office spaces and nuetral loading question

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copper123

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I am laying out branch ckts for a remodel in an office complex. No prints to speak of and its kind of a design build. Nothing fancy. Just some new drop-in fixtures and new outlets. The outlets however will be powering all the office equipment in each space. I have touched briefly many times about the issues of Non linear loads and overloads and overloading of neutrals. My questions are this: How common is it to run multi wire ckts on a shared neutral that feed office spaces. We are starting to design the conduit runs and the wire fill for them. Its three-phase power and I am wondering if pulling multiwire ckts with a common are prudent. Also, can?t you even get overloading of you neutrals with just the new electronic ballast lighting? Anyhow, what is the norm now with the high electronic loads in offices? Does each ckt get its own neutral, or are they still shared. Multiwire sharing also helps on your derating count. You don?t have to count the neutral as a hot conductor. Actually 310.15 B 4 (C) tells us we need to count it I guess. Anyhow, any insight would be great!
Thanks in advance
 
Re: office spaces and nuetral loading question

A,B,C Phase can share a neutral. Lighting loads I share the neutral but go one size up if there is alot of flourescent lighting. If there are only a few lights or you are only using 2 of the 3 phases size the same as your branch circuit conductor. If the branch circuits are feeding a lot of electronic loads as in computers I don't share my neutrals.
Good luck.

[ September 13, 2005, 11:48 PM: Message edited by: highkvoltage ]
 
Re: office spaces and nuetral loading question

Originally posted by copper123:
Actually 310.15 B 4 (C) tells us we need to count it I guess. Anyhow, any insight would be great!
Thanks in advance
Click to expand...
(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral shall therefore be considered a current-carrying conductor.
Click to expand...
Provided it's a wye.

Nonlinear Loads Definition's FPN:
Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.
Click to expand...
From what I understand, it's common to run MWBC's to office cubicles.

From what I've heard, it is an overblown problem. I remember hearing second hand that more modern electronics have less wave distortion.
 
Re: office spaces and nuetral loading question

Thanks guys,
George, with the office cubicles, this is where I have heard about the problems. Extreme electronic loads on a multiwire ckt with one nuetral. Maybe they are now oversizing the nuetral conductor?
Thanks
 
Re: office spaces and nuetral loading question

Typical office area circuitry I've dealt with over the years all employ shared neutrals. Most office cubicle furniture I have worked with have oversized neutrals in the pigtail connection. However, all of the building wiring I have seen does not oversize the neutral for attachment to cubicle furniture or anything else. I have never witnessed any problems.
 
Re: office spaces and nuetral loading question

Copper123, I know you said you do not have much info but you should try to find out what type of office furniture harness they are getting. Better still if you get input on it.

Most office furniture makers offer at least 3 or 4 different wiring harnesses.

Some use multiwire circuits some use all two wire circuit and others still use both multiwire and two wire branch circuits at the same time.

Some need as few as one circuit per location some need 6 circuits per location.

Some want IG conductors along with normal EGCs.

The only way to plan and pull only what is needed is to get some more info.

If you go multiwire you must use handle ties or common trip breakers for the 2005 NEC
 
Re: office spaces and nuetral loading question

1-2-3,
dedicated circuits cost more money --- either will work but may cause problems in the future. the labor is nearly the same on the original installation of adding individual neutrals. most of the time, i have found out, the customer will pay the additional moneys to insure clean power to his equipment which he is dependent on to function as a business.

i had one engineer -- specified common neutrals to a "goldman sakes" brokerage office with about a hundred desk stations! at the pre-job meeting i confidentially brought this to his attention! he told me "publically" to mind my own business and do the installation as he layed it out on the job drawings. enough said!!! two years later, i was called to "goldman sakes" for a meeting with this same engineer who asked "why common neutrals were installed?". they were having equipment failure problems with copiers and computers. at this meeting -- he had a set of drawings---yep---showing dedicated circuits to the desk stations!!! only problem was, i still had the "as built" drawings -- and they didn't match----except for the dates--they were the same!!! get the picture!!! he then, in front of the "goldman sakes" people demanded i turn my drawings over to him! at that point i said two words!!! "goldman sakes" then had us rewire the entire underfloor electrical installation using dedicated circuits to every desk station. we would go in early in the morning and set up extention cords to sections and allow the firm to operate on temporary power while we re-pulled the necessary wiring for dedicated power. this was payed for by the engineer's "errors and omission" insurance company. this "was" one of the largest engineering firms in south florida -- they are no longer in business!!!!!!!!!!!!

many times work station problems are really caused by the way office workers arrange their equipment -- you can find a three circuit cubical operating on one circuit -- computer-laser printer-and 1200 watt space heater just cooking away! the computer supplier doesn't care -- just knows there seems to be low voltage or sags or surges and they are burning out boards!!! mixing these problems with common neutrals just adds fuel to the fire!!! my $.02
 
Re: office spaces and nuetral loading question

Thanks for all the input. This office area is not going to have any office cubicles in it. just small offices in full sheetrocked walls. But, each office will have a computer, printer, ect. A for instance: You could run a conduit down the hallway with a full boat. 3 hots and neut. Dump a dedicated ckt to each office and parallel the neutral. After reading your responses, it is more money and time, but by pulling a dedicated neut., it will give the customer a better installation.
Thanks for all the input. Pretty scary about the engineer story. My mindset is to document every thing. Anymore, it seems like taking a personal recorder with you would be prudent. Sir, could you please speak into the microphone and say that again.!
Thanks

[ September 14, 2005, 11:57 AM: Message edited by: copper123 ]
 
Re: office spaces and nuetral loading question

1-2-3,
the microphone thing doesn't work --- i was called before a neca board and brought a recorder--nobody would speak until it was off and the batteries removed!!! office layouts change from one occupant to the next within the same company.
one guy wants to look out the window --- and the next guy is afraid of heighths!!! it is hard to outguess them and about the time you have everything figured out and in one place---they want to remodel the entire place!!

another engineer made a major blunder on a life safety issue in a major building. we figured a way to solve the problem and discussed it with him. he told us to proceed with the work and he would revise the plans and iron things out with the building's owner. the additional work and materials ran $27,000... he never told the owner and then "told" he would make up the cost by providing us with other work. we never had a problem finding work --- and i can brake even by not even leaving my house in the morning -- i asked him if he thought it was a good idea for me to drive 30 miles each way to a jobsight to "loose" $27,000.00.. i had to take him to court before his "errors and ommision" insurance paid the costs. we found out that the engineer that approved the work and was the engineer of record for this buildings changes for years ---"had no license" -- he was trained in russia --- yes--they were different engineers.
 
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