Detecting Neutral

<Now I would to detect Neutral instead of Live.>

Not recommended. Leave the neutral alone. In the event of it going open-circuit, anyone trying to fault-find on a piece of equipment that is not operating will find it live, either confusingly or inadvertently. There are safety implications for that individual.

Here's another vote for "If it ain't broke, don't fix it".

Agree. if it ain't broke,don't fix it.

However, the idea behind is that:-

Currently if we need to install emergency light than additional point/cable has to be added on, that cost dollar and cents.

So instead of adding up more power points, we just tie up parallel to any light source that we want to fix emergency light. And since we are using neutral to trigger the light, switching off the main light switch would not activate the emergency light.

It will only activate when the Circuit breaker or Grid line trip

With this approach emergency light basically can be fixed as where the current lighting is...and coupled up with the new Bright LED the cost of purchasing and installing emergency light will be cheaper.

I hope my explanation is clear.

tq

It will only activate when the Circuit breaker or Grid line trip.

Except the breaker isn't hooked to the neutral, so that still won't get there!

You're gonna have to run more wire, or something even more expensive, wireless.

I don't know about your local regulations, you can probably switch over to low volt low power wiring. Low power such as communication wiring can be run much cheaper, than conduit, romex or even fishing new wires through existing conduit.

Why not connect the emergency lighting circuit to the "loop in/loop out" (or equivalent) terminals for the normal lighting: i.e. the live side of the light switch?

If your monitoring your lighting circuit from neutral (not to active but to ground) imagine what happens if there is either a earth fault, or someone adds a EL-trip breaker on to your lighting circuit in your switchboard.

as each circuit is measuring something on each light, there will be a certain amount of current getting off the Neutral return to the switchboard and back down the Earth line.

Advice would be not to alter the way things are supposed to be done, if you leave your currect job and the next guy cannot find the documentation you provided before you left, they could be in for 1 serious injury.

Whats a saving of a few cents when you have to pay out later after some poor guy is put in hospital, or worse.

Buy a small auto mains fail gen-set if you do not want to alter the circutry.

Why not use an optocoupler for galvanic separation of mains and low voltage? Connect the LED of the optocoupler in series with a resistor on mains and the phototransistor at the input of a NAND gate powered by the battery of the emergency light. The NAND input also needs a capacitor in parallel with a resistor to ground in order not to fool the trigger with 50/60Hz. One would need the light's circuit diagram to do the right design and to match logic levels.

This way, it doesn't mater any more which is neutral and which is phase (live) wire.

If you need more help, feel free to ask.

I know that the neutral is supposedly at earth potential, but I also know you can get zapped off the neutral on a 480-277 wye lighting system.

If they are self contained fittings the loss of either live or neutral will cause the fitting to operate from its own battery power source. If it is a central battery system and you need to detect failure on a specific part of the system, put a relay across the supply and the loss of either live or neutral at that point in the circuit will cause the relay to drop out. You can use the relay contacts as the trigger for your battery system. It is generally considered bad practice and not allowed in GB to switch a neutral for control purposes.

hope this helps

Hottech, I thought about it but we need to use passive component rather than active component since active component will consumed the battery and when actual power failure happen then we might loose some of our back-up power. No doubt optocoupler drains small current but assuming we went out for 1 week vacation and upon returning home there'sm a power failure...then probably that time our battery has been drained.

Kyoto, no offence bro, lets talk on single phase rather than 3 phase.

Shyam, yes there's a potential between neutral and earth. This is what I want to make use off to trigger the EL when actual power failure happen.

rgds

sufian

But isn't your main objective to avoid running a wire from the line side of the switch?

What sort of detection do you need, per room per, floor, per building?

I've seen emergency lights run off the lighting or wall outlet circuits, even a dedicated circuit. You really only need to know if the sub panel loses power.

I did some work @ a factory where the problem was momentary outages [3-5seconds] just long enough to turn off all the HPS [high pressure sodium] lighting. The ballasts required 7 minutes to cool off [reset], meanwhile the whole place was dark, as the e-lights had power. We replaced strategic HPS fixtures w/400w fluorescent. Not quite as efficent, but these outages happened @ least once a month. A few KWH was a fair trade for the safety of 60 workers. There was also some savings of product that could be salvaged, since the lines could be restarted more quickly, since everyone didn't have to evacuate.

So, what your saying is that you run some fluro's 24/7?

I have seen this before, you place them to aid in exit navigation

Actually the whole place ran 24-7

the fluro's looked the same as the HPS fixtures, used 10 of those U shaped bulbs used for recessed lighting & draw more current than the HPS equivalent. The difference is the flouro's would come back on instantly.

Dear Garth

Detection of power failure is possible within single power cycle which is about 20ms for 50Hz and bit less for 60Hz. However, 100ms or almost 5 mains power cycles may be ideal to let relay come into action on power fail or over voltage kind of fault.

Lightning pulse is often less than 10us and only some times may be as large as few ms and never to 20ms or larger. Million volts running into ms can burn our everything around.

The amount of energy that safety device can accept comes from this short time duration and very high current making it still a very limited energy not resulting into lot of heat output.

It is not the heat but ions from plasma that destroy the material and equipments. Breakdown of dielectric barrier is often the main cause and then you also see an avalanche formation and more damage.

While power failure detection is very well possible by simple device which gets activated by potential using only small current.However, to be safer side that false tripping is not caused by some fast RF signal or kick-off negative pulse from power device in problem, some forced amount of current is wasted into load with sensors like CT placed in parallel. Load can be both resistive and capacitive in parallel such that more load is to high frequency changes and they are unwanted if are above 50Hz/60Hz or 400Hz which may be the source frequency of your incoming power point.

Measurement you do on step down transformer output to make then isolated, safe and readable by instrument like PLC and other LOGIC devices. Loads to kill noise to the power measurement is to be placed immediately on the secondary coil output and not after the rectified output. The reason is that the diode act as peak detector and may charge the capacitor to peak voltage of the noise pulse making false reading in measurement. Placing the load before rectifier diode kills the noise ahead of it becoming a measurable voltage and then you meter becomes very stable.

Do not use the measurement power source to drive the meter power as meter may draw different current in time and may cause functions in the measurement. Use separate transformer or at least separate winding on same transformer to isolate the meter and measurement voltage source. Time constant for signal averaging you can change to the desired level using capacitor C and discharge resistance R based RxC time constant. Usually 1s time constant is idea to suit almost all types of relays made in the world. Making it faster will require faster relay to respond else will be of no practical advantage. larger time constant may cause more dead time. Best thing to do is to look into the dead time tolerated by your systems and then set it between 100ms to 1s range or use variable setting in that range.

It may also be vise thing to do to look into tolerance level desired by the process, when you monitor power quality and the accuracy to which your measurement need to be. There is clear relationship between precision and cost involved. Do to the level you really need it and not what is supposed to be "the best".

Usually there is no three phase lighting fixture. The single phase lighting system is derived from a three phase system. A three phase breaker pane with single phase circuits.

Sometimes, passive components can drain more power than active ones... A bare wire can do the trick .

What puzzles me this time is how come the backup battery is not charged automatically? I don't know exactly what's your application, but usually an emergency light battery + charger never takes vacation and is rigorously scheduled to be replaced when its time goes by. I used to do this job for hospitals and other public buildings where that is the case.

This idea is almost certain not to meet code anywhere.