Leaking current


  #1  
Old 04-22-05, 06:19 AM
tylandr
Visiting Guest
Posts: n/a
Leaking current

Greetings All,

I'm replacing an old flourescent fixture in the kitchen wired between (2) 3-way switches. With the circuit breaker on, I'm getting about 50+ volts coming out of the wires that would go to the light when I shut off either switch. I just replaced both switches with brand new ones and was sure to wire them the same way the old ones were (which have been there 20 years).
The bottom line is this - with 3 way switches, shouldn't there be NO current going to the fixture when they are turned off? What would be a likely cause?

Love the site - forgive my ignorance.
 
  #2  
Old 04-22-05, 06:59 AM
J
Member
Join Date: Nov 2002
Location: SC
Posts: 156
Upvotes: 0
Received 0 Upvotes on 0 Posts
Did the circuit work before you replaced the switch? Are you sure you wired the new ones in like the old ones were? You can't go by the location of the screws, you have to go by the color of the screws. One will be a different color (usually dark) than the other 2.
 
  #3  
Old 04-22-05, 07:03 AM
J
Member
Join Date: Sep 2000
Location: Fayetteville, NY, USA
Posts: 969
Upvotes: 0
Received 2 Upvotes on 2 Posts
Testing at the switch for juice/no cuice can be confusing with 3-ways. One leg is always going to be hot. If you tested black-to-white at the ceiling box you should see 115v +/- when the switch is on, and zero volts when the switch is off. But I can't explain the 50 volt reading. Sorry. I think in part it depends on how you are testing. Test each hot wire to a known ground and then see what you get.

And please don't apologize for ignorance. We all know different stuff. You're willing to learn, and that's good. And it is what this site is for!

Juice
 
  #4  
Old 04-22-05, 08:05 AM
R
Member
Join Date: Sep 2001
Location: Yorktown, VA
Posts: 301
Upvotes: 0
Received 0 Upvotes on 0 Posts
tylandr,

I usually wait for John Nelson or racraft to answer electrical questions, but 3way switch circuits are notorious for exhibiting symptoms like this. I believe you are measuring so-called phantom voltage. In 3way circuits, you have a totally unloaded wire in a jacket with an energized wire. The voltage capacitively couples to the wire with no load. It is harmless, normal, and would disappear if connected to a load.

You may want to wait for John or racraft to confirm.
 
  #5  
Old 04-22-05, 08:18 AM
tylandr
Visiting Guest
Posts: n/a
Thanks to all so far for the replies. After I posted to begin with, I realized I should have been more clear. When I put the new 3-way switches in, I was careful to ensure that the wire placement was exactly as before - (taking into account the different shaded screws). My original problem was that after hanging a new low-voltage rail light, the transformer became warm to touch (no big deal), but the shaft that the rail actually draws the current from was burning hot - enough to make me think I was blistered. The end result was the transformer failing.

The lighting company came out and said that it was due to some current leaking (my term not his) into the transformer even though the switch was off. His suggestion was to replace the switches since they were 20 years old.

Now, with the switch in the off position, I get the leaking current. With the meter on the wires and the switch turning on, I get the full monty on the current. No matter which switch I test, the results are the same.

From what I've found on the net, my next guess would be to pull the switches out and attempt to diagram the wiring. But, since the previous flourescent light fixture worked for 20 years, I can't help but think the wiring is ok.



Does that give anyone more to go on?

Many thanks.
 
  #6  
Old 04-22-05, 08:42 AM
J
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 8,059
Received 521 Upvotes on 426 Posts
First off you are not measuring current. You are measuring voltage.
What type of meter are you using? If it is a digital meter then the voltage reading is probably false(phantom voltage).
Second, where are you measuring voltage? It takes two points to get a voltage reading. Tell us both points. eg hot to gound, hot to neutral. Note that in switch circuits not all whites are neutral. If you are measuring a traveller voltage you could get strange readings.
If the light goes on and off properly, it is probably wired correctly. Voltage doesn't leak through a switch. That is just hogwash of an explanation.
 
  #7  
Old 04-22-05, 09:31 AM
tylandr
Visiting Guest
Posts: n/a
I'm not using a digital meter, but one with a needle (think speedometer and you've got it). I'm putting the leads to the both wires coming out of the box that the old light were hooked to. I'm not using the meter at the switch but up at the ceiling box.

