# 200% rated neutral?



## cuba_pete (Dec 8, 2011)

This is kind of old-school common practice in commercial and industrial. They're counting on the load being unbalanced in the future. A high-harmonic load is compensated for with this method. Lightly loaded VFD's produce unbalance and more harmonics.

If the transformer is sufficiently K rated then this isn't an issue. With no regular PQ surveys the upsized neutral is just hedging the bet.


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## tates1882 (Sep 3, 2010)

cuba_pete said:


> This is kind of old-school common practice in commercial and industrial. They're counting on the load being unbalanced in the future. A high-harmonic load is compensated for with this method. Lightly loaded VFD's produce unbalance and more harmonics.
> 
> If the transformer is sufficiently K rated then this isn't an issue. With no regular PQ surveys the upsized neutral is just hedging the bet.


The 29 Vfds all have a hormonic filter in place. Its a custom built panel with no space for expansion. Just seemed overkill after spending money on filters.


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## cuba_pete (Dec 8, 2011)

That's good argument, but doesn't guarantee against the future.

It's still common practice for some engineers/electricians.


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## sbrn33 (Mar 15, 2007)

They just mean the panel board. pretty common nowadays. what does the schedule say for wire sizing.


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## RePhase277 (Feb 5, 2008)

The harmonics generated by the VFDs won't matter because they don't use the neutral anyway.


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## cuba_pete (Dec 8, 2011)

If the EE didn't expect future single phase loading, then they wouldn't be _delivering_ the neutral in the _first_ place.

High 3rd phase harmonic can cause high neutral current. The EE doesn't know what the future holds, including VFD engineering. Current IEC regulations for the VFD's should eliminate 3-phase concerns, though, sure.

200% does seem like overkill in an industrial situation. But they are _delivering _a neutral, so maybe there is _future_ growth that the OP doesn't know about (173% current with unbalance and/or harmonics, yada, yada, yada).

Oversized neutral=no limited growth


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## eddy current (Feb 28, 2009)

Most important is that is how it was priced. 

Engineers overkill all the time. If the customer wants it, and the engineer specs it, that means that your boss priced it that way and that is what the customer and engineer are expecting to see when the job is done.


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## tates1882 (Sep 3, 2010)

sbrn33 said:


> They just mean the panel board. pretty common nowadays. what does the schedule say for wire sizing.


Grounded and ungrounded are both the same size. No reduction.



cuba_pete said:


> If the EE didn't expect future single phase loading, then they wouldn't be _delivering_ the neutral in the _first_ place.
> 
> High 3rd phase harmonic can cause high neutral current. The EE doesn't know what the future holds, including VFD engineering. Current IEC regulations for the VFD's should eliminate 3-phase concerns, though, sure.
> 
> ...


I'm not sure why they are spec'ing a neutral. I'm involved heavily with the design, it was at my suggestion that they removed the 29 vfds from the ICP I'm building for the job. They came back wanting all the OCPD for the VFd's to be in the ICP, I suggested it would be cheaper to just use a panel board for OCPD. Now the owners basically are asking why 200% and if I thought it was needed, I replied "I've never seen an upsized neutral in a panel board when steps have been taken to mitigate the harmonic load at the VFD but I would defer to the EE's suggestion." 



eddy current said:


> Most important is that is how it was priced.
> 
> Engineers overkill all the time. If the customer wants it, and the engineer specs it, that means that your boss priced it that way and that is what the customer and engineer are expecting to see when the job is done.


I'm the boss and the customer doesn't know heads from tails about harmonics or electrical equipment. Which is why I'm doing some research on the subject. An increased neutral panel is $4K more and the customer about fainted.


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## telsa (May 22, 2015)

eddy current said:


> most important is that is how it was priced.
> 
> Engineers overkill all the time. If the customer wants it, and the engineer specs it, that means that your boss priced it that way and that is what the customer and engineer are expecting to see when the job is done.


bingo.


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## cdslotz (Jun 10, 2008)

tates1882 said:


> Grounded and ungrounded are both the same size. No reduction.
> 
> 
> I'm not sure why they are spec'ing a neutral. I'm involved heavily with the design, it was at my suggestion that they removed the 29 vfds from the ICP I'm building for the job. They came back wanting all the OCPD for the VFd's to be in the ICP, I suggested it would be cheaper to just use a panel board for OCPD. Now the owners basically are asking why 200% and if I thought it was needed, I replied "I've never seen an upsized neutral in a panel board when steps have been taken to mitigate the harmonic load at the VFD but I would defer to the EE's suggestion."
> ...


