Author Topic: AC input wiring (Read 5699 times)

bungy · « **on:** September 04, 2009, 10:17:21 pm »

I thought I was pretty good at wiring AC, but this issue has me stumped. I want to wire a few outlets to the inside of my cabinet and have a single detachable cord supplying the power.
One outlet will always be hot (the PC will always be on and controlled by a pushbutton on top of the cab), and the other outlet will be switched on & off with a toggle switch on top of the cab (This will power the monitor, marquee, illuminated trackball, and coin reject lights).

I wired the two outlets and switch in what I thought was the correct way, but my switched outlet was showing 46 volts on my multimeter when it was off. It went up to 120 volts as expected when the switch was on. I systematically swapped out each receptacle and switch to check if there was a defective part, but I got the same results.

So now I've stripped the setup down to one outlet controlled by a standard lightswitch and I'm still seeing 18 volts when the switch is off (and 120 when it is on). What could be causing this? I tested with a receptacle tester and it appears to be wired correctly.

The first pic shows the type of connector I'm using and the second one is a barebones test setup. The incoming neutral wire goes directly to the left side of the outlet and the hot wire goes to the switch. The other side of the switch comes back to right side of the outlet. Each part is connected to the incoming ground wire. Am I doing this wrong, or is there some other principle of AC that I'm not taking into account?

Kevin Mullins · « **Reply #1 on:** September 04, 2009, 11:39:19 pm »

Kill the breaker for that particular wall outlet you are using as a power source and measure it.

bungy · « **Reply #2 on:** September 05, 2009, 01:10:29 am »

I tried a few outlets throughout the house with the same results. One of them I know for sure doesn't carry a voltage when the breaker is off because I had worked on it recently.

BobA · « **Reply #3 on:** September 05, 2009, 11:54:49 am »

To quickly check all your outlets and wiring get an AC outlet tester. Works well and spots your wiring problems quickly.

bungy · « **Reply #4 on:** September 05, 2009, 04:36:52 pm »

Yes, I have been using that in combination with a digital multimeter. The outlet tester indicates that everything is wired correctly, but checking with the multimeter shows that there is still some voltage making it to the outlet when it should be off

BobA · « **Reply #5 on:** September 06, 2009, 09:00:54 am »

Are you confident that the multimeter readings are correct?

bungy · « **Reply #6 on:** September 06, 2009, 09:09:51 am »

Yes, it has never (as far as I can tell) given a questionable reading. I have compared my Fluke side by side with a radio shack model and mine seemed more sensitive and consistent.
Also when I had it wired with two outlets, I was getting about 46 volts on the switched one. When I plugged in the receptacle tester, the lights were glowing very faintly.

SirPeale · « **Reply #7 on:** September 06, 2009, 09:37:29 am »

I've seen this before, but I can not remember what causes it.

Kevin Mullins · « **Reply #8 on:** September 06, 2009, 10:32:37 am »

Quote from: SirPeale on September 06, 2009, 09:37:29 am

I've seen this before, but I can not remember what causes it.

I have too, which is why I wanted to back up to the actual power side of things. (measure the wall outlet)
Thinking it was like reading voltage off the ground side or something, but I can't remember now either. Ground being tied to neutral type thing.

DaOld Man · « **Reply #9 on:** September 06, 2009, 10:53:57 am »

You cant really trust some digital multi-meters in a case like this. They draw such a tiny amount of current that they will measure voltage created by capacitance or inductance, which is in the milli or even micro amps. Usually putting any kind of load at all on the circuit will drop the voltage to zero.

At least thats what I was thinking until you said the lights on the plug-in tester glowed very dimly.

My first thought would be that the circuit in question is getting "bleed over" from another circuit, could be two (un-insulated part) wires barely touching inside a junction box or the breaker panel.
Also, have you measured voltage hot to neutral, ground to neutral, and hot to ground?
In a USA type house wiring, the hot goes back to the breaker, or fuse, and the ground and the neutral tie together in the circuit breaker panel, or fuse box.
So with the breaker on, you should read ~110VAC hot to neutral, hot to ground, but nothing ground to neutral.

One thing you can do is put the volt meter on your suspect circuit, then turn off one breaker at a time to see if this circuit is somehow getting some bleed over from another circuit.
If the voltage goes to zero when you turn off a certain breaker, then that is your problem circuit.

Fixing this problem may not be so simple. But I would start by checking the wires in the ceiling lights, these usually are junction boxes too, however I dont run more than one feeder circuit to a ceiling box, but I have seen it done with 2 feeders inside the box..

Just to verify that the problem is not in your cab wiring, have you measured the voltage on the wall outlets with your arcade cab unplugged?

