Replies

1. 
   CAP_ | Nov 06, 1999 04:28am | #1

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   Dave,

   Call your electrical utility company and say "loose neutral". If they aren't out there within a day, call back and get the chief of maintenance and say, "loose neutral".

   I gather that ALL of the lights in your house flicker when a motor kicks on. That implies that the power company's neutral connection (on the low-voltage side of the pole-top transformer) is loose. That's not good.

   If there are neighbors on the same transformer secondary, see if they're experiencing the same thing. If they are and also call the power company, you'll probably get real quick action.

   It could be a problem in your panel, but the power co. will come out for free and if it's not their problem, THEN you can call an electrician to troubleshoot your panel. The line crew might even take a quick look if you pass the attitude test.

   Good luck.

2. 
   Guest_ | Nov 06, 1999 05:36am | #2

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   I think that the loose neutral could cause the problem, but it is also very possible that the starting current of the motor is strong enough to cause the lights to dim but not strong enough to trip a breaker. I work with electrical distribution systems associated with nuclear-powered ships and submarines and can tell you that starting a huge motor will cause a momentary current surge, which causes a momentary voltage drop, which you can visually witness as all the incandescent lights dimming. V=I^2 * R. The wiring has fixed resistance. Changing the current appreciably can have a noticeable effect on voltage if the current is pushing the limit of that allowed for a specific wire gauge.

1. 
   Guest_ | Nov 06, 1999 05:54am | #3

   *I know very little about electrical issues however let me share this with you. When having a couple of electricians spec out a fairly large all electric house I'm building, both electricians told me that if I went with a 200A service, there may be some dimming of lights when the AC unit or other large appliance started up. They each told me that I needed to go to the next larger sized service in order to positively avoid this. Either they both went to the same salesmenship school, or there may be something to this "dimming Lights" thing.

1. 
   Guest_ | Nov 06, 1999 06:14am | #4

   *I concur. My current house is small-ish (1600 SF) and has 200 amp service, yet my lights dim when I turn on certain appliances, such as a television, the electric forced air furnace, or a 1500-watt hair dryer. The dimming is explicably more pronounced for lights on the same circuit, but some degree of dimming does occur on all circuits.BTW, what is the next size electric service?

1. 
   Guest_ | Nov 06, 1999 06:14am | #5

   *Yes, basically when the current runs up the resistance of the feeder becomes a big issue. When a motor starts it momentarily draws a lot of current. Actually, whenever ANY load is added the voltage sags a bit; you can test this by attaching a sensitive voltmeter to a branch circuit and turning on a few lamps. Undersize branch circuits (either in gauge or length) will experience excessive voltage sag on that branch; the same for undersize service, except now the whole house is starved for voltage. It's like trying to force a lot of water through a small pipe.Incandescent lights are particularly sensitive to voltage drop. A voltage loss of 10% translates into something like a 30% loss in light output. Also, I believe IsquaredR refers to the power dissipated in the conductor? I think you want E = IR, R being the sum of the load and wire resistance ... at low current the load resistance is high relative to the wire's and determines current flow at reasonably constant voltage; but as load resistance drops to a fraction of an ohm (high load) it becomes irrelevant and the wire's resistance important, choking current flow and causing voltage (I*R) to sag. (Or something like that, it's been a while!)BTW, we have a small house with 150-amp service but no dimming when the dryer or furnace blower or electric space heater fire up. Perhaps this is because most of the larger appliances are served by dedicated home runs to the breaker box (since I got here), segregated from dedicated lighting circuits, or that our drop cable is short.Certainly the present problem could have several causes and should be fixed. I like using the free option first, and the utility guys seem to know what they're doing. I believe 100 amp service is pretty much considered inadequate now, and may not even meet code for your house. Every year we seem to find more uses for electricity...

1. 
   Guest_ | Nov 06, 1999 06:16am | #6

   *Chris,Could you explain V=i^2*R?I'm not sure what V is in that formula.I know that power disipated as heat, usually designated as Ro (Greek letter for P), is often calcualted as i^2*R.I'm just a formula junkie and I need a hit.-Ryan

2. 
   Guest_ | Nov 06, 1999 06:24am | #7

   *Feeder wires that are too long or under sized can have a big effect on this. So can undersized (even if safe) wires in branch circuits.I ran into a similar problem when several large circulating pumps would start. We first put them on their own circuit. Then we used larger wires from the distrubution panels to the local circuit breakers. Then we had the utility put in larger feeder cables to the building. An Engineer for the utility finally solved our problem.The transformer was causing the problem. The transformer was adequately sized, actually larger than needed. Transformers, by their nature, cause electric supply to lag behind demand. The larger the transformer, the bigger the problem. The transformer could supply the all the power we needed, even the extra needed at start-up. It just took it a second to do so.We had a second transformer installed with a new service entrance that only supplied these motors (and an airconditioner for my closet/office that I slipped into the work order.)