Offer a voluntary deduct to the GC/owner. If they want the deduct, the EE can either accept it or not.
You are off the hook and so is the EE...the owner is liable for any future damage on his 29 VFD's....which $4K would be a drop in the bucket


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## telsa (May 22, 2015)

A customer at this scale HAS THE BUDGET.

$4,000 is nothing to him.


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## RePhase277 (Feb 5, 2008)

What is the neutral for? Why is it there if this panelboard is for motor drives? Are there any single phase loads coming out of it?


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## Signal1 (Feb 10, 2016)

I have a feeling this engineer got burnt somewhere by under sizing or not anticipating the need for a larger neutral.
I bet he/she designs every job like this now. You know how engineers like to boilerplate things.


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## cuba_pete (Dec 8, 2011)

Good thread


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## telsa (May 22, 2015)

RePhase277 said:


> What is the neutral for? Why is it there if this panelboard is for motor drives? Are there any single phase loads coming out of it?


While the OP phrased the issue as engineering... the play has to be politics.

About which, we here, commenting, are totally in the blind.

It would appear that the OP is a co-EE on this project. 

That's weird, right there.

It smells like the EE is not being paid well... used 'old work' -- again... and punched his craft out the door.

The OP appears to have a patron that has a Very Big Budget... but wants to make the nickels bleed.

So the patron spends 'nothing' on the EE and gets back a canned solution.

For a neutral -- at all -- smells of a canned solution.


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## dmxtothemax (Jun 15, 2010)

QUOTE [ Can anyone provide some clarification of why the EE is think this ]

My best guess is that he is thinking L O N G term reliability.
Perhaps that was part of the original contract conditions
That the system be built with long term reliability in mind.

:thumbsup:


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## Big John (May 23, 2010)

cdslotz said:


> Offer a voluntary deduct to the GC/owner. If they want the deduct, the EE can either accept it or not....


 Good solution; puts the ball in their court.

IMO this sounds like BS boilerplate. Yes, you can get triplen harmonic overload on a neutral, but I've only ever heard of that when it was *in addition* to a very severe single phase neutral load, which you should not have when running 3ø drives.

I used to see tons of specs for 200% neutrals and K rates transformers in high tech commercial, and I can't recall any that ever even came close to being necessary. It's just overbuilt CYA.


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## Jlarson (Jun 28, 2009)

I wouldn't even pull a neutral let alone an oversize one.


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## frenchelectrican (Mar 15, 2007)

Jlarson said:


> I wouldn't even pull a neutral let alone an oversize one.


I agree with that one and for the OP part I will just ask to get the High K rated transfomer to isolated the harmonic load for VSD's 

as far mark the panels saying no netural so they will get their attetion when someone try to do a funny idea to add a single phase circuits.,,


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## cdslotz (Jun 10, 2008)

Who cares? If they over-spec everything, it's no skin off my nose.
The higher material costs are, less labor risk for me, more profit for me.
Also, I can pick apart specs and offer VE all day long....give them back half....more money for me...
Quit scratching your heads over an EE's motives...use it to your advantage


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## Paulusgnome (Mar 28, 2009)

I don't suppose it is possible to actually ask the engineer for a sanity check on this? It does sound like the fat neutral is a bit redundant but there may be a reason.


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## tates1882 (Sep 3, 2010)

Paulusgnome said:


> I don't suppose it is possible to actually ask the engineer for a sanity check on this? It does sound like the fat neutral is a bit redundant but there may be a reason.


 Nah he was instantly on the defense when I mentioned the increased rating. I think like Signal1 said he was burnt in the past and its a CYA thing.


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## tates1882 (Sep 3, 2010)

RePhase277 said:


> What is the neutral for? Why is it there if this panelboard is for motor drives? Are there any single phase loads coming out of it?


 I have no idea. No single phase loads and no space for future expansion. 



telsa said:


> While the OP phrased the issue as engineering... the play has to be politics.
> 
> About which, we here, commenting, are totally in the blind.
> 
> ...


