lights flicker after installing new load center

Reply

  #1  
Old 10-11-15, 06:08 AM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
lights flicker after installing new load center

The installation of my new QO load center went well. The power company pulled my meter and disconnected me in the alley so I could do the work. The inspector required me to change my SE conductors from the meter to the panel because the old ones were undersized. That was the only surprise.

But now, whenever my a/c comes on, my lights flicker. Even worse, my lights flicker when the a/c of either of my two neighbors who are connected in the same box in the alley comes on. What's going on here? A bad neutral? I'm measuring 121.7V and 121.9V from each hot to neutral.

I know I torqued down the SE conductors in the load center properly. But I am not certain that I got enough torque inside the meter socket. I tightened them down with my screwdriver until I couldn't turn them anymore, but I honestly wasn't sure about it. The power company electrician checked them by tugging on them when he put my meter back in.
 
Sponsored Links
  #2  
Old 10-11-15, 06:52 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,597
Upvotes: 0
Received 13 Votes on 11 Posts
Even worse, my lights flicker when the a/c of either of my two neighbors who are connected in the same box in the alley comes on.
That indicates the problem may be too much load on the Poco transformer. You can talk to them but don't get your hopes up. They will probably say some flickering is normal. If it was just your you could try a hard start kit on your A/C but that won't help with the neighbors.
 
  #3  
Old 10-11-15, 08:49 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,845
Received 8 Votes on 6 Posts
If it happens all over the house it could be a connection issue at the power company equipment. If it is only one circuit you need to check those connections in the panel. If you didn't add load I would rule out the transformer being too small.
 

Last edited by pcboss; 11-21-15 at 04:55 PM.
  #4  
Old 10-12-15, 06:16 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,922
Upvotes: 0
Received 37 Votes on 35 Posts
Sounds more like a connection wasn't remade solidly after the cutoff. You probably ought to have the power company out to re-check the drop and transformer. Maybe screwing around with the drop pulled something loose.
 
  #5  
Old 10-12-15, 04:26 PM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
Power company came out today to check. I wasn't here. They left me a note:

Voltage check ok: 120/240
Load test ok: 117/117

I doubt they checked their connections in the alley. Would a load test reveal a bad neutral connection?
 
  #6  
Old 10-12-15, 06:32 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,845
Received 8 Votes on 6 Posts
A load test will show a poor neutral connection. The voltage will swing under load, more under heavier loads.
 

Last edited by pcboss; 11-21-15 at 04:55 PM.
  #7  
Old 10-12-15, 07:58 PM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
Ok, anything else I can do here? I don't like that this started right after I replaced the load center, but maybe there's nothing I can do about it?
 
  #8  
Old 10-12-15, 08:00 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,845
Received 8 Votes on 6 Posts
The issue needs to be dealt with, but you need to find it. Is it the whole house or one circuit?
 
  #9  
Old 10-13-15, 06:04 AM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
I've noticed the problem on multiple light circuits so it appears to be the whole house. And it's happening on adjacent breakers in the load center, so it's not just on one hot conductor.

The compressor starting should cause an equal drop in voltage across both hots, right? Could I do my own "load test" on my side of the meter by switching off every other circuit so all the load is on one hot?
 
  #10  
Old 10-13-15, 07:00 AM
Member
Join Date: May 2015
Location: USA
Posts: 3,138
Upvotes: 0
Received 0 Votes on 0 Posts
You said you notice this both when your a/c starts and when neighbor's starts. Is the magnitude of the blink about the same either way?

When you installed the new panel, did you happen to move the breaker for the a/c from the top of the panel to the bottom?
 
  #11  
Old 10-16-15, 05:10 PM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
To summarize, here's everything that changed:
  • load center replaced
  • service entrance conductors changed (previously, hots were #1/0 aluminum and neutral was #2 aluminum. Now all are #2/0 copper.)
  • power company disconnected and reconnected power in the alley
  • power company pulled meter and restored meter

Power company returned and said everything looks ok to them, but I don't know if they checked both the alley connections and the meter.

The problem is definitely worse when my A/C comes on rather than my neighbor's.

The breaker for the A/C is 2nd from the top of the panel. All of my light circuits are at the bottom of the panel.

