220.61 (B) (2) Applying additional neutral derating

[Jpflex]

If you have calculated a single phase 120/240 Volt, 18 unit multi-family dwelling load calculation at 277,104 VA for ungrounded conductors and 181,944 VA for grounded conductor (demands for stoves and dryers included)

Then 220.61 (B) (2) permits derating an ADDITIONAL 70% to the already reduced neutral ampacity if:

1. The calculated neutral conductor current is over 200 ampere and
2. The neutral conductor load is OTHER THAN NONLINEAR LOADS such as electric discharge lighting


My question is that every home is expected to have non linear load computers connected to the general purpose lighting load receptacle branch circuits or leds or fluorescent lights possible in the future so would applying an addition 70% neutral ampacity reduction be acceptable. We cannot know what loads will be served later but a service is installed now!

Or what if you have one small LED light bulb in a one closet? Would just one reactive non linear load stop you from being able to use this demand reduction?

 

[LarryFine]

I believe it is a reduction to 70%, not a reduction of 70%.

The universal neutral minimum is the required EGC size.

 

[Jpflex]

Ok ok getting picky on wording lol but my intention was 70% of previously defeated neutral grounded conductor

 

[Jpflex]

Defeated = derated (phone changed word)

 

[LarryFine]

Didn't mean to be pedantic; that's a big difference.

Non-linear loads are actually less prevalent today.

 

[Jpflex]

Didn't mean to be pedantic; that's a big difference.

Non-linear loads are actually less prevalent today.

I’m aware that many reactive or non linear loads have much improved power factor and less distortion on voltage current waveforms but this code is still here.

The code says we can’t derate the neutral that is over 200 amperes to an additional 70% with these type of loads?

So will having one or two small LED bulbs common for lighting actually stop us from using this rule for an entire grounded conductor feeder or are we really going to have to install all units with old school inefficient incandescent resistive bulbs just to qualify?

 

[Jpflex]

I believe it is a reduction to 70%, not a reduction of 70%.

The universal neutral minimum is the required EGC size.

I just meant the neutrals ampacity is reduced to 70%

 

[LarryFine]

ISo will having one or two small LED bulbs common for lighting actually stop us from using this rule for an entire grounded conductor feeder or are we really going to have to install all units with old school inefficient incandescent resistive bulbs just to qualify?

I say neither. If you're really concerned, ask whomever will be plan reviewing or inspecting.

 

[Jpflex]

I say neither. If you're really concerned, ask whomever will be plan reviewing or inspecting.

So it’s up to the inspector but technically this is what the code states?

 

[don_resqcapt19]

I just meant the neutrals ampacity is reduced to 70%

There are two parts to 220.61(B) that will apply to your example.

First you can reduce the calculated neutral load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and electric dryers where you have determined that load by using Tables 220.54 and 220.55, to 70%.

The second part lets you reduce the neutral load that exceeds 200 amps to 70%. So if the calculated neutral load is 400 amps, the neutral conductor would have a minimum ampacity of 340 amps.

While the code does not say it, there is no additional neutral current for non-linear loads on a single phase system. The neutral current is not additive like it is with a 3-phase system.

From Hammond Power Solutions:
Today, non-linear loads make up a large percentage of all electrical demand. Rectified input, switching power supplies and electronic lighting ballasts are the most common single-phase non-linear loads. Harmonic currents and voltages produced by single phase, non-linear loads which are connected phase-to-neutral in a three phase four wire system, are third order, zero sequence harmonics (the third harmonic and its odd multiples – 3rd, 9th, 15th, 21st, etc., phasors displaced by zero degrees). These third order, zero sequence harmonic currents, do not cancel but add up arithmetically on the neutral bus, creating a primary source of excessive neutral current.

 

[Jpflex]

There are two parts to 220.61(B) that will apply to your example.

First you can reduce the calculated neutral load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and electric dryers where you have determined that load by using Tables 220.54 and 220.55, to 70%.

The second part lets you reduce the neutral load that exceeds 200 amps to 70%. So if the calculated neutral load is 400 amps, the neutral conductor would have a minimum ampacity of 340 amps.

While the code does not say it, there is no additional neutral current for non-linear loads on a single phase system. The neutral current is not additive like it is with a 3-phase system.

With that said, if the customer told me he later planned to install fluorescent lighting then would I have to install a larger neutral conductor (without 70% derating over 200 I amperes?). Perhaps you already answered this?

I need a good book on harmonic currents and its application in NEC any ideas?

 

[don_resqcapt19]

With that said, if the customer told me he later planned to install fluorescent lighting then would I have to install a larger neutral conductor (without 70% derating over 200 I amperes?). Perhaps you already answered this?

I need a good book on harmonic currents and its application in NEC any ideas?

In my opinion, there is no issue with non-linear loads on single phase systems as far as neutral current.

Not sure about any books, but over the years there have been lots of articles in the various trade magazines, but in almost all cases, those articles were written by someone who has an economic interest in helping you solve those "problems"...in other words there articles were not unbiased articles, but advertisement identifying as articles.