Our classrooms are set up with 2 single pole switches, that are on a mwbc. One set of lights will not work unless the other switch is on. Once that switch is on the other works fine. I have not looked into this yet. Just thought I would get some advice before Monday. I'm guessing the is a neutral not connected on the one the wont power on unless the other is on?
Switches
- Thread starter Mparn
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The second switch is being fed from the wrong terminal of the first switch.
kwired
Electron manager
- Location
- NE Nebraska
If they are on separate legs of a MWBC he should have a line to line fault when both switches are on if that is the case.
Lost neutral is a valid possibility.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180707-1143 EDT
The original post is not clear.
There are two SPST switches controlling two separate sets of lights in a room. No mention is made of any abnormal light intensity.
If both switches are off all lights are off.
If switch A is turned on, then one set of lights turns on, presumably full brightness.
If switch A is off, and switch B is turned on, then no lights turn on.
If switch A is on, and switch B is turned on, then all lights are on, presumably at full brightness.
In other words the power source to switch B is obtained from the output of switch A. This is what Larry described. The MWBC of post #1 is of no importance. How in any way could an open neutral result in the logic of the presented problem?
For neutral to be a problem it would be necessary for the hot wires to both sets of lights to come from the output of switch A, and that switch B be wired in the neutral of light set B. One would have to work hard to do this. Thus, Larry's suggestion seems logical, and a likely mistake.
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The original post is not clear.
There are two SPST switches controlling two separate sets of lights in a room. No mention is made of any abnormal light intensity.
If both switches are off all lights are off.
If switch A is turned on, then one set of lights turns on, presumably full brightness.
If switch A is off, and switch B is turned on, then no lights turn on.
If switch A is on, and switch B is turned on, then all lights are on, presumably at full brightness.
In other words the power source to switch B is obtained from the output of switch A. This is what Larry described. The MWBC of post #1 is of no importance. How in any way could an open neutral result in the logic of the presented problem?
For neutral to be a problem it would be necessary for the hot wires to both sets of lights to come from the output of switch A, and that switch B be wired in the neutral of light set B. One would have to work hard to do this. Thus, Larry's suggestion seems logical, and a likely mistake.
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This happened when we changed the fixture over to led. Each fixture had the option to use either switch (each fixture had 2 switch legs, we capped off the one we didn't use).
Lighting is normal
When switch a is on, you can turn on/off switch b.
If switch b is on and you turn off switch a, all lights turn off.
When switch a is off and you turn switch b on, nothing happens.
Lighting is normal
When switch a is on, you can turn on/off switch b.
If switch b is on and you turn off switch a, all lights turn off.
When switch a is off and you turn switch b on, nothing happens.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180707-1432 EDT
Mparn:
I have no idea what your original circuit was before changing to LEDs.
This is an incomplete description for me to follow.
I don't know what your background is, but I don't think you have studied the field of logical circuits.
What Larry and I think your circuit is can be drawn on paper as:
At the left draw a circle with a one cycle sine wave in the center. This represents your AC voltage source.
From the top of the circle draw a line up some ways. Label it Hot.
From the bottom draw a line down some ways. Label it Common.
From this common wire draw a horizontal line to the right across the page.
From the top hot line draw a horizontal line a short distance and place a SPST switch and label it A.
From the right hand side of A place a light between A (output side) to Common. This is light A.
Also from the output side of switch A continue with a wire to the input side of a switch B.
From the output side of switch B place a light to Common.
This is the circuit Larry and I believe you have.
To correct this problem you want to move the input end of the wire to switch B to the input end of switch A. Then the two switches will be independent of each other.
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Mparn:
I have no idea what your original circuit was before changing to LEDs.
This is an incomplete description for me to follow.
I don't know what your background is, but I don't think you have studied the field of logical circuits.
What Larry and I think your circuit is can be drawn on paper as:
At the left draw a circle with a one cycle sine wave in the center. This represents your AC voltage source.
From the top of the circle draw a line up some ways. Label it Hot.
From the bottom draw a line down some ways. Label it Common.
From this common wire draw a horizontal line to the right across the page.
From the top hot line draw a horizontal line a short distance and place a SPST switch and label it A.
From the right hand side of A place a light between A (output side) to Common. This is light A.
Also from the output side of switch A continue with a wire to the input side of a switch B.
From the output side of switch B place a light to Common.
This is the circuit Larry and I believe you have.
To correct this problem you want to move the input end of the wire to switch B to the input end of switch A. Then the two switches will be independent of each other.
.
kwired
Electron manager
- Location
- NE Nebraska
So does one light always work but the other doesn't unless the first one is on?
My mentioning before of lost neutral was assuming nothing worked unless both switches were on, but you weren't really all that clear on exactly what the switch combinations are to make things work.
You may not have (too noticeable) varying light levels with electronic ballasts, and may not notice any variance at all if voltage is between about 108 and 290 volts on 120-277 rated ballasts.
Yes
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180707-1704 EDT
kwired:
What circuit can you draw where the neutral could be the cause of the logical operation that Mparn described?
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kwired:
What circuit can you draw where the neutral could be the cause of the logical operation that Mparn described?
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kwired
Electron manager
- Location
- NE Nebraska
Now that he has clarified a little more it is not a neutral issue. I was initially thinking he meant both switches must be on before any of the lights work, if that were the case it could be an open neutral issue.
That said even though design was supposed to be multiwire circuit and each switch on a different "leg", that obviously isn't what is happening or else there would be line to line fault when both switches are closed, if there were somehow interconection between them.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180707-2446 EDT
Mparn:
Relative to your post #7. Wiring at the fixture can not be the cause. Switch B and lights B have to be powered from the output of switch A.
My guess is that as you said it may have been a preexisting condition.
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Mparn:
Relative to your post #7. Wiring at the fixture can not be the cause. Switch B and lights B have to be powered from the output of switch A.
My guess is that as you said it may have been a preexisting condition.
.
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