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Old 01-27-2015, 11:19 PM   #1
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Default Harmonics

Delta/Delta feed to a Delta/wye configured transformer. If there is a ground grid just outside the building is it a good idea to take the XO bond uninterrupted out to the grid in order to lessen the effects of harmonics due to the vast switching power supplies in the installation rather that taking it to the transformer case/building steel?
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Old 01-28-2015, 12:20 AM   #2
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I would think it couldn't hurt to take it to the best ground possible...

I did a job adding a radio tower and a new PLC and their spec for the ground grid (to an existing site) was 3 - 60' rods and a 750 MCM cad welded or c-tapped in a "Y" configuration, to avoid circulating ground currents... I haven't had heard the term much before or since, but it made sense at the time - except the wire size baffled me...

I don't recall the distance we were spec'd a couple of times for an isolated ground grid to be away from the main service ground grid... One engineer said we had to tie the two grids together and he got "ALOT" of resistance from everyone, including the controls engineer.... He was insistent that they be kept separate and used only for the PLCs and DCSs...
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Old 01-28-2015, 01:30 AM   #3
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A ground is a ground. It's all one system. You don't hear that ground recirculating thing anymore, just like the isolated grounds for computers.
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Old 01-28-2015, 01:53 AM   #4
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This subject is beyond my pay grade but how does a ground affect harmonics produced by equipment that hum along the power lines?
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Old 01-28-2015, 07:12 AM   #5
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A ground is a ground. It's all one system. You don't hear that ground recirculating thing anymore, just like the isolated grounds for computers.
Recirculating current is very prevalent but has nothing to do with harmonics it has to do with hacky wiring or accidental faults on the neutral/grounded conductor and occasionally one side of a resistive heater faulting to ground.
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Old 01-28-2015, 07:13 AM   #6
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A ground is a ground. It's all one system. You don't hear that ground recirculating thing anymore, just like the isolated grounds for computers.
I agree, I do not see how a better Earth ground is going to do anything to minimize harmonics. From the source to the load and back, nothing is going to Mother Earth in that mix.
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Old 01-28-2015, 09:23 AM   #7
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Quote:
Originally Posted by RIVETER View Post
Delta/Delta feed to a Delta/wye configured transformer. If there is a ground grid just outside the building is it a good idea to take the XO bond uninterrupted out to the grid in order to lessen the effects of harmonics due to the vast switching power supplies in the installation rather that taking it to the transformer case/building steel?
Useless and won't meet code
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Old 01-28-2015, 10:55 AM   #8
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Quote:
Originally Posted by RIVETER View Post
Delta/Delta feed to a Delta/wye configured transformer. If there is a ground grid just outside the building is it a good idea to take the XO bond uninterrupted out to the grid in order to lessen the effects of harmonics due to the vast switching power supplies in the installation rather that taking it to the transformer case/building steel?
Excessive harmonics is a case for super neutrals, the grounding has nothing to do with it.
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Old 01-28-2015, 11:54 AM   #9
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Excessive harmonics is a case for super neutrals, the grounding has nothing to do with it.
What is a super neutral? Never heard that term.
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Old 01-28-2015, 12:11 PM   #10
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What is a super neutral? Never heard that term.
Not up on all the lingo here, but I am guessing IslandGuy is referring to an oversize neutral, which is one method to combat the effects of harmonics.

There are of course many other methods!

Borgi

Last edited by 51360; 01-28-2015 at 02:16 PM. Reason: Correction
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Old 01-28-2015, 12:11 PM   #11
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What is a super neutral? Never heard that term.
Ramen noodles me thinks, or big arse white wire
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Old 01-28-2015, 12:16 PM   #12
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Damn, Borgi and I both hit it at 11:11, he must of beat me by a second - same difference.
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Old 01-28-2015, 01:00 PM   #13
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In a high harmonics situation your neutral typically has a higher current than the phase conductors. With a regular sized neutral, you will overload the conductor. The oversized (super) neutral deals with that issue. It does not remove the harmonics.
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Old 01-28-2015, 01:45 PM   #14
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I think we digressed, the OP was questioning the use of the ground or ufer and not the neutral.
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Old 01-28-2015, 10:06 PM   #15
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Ideally you would take it to the best ground possible but that's irrelevant. Building steel, ground ring, all of it qualifies for use to attach the GEC.

To eliminate overload and overheating due to harmonics, you double the size of the neutral (going by the circular mils) or pull a second neutral from the secondary side to the subpanel(s) that secondary serves. That's what a super neutral is. A neutral increased in size to accommodate the extra load caused by harmonics

Most subpanels that serve a lot of computers or fluorescent lighting loads, or data racks are being spec'd out to have a 200% neutral
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Old 01-28-2015, 10:09 PM   #16
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Harmonics only affect neutrals of 120/208Y MWBC's and even then it's prob due to bad installations. Grounding won't help at all.

Super Neutrals?

Last edited by Helmut; 01-28-2015 at 10:15 PM.
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Old 01-28-2015, 10:14 PM   #17
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There are no harmonics in a 120/240V system, which is why they are used for applications where harmonic producing equipment is used.

Oversizing neutrals is a waste of money.
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Old 01-28-2015, 10:45 PM   #18
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Harmonics only affect neutrals of 120/208Y MWBC's and even then it's prob due to bad installations. Grounding won't help at all.

Super Neutrals?
So the Harmonic Filter on the side of the 1,000 hp VFDs I work on do nothing? I beg to differ....
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Old 01-29-2015, 12:54 AM   #19
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I can see the oversize neutral to a panel, but at the MDP to the xfmr,? How far do you go.
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Old 01-29-2015, 07:22 AM   #20
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Quote:
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What is a super neutral? Never heard that term.
IN 95% of the cases I have seen it used it is an over sell of copper.
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