When I hooked up the new light's transformer to begin with, the lights DID go off and on as expected using either of the 3-way switches. This was another indication to me that the switches are wired correctly.

But, the transformer got so hot, I couldn't touch it. Now that I have a new transformer ready to install, I don't want to do it until I know the problem is resolved.

BTW - I am making sure that the meter is set at the 150 volt setting on AC side of the dial.
 
  #8  
Old 04-22-05, 10:15 AM
G
Member
Join Date: Oct 2004
Location: USA
Posts: 676
Upvotes: 0
Received 0 Upvotes on 0 Posts
Search the web for phantom voltage.
----------------
Some transformer get hot. I don't like it either.
I think thay do the math to get a shorter life on things $$
If you cant touch it may or may not last.

The two main things that will kill a transformer is a Hi input voltage.
Or to Hi of a load, using a higher wattage bulb then the transformer can handle.

What's the wattage and voltage of the bulb?
What's the wattage and voltage of the Transformer ?
How many bulbs are connected to the one xfmr ?
 
  #9  
Old 04-23-05, 02:28 AM
tylandr
Visiting Guest
Posts: n/a
The transformer has

I/P 120V
O/P 12V
Auto stop protected & dimmable (I don't have a dimmer)
There are 6 35w halogens attached - mfg says is the max

I still don't get why the 2 wires coming out of the ceiling show approx 50v on the meter (which is in good working order) when the 3way switches are "off".
 
  #10  
Old 04-23-05, 03:15 AM
5
Member
Join Date: Nov 2004
Location: CA
Posts: 1,913
Upvotes: 0
Received 0 Upvotes on 0 Posts
One of the ways that 'phantom' voltage appears is if you connect a meter across an 'open' in the circuit. The internal resistance of the meter now completes the circuit, allowing some current to flow from the source, thru the load, which is comprised of the bulb and the meter, in series. Ohms law determines how many volts appear across the bulb and how many across the lamp. If measured simultaneously with a 'perfect' meter, the two voltages would add up to the source voltage, eg. 120.
 
  #11  
Old 04-23-05, 04:24 AM
P
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 1,983
Upvotes: 0
Received 0 Upvotes on 0 Posts
You are beimg astute by using a deflecting-needle type of testing instrument.

If the meter indicates 50 volts across the Black and White Branch-Circuit conductors at the ceiling outlet-box (COB) with no external connections to the Black & White wires,i.,e., the fixture disconnected then further investigation is needed.

I suggest you submit an exact description on the wire-connections inside the COB if there is more than 1 Black wire and 1 White wire present.

An open Neutral-connection ( White wire) in a 3-wire ( Black/White/Red) cable that connects to two circuit-breakers at the Service panel can cause an un-equal division of voltage across the connected loads with 160 volts across one load, and 60 volts across another load.You caold have 160 volts across the fixture with the 3-way switch-loop closed.

Good Luck & Enjoy the Experience!!!!!!!!!

Good Luck and en
 
  #12  
Old 04-23-05, 11:55 AM
tylandr
Visiting Guest
Posts: n/a
I've pulled the wires down from the here is layout of the COB....

I'm seeing 3 sets of wire (all 12 gauge w/ground). I'll try to be brief:

All whites are joined together

2 Black wires are joined - this is the leg where the black wire from the light was attached and is one side of the test I'm doing (and am seeing the 50v reading. I am assuming that the COB is in mid-circuit and this is passing voltage on to other fixtures/outlets.

There is a 3rd black wire that is by itself and was where the white side of the fixture was attached. This is the other leg of my 50v test reading.

I am assuming that this lone black wire is actually the "white" wire coming from the switch - in order to interrupt the flow.

Hate to assume too much - does this describe it well enough?

Many thanks.
 
  #13  
Old 04-23-05, 12:10 PM
tylandr
Visiting Guest
Posts: n/a
Maybe I was too brief.

The grounds are all tied together as well.
 
  #14  
Old 04-23-05, 10:29 PM
G
Member
Join Date: Oct 2004
Location: USA
Posts: 676
Upvotes: 0
Received 0 Upvotes on 0 Posts
Can you give us the.
Manufactures name of the units and model numbers.