3. 
   Guest_ | Nov 06, 1999 06:28am | #8

   *Oops! I confused two related formulas. P=power, I=current, V=voltage, R=resistance. P=I*V, V=I*R, thus ... P=I^2*R.

4. 
   Guest_ | Nov 06, 1999 06:38am | #9

   *Sheesh, no one ever listens to me. Oh well, all the better.

5. 
   Guest_ | Nov 06, 1999 06:44am | #10

   *Sorry Andrew,Went back an reread it. I see it now. You said it first.Use more pluses and square symbols. Words are great but anybody can use words. It takes a real show off to use the carrot to mean exponent.-Ryan

6. 
   Guest_ | Nov 06, 1999 06:12pm | #11

   *Yeah. I'm a words guy. And, unless you're unusually talented with vegetables, it's a "caret." :)

7. 
   Guest_ | Nov 06, 1999 06:48pm | #12

   *Yeah, I know. Read any of my posts and you'll see hundreds of those spelling errors. I still haven't got a grasp on this english thing. I've only been speaking it since I was 1-1/2.I used to spell check everything I sent out so I wouldn't look stupid but correcting errors took longer than typing the original message.

8. 
   Guest_ | Nov 07, 1999 09:08am | #13

   *Dave;I second CAPs advice. If all the lights dim, it points to a service and not a feeder issue.I had a similar problem. Powered up a 220V/30A table saw and the house lights dim. This is in a separate building but on the same 400A service.As CAP points out, you will need to get past the first line at the power co...mine informed me that (a) I needed and electrician to install a larger service, and when I pointed out I had a 400A service, (b) there is no such thing as a 400A service. Be persistant.I had a loose neutral and an unbalanced transformer...funny things happened to the one leg when the other leg was drawn down. Actually replaced the transformer last Dec 31...they loved me (double time).Good luck

3. 
   Don_Minter | Nov 08, 1999 04:40pm | #14

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   I don't mean to sound pedantic, but I think a little explanation may help.

   Usually, dimming lights associated with large motors being started can be attributed to too much current being pulled too quickly. This is termed the "in rush current" when starting a motor. This can reach 6 times the full load rating of the motor. A fifteen amp motor can easily pull 90 amps when starting. By the way, breakers do not trip "instantaneously" when their nameplate rating is exceeded. I won't go into the details, but there is a delay in the trip time related to the amount of overcurrent being pulled. This allows you to start 15 amp motors on 20 amp breakers.

   The power company supplies power to thousands of users. They provide voltage levels from the familiar household 120 Volts AC through upwards of 20 thousand volts to industrial users. To get all of these levels, they use transformers. You will have multiple transformers between yourself and the source (the generator at the power company). Each of these transformers can cause a delay in current when a large change is introduced. Since the motor you are starting is going to pull the current it needs regardless, the excess current draw causes the voltage to droop (not drop). This voltage droop is what causes the lights to dim.

   To compensate for the delays introduced by transformers and transmission lines, power companies install large banks of capacitors. These are what make up the bulk of the large steel structures you see well off the road on power company substations. You know, the ugly things with the big fences and the signs telling you to stay away. If you are very far from one of these stations, then your whole neighborhood is having this problem.

   So, Mr. Hipp should follow the advice that has been given. Ask the neighbors if they also experience this light dimming. If they do, then this is the power company's problem. If they do not, then I would have my lighting panel inspected by a competent electrician. Well, actually, I'd inspect it myself, since I know what not to touch (rule of thumb, if it is metal and not painted don't touch it. Rule of thumb 2, if it is metal and painted, don't touch it, until you check it with a meter, then don't touch it unless you have to).

   He mentions the house being built circa 1970. I think they used aluminum wiring around then. If he has aluminum wiring, then he needs to check EVERY connection in his house for tightness. Aluminum wiring is not inherently unsafe, but the connections tend to loosen over time, and should be checked periodically. Also, when they first started using the AL wiring, I seem to remember there being something about some commonly used (for copper wire) connectors that were not appropriate for aluminum. I was very young at the time, so I'm not positive about the connector issue.

