# [SOLVED] replacing wall switch



## sobeit

getting ready to install a wemo wall switch. The wemo wall switch has two black, one green and one white wire. The old wall switch has one black and one white wire. Not really sure how to connect. Don't want to burn down the duplex  Any guidance will appreciation.


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## etaf

*Re: replacing wall switch*

I'm not an expert, based inthe UK
But used to do a bit of wiring , before the laws changed here recently

have a look at this video
WeMo® Light Switch

what country are you in ?

in the UK , the main connections for light swithes are in the ceiling rose not at the switch
Then the live wire is taken from the ceiling rose to the switch and then back to the celing rose for the light 
So the switch just has two wires and both are live 
live feed
live return
But still use the normal 2/3 wire cable and have 
Black and red cables - both in this case live and the black should have a red sleeve over at the switch to show its NOT black neutral but live

sounds like you may have the same 
green is earth cable

https://en.wikipedia.org/wiki/Electrical_wiring

White is shown for the US as neutral - Which you may not have at the switch, in your case
Black is shown as live


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## Basementgeek

*Re: replacing wall switch*

Who wired this place? Since you are in USA, white wires are the Neutral wires.
Black wires are voltage.

You need to check the outlets, this switch controls, and see if they are wired the same way

BG


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## SABL

*Re: replacing wall switch*

One white and one black with no other wires.......two conductors only?? That means the switch is being fed through the light box......instead of the switch sending power to the light it is only completing or breaking the circuit. The white wire should be marked with electrical tape to denote that it is not really a neutral. It's common practice in some situations. The electrician saved a little wire by not having to 'backtrack' with another wire run when the power source was closest the light. Instead of running a 'feed' to the switch and having to run another cable to the light he fed the light.......saved 15-20 feet of wire, That's being a tightwad........:frown:

I don't think you can use the WeMo in this situation. One black wire is to supply power to the receiver and will need to have a neutral to complete the circuit.....that's why the switch has the white wire. The other black wire will feed the light when the switch is activated. If you only have two wires you don't have a neutral in the switch box. If you twist the black wires together your light will always stay on due to the way the electrician ran the wiring.


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## sobeit

*Re: replacing wall switch*

the following is the switch.


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## etaf

*Re: replacing wall switch*

appears to be wired the same as we do in the UK

using a normal 2wire or 3 wire cable (3rd cable earth normally)
and that only just supplies the live to the switch and then returns the live back to the light 
normal way of wiring over here , at least it was a few years ago

So its not going to work for you without a neutral


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## MPR

*Re: replacing wall switch*

As SABL mentioned above, the "neutral" wire rat the switch should have a bit of electrical tape or black magic marker on it to denote that it's really a hot wire.

You can readily ascertain if its wired as below by checking with a voltage tester across the two wires.










Note that you also may find weird light wiring in older homes with additions wired by non-electricians too. Best to check the light box and see how things are wired there before proceeding (for instance, some homeowner "electricians" will put the switch on the neutral wire instead of the hot wire -- this "works" to turn off the light but woe to a grounded person who sticks their finger in the socket with the switch "off"). Also, make sure that the power actually goes off at the switch and box after you have turned off the breaker. I was zapped pretty good once in a cross-wired basement addition when I thought I'd rendered everything safe only to find that the light I was working on was actually fed from two different sources! No wonder the bulbs kept burning out.


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## sobeit

*Re: replacing wall switch*

never heard of ground wire being called earth 

So basically everyone is saying the white wire on the installed switch is not neutral? There is no black tape or mark.


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## MPR

*Re: replacing wall switch*

Ground one probe of a voltmeter and then touch the other probe to the wire in question. If it's "hot" it will register voltage.

Note that with a switch you are actually just splitting the hot wire. You have voltage potential at the switch even when it's off and current going through it when it's on -- both input and output wires are "hot" wires.


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## etaf

*Re: replacing wall switch*

Earth is a common term in the UK for ground


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## MPR

*Re: replacing wall switch*

BTW, the reason that we don't use two black wires to and from a switch is that that Romex comes with one black and one white wire. This is why you black tape the white wire -- it shows people that it's actually a hot wire in this application.


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## Basementgeek

*Re: replacing wall switch*

Changing colors is shoddy workmanship 

Both ends must be marked.

BG


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## SABL

*Re: replacing wall switch*



sobeit said:


> never heard of ground wire being called earth
> 
> So basically everyone is saying the white wire on the installed switch is not neutral? There is no black tape or mark.


If there are only two conductors in the switch box you do not have a neutral at that point. The neutral is connected directly to the light in the light box as shown in MPR's sketch......the white wire in the switch box becomes part of the power source for the light and should be marked as such......but not always. The electrician knew what he had in mind and someone familiar (very familiar) with common wiring practice would quickly see what was done and how the circuit was made. Not my favorite way of doing things but I've done it in rare cases.......I prefer to feed the switch.

EDIT: BG is very correct and both ends of the white wire should have been marked.....:thumb:


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## sobeit

*Re: replacing wall switch*

what would have happened if I did not ask and went ahead and wired all the blacks together, wired the whites together and attached the green to the outlet box like I thought about doing?


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## SABL

*Re: replacing wall switch*

You would not have a completed circuit. You can feed both sides of the new switch but there's no place for the electricity to flow to. You wouldn't even get the receiver to work to energize the circuit. 

Is there a ground wire present or is the green wire on the switch??


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## sobeit

*Re: replacing wall switch*

green wire was on the wemo. no ground wire that I could see in the old box.


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## SABL

*Re: replacing wall switch*

You got short-changed on the wiring.....there is no neutral in the switch box to hook up to. I don't know if there is anything that can be mounted in the light box (or lamp-base) that can get the desired results.


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## sobeit

*Re: replacing wall switch*

I lied, I pulled the old wire through the box a bit more and found the ground. It was never uncovered from the three wire wire. (okay, I dont know the name)

I pulled a couple other panels and it looks like the whole apartment was wired that way. I was getting them for my amazon echo. so far the only wemo product that worked with it that will install in my apartment is the insight switch. The bulbs are not compatible with the echo - which I found out after purchasing. I am going to have to better research before buying and then returning. oh well...

Thanks for all the help - learned a bit today


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## MPR

The neutral wire is the return path for electrical current once it has passed through a load. If wired to code, the neutral wire is also grounded to the earth somewhere (here, this occurs at the transformer pole), which gives it zero potential relative to the local earth or anyone standing on it. However, if a neutral is _not_ grounded to zero potential relative to the earth then you can receive a shock from it. Recall that current flow only requires a potential _difference_.

The bare ground wire is an extra safety path for current to flow through. Current flow is greatest through the path of least resistance, as described by the equation I = V/R. Therefore, if a short circuit occurs in a grounded tool or appliance most of the current should flow through the ground wire and not you because you are more resistant to current flow than copper wire.

A careful reading of the Wiki article should clear things up:

https://en.wikipedia.org/wiki/Ground_and_neutral


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