Fuses for led lighting

[nicknorman]

Yeah so it's not exactly BS then.

 

It was at the date and time I posted it though.

[alan_fincher]

..............................but equally let's not kid ourselves that this will in some way remove the possibility of a fire. It might reduce it, but only very slightly.

 

Actually, how can you possibly know that the reduction of risk is only slight?

 

Can you definitely say in the cases we are being told about about faulty LEDs that they would definitely not have blown a 1 amp fuse, had that been the value, rather than (say) a 10 amp one they are still being supplied through, because the lights have been changed from tungsten based ones?

 

Have you measured the current drawn by one of these LED lights as it goes into failure mode, and the smoke starts coming out? Unless you have, or can quote a source that has, I would say the statement you have made is a pure guess, isn't it?

[Sea Dog]

Crikey, maybe the OP should put his halogens back in?

[GUMPY]

 

OK Nick, say you have a replacement bilge pump which calls for a 5A fuse, but the existing wiring and breaker is 10A, what do you do?

 

cheers, Pete.

~smpt~

The correct thing to do would be to leave the "breaker" as is.

And then put a 5amp fuse in the in line holder that is next to the pump. This is why most pumps come with inline fuse holders.

A fuse to protect the equipment shpuld be in or at the equipment not in the fusebox.

[nicknorman]

Actually, how can you possibly know that the reduction of risk is only slight?

 

Can you definitely say in the cases we are being told about about faulty LEDs that they would definitely not have blown a 1 amp fuse, had that been the value, rather than (say) a 10 amp one they are still being supplied through, because the lights have been changed from tungsten based ones?

Have you measured the current drawn by one of these LED lights as it goes into failure mode, and the smoke starts coming out? Unless you have, or can quote a source that has, I would say the statement you have made is a pure guess, isn't it?

I think I can summarise my position by saying that there is no "one size fits all" answer, rather each case has to be judged on its merits. But especially in the case of lighting, as per the OP, when it is SOP to have multiple lights off 1 fuse, some or all of which may be on or off, it is unrealistic to expect fusing to prevent a fire. A fire starts when something exceeds its combustion temperature. That thing may be quite small and thus require little energy to reach combustion temperature (viz relationship between energy, temperature and thermal mass). So in the case of a small circuit board on an LED bulb, 1/2 amp (6w) is probably plenty to get a small component very hot and either combust itself, or set fire to something adjacent. You just can't protect against that sort of thing by fusing.

[ditchcrawler]

 

Only true up to a point. There have been many occurences where correctly chosen fuses have saved expensive DC devices that were not faulty but simply overloaded. You should know better than to perpetuate this myth Nick. Your theory is indisputable but practice suggests you are generally wrong on this issue.

In that case the fuse should be in the equipment not back at the power distribution point. At one time nearly all electronic, including and probably more so the stuff with hot glowing things in them were fitted with fuses, often more than one.

[alan_fincher]

In that case the fuse should be in the equipment not back at the power distribution point. At one time nearly all electronic, including and probably more so the stuff with hot glowing things in them were fitted with fuses, often more than one.

 

Perhaps the source of the smoke and / or flames coming from these failed LED devices is actually the protective fuse they have built into them!

[by'eck]

In that case the fuse should be in the equipment not back at the power distribution point. At one time nearly all electronic, including and probably more so the stuff with hot glowing things in them were fitted with fuses, often more than one.

 

Not sure of the point you are making. If the device is fused internally that's fine. Many aren't though and given the need to protect the power feed cabling why do you need more than one of appropriate value at source?

[cuthound]

A fuse can never (or rarely) protect the appliance. Who comes up with this BS!

Consider a washing machine or dishwasher. The fuse has to be rated to at least cope with the water heating bit. But for a good chunk of the wash, the heater is not powered, so the remaining electronics and motor now has a grossly over-rated fuse that will not stop it going on fire if a fault develops.

Ditto in the case of an LED lighting circuit where only one, or all, of the lights might be on at any one time.

If the fuse was to protect the appliance, appliances would never go on fire but in the real world they do. Why? Because it is mostly impossible to design a fuse to protect a faulty appliance.

This is why some electrical equipment use internal fuses, so that thethe "sensitive" bits can survive in case of a fault. It is not however, common practice in domestic equipment.

[ditchcrawler]

This is why some electrical equipment use internal fuses, so that thethe "sensitive" bits can survive in case of a fault. It is not however, common practice in domestic equipment.

Once upon a time all TVs, Mains radios, HiFi s etc were fitted with fuses. Yes I am that old.

[Alan Saunders]

Whilst accepting the expertise above I have fused the DC circuits on my boat at ~double the maximum anticipated load to reduce voltage drop through warm fuses. The lower the fuse value, the better the protection. A modern installation would use contact breakers. As mentioned above, the capacity of the cable is far more, being sized to reduce voltage drop.

 

I have never considered the risk that an individual component may fail, e.g. an LED lighting unit. There seems to be a good case to individually fuse each unit.

 

There are also 'thermal fuses', often found within the windings of a transfomer, they trip at high temperature, not a specific current.

 

HTH, Alan

[nicknorman]

Whilst accepting the expertise above I have fused the DC circuits on my boat at ~double the maximum anticipated load to reduce voltage drop through warm fuses. The lower the fuse value, the better the protection. A modern installation would use contact breakers. As mentioned above, the capacity of the cable is far more, being sized to reduce voltage drop.

 

I have never considered the risk that an individual component may fail, e.g. an LED lighting unit. There seems to be a good case to individually fuse each unit.

 

There are also 'thermal fuses', often found within the windings of a transfomer, they trip at high temperature, not a specific current.

 

HTH, Alan

I think you make a good point. If you have a device that consumes 10A, and fuse it with a 10A, or even an 11A fuse, it will be thermally stressed each time the service is turned on and off, and it will not be too long before the service suffers a "nuisances" fuse blow.

[DHutch]

I also think it's fairly unlikely a failing LED 'bulb' or lamp would generate enough heat to cause fire, acrid smoke maybe, but unlikely fire. Most are replacing halogens, which typically are really quite well placed a safely accept high temperatures.

 

 

Daniel

[jenlyn]

I also think it's fairly unlikely a failing LED 'bulb' or lamp would generate enough heat to cause fire, acrid smoke maybe, but unlikely fire. Most are replacing halogens, which typically are really quite well placed a safely accept high temperatures.

Daniel

The one that burnt on me the other evening had a blue flame coming from it.

[NMEA]

This continual over simplistic absolute mantra of fuses being there to protect the cable always amuses me and collegues, an over current device is there to preotect the circuit, and that includes the conductor but is not limited to it, an over curerent device should be specified to protect the weakeast component downstream of it. In a cable supplying a distrubution panel it is indeed only the conductor but in many instances it is there as a simple and convenient way to protect the circuits radiating from that panel in a central known location too, overloaded pumps due to blockages, anything with a winding that can short and cause further damage and particularly electroniuc items, though many have either an internal or adjacent over current device. Example, a very long oversized cable used to minimise volt drop and protected by an over current device appropriate to the conductor cross section could cause issues in case of component failure.

Edited January 2, 2015 by NMEA