relays

I'm attending ETI right now and I was wondering if anyone could give me a crash course on relays and sequencers in an electric heat furnance or any other furnaces?

m1--------m2 Time delay
m3--------m4
(w)~~~~~~(c)

m1-to (1)side of breaker
m2-to (1)side of heat strips
m3-to (2)side if breaker
m4-to (2)side of heat strips
w-to white or w2 at thermostat
c-common side of transformer

What's ETI?

relays & starters & contactors & sequencers allow a small amount of current to switch on | off a larger amount of current. some have builtin time delay = time delay after circuit is shut off, or time delay before circuit is turned on -- control voltage may be anything from 2v to 440v, large current may be from 5 - 2000 amp. small current thru a coil activates plunger to close heavy duty contacts. Or, the whole thing may be solid state -- same principle --
TDO commonly used to hold down total current from supply side devices at one instant.

I was taught to think of a relay as a messenger it needs to relay a message ( elctricity ) to somewhere else when it is told to ( coil is energized ).

Get an old relay and take it apart.
do the same with sequencers,

It may help you to understand them

I have a degree in commercial electricity and can follow this entire thread, but what I don't know is WTH is "ETI"?

LOL

TIA,

md

Sory for using an analogy, there is a technical explanation for relays in any basic electricity book you can pick-up

I have found that using analogies helps people get started then there talent takes over once they have a general idea of what a components job is.