LEDs Tripping MCB

[parkview094]

I have just replaced one of our wall lights with a LED Tape light and associated power supply. As all was well, I replaced a second wall light fitting (on the same circuit) also with a length of LED tape light and an associated power supply.

Now, ~30% of the time that I turn those lights on, the MCB trips.

I understand this may be related to the inrush current of the 2 Power Supplies, but unfortunately the particular 12V drivers I have don't indicate what their expected inrush current is.

Running the 2 sets of tape of a single PSU won't work as they're at opposite ends of the same room. I've tried searching for 'low inrush current' PSUs, but the lowest I can find appears to still be rated at 20A. Can these ever work on a lighting circuit?

Anything I could try myself before getting an electrician in? Even then, what might be the options? Is using a type C MCB a solution or a hack?

 

[flameport]

may be related to the inrush current of the 2 Power Supplies,

Maybe, but it's also possible that one or both of them is just poorly designed, unsuitable or just faulty.

What is the rating of the LED tape, and the power supplies? Make/model? Were they obtained from dubious sources such as ebay?

using a type C MCB a solution

No.

 

[ericmark]

In the main switch mode power supplies do not have a great in rush, that is why we use inverters as motor controllers to reduce the start currents, when I put an energy meter on my fridge freezer you could see exactly what size the defrost element was as the inverter drive motor was around 70W and the defrost heater was 110W.

OK there must be some in rush to charge the capacitor, but not enough to trip a MCB. So it would seem either a silly size or faulty.

 

[parkview094]

The LEDs in question are these:
https://www.amazon.co.uk/LEDMO-Wate...D=51-FAsZr%2BpL&preST=_SX342_QL70_&dpSrc=srch
The only 'rating' that seems to be available is that the power supply is 12v 5a. The listing helpfully suggests that the 5m strip is 60w. That might be right as I see SMD2835's are rated at 0.1w ea and there's allegedly 600 on a 5m strip.
In reality I have 1x 2.5m strip and 1x35cm strip.

 

[ban-all-sheds]

Even an 80% efficient 60W PSU will only draw 326mA when running at maximum load.

 

[ericmark]

Input 0.6A at 100 ~ 240 volt in real terms only 0.6A at 100 volt at 230 volt it should be a lot less, the fig 8 lead rated at 2.5A there is no way that should trip a MCB unless faulty.

 

[ban-all-sheds]

"Many manufacturers of PCs and associated equipment, that are intended for commercial / industrial use, supply this information (often on-line) as a matter of course these days, for precisely the reason you state.

If no information is forthcoming, then the following "rule of thumb" might be useful for maximum inrush currents:
- Flat-Panel Monitors up to 322 : 15 - 20 A inrush
- Small SMPSU (<80 VA): 10 A inrush
- Larger SMPSU (or PCs) 80 - 650 VA: 20-25 A inrush
- Heavy SMPSU >650 VA (or Server, each input if more than one PSU): 35 A inrush."

 

[aptsys]

OK there must be some in rush to charge the capacitor, but not enough to trip a MCB. So it would seem either a silly size or faulty.

Unless it's a more bulky power supply which manages this, the inrush current is limited only by the wiring and the point in the AC cycle at which the power supply has power applied to it. Inrush current is likely to be at a minimum of tens of amps.

 

[parkview094]

This is where I am beyond my basic DIY knowledge of electrics, but I came across these:
http://www.powerpax.co.uk/power-sup...urrent-power-supplies-pln-20w-to-100w-series/
Which claim to be "low Inrush Current" LED drivers, specifically designed to "to protect against the tripping of MCBs". However, the inrush current is rated at 35A. How on earth can these ever be used on domestic lighting circuits? What am I missing?

 

[aptsys]

How on earth can these ever be used on domestic lighting circuits? What am I missing?

Because of fuse curves. 35A through a B6 breaker for one AC cycle will not cause it to trip.

 

[flameport]

the inrush current is rated at 35A.

That is a low inrush, compared to this: https://www.rapidonline.com/pdf/85-3794T_v1.pdf which is 75A, or this one: https://www.rapidonline.com/pdf/550866_v1.pdf which is 60A.

A 6A MCB does not trip at 6A, it would take between 18A and 30A to reliably trip with a continuously applied current.
However inrush is of very short duration (some examples in the Meanwell datasheet), so even if the peak is higher than 30A, a very short pulse won't necessarily trip the MCB.

Given the low price of the PSU you have got, and the lack of any real information about it, it is probably some generic thing which wasn't designed for any particular application and may well have a very large inrush current.
The fact it is supplied with a plug fitted also indicates it was not designed for use on UK lighting circuits.

A type C MCB trips at higher currents, between 30A and 60A in the case of a 6A type, however it's not just a case of changing it - the circuit wiring and supply must also be checked to ensure they are suitable, and that disconnection will occur within the required time, which is why I said it isn't the solution in the earlier reply.

Ultimately the solution is to use a good quality power supply from a reputable manufacturer which is designed for the purpose.

 

[parkview094]

I can purchase 2 of the 'low inrush' PSU's - but given they would be on the same circuit (switch), that could still potentially yield a momentary surge of up to 40A. Is there any way around that, or shall I just ditch one of the sections of LED tape for a regular light fitting.

 

[JohnW2]

Because of fuse curves. 35A through a B6 breaker for one AC cycle will not cause it to trip.

Indeed, and I would imagine that we would usually be talking of a much shorter duration than one cycle of 50Hz.

In fact, if one assumes that the inrush results primarily from a capacitor, then it's presumably the case that the higher the inrush (for switch-on at a given point in the cycle), the shorter will be its duration, both magnitude and duration being determined primarily by the capacitance of the capacitor (and resistance of wiring etc.).

It has been implied that cheaper SMPSUs may tend to have higher inrush currents, but I wonder how true that is (other than that, as you have also implied, 'high end' ones may have 'inrush-reduction' designed into them). I would think that that would be most likely to result from a higher value (aka 'more expensive) capacitor, and I would doubt that would be more common in cheap consumer products - but I may, of course, be wrong!.

In terms of this discussion, is not the practical fact that, primarily because of the short duration of inrush, a sensibly-designed 60W SMPSU is probably 'never' going to trip a B6 MCB?

Kind Regards, John

 

[JohnW2]

I can purchase 2 of the 'low inrush' PSU's - but given they would be on the same circuit (switch), that could still potentially yield a momentary surge of up to 40A. Is there any way around that, or shall I just ditch one of the sections of LED tape for a regular light fitting.

Maybe it's just me, but I do wonder whether this discussion may have got a bit dominated by considerations of inrush currents? As I've just written, the duration of the inrush is so short that I would have thought that it is extremely unlikley that a B6 MCB would ever be tripped by such a power supply. If SMPSUs of the sort of size we're talking about commonly tripped a standard lighting circuit MCB, we would surely be hearing about it all the time - which we aren't. For what it's worth, it's not something that I've ever personally experienced.

Kind Regards, John

 

[ban-all-sheds]

In terms of this discussion, is not the practical fact that, primarily because of the short duration of inrush, a sensibly-designed 60W SMPSU is probably 'never' going to trip a B6 MCB?

The OP has two being fired up simultaneously.

If SMPSUs of the sort of size we're talking about commonly tripped a standard lighting circuit MCB, we would surely be hearing about it all the time - which we aren't. For what it's worth, it's not something that I've ever personally experienced.

Maybe the OP's are egregiously poor.