The A/C power is on a 70A breaker that goes to a subpanel.

I did some voltage measurements in the panel. Here's what I measured:
  • baseline: 121.4V / 121.5V
  • all circuits on side A turned off: 122.3V / 121.3V
  • all circuits on side B turned off: 121.8V / 122.0V
  • baseline with A/C running: 121.8V / 121.0 V
  • after swapping hots on the 70A breaker with the A/C running: 121.7V / 121.0V

What can I try next?
 
  #12  
Old 10-16-15, 05:40 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,471
Received 16 Votes on 14 Posts
I think that Ray hit it in post #2, the utility distribution transformer is minimally sized for the average load. Oil-insulated utility distribution transformers are capable of handling large overloads for varying lengths of time without failing but a transformer larger than necessary for the average load wastes a lot of power and that power is a direct loss to the utility because it isn't metered to a customer.

Therefore, utilities routinely install transformers sized to the average load and during an overload condition the voltage WILL drop, often enough to be noticeable. Installing hard-start kits on the A/C compressors is a good idea under these circumstances and might lower the voltage drop upon starting to a level where the lighting will only be minimally objectionable.
 
  #13  
Old 10-16-15, 06:14 PM
Member
Join Date: May 2015
Location: USA
Posts: 3,138
Upvotes: 0
Received 0 Votes on 0 Posts
Well that's a good point, but what I don't understand, if that's the explanation, is why OP didn't see this before the panel swap?

The most obvious suspect is the connections OP made to meter base, as he said he wasn't sure they were truly tight. If one of the hots was connected poorly, you could get a dip on that leg when the a/c starts. But OP says lights dim on both legs. It can't be the neutral, because the a/c load (at least most of it) doesn't use the neutral. So if it is bad connection at the meter, it has to be both hots.

But that doesn't explain why OP sees dimming when neighbor's a/c turns on now, when he didn't before. Bad connections on his meter shouldn't change that at all.

The other fairly significant change was replacing the undersized conductors to the meter. 1/0 al with a #2 neutral is really undersize for 200 amp service. I suppose fixing this may have aggravated the current surge when the a/c starts because the impedance of the feed is lower now so the surge current would be higher. That could cause the transformer to droop when it didn't before. But again, this doesn't explain why blinking is seen when the neighbors' ac turns on.

Doesn't add up.

OP: are you positive you see the blinking when the neighbor's ac starts and you didn't before? Or are you just more aware of it now?
 
  #14  
Old 10-16-15, 07:54 PM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
Well, I can't be positive this wasn't happening before I swapped the load center, but I used to notice that the lights did NOT flicker when the A/C came on. The lights did used to flicker occasionally, but it was rare enough for me to think, "hmm, I wonder why the lights are flickering."

My old load center was a Federal Pacific box with separate bus bars for the light circuits. Electrically, you could think of it as a subpanel for the all the single-pole lights within the load center. (See image below.) The bus bars for the lights were isolated and connected to the service via a large breaker and wires. I'm wondering if this setup isolated the lights more from surges caused by the A/C. In other words, the problem was always there, but the Federal Pacific box isolated the light circuits.

Name:  old federal pacific load center.jpg
Views: 1031
Size:  47.6 KB
 
  #15  
Old 10-16-15, 08:53 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,471
Received 16 Votes on 14 Posts
Doesn't add up.
Yes, it does. You are simply not seeing the forest because of all the trees.

Prior to the installation of the new service conductors he had a significant voltage drop across those conductors whenever his A/C started. That voltage drop somewhat lessened the additional load on the transformer and therefore was not usually noticed on his lighting. Add in that his old "split bus" service panel had several more points where there could have been a significant voltage drop on the way to the lighting circuits and it can be seen that the accumulation of these various voltage drops could have definitely subjected the lighting circuits to enough of a constant voltage drop that the lowering of the transformer output voltage because of an overload condition would have been fairly minimal at the lighting circuits.

The dimming of his lights due to an event outside of his service is a CLASSIC symptom of an overloaded transformer. Since the voltage sag at the transformer does not go below the accepted range of the utility AND because it is of short duration, the utility is in no hurry whatsoever to put in a larger transformer. The dimming of the lights is a transient event, causes no harm to the transformer and is only a minor inconvenience to the customers.