DaOld Man · « **Reply #10 on:** September 06, 2009, 11:03:41 am »

Quote from: DaOld Man on September 06, 2009, 10:53:57 am

..
Just to verify that the problem is not in your cab wiring, have you measured the voltage on the wall outlets with your arcade cab unplugged?

I just wanted to add that I would do this the very first thing before I go pulling down ceiling light fixtures.
Make sure the problem you are seeing is in the house wiring and not your cab wiring before doing a lot (and it can turn into a whole lot) of work.
If it is in your house wiring, you may want to get a licensed electrician to check into it, someone you know is good.

bungy · « **Reply #11 on:** September 06, 2009, 11:45:03 am »

Thanks for the info.

In my basement I have 4 outlets that were installed by an electrician a few years ago. They are on their own circuit and they are not switched. I took some measurements on my setup using one of them while everything else on the circuit was unplugged. Inside the outlet box I read 118v hot-neutral, 118v hot-ground, ~0 neutral-ground and the receptacle tester checked out OK. I plugged in my test setup and took the same measurements with the switch on, results were similar: 119v hot-neutral, 119v hot-ground, ~0 neutral-ground. With the switch off I read 15.86v hot-neutral, 15.86v hot-ground, ~0 neutral-ground.

I will try turning off the breakers one by one later and see if that makes a difference.

DaOld Man · « **Reply #12 on:** September 06, 2009, 12:36:07 pm »

Looks to me like the problem is in your test rig. Maybe the switch is bleeding through, or some of that romex cable you are using.
15.8 volts on a digital multimeter is probably not bad, and will probably drop to zero if you plug your circuit tester into your test rig outlet, with your switch turned off.

BobA · « **Reply #13 on:** September 06, 2009, 02:06:54 pm »

I see your outlet and the light switch and they look to be wired OK but what is the little rectangular item with black wires coming out of it in series with your hot line?

Kevin Mullins · « **Reply #14 on:** September 06, 2009, 03:44:43 pm »

Quote from: BobA on September 06, 2009, 02:06:54 pm

I see your outlet and the light switch and they look to be wired OK but what is the little rectangular item with black wires coming out of it in series with your hot line?

I believe that's just a terminal strip. (plug the wire in, tighten the screw)

DaOld Man - You are thinking along the same lines as me, but you sure put it in better terminology.

Quote from: bungy on September 06, 2009, 11:45:03 am

In my basement I have 4 outlets that were installed by an electrician a few years ago. They are on their own circuit and they are not switched. I took some measurements on my setup using one of them while everything else on the circuit was unplugged. Inside the outlet box I read 118v hot-neutral, 118v hot-ground, ~0 neutral-ground and the receptacle tester checked out OK.

I will try turning off the breakers one by one later and see if that makes a difference.

Turn the breaker off to those 4 outlets and take measurements the same way you have been doing on your test rig and see if they show the same voltage you are concerned with that shows up on your rig.
Essentially you have two identical setups..... the house, having a breaker as a "switch".
So thoroughly test THAT first.
If you get the same results there, then obviously so will your test rig.

Your rig/switch wiring looks fine to me.

For testing purposes ..... disconnect the ground wire on your rig and then test for voltage when the switch is off.

JustMichael · « **Reply #15 on:** September 07, 2009, 03:19:54 am »

May I ask a dumb question? Does the light switch light up when it is in the off position? These use power when "off" and allow somewhere between 12-24V of power through when "off"(which isn't enough to light a main room light).

Ed_McCarron · « **Reply #16 on:** September 07, 2009, 08:18:21 am »

Digital multimeter? 46 volts? Very possibly noise.

Try this: Make sure power is off. Insert meter probes. See 46 volts.

Its probably noise. DMM's pick up everything.

If it were me... I'd take a 100w lamp and plug it into the other side of the outlet as a load. If the voltage drops to zero, its noise. Voltage, yes, but currentwise in the milliamp regions.

Kevin Mullins · « **Reply #17 on:** September 07, 2009, 11:08:21 am »

Seen low batteries on a DMM do weird stuff like that too.

Quote from: Ed_McCarron on September 07, 2009, 08:18:21 am

If it were me... I'd take a 100w lamp and plug it into the other side of the outlet as a load. If the voltage drops to zero, its noise. Voltage, yes, but currentwise in the milliamp regions.

Good point.

ami-man · « **Reply #18 on:** September 08, 2009, 05:26:35 am »

Hi Bungy,

What voltage readings do you get on your wall outlet between the live and earth and neutral and earth?

It sounds to me that you are getting a voltage on the neutral between earth.
So it could be the earth bonding somewhere in your household that is the issue or that the bonding is not good from your supplier.

