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Discuss Low wattage after overloading MWBC in the American Professional Electrical Advice Forum area at ElectriciansForums.net

So this is a long one..

The other night my dehumidifier turned on and suddenly everything in 2/3rds of the house began cycling on/off and the lights that were on started strobing as well (led bulbs btw). I unplugged everything and reset the breakers, even though none were tripped. At this point, I was able to turn the lights on but they were dim and got dimmer with each new one switched on. The outlets would only power a night light.

After a lot of searching, I came to realize I had a MWBC. Nothing in the panel was labeled when I bought the house, so I figured all the circuits out. When it was all said and done, I had two 15's (one black wire to one leg, one red to the other), and two 20's (same config.). Everything else could be accounted for. The two 20's do nothing with the cb switched on or off but they do all have 120 coming from the breaker. One of the 15's will turn the utility and kitchen lights on and the other powers the bath, hall, beds, and porch lights. Also, noteworthy is the fact that the utility and kitchen lights are perfectly fine and they supply some voltage to the other lights as well, when both breakers are switched on.

The multimeter shows about .4 volts hot and .2 volts neutral starting from the first outlet and moving around the house until I get to the 3rd bedroom (these are the last 2 outlets) ..I say that because the last one only has one hot and one neutral. These 2 have about .8 volts hot and .4 at neutral.

I should add that there are some weird things that affect the lights being able to turn on. If I plug a night light into the first 3 outlets, I can switch all the beds and hall on.. but when I turn the bath light on, the other rooms go dark. If I don't use a nightlight in the outlet and instead turn on the back porch light.. the beds, hall, and bath can all be turned on at the same time. And if I turn on the carport light, it even gets a little brighter, but not so bright that it would blow the bulbs. Btw, the back porch light is controlled by the 15a that controls the beds and bath but it's in the same box as the kitchen lightswitch.. and both those switches show 1.4 volts.

I read that it could be an open neutral but I've been in every switch, outlet, and ceiling light and there's nothing that looks or smells burnt or broken. I also checked the neutrals at the panel. The other strange thing is that the outlet where the dehumidifier was plugged in doesn't let me switch the lights on when I plug a night light into it.. all the subsequent outlets don't as well. That made me think that was the most likely outlet where the damage would be.

I used a wire tracer from that outlet to the next and it doesn't seem like there's a break. Plus there's a little voltage going to all the outlets.. none are dead. But that voltage is definitely coming from the 15's and not the 20's, as it should be. I can cut into the wall if I have to but obviously I'd prefer to have some idea of where the damaged wire is first. Does any of my rambling description help to pinpoint the area I should be focusing on.. or is there a better tool to help find it?
 

Lucien Nunes

-
Mentor
Arms
Esteemed
If using more current from one outlet or light enables another to turn on or makes other lights brighter, you almost certainly have a broken / open-circuit neutral. The various lights and outlets on the two hot legs are then effectively in two groups in series across 240V, and changing the load on either group changes the voltage across both. This can result in anywhere between 0 and 240V appearing across appliances meant for 120, so damage can result if the power is left on.

Switch the affected circuit(s) off and get them tested for continuity throughout. There seems to be something wrong with your voltage readings, or the ground is broken too so that you cannot get valid readings, so I would not draw any conclusions from them. All the testing needed can (and should) be done 'dead' so that there is no risk of damage to your appliances or of fire.
 

Lucien Nunes

-
Mentor
Arms
Esteemed
In this context, what we would call a split-phase 3-wire circuit, both hots and a neutral.
That article is funny in how alien it looks in a UK context. We don't have split-phase finals in a domestic situation, nor do we have duplex breakers (two separate SP MCBs in one case fed from one busbar lug) so there isn't much opportunity for people to mistakenly connect one to the other.

BTW I think this thread needs to head over to the USA section!
 

Megawatt

-
Arms
So this is a long one..

The other night my dehumidifier turned on and suddenly everything in 2/3rds of the house began cycling on/off and the lights that were on started strobing as well (led bulbs btw). I unplugged everything and reset the breakers, even though none were tripped. At this point, I was able to turn the lights on but they were dim and got dimmer with each new one switched on. The outlets would only power a night light.