The most obvious suspect is the connections OP made to meter base, as he said he wasn't sure they were truly tight.
No, he stated:
I tightened them down with my screwdriver until I couldn't turn them anymore,
so unless he was using a jeweler's screwdriver the tightness was almost certainly sufficient. I will admit that there is a slight possibility that corrosion from the previous aluminum conductors may not have been thoroughly removed from the meter base connections but I really doubt that is the problem and IF it was he most likely would not see the transient events due to a neighbor's load increases.

1/0 al with a #2 neutral is really undersize for 200 amp service.
No, 1/0 aluminum is rated for 100 amperes at 60[SUP]o[/SUP] C. The maximum unbalanced load on a 200 ampere service is...100 amperes. Further, as you state, the neutral doesn't even enter the picture because the A/C IS a balanced load. All things taken together equals an overloaded utility transformer but not so overloaded as to require upsizing.
 
  #16  
Old 10-17-15, 06:49 AM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
That seems like a good analysis to me.

One other data point I just remembered... While I was doing the load center replacement work, I was borrowing power from my neighbor via an extension cord. I noticed that when his A/C came on, my work light flickered, and I thought, "That's annoying; I'm glad I don't have that problem." So I know my neighbor also experiences flickering lights when his A/C comes on. I'll have to ask him if he knows when my A/C comes on too.

It's still a mystery to me why I didn't have flickering lights before. I guess I have to assume it was some combination of the way the old Federal Pacific panel was wired and the smaller SE conductors.

What else can I do at this point? Keep pestering the power company? Ray suggested a hard start kit on my A/C, and I need to go learn about that. Are appliances like my fridge at risk due to this voltage drop? Is there such a thing as a "whole-house capacitor" I could wire into the load center?
 
  #17  
Old 10-17-15, 08:36 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,597
Upvotes: 0
Received 13 Votes on 11 Posts
The hard start kit is good but it won't solve the problem if your neighbors A/C is causing the flickering too.

One reason not mentioned is one (or more) of the neighbors on the same transformer may have increased their load at about the same time you redid your panel.
 
  #18  
Old 10-18-15, 02:15 AM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,471
Received 16 Votes on 14 Posts
What else can I do at this point? Keep pestering the power company? Ray suggested a hard start kit on my A/C, and I need to go learn about that. Are appliances like my fridge at risk due to this voltage drop? Is there such a thing as a "whole-house capacitor" I could wire into the load center?
I agree that a hard start kit would help with your A/C and you could help your neighbor to install a hard start in his A/C. They aren't all that expensive, generally less than $30 for the kit and a relatively easy install...meaning it is definitely a DIY job for anyone with some electrical experience. Try Ebay for the best selection and pricing.

I doubt that your refrigerator is at risk, unless the voltage drops to lower than 110 volts and according to the results given to you by the utility your voltage doesn't come anywhere near this low. I have never heard of any capacitive device used to lessen voltage sag under overload transients. Generally, capacitors are used for power factor correction in industrial facilities to reduce utility charges assessed due to low power factor. Since power factor is never considered in residential systems there is no advantage to adding capacitance to your system.
 
  #19  
Old 10-18-15, 06:30 AM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
Yesterday evening I was running my shop vac and noticed that the lights in the living room got brighter when the vac was on. So I did a test where I added a lot of load to one hot (two vacuums, microwave, and wife's hair dryer). I measured voltage and saw 119V on one hot and 126V on the other. Such a small difference, but noticeable on my lights. This must be a neutral problem, right? I'll try to get the power company back out to see if they can find it.
 
  #20  
Old 10-18-15, 06:36 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,471
Received 16 Votes on 14 Posts
Yes, having that much of an imbalance IS indicative of a neutral problem. I would try to be there when the utility people show up so that you can replicate the problem and let them use their meters to verify that a problem does exist.
 
  #21  
Old 11-20-15, 07:43 AM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
I had the power company out to the house today. For reference for other users, here's what the power company electrician had to say about my voltage question.

1. The voltage must be regulated to +/-5% per phase at the meter. That means a voltage difference of up to 12V between the two phases is acceptable.