Regards
Alan Hood
ami-man
UK

bungy · « **Reply #19 on:** September 08, 2009, 11:32:18 am »

Quote from: ami-man on September 08, 2009, 05:26:35 am

What voltage readings do you get on your wall outlet between the live and earth and neutral and earth?

I am getting about 118v between hot & ground and 0v between neutral & ground.

Quote from: Kevin Mullins on September 06, 2009, 03:44:43 pm

Turn the breaker off to those 4 outlets and take measurements the same way you have been doing on your test rig and see if they show the same voltage you are concerned with that shows up on your rig.

I tried this and did not read any voltage on the test rig.

Quote from: Ed_McCarron on September 07, 2009, 08:18:21 am

Digital multimeter? 46 volts? Very possibly noise.

Try this: Make sure power is off. Insert meter probes. See 46 volts.

Its probably noise. DMM's pick up everything.

If it were me... I'd take a 100w lamp and plug it into the other side of the outlet as a load. If the voltage drops to zero, its noise. Voltage, yes, but currentwise in the milliamp regions.

I also tried this and it dropped to about 0.5v. But what concerns me is that in my full setup (two outlets, one outlet switched (where I read 46v on the switched one)) when I plugged in my monitor when the switch was off, I heard a click as if the monitor were trying to turn on. That doesn't happen when I plug it into a power strip with its switch off.

I think I'll try to bring the test rig to work and measure it to try to eliminate my home's electrical system. Otherwise my theories at this point are that I'm using a bad connector for the incoming power cord, or the power cord itself has a problem.

speedklz · « **Reply #20 on:** September 08, 2009, 12:09:35 pm »

I have seen this before and usually it is a ground tied to nuetral somewhere and what you are reading a the voltage that occures from the nutral grounded into the ground itself or to a water pipe somewhere in the house and it can produce voltage but as stated it would be very little if any amps. so there is no problem with it. Alot of older houses have this going on it just build up a small voltage on the nutral line, kinda like static electrical charge. Nothing to worry about.

bungy · « **Reply #21 on:** September 08, 2009, 03:06:11 pm »

Regardless, I think I'm going to end up using a double pole switch. I just want to keep my monitor as safe as possible.

bungy · « **Reply #22 on:** September 09, 2009, 11:26:36 pm »

OK...
When I tested the voltage on my power strip on the same outlet I have been testing my arcade rig with, I got 0v when the switch was off and 118v when the switch was on. This is behavior I'm looking for, so I open up the power strip to see what he's doing differently.

Inside, the neutral is connected to the neutral bar, ground to the ground bar, and hot goes to the switch with the other side of the switch going to the hot bar. Exactly the same as my test rig. Except there are some electrical components between the neutral wire and the switched side of the hot wire (Pic 1). I don't recognize the components (looks like a resistor & ceramic capacitor, but I'm not convinced that's what they are), but I unsolder them anyway and try it on my rig. I connect them the same way, but at different points in my circuit. I even soldered in the switch from the power strip.

And I still read about 10v while the switch is off. (Pic 2)
This was supposed to be the easy part of my project, wtf is going on?

Continued in next post...

bungy · « **Reply #23 on:** September 09, 2009, 11:34:39 pm »

Next plan of attack: wire in a double pole single throw switch. This will block both the hot and neutral wires when it is off. Surely this will work.

I wired up my full rig with the DPST switch and check the voltage in the off position (Pic 1). 7.6 volts. Damn. It's better than the 46v or so I was getting before, but still unacceptable.

Voltage reading is normal when the switch is on, all outlets check out with the receptacle tester. (Pic 2)

Continued in next post...

bungy · « **Reply #24 on:** September 09, 2009, 11:50:25 pm »

What now? I happen to have an ATX power supply opened up on my bench and I cannibalized it for parts. It had a DPST switch connected to the input receptacle so I desoldered the whole thing and swapped it into my rig. I test the first ("always-on") outlet with the new main switch off (Pic 1). Zero volts. Turn the switch on and 117 volts (Pic 2). This is the behavior I want. But what is different? Nothing as far as I can tell. Maybe the switch is built to different tolerances.

But let's not jump to conclusions until we test the switched outlet.

Main power switch off, outlet switch off (Pic 3), 0v. OK.
Main power switch on, outlet switch off (Pic 4), 18v. WTF? At this point, the receptacle tester will glow very dimly when plugged in.
Main power switch on, outlet switch on (Pic 5), 118v as expected.

I am convinced this is not induced or static voltage. Am I doing something wrong? Does anyone see a problem with my setup?
I feel like I need an oscilloscope to troubleshoot this further.

