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A relay is a control device that allows a small voltage or current to control a larger voltage or current. Use this tag for questions about standalone relays in electrical or HVAC wiring -- questions about relays in appliances do not need this tag.

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Box mounting point

What are the chances of this setup passing an inspection? 4x4 box is mounted on a stud, relay attached to the bottom 1/2 knockout, transformer will be mounted at the front of the box. This is in ...
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3answers
64 views

How bad is it for my A/C unit if I cut the power while it's working?

I have a rental apartment with two a/c units. I installed magnetic contacts on the windows of each room and a small module (a sonoff basic flashed with tasmota firmware) that shuts off the a/c relay (...
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45 views

Double water pump relay

Here is my dilemma. I have two water wells; consequently, I have two deep well pumps. Presently I have a relay set up to switch wells each time the pressure switch requires water. They are labeled #1 ...
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1answer
58 views

using a relay to swich between main and solar power

I have both solar and mains voltage at my house and since the solar isn't enough to continuously power the house , we switch between it and mains when there is less sun.I was hoping to make an ...
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2answers
52 views

Smartify 50s low-voltage lighting system

I bought a house with a low-voltage lighting system, where the switches have low-voltage wires that power relays that actually power the full-voltage lights. I want to find out if I can take advantage ...
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0answers
21 views

Strange lamp behaviour

I have an exterior lamp that is controlled by a standard switch and a 'timed-relay' (I push a button and light stays on for 3 minutes), I think those two are wired in parallel as if the lamp is on and ...
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1answer
79 views

What is the function electrical device?

What is the function of the device in the picture. Unfortunately, I did not make a full diagram of how it was wired, but the hot and the corresponding neutral were connected by crimp-on leads on the ...
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31 views

Replace Refrigerator Capacitor along with Start Relay?

I recently smelled a very bad smell coming from my fridge and discovered a shorting and half melted start relay. The capacitor appears to be fine. Should I replace both pieces or do I only need the ...
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would these be compatible replacement solid state AC Relays?

I am replacing a relay for an appliance (stove). I cannot find a replacement relay, however I thought I'd confirm if the following relays would be compatible: 1) input 90-250 VAC output 24-440VAC 25 ...
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1answer
42 views

Connect the heater boiler through a relay instead of direct to the thermostat

I am wiring up a new thermostat for an old boiler, and the thermostat I am using needs a common wire (Proliphix NT130h -- I wanted an NT1X0e series, which use PoE and don't need C, but they are no ...
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1answer
21 views

How to use q12vac power to open trigger to switch a 12vdc n/c circuit

I have a 12vac fail secure lock that is to be changed to a 12vdc fail safe. If they were both the same voltage i would add a psu and use trigger from lock to switch n/c on relay but how do i deal ...
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Multi-zone heating and relais

I have a multi zone (2 zones and half) radiator heating system. Each zone has a thermostat and a relay that kicks the boiler but only two have the actuator (MVA 21) Next to the boiler I have 3 relays ...
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Help with Sain Smart 24V Relay Cycle Timer Module

I'm considering getting one of these: https://www.sainsmart.com/products/24v-relay-cycle-timer-module ...to force my 2nd floor thermostat to force heat on every so often (say, 1 minute every 15) to "...
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2answers
70 views

How to get the state callback from a relay switch

We have made an automation module with relay connecting the mains and the raspberry pi. We are maintaining the state for the switch on our server. We have the raspberry pi connected to the device over ...
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3answers
61 views

Relay before or after power transformer

For my project I plan on controlling an off-the-shelve LED lamp using a relay board which is connected to my Raspberry Pi. As can be seen from the Lamp image below, there is a power converter which ...
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1answer
79 views

PLC-Lighting Control-Plug n Play Operation with Relay

I am trying to build up a home automation system(retrofit) with existing conventional switches(230VAC). But I am looking for automation system without replacing existing conventional switches along ...
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4answers
78 views

How can I power a load from two separate circuit breakers?

On one circuit breaker I have a manual switch. On the second circuit breaker I have a motion sensing switch (using a mechanical relay). I have a number of lights wired in parallel as the load. The ...
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2answers
43 views

Condenser fan and compressor don't start, electrical looks good though?

After replacing the fan, starting capacitor, and running capacitor, the system ran normally for ~1 day. Now nothing is starting. I got a fieldpiece multimeter and tested all of new capacitors, ...
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960 views

How to connect Nest thermostat to Evaporative Cooler (Swamp Cooler)

I have reviewed the post here, Controlling 110v swamp cooler using Nest thermostat It discusses how to connect an evaporative cooler using 110v to a standard thermostat. I am looking for a specific ...
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2answers
50 views

How to add a lamp on the other side of the switch series?

I have a fairly standard setup here. A lamp controlled by 3 switches, the middle of which is a 4-way switch (but I think that's fairly irrelevant). I would like to add an extra lamp, controlled by the ...
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1answer
217 views

Attic Fan Furnace Interlock

I want to add a relay to my furnace so the attic fan can't run while the furnace burner is firing. Am I correct that the 24V side of the relay should be connected to the C and W terminals on the ...
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2answers
1k views

Isolation relay for Ecobee smart thermostat: NC or NO?

I've been looking for "isolation relays" to install an Ecobee 3 smart thermostat on my 2-wire T/T furnace (replacing a Honeywell round thermostat). I know I want to use the 24VAC transformer/relay ...
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2answers
240 views

Which current will pass through the relay when the generator and main supply are on?

I installed a relay for switching purpose With main supply and Generator. When there is no electricity from main supply relay change its coil to the generator. I want to know which will be the source ...
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67 views

Home Lighting Relay Characteristics

I have old electromechanical relays that were installed in a panel with a transformer as part of a remote controlled lighting circuit. It's a nifty setup except the relays are no longer manufactured. ...
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1answer
49 views

Submersible water pump relay question

Regarding -submersible residential style water pump relays- pumps fitted with a three wire cable which terminates into a submersible pump relay box--the red wire feeds the starting winding in the pump ...
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1answer
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Electrical Installation [closed]

Can someone help me please. I have the electrical diagram for connecting the power of an object. The main switch is 63A 4P threephase.I want to add three differencial relay 40A 4P which have the ...
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1answer
104 views

How can I package a relay (for lighting control)?

Right now I have 3 high-pressure-sodium lights (475W actual x 3) on a single light switch. It's a heavy duty switch, but these lights have magnetic ballasts (40 pound transformer) and they have a ...