Ronald Raygun wrote:
harry wrote:

On Mar 24, 5:41 pm, Ronald Raygun
wrote:

So here's a wee exercise for you. You have two lamps up a pole.
Call them lamp A and lamp B. You never want both of them on at
once, i.e. you want either both off, or A on with B off, or A off
with B on.

There is only a 2 core cable going up the pole, but that's OK
because they are on a DC supply and there are a couple of diodes
up there, wired so that the polarity of the supply determines
which bulb comes on.

Question 1 (easy): You are given a two pole changeover switch
with a centre off position. How do you wire the battery supply,
the switch's 6 terminals, and the cable to the pole to get what
you need?

Question 2 (more difficult): You don't like the changeover switch
and decide you would rather have two separate switches, one for
lamp A and one for lamp B. What types of switch do you need and
how do you wire them? The obvious solution involving two double
pole one way switches will short-circuit the battery if you are
stupid enough to turn both switches on at once. So you need a
safer solution which avoids that.

I never heard such drivel. Where would you find DC lighting up a pole
these days?

Firstly, I said this is an exercise. You can't dismiss exercises on
the basis of them "being drivel" because they are often contrived.

Secondly, it isn't drivel, and in this instance isn't contrived. As
I have explained elsewhere, it's on a boat.

Now just answer the question, if you can.

Well I used 2g 2way light switch.

Is there a prize?

--
Adam