Low Voltage in a new house

[Dennis Alwon]

I am posting this for member Lejos who was having trouble posting. Lejos remember that posting may take awhile on your first posts. His post attempts do not appear to have made it so here it is.

Having a problem with voltage drop in new house. The lights dim when an iron or vacuum is turned on and the voltge drops 2-3 volts on the circuit.I checked all connections at the service and everthing is tight. I called the PC and they changed the tranformer at the pole and pulled the underground and checked the service wires. They put meters in side the house and at the service and said the voltage is droping in the house,but not at the service.
The service is a 200 amp actually the service is larger than needs to be. The house is 1800 sq. and has ac,dryer,and a range. The power pole is about 200 ft away for the house. I checked the voltage at the supply side of the meter and the voltage is fluxsuating 2-3 volts. The PC is saying their side is ok.

 

[Dennis Alwon]

I don't think a voltage drop of 2 or 3 volts is really that bad considering the trany is 200 feet away. Of course, it would depend on the size the Podco ran to the meter.

Make sure all your connections are tight. Not sure what else you can do.

 

[iwire]

I was thinking 2 or 3 volts is to be expected.

And for whats it's worth there are no posts pending approval.

 

[Lxnxjxhx]

10 A at 3 v = 60' (120' round trip) of AWG #14.

 

[brian john]

Light flicker (dimming and restoration of light to near preflicker level) of lights from motor inrush) is a byproduct of several factors and generally is difficult to over come.

AC motor loads (in particular compressors) but all motor loads have inrush currents. These inrush currents result in voltage drop in the branch circuit, panel bus, service laterals, utility transformer and possibility the utility HV feeders.

Flicker is in addition user dependent; some people are more susceptible to flicker. For some reason flicker seems to bother women more that men (based upon personal experience).

A Voltage Drop (VD) as little as 3 volts on a nominal 120 VAC system is noticeable (by me), 2.5% VD.

We have had cases were the VD was all a byproduct of primarily single phase 120 VAC loads, in these cases we were able to put the lighting on L1 and all the motor loads on L2, the HVAC compressors were something the homeowner had to live with. This minimizes the flicker.


To test for this VD and resulting flicker to determine the source of the inrush, use a min max amp clamp and min max multimeter at the main service watch the lights(it may take two workers) and correlate to the meters.
__________________

 

[Lxnxjxhx]

is noticeable

is noticeable

For incandescent bulbs a 3% voltage drop gives 100 x [1-{(0.97)^(3.5)}] = 10% drop in intensity.

 

[brian john]

10% drop in intensity.

I have been hired by contractors and home owners, almost all women or men trying to pacify their wives or customers, to determine the cause of flicker. I would really like to know how you arrived at this percentage (Seriously). I can tell you most of the woman involved swore it was a 100% drop in intensity. After the last job I did I increased my rates for this service, due to the massive head ache I had at the end of the day.

 

[Lxnxjxhx]

I would really like to know

I would really like to know

Incandescent lamp intensity varies with the voltage raised to the 3.5 power. Life varies with the voltage raised to the 12 power. The cold filament resistance is 10x to 15x lower than the hot resistance.
If you don't have a scientific calculator to handle this you can put a formula into a spreadsheet.

So, running on 97% of the original voltage gives you (0.97/1.00)^(3.5) = ~0.9 [that is, 90%] of the original brightness.

I'm sure each lamp manufacturer has their own pet exponents and, with advancements, these numbers might be somewhat different.
When they want more accuracy they use nomographs, which take into account all kinds of effects not covered in the 3.5 exponent.

I'd e-mail manufacturers for these formulas if you need them unless you can readily find them on the Internet.

Also, electric heat applies the load in steps, which isn't so noticeable, so I don't think it's the dimness as much as the change.

Scientific calculators and spreadsheets come in very handy for debunking salespeople's puffery.
Let's say you bought your house 13 years ago for $100K and now it's worth $400K. What yearly interest rate would you need to equal this?
X^13 = 400/100, so X = (400/100)^(1/13) = 1.11. That is, 11% interest.
If you even make 5% you're probably doing well, and the fees at each end make this even less. Don't tell your realtor.

And there is the "Rule of 72", which I used when a co-worker tried to tell me that I could double my money in seven years with US Savings Bonds (which he was pushing). He somehow got transferred somewhere else after this.

If the price of bread doubles in 18 years, what's the rate of inflation? 72/18 = 4%.