Higher Voltage measured at equipment.

[c_picard]

When under load, if we see a Higher measurement (~256V)at the equipment terminals than at the breaker feeding the equipment(~245V), would you start by checking the mechanical propertied of the circuit? Total length of circuit is only about 15ft, current 20A.

Torque at terminations?

 

[augie47]

Excuse the elementary question..but..are you using the same meter at both locations and what is the time frame between measurements ?

 

[c_picard]

No worries...great question.

Same meter, and verified data using remote monitoring of the equipment(PV Inverter).

Not instantaneous measurements at both locations, but have repeated the test several times and results are consistent.

I have seen this be a grid issue before (xfmr inadequately sized), but in those instances voltage readings are high at the service also.

 

[gar]

130605-0936 EDT

c_picard:

I believe your circuit description is inadequate.

In your first post there was no mention of a PV inverter. Thus, results seemed fishy.

A more accurate description is needed. Breaker feeding equipment implies the source of energy is from the breaker to the equipment. The word equipment in an electrical circuit as described in the first post would imply a load using energy. In this case except for resonant circuits the voltage at the load would be lower than at the source (breaker).

It appears from your second post that equipment is a PV inverter supplying energy to a system when you made your measurement. In this case it would be expected that the source voltage (inverter output) would be slightly higher than the destination of the energy (breaker being back fed).

11 V at 20 A is about 0.55 ohms. If we assumed #12 copper wire, then room temperature resistance is about 1.6 ohms per 1000 ft. Your length is 30 ft or about 0.03*1.6 = 0.0048 ohms. Something is wrong.

A better measurement is to measure the voltage drop along each leg of your circuit. Measure the voltage drop across each termination point, and along each wire.

Put your meter probes directly on each end of the 15 ft wire. Not on the terminal where the wire is terminated. At 0.0024 ohms and 20 A the voltage drop (difference --- your measurement) should be about 0.048 V or 48 mV. Do this on each wire.

See if this gives you a direction. Note: it is always better to make a direct measurement rather than taking the difference between two large numbers.

.

 

[c_picard]

Thanks for the guidance, and patience, this is a bit of a first year apprentice math problem! Apologies the original question wasn't as clear as it could have been.

I'll use the methods you describe to try and pinpoint where the point of high resistance is; I agree that something is wrong.
I had not thought of directly ,easuring the Vdrop on each conductor. This will be easy, the total circuit length was 15ft (7.5ft one-way).

Inverter is right next to main panel. I started off with a misunderstanding of how the inverter interacts with the breaker, I was led to believe that inverters behave as a load when troubleshooting, but clearly that doesn't make sense. i just never questioned it before.

 

[iwire]

Is the meter a true RMS one?

Maybe it is my own lack of education but I can't see how voltage could really increase as the measurements are taken closer to the load.

 

[GoldDigger]

Is the meter a true RMS one?

Maybe it is my own lack of education but I can't see how voltage could really increase as the measurements are taken closer to the load.

Because the "load" is actually a grid tied inverter. The power is flowing toward the panel.

 

[GoldDigger]

Inverter is right next to main panel. I started off with a misunderstanding of how the inverter interacts with the breaker, I was led to believe that inverters behave as a load when troubleshooting, but clearly that doesn't make sense. i just never questioned it before.

Right! The voltage waveform (shape and approximate voltage) is that supplied by POCO. During the positive peak of the AC wave if current is flowing from POCO to device the device is a load. If current is flowing from device to POCO the device is a supply. If all you look at is the magnitude of the current in one wire rather than the magnitude and phase you cannot tell the difference. But the wire resistance shows you the direction of the current, and it will either add to (supply) or subtract from (load) the POCO voltage.

 

[iwire]

Because the "load" is actually a grid tied inverter. The power is flowing toward the panel.

Well that certainly changes things.

 

[jumper]

I moved this thread to the PV forum.

 

[SolarPro]

Check the terminal torque values. A loose connection will increase resistance and cause voltage rise.

Here's a link to an article on the topic:

http://solarprofessional.com/articl...iderations-for-utility-interactive-pv-systems

 

[broadgage]

With any normal load such as a lamp, heater or motor, the voltage at the load will allways be less than at the panel, the difference may be significant or it may be trivial, but it will allways be less at the load.
An apparently higher reading at the load would suggest a defective instrument, operator error or a change in line voltage between taking the two readings.

In this case however what is connected is not truly a load at all, but is a SOURCE of energy.
The voltage at the source (grid tied inverter) will allways be higher than at the panel.
Again the difference may be significant, or may be trivial, but it MUST be higher at the inverter (presuming that it is running)

 

[kwired]

I find it a little hard to believe you will see any significant difference in voltage on either end of a conductor only 15 feet long unless there is some resistance in connections and you are measuring on each side of those connections, or the conductor is loaded well beyond its ampacity.

 

[GoldDigger]

I find it a little hard to believe you will see any significant difference in voltage on either end of a conductor only 15 feet long unless there is some resistance in connections and you are measuring on each side of those connections, or the conductor is loaded well beyond its ampacity.

And since the load is only 20A, the overloaded conductor is very unlikely.
Maybe the OP will come back to tell us where the problem was found. Wherever it was, it would have been developing a LOT of heat (11V times 20A).
The suspense is [reasonably likely to cause permanent injury and/or death].