I'm trying to connect the circuit of an emergency light and it has transformer at the input and also 12 LEDs.I want to know what precautions should I take while connecting the transformer and also the LEDs because the LEDs n the ICs will blow off if the connections are reverse.

Bst I cn ofer, sins you provided no make or model number of the unit your trying 2 connect,iz 2 read and follow the instructions.

It's a 9v 500mA transformer and the LEDs are 10mm white.I heard that I need to be careful while connecting the LED after checking its terminals.how should I do this? Are'nt the big terminal positive and short one negative?and the transformer has 3 wires to secondary side.I remember we should give the middle wire of three to ground and the longer wire as positive and shorter wire as negative from the rest 2 wires.is this correct?

Dimple,

Welcome to the electrical and lighting forum. Some general guidelines for posting in this forum. Use the English language as you were taught to use it in school. Miscommunication might result in death if instructions are not carried out correctly.

You missed the tongue-in-cheek swat at your writing and communication skills.

Poor communication on this forum can get you seriously hurt. Electricity is not the place to misread a response.

First are you talking about an AC to DC transformer? Can you tell us the make and model of the unit you are trying to install?

Are you installing the exit sign in a commercial venue? If so you will need a licensed electrician to do the work.

Sounds like the transformer is AC, You will need a rectifier to convert to DC, and need to know ma and voltage of LED's(to determine resistor).
If you connect the LED's backwards, no damage, they just won't light, just reverse the connections.
If the 10 LED's are in 1 chip/array, what is the required voltage?

Sounds like the transformer is AC, You will need a rectifier to convert to DC, and need to know ma and voltage of LED's(to determine resistor).
If you connect the LED's backwards, no damage, they just wont light, just reverse the connections.
If the 10 LED's are in 1 chip/array, what is the required voltage?

The circuit takes 9v 500ma to on and also charge the battery.its the circuit of an emergency light.it has an IC(LM317) too.will it get damaged if the LEDs are connected in reverse?these LEDs have 2terminals of which one is long and the other short.we represent an LED while drawing as a triangle with a line at its tip.so what do these 2terminals represent?

Google Image Result for http://www.electronics2000.co.uk/images/data/LED.gif (http://www.google.com/imgres?imgurl=http://www.electronics2000.co.uk/images/data/LED.gif&imgrefurl=http://www.electronics2000.co.uk/pin-out/led.php&h=285&w=416&sz=5&tbnid=hI4PAQz9lNQSpM:&tbnh=86&tbnw=125&prev=/images%3Fq%3Dled%2Banode%2Bcathode&usg=__HOuNgT0s57t-K0y3PCqDeq09z4Y=&ei=zwYpS8mrINOUtgfvidSADw&sa=X&oi=image_result&resnum=8&ct=image&ved=0CB0Q9QEwBw)

Here's where you can find your Pot:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=262965&k=2.2k%20pot

Strat,

Here is the design information that Dimple added to another item. Clearly this is either for a different country or a commercial site.

The trans former requires a 230 VAC 50 Amp input. I would not expect to find this arrangement in a residence here in the U.S.A.

Google Image Result for http://www.electronics2000.co.uk/images/data/LED.gif (http://www.google.com/imgres?imgurl=http://www.electronics2000.co.uk/images/data/LED.gif&imgrefurl=http://www.electronics2000.co.uk/pin-out/led.php&h=285&w=416&sz=5&tbnid=hI4PAQz9lNQSpM:&tbnh=86&tbnw=125&prev=/images%3Fq%3Dled%2Banode%2Bcathode&usg=__HOuNgT0s57t-K0y3PCqDeq09z4Y=&ei=zwYpS8mrINOUtgfvidSADw&sa=X&oi=image_result&resnum=8&ct=image&ved=0CB0Q9QEwBw)

Here's where you can find your Pot:
Digi-Key - P16NP-2.2K-ND (Manufacturer - P16NP222MAB15) (http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=262965&k=2.2k%20pot)

Thank you... the LED picture served me the answer :)

I'm from india and as you know a general transformer has 2wires to the primary side n 3wires to the secondary.I want to know how to connect the 3wires to the further circuit.as per my knowledge the middle wire is to be grounded and the longer wire represents positive and the short wire represents negative among the rest two wires.is this correct?

A transformer converts AC voltage UP, Down, or the same(isolation). I wouldn't use the center tap on the secondary, cap off.
Check voltage on 2 remaining wires on the secondary, and then go through a Full Wave Bridge Rectifier as shown on your circuit.