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Discussion Starter · #1 ·
Hey guys,

New to the site and I have a question about wiring.

I live in a house built in 1922. I recently undertook a project to change out all the light switches in the house (first time doing this). I am about 25% done. I noticed last night that on a 3-way switch I changed out when I toggle the switch on and off, I can see a blue arch inside the switch box. This doesn't seem normal.

I should also add the wiring appears to be original as there is cloth on the old wire (which I peeled back a bit because i was scared the cloth could catch fire).

Any help is greatly appreciated. Thanks.


KC
 

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I noticed last night that on a 3-way switch I changed out when I toggle the switch on and off, I can see a blue arch inside the switch box. This doesn't seem normal.
If other identical switches that are switching the same load also have a blue arc inside, I'd say this one is likely OK.
You should not be able to prolong the arcing time by slowly moving the switch lever, though. There is supposed to be a snap-action.
The arc should be bigger when opening the contacts than when closing them.

You can test the switch contacts. Put a closed switch in series with 120vac in series with a 10A load [a hair dryer or toaster].
Less than 30 mVac across the closed contacts is good, more than 100 mVac is bad.

Another way is to listen to the switch arcs with an AM radio tuned between stations. Hold the radio close by the suspect switch. If the crash of static from one sounds way loud or long in duration compared to the others, I'd wonder why.
 

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Thanks. So the blue arch is normal?
Can't say for sure, but AFCIs do have to detect the difference between good arcs and bad arcs.
Probably a blue arc with a yellow flame around it is bad or is very high energy.
Arcing is much worse with motor (inductive) loads.
They are less when arc suppression networks are used but wall switches never use them, instead they depend on hefty contacts to withstand the arc temps.
 

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What are the switches switching? A lot of lamps? If so, you are just seeing the current flow being interrupted. (More noticable with cheap switches and several amps of current flow) If it is only switching one light or a bank of lights of lower wattage.

I just thought of something based on these details.

built in 1922....3-way switch...wiring appears to be original
Many houses built during this time period had what they call a "carter system" 3 way switch setup. It is long illegal (around 1928?) And it consisted of hot and neutral wires coming into each switch box, and a single wire going up to the light from each switch. It saved wire, at the cost of switching the neutral. Basically, the switches "choose" whether the light gets hot or neutral- if the light gets a hot from both switches, the light doesnt work. If the light gets two neutrals, the light does not work. It only works when one of the switches is hot, and one is neutral.

Modern snap switches are made slightly different internally then the old switches that really did snap. I believe that the contacts differ in how they make and break. I think it is possible for there to be a very momentary short circuit to occur across the traveller terminals (terminals on the switch with the same color, where hot and neutral would be connected with the carter system I mentioned) with some switches due to the way they are designed.

You could try another switch, or a heavier duty switch.

Just an idea.
 

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Discussion Starter · #6 ·
This is in a stairway. There is one light at the top of the stairway and one at the bottom. There are 2 switches at the top of the stairway and 2 at the bottom. 1 switch at the top and bottom control the light at the top of the stairway and 1 switch at the top and bottom control the bottom of the stairway.

One thing that looked odd to me (an attorney, not an electrician) was that the wire that I presume is the 3-way wire is actually one wire that is split at the end *and then connected to the switches). Each end attaches to the switches in the box (1 being for the light at the top of the stairs, one at the bottom).


KC
 

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There is one light at the top of the stairway and one at the bottom. There are 2 switches at the top of the stairway and 2 at the bottom. 1 switch at the top and bottom control the light at the top of the stairway and 1 switch at the top and bottom control the bottom of the stairway.

One thing that looked odd to me (an attorney, not an electrician) was that the wire that I presume is the 3-way wire is actually one wire that is split at the end *and then connected to the switches). Each end attaches to the switches in the box (1 being for the light at the top of the stairs, one at the bottom).
You mean the split wire originally had only one cloth covering and some of the wire strands went to one switch and the rest of the wire strands went to the other switch?

I hope that these strands are not left bare. This can be corrected temporarily by taking them off the switches, twisting them back together (make doubly sure they used to be twisted togethyer), and covering with electrical tape. Cut two pigtails (short lengths of new wire about 6 inches each) and wire nut them to the taped wire. Connect a pigtail to each switch.

This fix will not change or stop the blue arc you see in the new switch.
 

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I've got the same problem with old cloth covered rubber insulation. When I have a problem, I wrap electrical tape around the wire, or use a piece of heat-shrink tubing (without melting it).
I have decided to leave well enough alone until I get the time/desire to rewire the circuit, unless something breaks, in which case I am prepared to rip stuff out and rewire.

I wouldn't worry too much about a little blue spark in the switch. As was already said, breaking the circuit running a few amps will produce a brief spark. I never notice it, but then, I'm not looking for it<g>

FW
 
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