Lower Voltage on One Circuit

[bad_idea]

I have a 15amp 120volt circuit in the house that reads lower than the other circuits. It is noticeable - the lights dim when things turn on. I did some testing and these are my results:

Read 120volts at all of the breakers.
Read 120volts at the outlets on the circuit with no load.
Read 110-113volts at the outlets on the circuit with a heater plugged in. Checked a couple of them.
Read 120volts at the breaker with the heater on.
Read 116volts at another 15amp outlet in the house with the same heater plugged into it.

I tightened every connection in the main panel - found several were less than tight but snug. Pulled the breaker out on the circuit in question - has goo on the connection to the buss bar with no signs of arcing. The breaker in question is a GFCI breaker - it pops when the test button is pushed and resets. Have not had issues with random pops of the breaker.

What are the likely causes of the issue? How severe is the issue? Something to live with or something to tear the house apart until I fix it?

 

[couch67]

I'd start by checking the connections at the outlets. I suspect there's a loose/bad connection at one of them. If you know the order how the outlets are fed from the panel, I would go in that order.

 

[FMB4]

Beware of the 'push-in' type outlets where you simply push the stripped wire into a hole rather than tightening a screw down on the wire. Most, if not all, of these type of outlets have both 'push-in' and 'screw down' terminals.

Also check for wire ends that are fouled with 'plaster' and/or paint.

 

[u2slow]

The connected load, length of the circuit, and wire gauge all affect the voltage drop. Up to 10% loss at a device is considered satisfactory.

The lights you notice dimming are likely on the same circuit as the heater.

 

[Innovate1]

It's a bad connection somewhere between the breaker and the receptacle. Turn off the breaker and identify all the receptacles on the circuit. Turn it on with the heater on and measure the voltage at the receptacles and if you work you way away from the breaker you should see 120 until you see a sudden drop. That's where the bad connection is.

This is a fire hazard so good to check it out. Might want to do the same thing on other circuits. Or change all the backstab connections to the screw terminals depending on what you find.

 

[yatg]

Check any wirenutted connections in the boxes too. Hots and neutrals.

 

[Terry D]

Slight dimming of lights when other loads come on is normal. Whether they are on the same circuit or not. If on a different circuit, you are just getting a slight voltage drop across the mains of your panel. Now if they are dimming a whole lot, or stay dimmed, then that's a concern. Plugging your heater in is also creating a voltage drop. And as already said, the length and the size of wire plays a part in that. I would not be real concerned
It sounds like you have already checked connections in the panel. Maybe also check connections at the devices also. I would suggest if you were planning on keeping the heater in use, is to run a dedicated 20 amp circuit

 

[sparky 1971]

Terry nailed it. It's voltage drop. It's probably a 15 amp circuit, 14 gauge wire, it could be 12 gauge, but a couple of miles of wire between the breaker and point of use outlet, which is compounded exponentially by the space heater. When I get calls similar to this and the "I have a junk breaker that needs changed" in the winter time, the first question I ask is if there is a space heater involved. If they say yes, I tell them it will be a helluva lot cheaper to throw the space heater in the nearest dumpster and turn the stat up a couple of degrees than for me to run a 20 amp circuit for it.

 

[Innovate1]

7 - 10 V is a lot of drop for just wire resistance. Plugging in some numbers to Southwires calculator.
Assume 14 AWG copper and 15A circuit with a 50' run and 12A current. This gives 3.2V drop. Terry and sparky both do this professionally and I don't but I wouldn't just write it off as voltage drop. Seems like more than that to me. Substitute your own numbers with estimate of wire run length and plug those into a calculator. I have seen some things that got very hot from loose connections. 116V isn't much concern. 110-113V is. Any chance the wiring is aluminum? If so I would be even more concerned but even with copper I would be pulling some covers and checking things.

 

[u2slow]

Supposing you have 112V at the heater.... you may be losing 4V getting there and losing another 4V back. That's still 120V at the breaker.