JustMichael · « **Reply #25 on:** September 10, 2009, 12:13:44 am »

Have you verified your switches to see if they are working the way you think they should? Have you tried tested the continuity through switches when they are in the on and off positions? The switches must be by themselves (nothing attached to them) when you do the test.

bungy · « **Reply #26 on:** September 10, 2009, 12:17:56 am »

Yes, I have checked the switches for continuity in on & off positions and while unwired. I have tried a Gardner Bender SPST & DPST, a couple Leviton lightswitches, and the power strip switch. All appear to be functioning correctly.

JustMichael · « **Reply #27 on:** September 10, 2009, 03:23:15 am »

Since you said when a load is plugged in the voltage drops to .5V when the switch is off, that sounds like you are getting an induced voltage in the piece of romex that goes from the hot, to the switch and back down to the outlet. I'll bet if you use a shorter piece of romex you will get less voltage. You will need to put some distance between the wire going from the hot to the switch and the wire going from the switch to the outlet. This should solve the problem.

bungy · « **Reply #28 on:** September 10, 2009, 08:38:56 am »

I wondered about that, but I figured if it works in my walls, why wouldn't it work in my cabinet? I'll give it a try and see what happens.

speedklz · « **Reply #29 on:** September 10, 2009, 01:51:27 pm »

Remember in all this that AC is Alternating current and it goes both ways and switches 60 times a second, so shutting off the flow from one line does not shut it off from both, also a digital multi meter is not spec on acurate reading AC, it takes the an average reading so at smaller voltages there is gonna be some mis-reading. There may be no voltage at all flowing but the meter will read a small amount ( 10-40 volts) because of inductence in the meter between two long peices of wire. IF you dont beleive me put the meter on ohms and look at the reading then touch the leads togather and they zero out. So dont trust the meter. Or plug something into the outlet and check the amps reading on it, see if anything is flowing.

bungy · « **Reply #30 on:** September 10, 2009, 07:13:57 pm »

Ok, I'll concede that it's inductance. I cut off the outer insulation of the romex and put some distance between the switch wires as JustMichael suggested and my voltage reading was 0.8. As I moved the wires together, the voltage started increasing. Strange phenomenon (to me).

Thanks everyone for your help!

DaOld Man · « **Reply #31 on:** September 11, 2009, 06:59:50 am »

I would get rid of the romex. It isnt very flexible and not good for a arcade cab, IMHO.
Also, the blue thing you removed from the power strip is a MOV.
(Metal Oxide Varistor). In short and dirty description, it "shorts out" when voltage over its rating is reached.
This is what the power strip uses for surge protection.
I think it is the first time I have seen a resistor used in series with one though, if that is what the other device is.
I would either replace the MOV in the strip, or buy a new strip. These MOV's have been known to burn completely out when hit with a lightning surge, so they need to be enclosed so they cant catch anything on fire.

kegger · « **Reply #32 on:** September 11, 2009, 10:10:34 am »

At a quick glance you have wired your first picture incorrectly.

You never put a switch on your neutral. Neutrals needs to be tied together and go directly
to the neutral side of the outlet.
This could be why your voltage is funny. The neutral comes from the romex feed
and should go directly to the neutral side of the outlet.
Also Fluke meters are very sensitive and give false readings when the batteries are dying or low. I'm not saying that is the problem but just a heads up for you. Final thing is make sure the outlet you are plugging into (the source) that all the neutrals are ok there too.

99% of the time a voltage problem is some type of neutral or grounding issue.

kegger · « **Reply #33 on:** September 11, 2009, 10:19:11 am »

Sorry for the last post taking a harder look at the first picture it look to be ok.

sarge · « **Reply #34 on:** September 11, 2009, 07:30:15 pm »

Thats not a resistor in line with the MOV, it's a fuse.

Kevin Mullins · « **Reply #35 on:** September 11, 2009, 08:54:40 pm »

I was thinking that too, either a PICO type fuse or a thermal fuse.

And the other component doesn't "short" when it gets hot, it should "open".

DaOld Man · « **Reply #36 on:** September 12, 2009, 01:22:02 pm »

An MOV's resistance drastically decreases when voltage goes above it's rating, to the point that it effectively shorts the incoming voltage, reducing it.
The resistance decrease is linear with the voltage increase, but I did say it was a short and dirty description.

http://en.wikipedia.org/wiki/Varistor

How it works:

http://electronics.howstuffworks.com/surge-protector1.htm

Kevin Mullins · « **Reply #37 on:** September 12, 2009, 01:54:33 pm »

I could have swore there was a little oompa loompa in them things swithcing it on and off.

But you're right.... I learn something new every day. I was under the impression they were more of a thermal "switch".
Should have known better, similar things in a degauss circuit on monitors.
Thanks for the clarification.


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