Yup sticky situation for sure, I was originally hired by the architect to review the electrical drawings and provide any relevant corrections. There was a ton of corrections, phone calls between the architect, EE and me by the end of which I think the EE was pissed. Next was to provide a spread sheet for the electrician that denoted what size, type, quantity and connection type was needed for the owner supplied equipment. Also to provide a rough design and load calcs for an ICP. The ICP was to have 47 ATL combo motor starters, 120 & 24 vac control,14 interposing relays, 96 function relay logic board. Then they added interviewing the electrical contractors bidding on the job, reviewing VE, and site inspections periodically. Next they wanted me to build an ICP that included 29 vfds, ocpd for each vfd, filters, 16 ATL combo motor starters, two control transformers, 56 interposing relays, 96 function relay logic board. After kicking around the design, I suggested the removal of vfds/filters from the ICP. They still wanted the OCPD's to be located in the ICP to avoid having add additional panels/breakers but after some review a separate panel board was a no brainer. I think it was the EE that either recommended using VFDs in place of the ATL starters or signed off on the idea but I don't think he realized the size or cost of an ICP with that many vfd's. The heat load alone would be intense probably unmanageable considering they allotted space for a 120"w X 90"t X 24"d enclosure. I can't remember all the sizes but it was something like 2-40hp, 2-20hp, 15-10hp, 10-15hp vcd's with filters. Long story short I think I probably caused a headache for the EE and now he's returning the favor.


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## RePhase277 (Feb 5, 2008)

Sheesh... I think it's a no-brainer then. If this panel is full, and there are no single phase loads of any sort, there is no need for a neutral, let alone a super neutral.


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## cdslotz (Jun 10, 2008)

> Nah he was instantly on the defense when I mentioned the increased rating


of course he is.....you're questioning his design....duh!


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## telsa (May 22, 2015)

cdslotz said:


> of course he is.....you're questioning his design....duh!


What you have to watch out for is a budding EE who's getting his marching orders from above -- a canned solution -- and you're making him look stupid -- during his early daze on the job.

I well remember a budding EE who was delirious that my actual build of his cluster looked like a dream.

He was so proud, his second project, that many a photo was taken, by me, of him, and his executed project. The changes involved were rather remarkable, BTW.

It went from an L cluster to a clean, straight line up... much cheaper and quicker to build.

He was so gobsmacked that he ran around like a kid Christmas morning... taking no end of his own ( official ) photos for his portfolio.

His next work required a miracle worker -- me -- to get the job done. Don't blame him. Blame the architect. He came up with a dream building that lacked any provision for its feeders. They had to jump from floor to floor -- without any 'window.' That _*was*_ charming.

The super was semi-astounded that I could even get them in the building. They were jumping all over the place. [ left, right, over, and back ]


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## Bird dog (Oct 27, 2015)

Some architects & engineers need to have their wings clipped. Reminds me of the draft drawings that don't exist in reality (they're optical illusions).


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## cuba_pete (Dec 8, 2011)

RePhase277 said:


> Sheesh... I think it's a no-brainer then. If this panel is full, and there are no single phase loads of any sort, there is no need for a neutral, let alone a super neutral.


Well, that's enlightening info we weren't presented with by the first post...so yeah, completely different scenario.

Unless you have sub-feed lugs and the EE has plans to allow for that in the future, and is making the neutral available...though I _seriously_ doubt the EE is seeing that far ahead.


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## tates1882 (Sep 3, 2010)

cuba_pete said:


> Well, that's enlightening info we weren't presented with by the first post...so yeah, completely different scenario.
> 
> Unless you have sub-feed lugs and the EE has plans to allow for that in the future, and is making the neutral available...though I _seriously_ doubt the EE is seeing that far ahead.


Would this info have changed your original answer?


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## cuba_pete (Dec 8, 2011)

Yup.

#24 was a lengthy bit of additional info.


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## tates1882 (Sep 3, 2010)

cuba_pete said:


> Yup.
> 
> #24 was a lengthy bit of additional info.


True but either way would you be willing to take liability for VE'ing a 100% neutral? 

I feel like even know I'm knowledgeable, have years real life experience, a licensed master electrician and have 1 million in liability coverage, I would be hesitate to accept liability for VE in this case. I think if it came down to a legal battle my calculations when compared to those done by a licensed PEE wouldn't mean very much and I would be left holding the bag.


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## RePhase277 (Feb 5, 2008)

tates1882 said:


> True but either way would you be willing to take liability for VE'ing a 100% neutral?
> 
> I feel like even know I'm knowledgeable, have years real life experience, a licensed master electrician and have 1 million in liability coverage, I would be hesitate to accept liability for VE in this case. I think if it came down to a legal battle my calculations when compared to those done by a licensed PEE wouldn't mean very much and I would be left holding the bag.