If you have any back-stabbed receptacles in the mix - especially if they pass-thru - it would be best to eliminate them.

 

[sparky 1971]

7 - 10 V is a lot of drop for just wire resistance. Plugging in some numbers to Southwires calculator.
Assume 14 AWG copper and 15A circuit with a 50' run and 12A current. This gives 3.2V drop. Terry and sparky both do this professionally and I don't but I wouldn't just write it off as voltage drop. Seems like more than that to me. Substitute your own numbers with estimate of wire run length and plug those into a calculator. I have seen some things that got very hot from loose connections. 116V isn't much concern. 110-113V is. Any chance the wiring is aluminum? If so I would be even more concerned but even with copper I would be pulling some covers and checking things.

50' is nothing for a circuit length in a house. A home 40' long with a panel at one end could easily have 150' of wire in a circuit by the time it got to the opposite corner. Think about coming out of the panel, up the wall, across the attic to the room where the circuit is, down the wall to the first outlet, out of that outlet to the next, whether it be through holes drilled through the studs or back into the attic, back down to the next outlet and so on and so forth. Add on 10-12" inches in each box for wires in and out, another two feet or so in the panel and it adds up to a **** ton length of cable. Not saying this is the case, but it could very well be. 50' is probably the best case scenario for the circuit closest to the panel. You wouldn't believe the amount of romex that a home can devour. I just ran it with 13 amps (12.5 for a 1500 watt heater and a couple of lights) on 100 feet of 14-2 and got a drop of 7.5 volts.

 

[FredWanaker]

what is the wattage of the heater. 1500 watts is common on small heaters but I have seen some up to 1800 watts. 1500 watts is around 13 amps. 13 amps on a 15 amp circuit with a long run is going to pull the voltage down. The only way I know to isolate where the loss is, is measure the voltage at any other places it ties to along the way. It is not uncommon for one circuit to go thru 3 or 4 receptacles in the house. If you have a thermal camera you may find a spot where the loss if heating that connection. Measuring voltages without a load really doesn't give you much other than it is connected although sometimes one side of the panel may be overloaded.

 

[BillK]

Read 116volts at another 15amp outlet in the house with the same heater plugged into it.

Is that outlet a lot closer to your main panel than the original one ?

 

[ttpete]

Supposing you have 112V at the heater.... you may be losing 4V getting there and losing another 4V back. That's still 120V at the breaker.

If you have any back-stabbed receptacles in the mix - especially if they pass-thru - it would be best to eliminate them.

I had it happen last week. We started pulling outlets, working around the room. That involved pulling books off bookshelves to access unused outlets, all backstabbed. We finally found one with the hot side out. We corrected all of the backstabbed ones and put the room back together. I think it got hot enough that it took all of the tension out of the spring backstab gripper.

That addition was built around 1971. We were running an electric heater, and the circuit failed with a loud pop.

 

[wyliesdiesels]

The connected load, length of the circuit, and wire gauge all affect the voltage drop. Up to 10% loss at a device is considered satisfactory.

The lights you notice dimming are likely on the same circuit as the heater.

according to who? The NEC recommends 5% for branch circuits....

 

[wyliesdiesels]

I have a 15amp 120volt circuit in the house that reads lower than the other circuits. It is noticeable - the lights dim when things turn on. I did some testing and these are my results:

Read 120volts at all of the breakers.
Read 120volts at the outlets on the circuit with no load.
Read 110-113volts at the outlets on the circuit with a heater plugged in. Checked a couple of them.
Read 120volts at the breaker with the heater on.
Read 116volts at another 15amp outlet in the house with the same heater plugged into it.

I tightened every connection in the main panel - found several were less than tight but snug. Pulled the breaker out on the circuit in question - has goo on the connection to the buss bar with no signs of arcing. The breaker in question is a GFCI breaker - it pops when the test button is pushed and resets. Have not had issues with random pops of the breaker.