After a lot of searching, I came to realize I had a MWBC. Nothing in the panel was labeled when I bought the house, so I figured all the circuits out. When it was all said and done, I had two 15's (one black wire to one leg, one red to the other), and two 20's (same config.). Everything else could be accounted for. The two 20's do nothing with the cb switched on or off but they do all have 120 coming from the breaker. One of the 15's will turn the utility and kitchen lights on and the other powers the bath, hall, beds, and porch lights. Also, noteworthy is the fact that the utility and kitchen lights are perfectly fine and they supply some voltage to the other lights as well, when both breakers are switched on.

The multimeter shows about .4 volts hot and .2 volts neutral starting from the first outlet and moving around the house until I get to the 3rd bedroom (these are the last 2 outlets) ..I say that because the last one only has one hot and one neutral. These 2 have about .8 volts hot and .4 at neutral.

I should add that there are some weird things that affect the lights being able to turn on. If I plug a night light into the first 3 outlets, I can switch all the beds and hall on.. but when I turn the bath light on, the other rooms go dark. If I don't use a nightlight in the outlet and instead turn on the back porch light.. the beds, hall, and bath can all be turned on at the same time. And if I turn on the carport light, it even gets a little brighter, but not so bright that it would blow the bulbs. Btw, the back porch light is controlled by the 15a that controls the beds and bath but it's in the same box as the kitchen lightswitch.. and both those switches show 1.4 volts.

I read that it could be an open neutral but I've been in every switch, outlet, and ceiling light and there's nothing that looks or smells burnt or broken. I also checked the neutrals at the panel. The other strange thing is that the outlet where the dehumidifier was plugged in doesn't let me switch the lights on when I plug a night light into it.. all the subsequent outlets don't as well. That made me think that was the most likely outlet where the damage would be.

I used a wire tracer from that outlet to the next and it doesn't seem like there's a break. Plus there's a little voltage going to all the outlets.. none are dead. But that voltage is definitely coming from the 15's and not the 20's, as it should be. I can cut into the wall if I have to but obviously I'd prefer to have some idea of where the damaged wire is first. Does any of my rambling description help to pinpoint the area I should be focusing on.. or is there a better tool to help find it?
Kmp567 welcome to the forum and after reading your post. You need to call your power company, I suspect you have a bad connection coming from the power company to your panel. They will not charge you but I think that’s where you problem is and that’s about all it can be. Nothing is going to make your house do what you described except a poor connection. It sounds like you have a loose connection on one of the phases. Good luck and call the power company
 

Megawatt

-
Arms
Kmp567 welcome to the forum and after reading your post. You need to call your power company, I suspect you have a bad connection coming from the power company to your panel. They will not charge you but I think that’s where you problem is and that’s about all it can be. Nothing is going to make your house do what you described except a poor connection. It sounds like you have a loose connection on one of the phases. Good luck and call the power company
Kemp did you call the power company
 
  • Thread Starter Thread Starter
  • #8
Kemp did you call the power company
They're actually here now. I'm sitting in the dark waiting for them to replace the whole line. The guy said that there were some weird splices but that he didn't think the voltage was all that off from normal.

So is the poco’s neutral the most likely issue? The house was built in '55, btw. He said if that doesn't fix it then it must be on my end.

Guess we'll see..
 

Megawatt

-
Arms
They're actually here now. I'm sitting in the dark waiting for them to replace the whole line. The guy said that there were some weird splices but that he didn't think the voltage was all that off from normal.

So is the poco’s neutral the most likely issue? The house was built in '55, btw. He said if that doesn't fix it then it must be on my end.

Guess we'll see..
It’s on their end no worries or they wouldn’t be replacing the whole wire from the pole to your house
Post automatically merged:

It’s on their end no worries or they wouldn’t be replacing the whole wire from the pole to your house
No I don’t think it is the neutral I think you was loosing one of the phases or hot wire what ever you want to call it and let me know what the outcome is
 

Megawatt

-
Arms
So this is a long one..

The other night my dehumidifier turned on and suddenly everything in 2/3rds of the house began cycling on/off and the lights that were on started strobing as well (led bulbs btw). I unplugged everything and reset the breakers, even though none were tripped. At this point, I was able to turn the lights on but they were dim and got dimmer with each new one switched on. The outlets would only power a night light.