His calculations and yours would be the same: 0 amps.


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## cuba_pete (Dec 8, 2011)

Yeah, what he said. ^^^

If the neutral isn't/_will not be_ used by any load (and if it were up to me entirely) then there is absolutely no reason for pulling it to a panel. It _does_ nothing.

I googled a thread for you from other knowledgeable types of yore.


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## frenchelectrican (Mar 15, 2007)

cuba_pete said:


> Yeah, what he said. ^^^
> 
> If the neutral isn't/_will not be_ used by any load (and if it were up to me entirely) then there is absolutely no reason for pulling it to a panel. It _does_ nothing.
> 
> I googled a thread for you from other knowledgeable types of yore.


It the same way with me and AFAIK .,, any panel without neutral is not being used I would not bother pull it there.

I am sure I did mention it before just put a sign to warn any other wannabe dolts that there is no netural in there. ( ya some inspectors do approve this methold as well )


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## tates1882 (Sep 3, 2010)

Well the plot thickens! I asked for the AFC at the breaker feeding the panel in question, the engineer won't give an AFC value but did say the panel would need to be 65kAIC rated. Now the AFC provided by the Pco was 30000 amps, its what the EE has on the prints, and its what all the suppliers used for designing AIC ratings on panels. The EE has right on his prints on the one line showing the service main an kAIC rating for the main breaker as 42kAIC. WTF.


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## JRaef (Mar 23, 2009)

Trust me, there are a LOT of EEs out there, including those with PE licenses, that know virtually nothing about harmonics, and it scares the bejeebus out of them. So rather than pay attention and learn, they just throw money at things, usually OTHER people's money, to over build equipment. I just did a seminar on harmonic mitigation for VFDs last week, several of the attendees were PEs, who I would have though didn't need to attend. One of them had a difficult time with me telling him that triplen harmonics are not a thing with VFDs (unless fed with a single phase source). I had to go over that several times. He was probably a guy that has been specifying 200% neutrals on 3 phase panels and MCCs that are feeding VFDs.

Now, that said, the 200% neutral IS a good idea on a 480/277V panel that is feeding 277V LIGHTING ballasts, because now they are ALL non-linear loads and create triplen harmonics. So to the earlier points, if he is thinking that by it's mere existence, someone in the future MIGHT add single phase lighting to this panel, he is doing the right thing.


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## tates1882 (Sep 3, 2010)

JRaef said:


> Trust me, there are a LOT of EEs out there, including those with PE licenses, that know virtually nothing about harmonics, and it scares the bejeebus out of them. So rather than pay attention and learn, they just throw money at things, usually OTHER people's money, to over build equipment. I just did a seminar on harmonic mitigation for VFDs last week, several of the attendees were PEs, who I would have though didn't need to attend. One of them had a difficult time with me telling him that triplen harmonics are not a thing with VFDs (unless fed with a single phase source). I had to go over that several times. He was probably a guy that has been specifying 200% neutrals on 3 phase panels and MCCs that are feeding VFDs.
> 
> Now, that said, the 200% neutral IS a good idea on a 480/277V panel that is feeding 277V LIGHTING ballasts, because now they are ALL non-linear loads and create triplen harmonics. So to the earlier points, if he is thinking that by it's mere existence, someone in the future MIGHT add single phase lighting to this panel, he is doing the right thing.


Great info as per the usual, thank you. I would love to sit in on one of your seminars or classes. Any chance you have one in the greater Pac NW?


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## frenchelectrican (Mar 15, 2007)

JRaef said:


> .
> 
> Now, that said, the 200% neutral IS a good idea on a 480/277V panel that is feeding 277V LIGHTING ballasts, because now they are ALL non-linear loads and create triplen harmonics. So to the earlier points, if he is thinking that by it's mere existence, someone in the future MIGHT add single phase lighting to this panel, he is doing the right thing.


That is pretty common over here to do that with our Wye system we genrally upsize the netural some. only on lighting loads ., ( 415Y240 volts in our system ) 

Non lighting loads we just ingore it. run it as conventail arrangement.


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## RePhase277 (Feb 5, 2008)

Could just avoid all this harmonics nonsense by using a delta secondary, but nooooooooo...