What are the likely causes of the issue? How severe is the issue? Something to live with or something to tear the house apart until I fix it?

likely a high resistant connection such as a back-stabbed outlet. Used to see it all the time back when i did a lot of service calls...

 

[Innovate1]

50' is nothing for a circuit length in a house. A home 40' long with a panel at one end could easily have 150' of wire in a circuit by the time it got to the opposite corner. Think about coming out of the panel, up the wall, across the attic to the room where the circuit is, down the wall to the first outlet, out of that outlet to the next, whether it be through holes drilled through the studs or back into the attic, back down to the next outlet and so on and so forth. Add on 10-12" inches in each box for wires in and out, another two feet or so in the panel and it adds up to a **** ton length of cable. Not saying this is the case, but it could very well be. 50' is probably the best case scenario for the circuit closest to the panel. You wouldn't believe the amount of romex that a home can devour. I just ran it with 13 amps (12.5 for a 1500 watt heater and a couple of lights) on 100 feet of 14-2 and got a drop of 7.5 volts.

I know there can be lots of wire in a house. I installed over 5000 ft of 12-2 in my house (14 is not allowed here) and it's not a mansion. It may be just voltage drop due to wire length and resistance but if it was my house I would be doing some checking to make sure.

 

[bad_idea]

Is that outlet a lot closer to your main panel than the original one ?

It is. I'm beginning to think this is perfectly normal and to be lived with.

 

[bad_idea]

Thank you for all of the comments and information guys. I have a plan now.

The heater is 1500w.

I will pull all of the outlets in the room and go from back stabs to the screws on the sides of the outlets. The house was built ~15 years ago, is it safe to assume the outlets are still good? I can replace them all if needed, cheap insurance?

I will also tap into the bathroom 20 amp circuit and install an outlet in the room. There is already a junction box in the attic for the circuit, will be easy to run it over. Unfortunately the heater is necessary as the room is cold and upgrading the ducts isn't in the cards.

 

[Innovate1]

If the spring tension is good when inserting a plug and there are no signs of heating on the wires and back you should be good to reuse the outlets (technically, NEC calls any load point an outlet and calls these receptacles). For a little more than the cheapest of receptacles they make them that have screws and clamp bars (instead of spring clamps) that take a straight wire in the back. Lots less messing with wrapping wires around screws but either is ok if using the screws. Others may chime in with more details but there are rules about bathroom circuits. Recent versions of the NEC requires that a bath receptacle circuit not include other rooms. I wouldn't be too worried about violating this rule although I would consider that if someone is using a blow drier or large load in the bathroom when the heater is on it will likely trip the 20A breaker.

 

[Terry D]

Thank you for all of the comments and information guys. I have a plan now.

The heater is 1500w.

I will pull all of the outlets in the room and go from back stabs to the screws on the sides of the outlets. The house was built ~15 years ago, is it safe to assume the outlets are still good? I can replace them all if needed, cheap insurance?

I will also tap into the bathroom 20 amp circuit and install an outlet in the room. There is already a junction box in the attic for the circuit, will be easy to run it over. Unfortunately the heater is necessary as the room is cold and upgrading the ducts isn't in the cards.

Its hard do diagnose something like this over the internet. But in my past experiences, I have seen a large load like this cause a voltage drop. I'm not saying that it couldn't be something else. That is why I suggested to check the connections at the devices also. If you pull out one receptacle and it is back stabbed, then probably your whole house is. Back stabbing can cause issues.

As far as tapping off your 20 amp bathroom receptacle circuit for this heater, I wouldn't do it. The bathroom receptacle circuit is only allowed to feed receptacles in the same bathroom or other bathrooms, it can not feed other receptacles or lights outside the bathroom(s). There is a exception that you can run a dedicated 20 amp circuit and feed one whole bathroom on it, lights and fan also. But it still cant leave that one bathroom. So unless the receptacle for the heater is going to be in a bathroom, it would be a code violation. Plus if someone had a hairdryer or curling iron plugged in also with that heater on, It will trip the circuit. Best is to run a dedicated circuit.