Keep in mind I don't know what you have, the answers are general


Your post # 5
"the transformer became warm to touch (no big deal), but the shaft that the rail actually draws the current from was burning hot - enough to make me think I was blistered. The end result was the transformer failing"
---------
The rails should not get hot.

Is the heat from the lights heating the rail ?
one or more lights may have a large wattage bulb 100 watt ?
You may have a shorted light.
Bad connection at rail light mounts.
Bad connection inside the rail. wire to rail connection.
light not properly seated in rail makeing a short.
Shorted rail.
------------------
-------------------
Your post # 7
"But, the transformer got so hot, I couldn't touch it. Now that I have a new transformer ready to install, I don't want to do it until I know the problem is resolved."
--------
The first xfmr was warm.
The new xfmr gets hot.

Answers.
You got a smaller xfmr. making the new one run hot.
You have a shorted rail.
You have a shorted light.
light not properly seated in rail makeing a short.
one or more lights may have a large wattage bulb 100 watt ?
--------------
--------------
Seeing that you had it working with the new xfmr.

Try this but not to long.
Try it first with no lights just with the rail.
Then see if the xfmr or the rail gets hot.
Then try each light one by one.
See if something get hotter.
 
  #15  
Old 04-24-05, 03:11 AM
R
Member
Join Date: Sep 2001
Location: Yorktown, VA
Posts: 301
Upvotes: 0
Received 0 Upvotes on 0 Posts
Hello tylandr,

From your description of the connections and wire types in the box, I'll have to admit that I'm a bit confused. I would have expected the white wire from the fixture to be connected in with the other whites or maybe for one of the whites to be connected in with the blacks for a switch loop. Did I read it correctly, that the black from the fixture is connected in with the two blacks and the white from the fixture is connected to the lone black? I am definitely confused.

That said, are you positively sure that all is connected EXACTLY as it was before? If you are, then here are couple of thoughts.

One: If you connect it back up and it works with the switches like you said, then measure the voltage at the two fixture (transformer?) leads with the lights off, then with them on. You should read zero (0) volts with the lights off and 120VAC (approx.) with the lights on...never 50. You have to make sure your leads are connect to the load (transformer) when doing this test...nothing disconnected. If the voltage on the load is 120VAC when the lights are on, then you are not going to hurt the transformer, assuming you are within the load capacity with the lights you have connected.

If you ever read something higher than the 120VAC, i.e. 150 or so, then you have definite problem and need to examine your connections more closely.

Two: Now for meters. I hear many arguments against using digital meters when troubleshooting electrical circuits. I couldn't agree more, but one possible misconception that may be derived from this argument is that an old fashioned Volt-Ohmeter is immune to problems like phantom voltage. While much less susceptible, they are not immune. I have measured 40 or more volts many times in circuits with an Amprobe VOM and with a Simpson 260, which is probably one of the most reliable and accurate meters that has ever been made. The impedance of this meter is only 1Kohm/volt on the AC scales. That's LOW, and I can still pick up phantom voltage.

have fun,
 
  #16  
Old 04-24-05, 07:17 AM
P
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 1,983
Upvotes: 0
Received 0 Upvotes on 0 Posts
What is possible is that the switch-loop has been inserted in the Neutral ( White wire) side of the circuit because there is a leak-to Ground in the Black wire of the 2-wire cable to the switch-loop.

With this connection, the circuit is completed thru this path---- Black wire ( live lead) to Black fixture lead to the lamp-socket, thru the lamp to the White fixture-lead , White fixture-lead to the Black wire of the 2-wire cable in the switch-loop , thru the switch-loop to the White wire of the 2-wire switch-loop cable & back to the fixture where this White wire connects to the 2 White Neutral wires, completing the circuit.

If the switch-loop was inserted in the "live-lead" ( Black wire of "Feed-In" cable), and the Black wire was Grounded as presumed, the breaker would trip. Because the Neutral ( White wire) is a Grounded circuit-conductor, a Grounded-to-Ground connection would not conduct a "Fault" current and the circuit would operate.

The 50-volt reading very likely is a reading of voltage-to-Ground, and a Ground in the Black wire of the 2-wire switch-loop would explain the existing connection.

Good Luck & Enjoy the Experience!!!!!!!!!!
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: