Current project: LED Indicator on 120 VAC (isolated) & GFCI questions

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
Building a roll-out island for the kitchen. The plan is to have an outlet available for small appliances (low amperage). I want to supply power via a plug and an outlet with a circuit breaker to protect the circuit.

The essence of what I'm asking is the two indicator LED's: They will be super bright LED's but they don't need to be bright at all. I'm willing to bet it can be done with 5 mA current. According to the drawing below, do you see any issues with that part of the plan.

The second question I have is the GFCI outlet: Will it work if it is isolated via the isolation transformer?

The system will be plugged into a 20 amp service (120 VAC) but I want to use a 14 gauge cord, hence the 15 amp breaker located on the island. On the lower (schematic) I didn't bother to draw the isolation transformer. As for the capabilities of the transformer - that's an issue for a later discussion.

ANY ISSUES?

Island Power.jpg
 

LesJones

Joined Jan 8, 2017
3,290
A GFCI (Which we call an RCD in the UK.) will not work on the secondary of an isolation transformer unless one side of the secondary is earthed. (Which defeats the purpose of the isolation transformer.) With an isolation transformer (With NEITHER side of the secondary earthed.) you could touch either side of the secondary winding and earth and not get a shock as there is no path for the current. (So a GFCI would not trip.) The same sort of reasoning would apply if the GFCI was on the primary side of the isolation transformer. NOTE A GFCI will NOT protect you if you touch line and neutral.
With an AC supply if you just connect a suitable value resistor in series with an LED it will be destroyed by exceeding it's reverse breakdown voltage on the half cycle when the LED does not conduct (Forward biased.). You will need to connect a diode in parallel with the LED so it conducts on the half cycle when the LED would be reversed biased. This will limit the reverse voltage across the LED to about 0.7 volts.

Les.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
Thank's @LesJones. I hadn't considered that. Hence good reason to ask such questions.

My reason for considering the GFCI is because there is a chance the wife might move the island within 3 feet of the sink. Not real sure on code but I think GFCI's are required within 3 feet. It may be 6 feet - I don't know. I just want to keep the wife safe. But with isolation it may be unnecessary.
 
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