2. The load test done at the meter was basically a massive 20A hair dryer. The load is applied to one phase at a time. At my meter, a drop of 3.5V was measured on each phase. Since this remained within the 114V-->126V range (i.e., +/-5%), it's acceptable.

Thanks to everybody for all the advice!
 
  #22  
Old 11-20-15, 02:34 PM
Member
Join Date: Mar 2010
Location: USA
Posts: 3,441
Upvotes: 0
Received 9 Votes on 9 Posts
Reviewing the bidding:

1. You did not notice dimming or flickering before you did this project.
2. You now notice some seesawing of voltage (some lights brighten under load elsewhere).

Conclusion: There is some difference or compromising regarding the neutral that was not there before. While you might let it go for the time being, you should keep an eye on things in case it gets worse.
 
  #23  
Old 11-20-15, 11:06 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,471
Received 16 Votes on 14 Posts
If the power company electrician actually used the term "phase" and mentioned "two phases" then he is not all that bright. You have a SINGLE PHASE service, the two wires are LEGS off of the center-tapped transformer secondary. Two-phase power is extremely rare and only used in a very few, very old industrial situations.

I would call the utility and demand to speak with an electrical engineer.

I am still leaning to the problem being an undersized transformer for the total load.
 
  #24  
Old 11-21-15, 07:36 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,911
Received 17 Votes on 12 Posts
If the power company electrician actually used the term "phase" and mentioned "two phases" then he is not all that bright.
Power companies don't employ electricians, they employ linemen. The guy the OP had at his house evidently was a lineman who had advanced his career to be a trouble guy. His terminology was definitely wrong, but I can excuse that if he was just trying to explain the situation to the homeowner in terms the homeowner could understand. From the beginning of this thread we have been talking about flickering, but I seriously doubt that is what is happening. Flickering is almost always caused by a poor connection and happens erratically. Since the problem only occurs when the a-c compressor is starting, I believe what the OP is getting is no more than a somewhat normal dimming of his lights. Yes, the transformer could be overloaded too making the problem worse. It is the homeowner's responsibility to inform the power company when loads are added, but few actually do this. Some dimming is perfectly normal even in a new subdivision. Furd is right, the OP needs to discuss this with an engineer, but in the end I believe the hard start kit installed on the a-c condensing unit is the best solution.
 
  #25  
Old 11-21-15, 07:48 AM
Member
Thread Starter
Join Date: Feb 2014
Location: USA
Posts: 164
Upvotes: 0
Received 0 Votes on 0 Posts
I've got the A/C hard start kit on my list of things to do before next summer.

Yesterday the lineman did find a very loose connection on one of the legs on the power company side of the meter socket. Maybe that was causing some of the dimming I was seeing when the A/C would come on. It did not affect the difference in voltages on the two legs when I apply a lot of load to one leg.

Electrical loads are pretty low right now since my neighbors and I all have gas heat. I'll repeat the measurements this summer when loads are high again. Even if I talked to an engineer, I don't think I'll get any action from the power company unless they can measure the problem themselves.
 
  #26  
Old 11-21-15, 07:56 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,911
Received 17 Votes on 12 Posts
Yesterday the lineman did find a very loose connection on one of the legs on the power company side of the meter socket.
That might solve the problem. Was this connection just made up when your panel was changed or was it a poor connection before that? If the loose connection has been there all along it wouldn't likely be causing dimming to be worse than before the panel change.
 
  #27  
Old 11-21-15, 01:28 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,471
Received 16 Votes on 14 Posts
Power companies don't employ electricians, they employ linemen.
I will concede that SOME power companies may not employ electricians but the utility I worked for (forty years ago) did indeed employ electricians, albeit ONLY for inside (inside the utility's premises) construction. I rarely had any contact with the line-workers (yes, we had women line-workers) but of those I did talk with they were generally pretty sharp people.
 
  #28  
Old 11-21-15, 05:33 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,911
Received 17 Votes on 12 Posts
I rarely had any contact with the line-workers (yes, we had women line-workers) but of those I did talk with they were generally pretty sharp people.
Thinking back many many years ago I had a friend whose daughter worked on a crew for the electric utility, the blasting crew. She was good at her job and in just a few years was the crew leader. She was defintely pretty sharp.....and was good at her job too.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes