joe tedesco
Senior Member
- Location
- Boston, Massachusetts
Where did the 106% come from?
Please explain this change in 240.4(C)
- Thread starter joe tedesco
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charlie
Senior Member
- Location
- Indianapolis
Re: Please explain this change in 240.4(C)
Joe, if you multiply 380 amperes by 105%, it gets you to 399 amperes and not 400.
Joe, if you multiply 380 amperes by 105%, it gets you to 399 amperes and not 400.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Please explain this change in 240.4(C)
If I am reading Joe and Charlie's posts correctly, it seems to me that the intent is to be able to use (4) sets of parrellel 500KCMIL conductors to establish a 1600 service. I don't understand this. Thats 80 amps per phase shy of 1600 amps. Isn't the concept of an OCPD to protect the conductors??? It just seems like wer're going backwards here. Just my two cents
If I am reading Joe and Charlie's posts correctly, it seems to me that the intent is to be able to use (4) sets of parrellel 500KCMIL conductors to establish a 1600 service. I don't understand this. Thats 80 amps per phase shy of 1600 amps. Isn't the concept of an OCPD to protect the conductors??? It just seems like wer're going backwards here. Just my two cents
charlie
Senior Member
- Location
- Indianapolis
Re: Please explain this change in 240.4(C)
The following is the substantiation from the proposal:
"By making this change, a 1600-ampere service could be wired with four sets of 500 kcmil, Cu., 75 degrees C wire. This was done for years without any problems and no problems have been encountered for the existing 800 amperes or less, as permitted now in 240.3(B). Of course, all the other code provisions would have to be followed.
Below 800 amperes, the NEC already allows conductors to be protected at the next standard device rating, effectively allowing these conductors to be protected and up to 18 percent above their allowable ampacity. This practice has proven successful in many thousands of NEC installations and in years of practice. This successful practice is with conductors that are smaller and heat more quickly than those above 800 amperes. Also, the overcurrent protective device is smaller and more sensitive to the wire size below 800 amperes. It would seem that, if anything there would be more technical merit in restricting the smaller devices and conductor, but again long successful practice and experience supports the exiting latitude given in 240.3. Submitted are time-current characteristic curves that illustrate that 4 sets of 500 kcmil Cu conductors are adequately protected by conventional fuses or molded case circuit breakers at an applied voltage of 480 V nominal. See enclosures 1 through 5. Generally shown are the cable damage curves. Then the curves for the breaker or fuse that might be used to protect the cable are shown. As long as the protective device curve is below and to the left of the cable damage curve the cable will be protected from damage. The plots show much conservatism that even 3 sets of conductors can be used safely rather than 5 or 6 sets. Time is on the "y" axis and current in hundred of amps is on the "x" axis of the plot. So if there is a current of say 80,000 A (fault current), draw a vertical line on the 800 (800 x 100 = 80,000). Then go up to the cable damage curve and read the corresponding time of 0.95 seconds for 3 sets of 500 kcmil Cu. As long as the protective device operates faster than this time value, the cable is acceptably protected. Protection Engineers usually keep a small buffer below the damage curve for a margin of safety. It is suspected most protective devices will operate in 4 to 8 cycles, so worst case is 0.2 seconds. As shown, there is a large margin between curves at that speed.
Note: Supporting material is available for review at NFPA Headquarters.
Panel Meeting Action: Accept in Principle
In the Recommendation, add the following:
"(4) The overcurrent device has been listed for use with the smaller conductors.""
The list item (4) was necessary because some OC devices depend on the mass of the wire for heat control. The bottom line is that we know the wire will handle the load, we have to make sure the OC devices have been tested for the application.
The views and opinions expressed herein are solely those of the author and do not necessarily represent the views of any organization.
[ August 15, 2003, 02:20 PM: Message edited by: charlie ]
The following is the substantiation from the proposal:
"By making this change, a 1600-ampere service could be wired with four sets of 500 kcmil, Cu., 75 degrees C wire. This was done for years without any problems and no problems have been encountered for the existing 800 amperes or less, as permitted now in 240.3(B). Of course, all the other code provisions would have to be followed.
Below 800 amperes, the NEC already allows conductors to be protected at the next standard device rating, effectively allowing these conductors to be protected and up to 18 percent above their allowable ampacity. This practice has proven successful in many thousands of NEC installations and in years of practice. This successful practice is with conductors that are smaller and heat more quickly than those above 800 amperes. Also, the overcurrent protective device is smaller and more sensitive to the wire size below 800 amperes. It would seem that, if anything there would be more technical merit in restricting the smaller devices and conductor, but again long successful practice and experience supports the exiting latitude given in 240.3. Submitted are time-current characteristic curves that illustrate that 4 sets of 500 kcmil Cu conductors are adequately protected by conventional fuses or molded case circuit breakers at an applied voltage of 480 V nominal. See enclosures 1 through 5. Generally shown are the cable damage curves. Then the curves for the breaker or fuse that might be used to protect the cable are shown. As long as the protective device curve is below and to the left of the cable damage curve the cable will be protected from damage. The plots show much conservatism that even 3 sets of conductors can be used safely rather than 5 or 6 sets. Time is on the "y" axis and current in hundred of amps is on the "x" axis of the plot. So if there is a current of say 80,000 A (fault current), draw a vertical line on the 800 (800 x 100 = 80,000). Then go up to the cable damage curve and read the corresponding time of 0.95 seconds for 3 sets of 500 kcmil Cu. As long as the protective device operates faster than this time value, the cable is acceptably protected. Protection Engineers usually keep a small buffer below the damage curve for a margin of safety. It is suspected most protective devices will operate in 4 to 8 cycles, so worst case is 0.2 seconds. As shown, there is a large margin between curves at that speed.
Note: Supporting material is available for review at NFPA Headquarters.
Panel Meeting Action: Accept in Principle
In the Recommendation, add the following:
"(4) The overcurrent device has been listed for use with the smaller conductors.""
The list item (4) was necessary because some OC devices depend on the mass of the wire for heat control. The bottom line is that we know the wire will handle the load, we have to make sure the OC devices have been tested for the application.
The views and opinions expressed herein are solely those of the author and do not necessarily represent the views of any organization.
[ August 15, 2003, 02:20 PM: Message edited by: charlie ]
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Please explain this change in 240.4(C)
Thanks again Charlie!
Thanks again Charlie!
joe tedesco
Senior Member
- Location
- Boston, Massachusetts
Re: Please explain this change in 240.4(C)
Thanks charlie, do the NFPA Regulations permit committee members to answer code questions on behalf of their committees, or are they personal opinions?
Thanks charlie, do the NFPA Regulations permit committee members to answer code questions on behalf of their committees, or are they personal opinions?
charlie
Senior Member
- Location
- Indianapolis
Re: Please explain this change in 240.4(C)
I don't know of any restrictions; however, the views and opinions expressed by me are solely mine and do not always represent the views of the NFPA or CMP-10.
I would assume the same would apply to all the panel reports given to IAEI meetings, Code revisions classes, etc.
[ August 13, 2003, 10:37 AM: Message edited by: charlie ]
WOW, good question Joe!
I don't know of any restrictions; however, the views and opinions expressed by me are solely mine and do not always represent the views of the NFPA or CMP-10.
I would assume the same would apply to all the panel reports given to IAEI meetings, Code revisions classes, etc.
[ August 13, 2003, 10:37 AM: Message edited by: charlie ]
- Location
- Massachusetts
Re: Please explain this change in 240.4(C)
Rebroadcast of these opinions without the express written permission of Charlie the Utility Power Guy, CMP-10 and the NFPA is strictly prohibited.
joe tedesco
Senior Member
- Location
- Boston, Massachusetts
Re: Please explain this change in 240.4(C)
Charlie, yes I agree that all of the replies, seminars and reports should make it clear about "opinions rendered"
This is in the NFPA Regulations Governing Committee Projects, and even some of the code scholars can put this in their replies so as to cover there butt!
:roll:
[ August 13, 2003, 02:49 PM: Message edited by: joe tedesco ]
Charlie, yes I agree that all of the replies, seminars and reports should make it clear about "opinions rendered"
This is in the NFPA Regulations Governing Committee Projects, and even some of the code scholars can put this in their replies so as to cover there butt!
Probably a good idea for this to be added here on the board somewhere, you agree?
:roll:
[ August 13, 2003, 02:49 PM: Message edited by: joe tedesco ]
Re: Please explain this change in 240.4(C)
Joe,
I thought that is what was understood when becoming a member of these types of Bulletin Boards when originally signing-on.
Glenn
Besides, Joe, only me and another that is not living has never made a mistake, I wish.
:roll:
Joe,
I thought that is what was understood when becoming a member of these types of Bulletin Boards when originally signing-on.
Glenn
Besides, Joe, only me and another that is not living has never made a mistake, I wish.
:roll:
Re: Please explain this change in 240.4(C)
Charlie, we have never thought you were responding with anything but your expertise, professional oppinions, and overall instructor and training information.
Thanks, and please don't quit doing exactly that.
Roger
Charlie, we have never thought you were responding with anything but your expertise, professional oppinions, and overall instructor and training information.
Thanks, and please don't quit doing exactly that.
Roger
- Location
- Massachusetts
Re: Please explain this change in 240.4(C)
I see the need for a warning like that in the NECH as that could easily (and often is) taken as formal interpretation, but I fail to see the need at a commercial internet forum.
Does anyone foresee someone reading some incorrect information here on this board, basing an installation on that information and later failing an inspection because it was not a Formal Interpretation of the NEC??
Any qualified person should know that the only Formal Interpretation of the NEC? would come from the NFPA and not an internet forum and if they do not know that shame on them for not checking further.
JMO, Bob
I would hate to see that happen here, just one more needless warning in our life's, like the majority of warnings that come with consumer products.
I see the need for a warning like that in the NECH as that could easily (and often is) taken as formal interpretation, but I fail to see the need at a commercial internet forum.
Does anyone foresee someone reading some incorrect information here on this board, basing an installation on that information and later failing an inspection because it was not a Formal Interpretation of the NEC??
Any qualified person should know that the only Formal Interpretation of the NEC? would come from the NFPA and not an internet forum and if they do not know that shame on them for not checking further.
JMO, Bob
joe tedesco
Senior Member
- Location
- Boston, Massachusetts
Re: Please explain this change in 240.4(C)
Most of the replies here come from only a few people who seem to have all of the answers, all of the time, and that is good, but the issue was related to the way in which a member of the NEC committee replies.
I would ask those of you to sit on a committee for a few cycles and see exactly what happens when they discuss the proposals sent in by the public, or by others who have a lot to gain.
Replies here are just like you are writing a letter, and for the over 8000 plus members should not be considered as cut in stone.
How many of you think that you could serve on a committee, or even be considered for membership on one.
How many of you have voted at annual NFPA meetings to adopt the code.
Its nice to see people who are just starting out give their "opinions" they have and share.
I asked Charlie the question --- please let him answer it, he thought my question was a good one!
Look here at Section 6 for the rules related to committee members:
http://www.nfpa.org/PDF/Projects.pdf?src=nfpa
[ August 14, 2003, 01:33 AM: Message edited by: joe tedesco ]
Most of the replies here come from only a few people who seem to have all of the answers, all of the time, and that is good, but the issue was related to the way in which a member of the NEC committee replies.
I would ask those of you to sit on a committee for a few cycles and see exactly what happens when they discuss the proposals sent in by the public, or by others who have a lot to gain.
Replies here are just like you are writing a letter, and for the over 8000 plus members should not be considered as cut in stone.
How many of you think that you could serve on a committee, or even be considered for membership on one.
How many of you have voted at annual NFPA meetings to adopt the code.
Its nice to see people who are just starting out give their "opinions" they have and share.
I asked Charlie the question --- please let him answer it, he thought my question was a good one!
Look here at Section 6 for the rules related to committee members:
http://www.nfpa.org/PDF/Projects.pdf?src=nfpa
[ August 14, 2003, 01:33 AM: Message edited by: joe tedesco ]
- Location
- Massachusetts
Re: Please explain this change in 240.4(C)
I do not care if those comments are aimed at me, you posted a question on a public forum and I gave you my opinion.
I also signed my post JMO.(Just My Opinion)
No one is stopping Charlie from answering if and when he wants to.
If you require a response from Charlie exclusively, may I suggest a Private Message to him.
It might be good to remember that you and I are both guests here at this forum.
Why would you think you should set policy here? :roll:
Will you next request I put a NFPA courtesy link on my posts here?
The fact this forum has more than 8000 members is a testament to the fact it is a great site as it is.
Again JMO, Bob
I only think I have all the answers
Joe, Which one of us is "just starting out" Roger, who has been in the trade since 75, gwz2, who is an inspector or myself, I have been in the trade 20+ years.
I do not care if those comments are aimed at me, you posted a question on a public forum and I gave you my opinion.
I also signed my post JMO.(Just My Opinion)
No one is stopping Charlie from answering if and when he wants to.
If you require a response from Charlie exclusively, may I suggest a Private Message to him.
It might be good to remember that you and I are both guests here at this forum.
Why would you think you should set policy here? :roll:
Will you next request I put a NFPA courtesy link on my posts here?
The fact this forum has more than 8000 members is a testament to the fact it is a great site as it is.
Again JMO, Bob
joe tedesco
Senior Member
- Location
- Boston, Massachusetts
Re: Please explain this change in 240.4(C)
Bob:
I too am allowed to post my personal opinions, and you shouldn't get upset when you read my replies so early in the morning.
How do you know that I was talking about you or the others?
See that's what is wrong with these boards, we can't look each other in the face, as we would across the table when discussing certain issues.
Again, my comments were related to the following part in the NFPA Regs.
