LED lamp startup currents and MCB/RCBO

This was mentioned in a webinar yesterday … the answer seems to be that there is a huge amount of variation between designs (some are ‘soft-start’ and have little or no startup surge,  others are horrible and can only have a few on an MCB) - so it's really a matter of asking the manufacturer.

   - Andy.

Sadly agree, there is very little standardization even about how to repeatably measure inrush, and how fast an event can be before it  can be ignored. 

This leaves us with calling the makers or trying a few.

M.

I have just installed two 250W 24 power supplies for LED tape. I have put them both onto one C6 and am crossing my fingers as when I read the spec it was 70A inrush each. According to the Hagar tech specs for fluorescent lights I need a C20 or B32 to cope with 140A of inrush. 

I have found a FAIRLY reliable rule of thumb is not to exceed 10% of the nominal capacity of the circuit, for lamps switched in groups.

So a standard 6 amp lighting circuit is good for about 1,380 watts of incandescent bulbs. So by this rule of thumb it should be good for about 140 watts of LEDs. That is a lot of LED lamps.

Another approach that will often give a similar result, is to size lighting circuits by the old rule of a “100 watt lamp for each light” even if LED lamps of much lower wattage are to be used. That would give a limit of about 13 or 14 lamps on a 6 amp circuit.

Weirdbeard: 
 

https://communities.theiet.org/discussions/viewtopic/1037/27010#p149029

wth

In yesterday's webinar, the rule of thumb of 6 x for motor start-ups was mentioned. That accords with the manufacturer's data for some of my machines. I suspect that the inrush for motors may be a little longer than for LED lamps, but how about 10 x as a rule of thumb for LEDs?

What about  employing startup-current suppression  (local to light unit or otherwise) … what ready form might that take and what are the implications ?

Interesting comments on some approaches.   It would seem sensible, as touched upon above, to liaise and stick to a manufacturer using their confirmed properties.

Still, in trying to get an understanding (if that is possible), I always find making  up an example useful, so (using same as for some of the surge questions that have been on my mind):-

same-time startup one circuit   of  600 - 900 w   of LED lamps    over   a  ~100m run

Based on one's experience and/or expert or rule of thumb knowledge, is it likely that a type C MCB/RCBO  e.g. of 10 or 16 amps  would hold up ?

It may be the case that consulting the lamp manufacturer and then passing on to the  protective device manufacturer to see what's likely is the only sure way, without some standardisation etc.

Habs.

psychicwarrior: 
 

What about  employing startup-current suppression  (local to light unit or otherwise) … what ready form might that take and what are the implications ?

 

Interesting comments on some approaches.   It would seem sensible, as touched upon above, to liaise and stick to a manufacturer using their confirmed properties.

 

Still, in trying to get an understanding (if that is possible), I always find making  up an example useful, so (using same as for some of the surge questions that have been on my mind):-

same-time startup one circuit   of  600 - 900 w   of LED lamps    over   a  ~100m run

Based on one's experience and/or expert or rule of thumb knowledge, is it likely that a type C MCB/RCBO  e.g. of 10 or 16 amps  would hold up ?

 

It may be the case that consulting the lamp manufacturer and then passing on to the  protective device manufacturer to see what's likely is the only sure way, without some standardisation etc.

Habs.

 

just to add … i came across this helpful piece for an insight !