Harmonics Question.

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Knuckle Dragger

Knuckle Dragger

Master Electrician Electrical Contractor 01752
Location
Marlborough, Massachusetts USA
Occupation
Electrical Contractor
I was helping out a fellow electrician this week with meter assembly replacement. The pad mount transformer is feeding a four gang pedestal mounted meter socket on the same concrete pad (the line and all four loads are underground).

There were a lot of issues with this one job but I want to deal with one just to make a long story short.

The original neutrals were bugged together I am talking the 350mcm and all four 4ott cable to make one big splice that never made it into the meter sockets, they were spliced in a can that made up the pedestal so only the two 4ott loads went into a 2inch pvc conduit. I would say the total distance from the meter socket load and the neutral wad was 22 inches.

My question is what kind of harmonics issue are we dealing with?

Footnotes:
Each load feeds a 200amp residential panel, electric heat, hot water, a/c stove etc.
Thanks for your help!!
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Knuckle Dragger said:
Thank you!!
It is 120/240 volt.
There is no harmonics issue because basically because the two hot legs of different potential are cancelling each other out.
Am I understanding that correctly?
Click to expand...
What will happen is that for three wire single phase service the triplen (odd multiple of three) harmonics will still cancel out on the neutral, if balanced. But if you have a load that is generating second, fourth, or other even harmonics then they will add in the neutral and you could have a problem with service and feeder neutral sizing and MWBCs.
However, there are few types of loads that will generate a strong even harmonic current, since it would affect the positive and negative voltage peaks differently.
A single diode half wave rectifier would be one possibility.
 
Knuckle Dragger

Knuckle Dragger

Master Electrician Electrical Contractor 01752
Location
Marlborough, Massachusetts USA
Occupation
Electrical Contractor
GoldDigger said:
What will happen is that for three wire single phase service the triplen (odd multiple of three) harmonics will still cancel out on the neutral, if balanced. But if you have a load that is generating second, fourth, or other even harmonics then they will add in the neutral and you could have a problem with service and feeder neutral sizing and MWBCs.
However, there are few types of loads that will generate a strong even harmonic current, since it would affect the positive and negative voltage peaks differently.
A single diode half wave rectifier would be one possibility.
Click to expand...

Thanks !!
I know you said there are few but where would I find a single diode half wave rectifier load in a residential setting. (what appliance would produce this)?
 
Besoeker

Besoeker

Senior Member
Location
UK
ptonsparky said:
I am sure he has what you need. Stop at the new shop down the street from him and you will be happy with whatever Dave gives you.
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Bit of a long (and expensive!) trip for me to make without having a comprehensive technical specification to peruse...........
:)
 
D

dlspooner

Member
Location
West Linn
Knuckle Dragger said:
I was helping out a fellow electrician this week with meter assembly replacement. The pad mount transformer is feeding a four gang pedestal mounted meter socket on the same concrete pad (the line and all four loads are underground).

There were a lot of issues with this one job but I want to deal with one just to make a long story short.

The original neutrals were bugged together I am talking the 350mcm and all four 4ott cable to make one big splice that never made it into the meter sockets, they were spliced in a can that made up the pedestal so only the two 4ott loads went into a 2inch pvc conduit. I would say the total distance from the meter socket load and the neutral wad was 22 inches.

My question is what kind of harmonics issue are we dealing with?

Footnotes:
Each load feeds a 200amp residential panel, electric heat, hot water, a/c stove etc.
Thanks for your help!!
Click to expand...
The lighting is the primary source of the harmonics induced by it's nonlinear load
 
Besoeker

Besoeker

Senior Member
Location
UK
dlspooner said:
The lighting is the primary source of the harmonics induced by it's nonlinear load
Click to expand...
Almost everything electronic in non-linear.
Computers, televisions, CFL and LED lighting, printers, washing machine motors, wall warts.............
 
Z

zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
Besoeker said:
Almost everything electronic in non-linear.
Computers, televisions, CFL and LED lighting, printers, washing machine motors, wall warts.............
Click to expand...

True, but how non-linear are they really? Phase-control dimmers and speed controllers can be downright ugly, but don't most modern electronics have PF control and harmonics mitigation? If I still had access to a decent power analyzer, I'd just check.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
GoldDigger said:
Yup, the direct drive multiple pole kind. But I suspect they have PF correction in their power supply too.
Click to expand...
Is that a sign I haven't had any dealings with washing machine motors in a long time?

So I take it the "essential parts" are still the same? :D
 
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