 

[sparky 1971]

I wouldn't be concerned about re-using the existing receptacles. I hope that the back stabbing is only for connection and not the feed through. If they are fed through , make sure to pigtail the wires so there is only one hot and neutral per device. As far as getting power from the bathroom, code says that's a no no but you're going to do what you want. The fact that there is a junction box for the bathroom makes me think that all of the bath outlets are on the same circuit. I'd probably do the same thing if it were mine, but expect problems if hair fryers are being used. If you have fairly easy access to the panel just run a new circuit.

 

[Citation]

OP, I would feel better if I knew where the drop was coming from. My last house was wired with back stabbers when I moved in. I was using a space heater and found one outlet that wasn't in use but was over heating. It was between the heater and the breaker and had been wired with back stabbers and the current was carried through the outlet vs using a pig tail.

A first check is if you know what outlets are between the heater and the breaker, are they wired with a pigtail or is the current carried through the receptacle itself? If carried through the receptacle, changing to a pigtail may help. Also, if you have an IR thermometer you can check to see if any of the outlets are getting warm. Worst case is something like I had where all the voltage loss was in one overheating receptacle.

I didn't read all the above replies so please forgive if this is repeating prior advice.

 

[u2slow]

according to who? The NEC recommends 5% for branch circuits....

Up to 10% under and up to 5% over are basic equipment tolerance guidelines.

The fact this branch circuit is bearing the v-drop (and not just low system voltage)... either this branch is overloaded or there's possibly a poor connection.

 

[bad_idea]

You all are trying to work me to death. There is a plenty of open slots in the panel and I have the materials in the garage (wired the garage when I built it a couple years ago, with an inspection to code).

I’ll run a new circuit. Any tricks for fishing the cable through the top of the breaker panel without cutting sheet rock? No way am I tearing up the wall in the wife’s laundry room - I’d never hear the end of it.

 

[Terry D]

Post a picture

 

[Innovate1]

Is the wall insulated? If so that's going to be really tough to do.

 

[Wrench97]

I'd check all the connections at all outlets on the circuit before thinking about pulling new wire..............................

 

[Terry D]

I'd check all the connections at all outlets on the circuit before thinking about pulling new wire..............................

He's not wanting to replace the wire on the existing circuit. He is wanting to add a circuit for the heater

 

[bad_idea]

The panel is on an interior wall. I have easy access to the top plate of the wall from the attic. The panel is a sub panel, the main panel is a combo meter and main panel on the outside of the house. I will kill the main breaker on the main panel when I work in this panel.

 

[Terry D]

You have to get the knock out removed from the top of the panel. They are made to be knocked out from the outside in. Try to pop ot down worh a screwdriver from the inside. If that wont work, drill a hole in it and stick a screwdriver in it ro pop it out. As long as wall is not insulated and the top plate is accessible. You will probably see other wires xoming through it, carefully drill about a 1 1/2 hole through the plate. Have someone shine a flashlight up through the knock out. You should see it from the attic. Use a fiberglass fish stick, and fish it down into the panel. Put a metal connector on the romex, make sure to remove the lock nut, tape it on the stick, pull it down into the panel so the threads of the connector come through the hole and put the lock nut on

 

[SlappyWhite]

Another option if you do not have the fibreglass fishing stick. Remove the knock-out like @Terry D noted. Same limits if the wall is insulated etc.

Takes two people... drill a hole in the top plate as close to above the panel knock-out as you can figure. Tie a nut on a string that will fit through the two holes. Send a strong flexible "mechanics" magnet through the knockout hole and have someone send the nut down, search around with the magnet. It may take a couple tries but once you catch the nut with the magnet pull the string through and use it to pull the wire down. Power off of course. BTW I use this technique to fish wire to an existing electrical box (switch) through to the basement without breaking the wall. Nut and string through the knock-out and magnet through the hole on the bottom plate/basement. Fish the wire afterwards.

