What is a DP switch

[trossachs]

Just out of curiosity, i am looking to change a plastic light switch in my kitchen to a chrome one, i have seen 20A DP switches for sale. Can anyone tell me what the difference is between a normal switch and a DP switch.

Also I plan to change my cabinet light switch also. Their are 12 x 20W cabinet and worktop lights fed from 3 x 12V/80W transformers, and 2 FLourescent 240V/20W strip lights. What kind of switch would I need on this as I make it the Amps would be 20.17A.

Any advice would be appreciated.

 

[Big_Spark]

Right, a DP is a DOUBLE POLE switch, these break both the NEUTRAL and PHASE conductors of a circuit. Normal Light switches are SP or SINGLE POLE, they only break the Phase (Live) conductor as there should not be a neutral at the switch. There may be in some circumstances, but not often, when you take off your existing switch you will see two cables in the switch, a RED, and likely a BLACK, this black should be marked with red sleeving or tape as it is in fact the live return to power the light.

With regards your cabinet lights, not sure where you get 20A from for the load on the switch.

3 x 80W = 240W / 230V = 1.04A

2 x 20W = 40W / 230V = 0.17A

Totals

280W / 230V = 1.217A

Therefore a standard light switvh is all that is required.

 

[trossachs]

So I take it the fact that the 3x80W running at 12V is wrong, and you actually calculate the current from the 230V supply

 

[Big_Spark]

So I take it the fact that the 3x80W running at 12V is wrong, and you actually calculate the current from the 230V supply

That is correct, power drawn from a system stays the same regardless of voltage, however the current changes with the voltage.

On the 12V side of the transformers the combined total is 20A as you say, however 230V / 12V = 19.16, therefore the current will be 19.16 times lower on the 230V side of the transformer or 20V / 19.16 = 1.04

If you UP the voltage, you lower the circuit current, however if you DROP the voltage, you will increase the current in direct proportion to the drop in voltage.

 

[IanDB]

Or put another way:- Wattage (Watts) = Voltage (Volts) x Current (Amps)