Switch before or after transformer?

[jonplapham]

Hello-

I'm planning to install a bunch of LED lights in my kitchen cabinets. The idea is to have a small LED strip turn on automatically when opening the cabinet door. I've found a 12v LED strip that can be cut into 30cm long sections that will be perfect for my application, along with some magnetically activated door switches.

My question is:

A) Is it better to run 120/240v through each cabinet door switches, and then go to the LED transformer (driver) and finally the lights?

or

B) Or, is it better to place the door switches on the low 12v voltage side of the transformer (driver)?

I made a simple drawing to show you what I mean.

My thoughts are that A has the advantage that the transformer is completely isolated when the doors are closed. B has the advantages that it is safer (is it?) in that the switches are 12v in case someone pulls out a wire accidentally. Additionally, B would be cheaper to install because multiple lights could share a single appropriately dimensioned transformer instead of needing separate transformers for each light.

Thanks for any insights!!

-Jon

PS: I won't be doing this install myself, I'll use a licensed electrician. I just want to have a plan and understand the issues beforehand.

 

[Charlie_]

I would go for the elv option..
Check the door switches can take the extra current

 

[Deleted member 26818]

If the transformer is permanently on, it will eventually burn out and cease working.
Then again, if it is frequently switched on and off, it will eventually burn out and cease working.

Having the transformer permanently on will likely use more electricity. How much more will depend on the efficiency of the transformer.

ELV is safer than LV, though often the wires used with ELV are less robust than those used for LV, so are more prone to damage.

 

[Bobster]

If the transformer is permanently on, it will eventually burn out and cease working.

Having the transformer permanently on will likely use more electricity. How much more will depend on the efficiency of the transformer.

Care to explain?

 

[Deleted member 26818]

Care to explain?

Explain what?

 

[telectrix]

forget the driver. install a 12V PSU .use the mag contacts to trigger a 12V relay (inside the PSU) so that the mag.contacts don't carry the load current. Wiring can then be done in alarm cable.

 

[Bobster]

Explain what?

Why a powered transformer would burn out.

 

[Deleted member 26818]

Gets hot, insulation breaks down TX fails.

 

[telectrix]

could always add a fan. here's a few:

 

[DefyG]

Some LED drivers are 'continuously' rated and can be left 'on' 24/7 and therefore switching 12/24v wouldn't be an issue.
If the doors are closed and therefore 'no load' there wouldn't be any significant current flow to cause any premature overheating or failure of the driver if a non continuously rated driver was used either.
Doesn't mean that they can stuffed into a ceiling void with thermal insulation though!

 

[dwilko]

Hi jonplapham i'm thinking of a similar project. where did you get your LED Strips from?

 

[PAUL LED]

Hi, In my opinion it is better to switch the low voltage side of an LED system as LED drivers have a large inrush current when switched on which can cause issues with sensitive circuit breakers. As long as the driver is rated correctly with the right tolerance (recommend 75% of the driver value) then you should have few issues with drivers.

I would also strongly recommend 24v LED tape rather than 12v. This is a more professional solution as there is less voltage drop and also 24v LED Tape draws half the current than the 12v tape equivalent on the low voltage side.

LEDTechnologies.co.uk have many help documents and recommendations to help you install your LED tape.