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## frenchelectrican (Mar 15, 2007)

RePhase277 said:


> Could just avoid all this harmonics nonsense by using a delta secondary, but nooooooooo...


I would like that idea too .,, as long ya aware of some VSD you may have to tweak a little to work with delta system. 

That I rather to run in that fashion so dont have to deal with bunch of stinka allover the place.,,


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## Jlarson (Jun 28, 2009)

I learned to avoid any and all conversation about three phase and or harmonics with most all EE's. Mind numbing.

And all drawings suck. Big part of my current job is to red line all the electrical and I&C prints done in house and by contract engineers. Several projects I've already reviewed have been so bad I've started from scratch.


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## Bird dog (Oct 27, 2015)

tates1882 said:


> Great info as per the usual, thank you. I would love to sit in on one of your seminars or classes. Any chance you have one in the greater Pac NW?


Fly in or drive to attend. I've done that for seminars.


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## Bird dog (Oct 27, 2015)

A good while back I worked on schools that had computer panels with 200% neutrals, K rated xfmrs and transient protection for the panel.


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## tates1882 (Sep 3, 2010)

Here is my reply to the architect regarding the EE's 42&65kAIC value regarding AFC.

JIM BOB, 

I'm not trying to be a PITA but I don't feel BOB JIM's figure is correct, heres why:

1. The value he's provided is the Ampere Interrupting Capacity of the breaker. The AIC rating indicates the maximum fault current (in amps) that an overcurrent protection device (circuit breaker, fuse, etc.) will safely clear when a fault is applied at the load side of the overcurrent protection device. This is not AFC.

2. I'm asking for the Available Fault Current. Available fault current (SCA) is the current in amperes that is available at a given point in the electrical system. This available fault current is first determined at the secondary terminals of the utility transformer(by the utility) then can be calculated for any given point in the system, using conductor size, length, type, conduit type, motor contribution and the AFC at the transformer secondary. 

3. In order to be compliant with 2014 NEC 110.24, the service equipment shall field mark with max available fault current and the date of which the calculations were performed. According to the prints sheet E3.3 the AFC is 24943 not 42kAIC. 
Here is a good read on the subject. https://www.jadelearning.com/jadele...-short-circuit-current-rating-of-equipment-2/ 

4. A lot of people in the industry don't understand how nec 110.9 and 110.10 is actually applied. In 2005 the NEC added ART. 409, 409.22 states: An industrial control panel shall not be installed where the AFC is greater than the SCCR. In 2008 the NEC adding SCCR to 110.10 stating that: The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. 

Prior editions of code paragraph 110.10 had no mention of Short-Circuit Current Rating (SCCR). It generally required equipment to be protected by overcurrent protection enough to prevent extensive damage. This the old way both AIC and SCCR were interchangeable, commonly known as the withstand rating and as long as the OCPD(breaker or fuse) was rated high enough for the AFC then the down stream equipment was good to go.

Its very important that this is figured correctly, case and point would be the Arc flash event at XYZ in 2015. Had the SCCR matched or was greater than the AFC then its likely that there would haven't be so much equipment damage when the phase to phase fault occurred. Also accurate AFC and SCCR is imperative for the maintenance team to be able to calculate Arc flash hazard and take steps to mitigate the risk to personnel. 


Thoughts?


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## JRaef (Mar 23, 2009)

Well thought out, well stated. Looks like something I'd write. :thumbsup:

But, I'll betcha he won't read anything more than the 1st and last paragraph. I had a great boss once who taught me that no matter what amount of great info I put in the middle, only the first and last paragraph will matter. The first one sets the tone, too aggressive and they stop there. So put in some platitudes and maybe a complement, even if you have to choke on it. The last one is where they jump to get the gist of it, so you summarize in a way that leads them where you want them to go, and if they agree, they might go back and get details from the middle.

It's sad, but I've seen her proved right time and time again.

Oh and, OMG, I can't tell you HOW MANY times I've had that argument over the difference between "AIC rating" and AFC (SCA). It's mind boggling... :wallbash:

Oh and by the way, SCCR was first mentioned in the 2005 code, in Article 409 for "industrial control panels", so it only applied there at that time. What changed only recently was the addition in 110 that expanded the concept.


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## cdslotz (Jun 10, 2008)

> I'm not trying to be a PITA but I don't feel BOB JIM's figure is correct, heres why:


I'm sure he didn't get past that line.....haha!

wait....one guy is named Jim Bob and the other is Bob Jim?


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