Next option, just cut the drywall at the top of the panel and patch it afterwards.

 

[bad_idea]

I would rather attempt *********** with a football than tell the wife I'm going to cut a hole in the laundry room wall. I have a set of fish sticks and have gotten fairly decent with them. Thanks guys. Will hopefully get to this project Saturday.

 

[sparky 1971]

I occasionally have decent luck getting the knockout out by running a self tapping screw into it from the inside and grabbing the head with pliers. Of course, there are also times that doesn't work worth a pinch of **** and I wind up beating the hell out of it with a big screwdriver and linemans pliers. Rackatiers makes a tool for removing flush mount panel knockouts, but I have yet to see one in person.

To get into the panel, after removing a knockout, I've put duct tape over the hole from inside the panel, then gone into the attic and dropped a length of plumbers chain down. Then gone back to the panel, removed the tape and fished around through the hole with a piece if #12 wire with a small hook bent on the end of it until I snagged the chain and pulled it through the hole. Hook the wire to the chain and pull it on in. And sure to put a piece of cardboard over the main to keep from blowing it up though, but don't worry about the cardboard or tape if you plan on killing the main. After the wire is in, I use a snap in plastic bushing to sleeve it. I've never tried the method with the magnet and nut on a string, that seems like a good idea though. I've tried fish sticks, but didn't have any luck because I'm usually by myself, it's next to impossible to push the rod through two holes 5' apart when you can't see the second one.

Nothing will take the place of a second set of hands and eyes, it's a real ***** to keep going from the attic to the panel just to find that the job isn't coming together as planned and whatever you're using to fish isn't there yet because it's caught on an existing wire. I got sick of a lot of stuff and have a 99% of the time I won't go into an attic policy.

Oh yeah, this might be the most important piece of advice. Get practiced up with the cuss words, you're probably going to use all of them, especially if you're in the low spot of the attic with your back jammed up against the roof trusses and/or in an insulated wall.

 

[PoorUB]

I would just "toss in the towel" and cut an access hole above the breaker panel and cover it with a plastic access panel like you have just to the right of the panel. Then next time you want to add a circuit you just pop off the panel.

Give mama a stiff drink and tell her to relax!

 

[bad_idea]

She don’t drink. LOL!

I like the access panel idea. I can put one on the other side of the wall if needed. Will make future work that much easier.

 

[Innovate1]

Access panel is the easiest and maybe on the other side if that makes everyone happy. But there have been some good suggestions on getting the wire in without cutting the wall if you want to do that. You can trim the drywall just a little at the top of the panel to see where things are and still cover the gap with the panel cover. I have used the chain trick before with good luck. I put a section of PVC conduit from the panel to the attic when this place was built to make such things easier...

 

[mcbane]

...carefully drill about a 1 1/2 hole through the plate....

Remember to make the 1-1/2" hole rodent tight afterwards. If you ever get mice in the attic they will fall through that hole and get stuck on top of your electric panel. I once opened a wall to find a half dozen decayed mice that had fallen through a hole in the top plate - it explained the foul odor in that location.

 

[PoorUB]

She don’t drink. LOL!

I like the access panel idea. I can put one on the other side of the wall if needed. Will make future work that much easier.

Must be a closet on the back side?

If that is the case maybe just open the stud bay all the way to the ceiling and make a cover panel out of a sheet of 1/2" or 3/4" PVC and screw it in place.

 

[bad_idea]

It is. The air handler, water softener, and water heater are in there. My reservation is the water softener. It is immediately below the area I would have to cut out. Not a fan of drinking drywall dust. Debating 'cover and protect' or 'remove and replace'. There are mechanical joints to ease removal, but of course leaks are more likely if I break the joints. It is also tight to get in there if I don't pull the softener. AND..... I don't feel like doing any of that ****.

On the bright side, I have plenty of other **** to keep me busy. I have time to sort out the best plan before I execute. Might be nuking it.