[RePhase277]

Now I know what the say about harmonics theoreticaly but I would like some input practically
I have heard rumors that it buned holes in cabinets in ny state and elswhere I have also heard that if you put a neutral with each circuit that this will eliminate them
Mabe we can get some input from overseas. GB Nor etc.

Yes, odd harmonic currents are additive on a shared neutral when more than one phase is involved. I have read that on 3-phase feeders supplying HID lighting with say 100 amps on each leg, the neutral current may be as high as 140 amps!

This occurs with fluorescent as well, and computer equipment. Pretty much anything with an electronic switching power supply. You can either over-size the neutral, so called "super neutrals", or use a separate neutral for each leg. As far as pipe fill goes, whether you use a super neutral or three individual neutrals, they are considered current carrying.

InPhase277

 

[gampa]

I have read a lot of theory on this subject but what I am driving at is there anyone who has seen resultant problems with harmonics
Electricity is a theory , what we have learned over the years is the practcal aspect of this phenominom. In reality we don't relly know what electricity is . We have theories and the older we get the more fasinating this phenominom is
eg : does electricity flow from pos. to neg outside the battery or neg to pos. also does electricty flow . Now harmonics can be a very bad thing or it can become a good thing Tesla experimented with Harmonics

 

[RePhase277]

I have read a lot of theory on this subject but what I am driving at is there anyone who has seen resultant problems with harmonics
Electricity is a theory , what we have learned over the years is the practcal aspect of this phenominom. In reality we don't relly know what electricity is . We have theories and the older we get the more fasinating this phenominom is
eg : does electricity flow from pos. to neg outside the battery or neg to pos. also does electricty flow . Now harmonics can be a very bad thing or it can become a good thing Tesla experimented with Harmonics

OK, yes I have seen the results of harmonics on neutrals. Granted, it was nothing fantastic, like cabinets with holes burned in them, but a real effect for sure.

I did the electrical remodel on the Golfsmith golf stores in Ga. The old low bay MH lights were powered from multi-wire circuits, with a shared neutral. As we started to replace them, from the front of the store to the back, I started finding overheated wirenuts in j-boxes as we approached the back. That is, the greatest load was nearest the panel. At the panel, the neutral was actually cooked, but the phase wires were fine.

We installed new lights that guaranteed low harmonics, but I opted to go ahead and go one size larger for the neutral to the first few j-boxes. I left the #10 phase conductors, and pulled in a #8 neutral to the first two j-boxes. I wish I had put an amprobe on that neutral, looking back.

InPhase277

 

[gampa]

Thank you for the input

 

[brian john]

I have been involved in harmonic investigations since the word became the BUZZ word, replacing "bad grounding" for the likes of the Kennedy assassination and the Lindberg kidnapping.

1. Most electrical systems I have encountered are over sized and harmonics is not an issue.
2. Harmonics as noted are blamed for many things, few if any are true.
3. In 25 plus years I have only ever run across a few systems with issues and as noted these were loaded to the max, casino, and call centers.
4. In the early days of VFD there were some utility transformer issues, because the utilities like to operate at or near full load for efficiency, the VFD's smoked their transformers.
5. Early electronic relays (protective relays on HV gear) did not recognize the distorted current waveforms and could malfunction.
5. With generators harmonics are an issue as the source impedance is so small when compared to the utility. I have had a few issues lately with elevators on generators where the elevators had VFD or converters.

There are cases where harmonics have caused issues, but most stories are overblown. We do hundreds of IR surveys every year over load neutrals show up due to the heat. Most overloaded neutrals are a result of improper installation, multi-wire branch circuit with two energized conductors on the same phase. I have NOT seen any lighting circuits of any type on a multi-wire branch circuit where current was excessive on the neutrals. This includes 3 phase 4 wire loaded to the max on the phase conductors.

Elevator start up on generator. Now this is a problem!

 

[RePhase277]

The Lindbergh Baby? Wow, Brian, you are absolutely ancient:thumbup:! You've got Keith Richards beat as the worlds oldest man!

But I guess I should add that on our lighting change out, this effect was only seen on one out of 11 total lighting circuits. That's why I wished I had put an amprobe on the circuit to see how many actual amps were flowing, because the actual connections were fine as far as we could find. No loose terminals on the neutral bar, and no bad taps. Just a fluke of nature, I guess?

InPhase277

 

[brian john]

Harmonics do cause issues, but IMO the concern has been overblown. Part of this is the copper industry and the PQ industry as they have solutions to problems, that while real are overblown.

When I go to customers sites and they have equipment operational issues the first thing said is we need more ground rods second thing is must be harmonics, and the solution? software glitch or hardware issue.