After a lot of searching, I came to realize I had a MWBC. Nothing in the panel was labeled when I bought the house, so I figured all the circuits out. When it was all said and done, I had two 15's (one black wire to one leg, one red to the other), and two 20's (same config.). Everything else could be accounted for. The two 20's do nothing with the cb switched on or off but they do all have 120 coming from the breaker. One of the 15's will turn the utility and kitchen lights on and the other powers the bath, hall, beds, and porch lights. Also, noteworthy is the fact that the utility and kitchen lights are perfectly fine and they supply some voltage to the other lights as well, when both breakers are switched on.

The multimeter shows about .4 volts hot and .2 volts neutral starting from the first outlet and moving around the house until I get to the 3rd bedroom (these are the last 2 outlets) ..I say that because the last one only has one hot and one neutral. These 2 have about .8 volts hot and .4 at neutral.

I should add that there are some weird things that affect the lights being able to turn on. If I plug a night light into the first 3 outlets, I can switch all the beds and hall on.. but when I turn the bath light on, the other rooms go dark. If I don't use a nightlight in the outlet and instead turn on the back porch light.. the beds, hall, and bath can all be turned on at the same time. And if I turn on the carport light, it even gets a little brighter, but not so bright that it would blow the bulbs. Btw, the back porch light is controlled by the 15a that controls the beds and bath but it's in the same box as the kitchen lightswitch.. and both those switches show 1.4 volts.

I read that it could be an open neutral but I've been in every switch, outlet, and ceiling light and there's nothing that looks or smells burnt or broken. I also checked the neutrals at the panel. The other strange thing is that the outlet where the dehumidifier was plugged in doesn't let me switch the lights on when I plug a night light into it.. all the subsequent outlets don't as well. That made me think that was the most likely outlet where the damage would be.

I used a wire tracer from that outlet to the next and it doesn't seem like there's a break. Plus there's a little voltage going to all the outlets.. none are dead. But that voltage is definitely coming from the 15's and not the 20's, as it should be. I can cut into the wall if I have to but obviously I'd prefer to have some idea of where the damaged wire is first. Does any of my rambling description help to pinpoint the area I should be focusing on.. or is there a better tool to help find it?
Do you have a panel outside with a meter or just a meter
 
  • Thread Starter Thread Starter
  • #14
I'll have to check when I get off work but I would think they would've checked that when they were testing the power (maybe not)

So then is it most likely that I've lost a hot and the intact neutral is supplying the few volts that are able to power LEDs, since the neutral is shared by the light switches as well?

I'm still confused why the cb wouldn't have tripped though when the dehumidifier kicked on originally.

What would happen if a neutral and hot were making constant contact somewhere in the circuit? I feel like it's more likely the wire's coating would melt before the heavy duty wire they used would.. but I'm just guessing at this point.
 
  • Thread Starter Thread Starter
  • #15
Also, does it seem like there's any significance to what I mentioned in my first post about how turning on the bathroom light killed the other lights?

I know it's difficult to assess stuff like that online w/o being able to see it but I feel like I'm going to end up needing to cut into the wall. I'd like to think that the damaged wire would be between the outlet the dehumidifier was on and the next bedroom, but in my experience, nothing is ever that simple...
 

Megawatt

-
Arms
I'll have to check when I get off work but I would think they would've checked that when they were testing the power (maybe not)

So then is it most likely that I've lost a hot and the intact neutral is supplying the few volts that are able to power LEDs, since the neutral is shared by the light switches as well?

I'm still confused why the cb wouldn't have tripped though when the dehumidifier kicked on originally.

What would happen if a neutral and hot were making constant contact somewhere in the circuit? I feel like it's more likely the wire's coating would melt before the heavy duty wire they used would.. but I'm just guessing at this point.
Please don’t cut in your wall, I have never heard of some of the weird stuff you said that was going on. Your problem is in that panel so please call an electrician so he can get.hands on and will find your problem.
Post automatically merged:

Please don’t cut in your wall, I have never heard of some of the weird stuff you said that was going on. Your problem is in that panel so please call an electrician so he can get.hands on and will find your problem.
It’s sounding like a neutral issue which can cause havoc in your house. It might be time to up grade your service. Good luck
 
  • Thread Starter Thread Starter
  • #17
So for the sake of curiosity.. why am I not seeing any sort of fluctuation across the circuit? I've read tons of posts from electricians discussing MWBC's and how they can cause 240v to go through lights and appliances but my voltage has never spiked.

It's as if the outlets aren't getting fed any voltage from the panel but they're still all connected to each other and receiving .4 volts from the light switches.
 

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