lights."