The courtesy link that I use on my site [and I see that you add it to] is just that a "courtesty" to NFPA.
So many people use the NEC and we all should remember that it has been around much longer than the members here, except for those who are older that the first publication.
I am impressed with your interest in the Code, and knowledge and you should never be offended if I make a comment that calls attention to something that needs clarification.
Where are you teaching classes in Massachusetts?
Bob:
I too am allowed to post my personal opinions, and you shouldn't get upset when you read my replies so early in the morning.
How do you know that I was talking about you or the others?
See that's what is wrong with these boards, we can't look each other in the face, as we would across the table when discussing certain issues.
Again, my comments were related to the following part in the NFPA Regs.
The courtesy link that I use on my site [and I see that you add it to] is just that a "courtesty" to NFPA.
So many people use the NEC and we all should remember that it has been around much longer than the members here, except for those who are older that the first publication.
I am impressed with your interest in the Code, and knowledge and you should never be offended if I make a comment that calls attention to something that needs clarification.
Where are you teaching classes in Massachusetts?
charlie
Senior Member
- Location
- Indianapolis
Re: Please explain this change in 240.4(C)
Sorry Joe, I went off in a different direction. I have been in contact with the other moderators about this situation. I do appreciate your questions and comments about this issue and (I think) we will be placing a disclaimer on the site.
If a disclaimer is not forthcoming, I think I will probably have to withdraw. The NFPA regulations are very specific.
Sorry Joe, I went off in a different direction. I have been in contact with the other moderators about this situation. I do appreciate your questions and comments about this issue and (I think) we will be placing a disclaimer on the site.
If a disclaimer is not forthcoming, I think I will probably have to withdraw. The NFPA regulations are very specific.
- Location
- Illinois
- Occupation
- retired electrician
Re: Please explain this change in 240.4(C)
Joe,
Why would anyone other than a member of one of the NFPA committees need or even want to use a disclaimer? I can see the NFPA rule, even though it is a major infringement on the First Amendment, for forum members that are associated with the NFPA, but can see no reason what so ever for the rest of us to use a disclaimer.
Don
Joe,
Why would anyone other than a member of one of the NFPA committees need or even want to use a disclaimer? I can see the NFPA rule, even though it is a major infringement on the First Amendment, for forum members that are associated with the NFPA, but can see no reason what so ever for the rest of us to use a disclaimer.
Don
joe tedesco
Senior Member
- Location
- Boston, Massachusetts
Re: Please explain this change in 240.4(C)
Don:
Disclaimer?, Just as a courtesy.
You can do what you want anytime you supply an answer to any question on the NEC.
Just trying to show where we should be careful.
Don:
Disclaimer?, Just as a courtesy.
You can do what you want anytime you supply an answer to any question on the NEC.
Just trying to show where we should be careful.
- Location
- Massachusetts
Re: Please explain this change in 240.4(C)
As much as I hate legal BS, it would be a shame not to have CMP members able to post here.
Instead of a long drawn out paragraph wouldn't a simple "in my opinion" or "just my opinion" statement before a CMP members post be sufficient?
Joe, I was not upset, I am disappointed Charlie agrees with you but I have to respect a man of integrity.
Bob
If it takes a disclaimer to keep members like Charlie posting, then lets have a disclaimer.
As much as I hate legal BS, it would be a shame not to have CMP members able to post here.
Instead of a long drawn out paragraph wouldn't a simple "in my opinion" or "just my opinion" statement before a CMP members post be sufficient?
Joe, I was not upset, I am disappointed Charlie agrees with you
but I have to respect a man of integrity.Bob
Re: Please explain this change in 240.4(C)
Charlie, if we need to petition Danny to hurry up and add the disclaimer let us know.
In the mean time someone should start a poll for a concensus on how many think this is BS.
IMO if you are not using a disclaimer saying your views expressed here are that of the NEC and NFPA, why do we have to disclaim your views aren't that of the NEC and NFPA.
If anyone wants to say a CMP member said on a public forum, is no diferent and has no more meaning than someone on the street saying a cop told him he can be arrested for murder. Does this mean the cop is giving away gaurded secrets or interpretations?
Roger
Charlie, if we need to petition Danny to hurry up and add the disclaimer let us know.
In the mean time someone should start a poll for a concensus on how many think this is BS.
IMO if you are not using a disclaimer saying your views expressed here are that of the NEC and NFPA, why do we have to disclaim your views aren't that of the NEC and NFPA.
If anyone wants to say a CMP member said on a public forum, is no diferent and has no more meaning than someone on the street saying a cop told him he can be arrested for murder. Does this mean the cop is giving away gaurded secrets or interpretations?
Roger
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