   Now, I have a question. What do you mean by a "loose neutral?" I've been around power for twenty years, and I've never heard the term. I know the difference between a neutral and a ground, and I'm well-versed in the technical aspect of electricity, so please enlighten me. Just the short version will do.

4. 
   Don_Minter | Nov 08, 1999 04:40pm | #15

   *
   I don't mean to sound pedantic, but I think a little explanation may help.

   Usually, dimming lights associated with large motors being started can be attributed to too much current being pulled too quickly. This is termed the "in rush current" when starting a motor. This can reach 6 times the full load rating of the motor. A fifteen amp motor can easily pull 90 amps when starting. By the way, breakers do not trip "instantaneously" when their nameplate rating is exceeded. I won't go into the details, but there is a delay in the trip time related to the amount of overcurrent being pulled. This allows you to start 15 amp motors on 20 amp breakers.

   The power company supplies power to thousands of users. They provide voltage levels from the familiar household 120 Volts AC through upwards of 20 thousand volts to industrial users. To get all of these levels, they use transformers. You will have multiple transformers between yourself and the source (the generator at the power company). Each of these transformers can cause a delay in current when a large change is introduced. Since the motor you are starting is going to pull the current it needs regardless, the excess current draw causes the voltage to droop (not drop). This voltage droop is what causes the lights to dim.

   To compensate for the delays introduced by transformers and transmission lines, power companies install large banks of capacitors. These are what make up the bulk of the large steel structures you see well off the road on power company substations. You know, the ugly things with the big fences and the signs telling you to stay away. If you are very far from one of these stations, then your whole neighborhood is having this problem.

   So, Mr. Hipp should follow the advice that has been given. Ask the neighbors if they also experience this light dimming. If they do, then this is the power company's problem. If they do not, then I would have my lighting panel inspected by a competent electrician. Well, actually, I'd inspect it myself, since I know what not to touch (rule of thumb, if it is metal and not painted don't touch it. Rule of thumb 2, if it is metal and painted, don't touch it, until you check it with a meter, then don't touch it unless you have to).

   He mentions the house being built circa 1970. I think they used aluminum wiring around then. If he has aluminum wiring, then he needs to check EVERY connection in his house for tightness. Aluminum wiring is not inherently unsafe, but the connections tend to loosen over time, and should be checked periodically. Also, when they first started using the AL wiring, I seem to remember there being something about some commonly used (for copper wire) connectors that were not appropriate for aluminum. I was very young at the time, so I'm not positive about the connector issue.

   Now, I have a question. What do you mean by a "loose neutral?" I've been around power for twenty years, and I've never heard the term. I know the difference between a neutral and a ground, and I'm well-versed in the technical aspect of electricity, so please enlighten me. Just the short version will do.

5. 
   Guest_ | Nov 09, 1999 09:34am | #16

   *
   400 Amps !!

6. 
   CAP_ | Nov 09, 1999 09:50am | #17

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   Don--

   "loose neutral" is a catch-all for a high-impedence condition in the service neutral conductor. Poor splice (loose split bolt in OLD service drops), loose clamp at x-former, etc.

   The high impedence of the neutral effectively reduces the ampacity of the service for the phase-to-ground. Phase-to-phase, no change.

   So what you get is voltage droop whenever a motor starts.

   Cliff

   ps you were't pedantic a'tall.

7. 
   Guest_ | Nov 09, 1999 09:37pm | #18

   *
   Don,

   I like your rule of thumb.

   Dave,

   Your problem is probably not a loose neutral. With a loose neutral when a load is applied to one leg, lights on that leg wil dim but lights on the other leg will get BRIGHTER. Loose neutral is a good term to get th utilities attention thou.

   Most likely your problem is an undersized drop from the pole or a poor connection to one or both of the hot leads (if ALL of your lights are dimming. When you upgrade to a larger service, the utility usually DOESN'T change the drop. I have a 100A service with almost 30 circuits and I have never measured over a 65A total load. I did have the utility put in a larger drop.

   Ron

8. 
   Dave_Hipp | Jan 04, 2000 11:29pm | #19

   *
   Moved into house built in 1971, with 100A service. Whenever a motor turns on (sump or well pump, washer, etc.) the lights dim in the house. Can this be fixed by balancing the breakers on each bus or do I need larger service (150A or 200A)?