Past issues of National Electric Code 1

[EEJaime]

Does anyone have a link or source where one might view previous versions of the NEC? I used to keep many of these but they haven't survived my last few office moves. I am looking for the 1982 version of the NEC.

The reason is that we are doing a major overhaul of a major airport terminal built in 1983-84. The power distribution is set up so that feeders to panels from the main distribution panels are set up as risers. Power is fed at 480V/3ph/4w from a main substation to Distribution panels in electrical rooms where transformers 480-208y/120v/3ph/4w feed local branch circuit panels.

The problem we are having is that the initial feed say from a level 1 distribution board to a level 2 panel is with 4#350mcm, feeds a 225 Amp, 480y/277v/3ph/4w panel equipped with a side wiring gutter. There, a 4#4/0 feeder is tapped to it in the gutter and then proceeds to level 3, (around 65' in length), to feed another 225A branch panel without overcurrent protection. This violates the NEC tap rules in the current code, (NEC 240-21(b)). Although I do not know how the code read that was in effect back then, I don't think it was very much different than it is now.

Do one of you gents with better knowledge of past codes know of a provision that would allow this? This is in a major metropolitan area with notoriously stringent codes and AHJ inspectors,( whom of course have noticed this condition), and do not want to listen to our arguments that it has been this way, running fine for over 20 years and we are not budgeted to rebuild the entire 500,000 square foot terminal buildings' distribution systems.

So if you have a link to where I can find this old code, or if you've run into this type of installation, your assistance would be greatly appreciated. Sincere thanks in advance.

EEJaime

 

[gepman]

The NFPA online archives only go back to 1999. I am certain that someone out there has a copy of the 1982 NEC. If not then contact the NFPA which would have an archive copy (

http://www.nfpa.org).

It sounds as if the branch panelboards do not have a main circuit breaker. If this is the case it doesn't sound as if there is any protection against overload and the system needs to be modified and/or replaced even if you don't have the budget.

 

[stevenal]

I'm looking at the '81 NEC. The cutoffs look pretty similar, with tap lengths not over 10, not over 25, and over 25. The last is for high bay manufacturing buildings, where the taps may not penetrate floors, walls , or ceilings.

 

[EEJaime]

gepman,
The panelboards have a main circuit breaker in them, which would limit the current on the feeder coming in, so I think that the feeder would be sufficiently protected. It is just that the AHJ has quoted the 25 foot tap rule because the occurs more than the alloted distance from the panelboard. Thank you for the link.

Stevenal,
Thank you for the information, I was fairly certain that that was the case. I do remember these rules from way back then, but wanted to get verification.

I have a related question, but I'll put that in a different thread. There may be others that can address my concerns as well.

 

[gepman]

I have thought of something that I would consider accepting if I was the AHJ. You could install a CT around each tapped conductor within the tap rule distance (should be room where the tap is made) and then shunt trip the breaker if any of the taps are overloaded. It depends on how reasonable your AHJ is.

 

[davidbeach]

How would that protect against a fault in the tap? The distance requirement isn't based on overload beyond the end of the tap, otherwise no need for a distance limit, but rather it is for fault protection and it was determined that risk was acceptable at 25 feet but not beyond.

 

[gepman]

I have attached a sketch. This is just a concept not a complete design. I should have said "tap" conductor not "tapped" conductor. I guess my terminology was not correct although a fault will usually also overload the conductors.

The concept is to measure the current on the tap conductors just after the tap (within the distance required by the tap rule). If their is an overcurrent or fault condition the 50/51 relay would trip the supplying circuit breaker with a trip coil (shunt trip). You would need to set it up so it was fail safe (i.e. a loss of signal to the trip coil would trip the supplying circuit breaker). I think that it meeets the intention of the code in that the measurement of the current takes place within the distance specified by the tap rule.

I am not saying that this is the best solution. After looking at your wire sizes (the ampacity was determined using conduit) I think that perhaps you could adjust or replace the breaker that I have shown as a 300/3 (if the actual load allowed it) or install a cable-in/cable-out enclosed circuit breaker at the location where I show the CT's for the 50/51 relay.

 

[davidbeach]

Oh, yes, if you trip the supply end for overloads/faults on the tap then a reasonably understanding AHJ should be willing to accept that; tripping the load end wouldn't gain anything.

 

[EEJaime]

That is an interesting idea gepman, I think I will float that to the AHJ and see if he would be willing to look at this as an "equivalent facilitation". Thank you all.

 

[gepman]

It would also work for your 4000A bus tap issue but see my post there.