I know how relays work; I replaced a fused one on my table saw switch and
changed it over to 240v, but that was all in a box.
I want to move my water pump switch from under the house to the kitchen.
There is already a problem with voltage drop, so I don't want to run a
switch leg. That means a relay.
Since the wiring from the switch to the relay only carries milliamps, does
it need #14 and full electrical boxes, or can I get by with something
simpler? (If there is anything on the internet that explains relay wiring,
I would be grateful for the link.)
For your 240 volt, you'll want a double pole normally open relay. The coil
voltage you want could be 24. The relay contacts must be capable of carrying
the load of the pump motor. There will be six connections on this type of
relay. Two Line- where your 240 volt power go, Two Load- where the two wires
go from your pump, and Two control wires- which when fed with 24 volts will
pull in your relay. You'll need a 24 volt transformer which could be fed
from your 240 volt power supply (look for a multi input voltage type) To
wire the control circuit: run one wire from the 24 volt side of the
transformer to one of the coil terminals on the relay. Run a two wire cable
from the second 24 volt terminal of the transformer to your kitchen switch
and back to the second coil terminal on the relay. The 240 volt stuff must
be enclosed in an electrical box of some sort and you can't mix line voltage
and low voltage wire in the same box unless there is a divider. You can
however run low voltage through a line voltage cable and not have this
However it depends on the relay!
If the relay is operated by the same 115 volts that is used for a wall
outlet or lighting etc. directly from a 115 volt circuit breaker or fuse in
the supply panel), I would suggest the answer is, yes. To meet code and
insurance requirements the maximum size of circuit breaker/fuse for anything
wired with #14 AWG is 15 amps. If wired with #12 AWG, 20 amp. I believe it
is unusual for any permanent standard voltage AC residential wiring that to
use smaller than #14 AWG and/or whether smaller breakers would normally be
available or understood by a anyone working on the wiring in the future?
Just because the relay might only take a few milliamps (one light bulb
plugged in to a standard outlet may take only 350 milliamps!) from a 15 amp
capable circuit, does not allow, as far as I know, reducing the size of the
wire or deviating from standard code approved wiring methods? Smaller gauge
wire could burn off, start a fire and the circuit breaker would never
operate to protect property and /or life.
If the relay is the type operated by low voltage, say by the out put of a
transformer and/or rectifier it may be possible to use low voltage wiring
techniques similar to those used for a door bell/chime (12 to 24 volts most
I respectfully suggest that you may have some very basic understanding of
how a relay works but may not be familiar with how to safely incorporate it
into standard methods of wiring to meet a whichever electrical code applies
in your area.
Many heating/cooling controls use low voltage to control relays and other
gear located at the furnace or AC unit. Suggest you look into using
something similar; a relay of a type suitable to handle the horsepower and
starting current of a water pump.
In alt.home.repair on Fri, 2 Sep 2005 19:44:20 -0230 "Terry"
For that matter, he could use the same transformer to power the right
relay. No extra electrical drain.
Except for the moment he pushes the button. That is if he is using a
latching relay. (might want to run another pair to light a light to
remind him the pump is on (although I guess he doesn't have one of
those now.) Otherwise, if he uses a regular relay, he'll need a
toggle switch to keep the relay energized. I suspect the doorbell
will work even then.
Yup, may not be.
If emailing, please let me know whether
or not you are posting the same letter.
Change domain to erols.com, if necessary.
Is there a reason you can't run a switch leg on heavier wire than needed,
e.g. 10 ga for a 15-amp load? That would reduce the voltage drop, and be
simpler to connect.
If it's 120VAC, it better be in electrical boxes and use 14 ga wire. Of
course, there are relays available that don't need 120VAC for the control
terminals. You shouldn't have much trouble finding one that you could
power off of a low-voltage transformer of some sort. (Thought you said
you knew how they work?)
Is Google broken *again* today? I *hate* it when that happens.
Wiring is sized based on the circuit protection, not the load. Some
have said you can cheat with light switches, but I wouldn't. If there
is a short and your circuit breaker trips at 20A, but your wire can only
carry 5A, you have a serious problem.
You can only sort of cheat.. the SWITCH is only required to
realiably switch the downstream load, but the wiring there
still has to be rated for the whole fused current.
Which I *THINK* means that you can theoretically get a resistive
short that will weld your light-switch in the on-position,
and still not blow the breaker, or start a fire by melting
the wires in your walls.
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