TCC Curves: What about events below .001 seconds?
TCC Curves: What about events below .001 seconds?
(OP)
We have LED drivers with a rated inrush of 185 amps at 200 microseconds (.0002 seconds. We are trying to determine how many drivers we can place on a 20 amp, 120v circuit. The circuit breakers TCC curves start at .001 seconds. Also, the fuse TCC start at .01 seconds. What happens if the event is shorter then the published TCC curve and is off of the curve? Will the breaker or fuse trip or is the event short enough that the energy will not all the overcurrent protection device to trip?
Thanks.
b
Thanks.
b






RE: TCC Curves: What about events below .001 seconds?
RE: TCC Curves: What about events below .001 seconds?
RE: TCC Curves: What about events below .001 seconds?
RE: TCC Curves: What about events below .001 seconds?
RE: TCC Curves: What about events below .001 seconds?
RE: TCC Curves: What about events below .001 seconds?
Your source impedance might also have an impact on how much current the LEDs draw.
RE: TCC Curves: What about events below .001 seconds?
The specification sounds rather bogus. I would expect the instantaneous trip on a 20A breaker would likely be close to tripping with a single driver when you did manage to close the circuit at a voltage peak and try to draw 185A. Two drivers would likely randomly trip the breaker each time you closed the circuit at a voltage peak.
RE: TCC Curves: What about events below .001 seconds?
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla
RE: TCC Curves: What about events below .001 seconds?
RE: TCC Curves: What about events below .001 seconds?
Figure for residential, available fault current can be as low as 750A.
RE: TCC Curves: What about events below .001 seconds?
From past experience I would say about 5 of those particularly high inrush units would be reliable on a 20A breaker.
One approach is to use a standard breaker and try it as dpc suggests. I'd wire the fixtures up as directly as possible and keep adding them until you get a trip. Knock off a few from that and go with that number in the installation. If after the install the different impedances involved you get a nuisance trip you then switch all the breakers to a C-curve. You won't have anymore trips. I'd keep that as a fall back tool though, as you'll be screwed if you start out with C-curves and then get nuisance trips.
I don't know what your situation is but if you can turn them all on with a zero voltage crossing switch then you will have no tripping issues up to the steady state circuit loading limit. This would be as simple as using a solid state zero crossing relay to turn on the circuits. That is one of the SSRs seen in this search depending, of course, on various details of your application.
DigiKey Search of 240V+/20A+ 120Vac triggered zero crossing SSRs
Keith Cress
kcress - http://www.flaminsystems.com