240.4(B) (upsizing a CB size)

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jaggedben said:
Not that I saw. Please cite chapter and verse or else explain your logic in detail.



The OCPD at the load end has nothing to do with that!
:happyno:
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Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.
 
I am the OP, and I'm sorry for not chiming in sooner. I think, so far, the answers are summarized into these two...
1. "Because NEC says so."
In other words, we don't know why.
2. "We do not have the same level of protection for a tap as we do for a feeder."
But nobody seems to be able to actually explain why the different level of protection although both conductors are protected against overload by the same OCPD (the one in between the tap and the feeder).

I appreciate all your replies. I hope I can get the answer as to why.
 
jumper said:
Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors.
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Gotcha on the citation. It's still a rather baffling entry, in that by definition tap conductors can have an upstream OCPD 'upsized' by practically any number of sizes. One is left to dope out by process of elimination that it must refer to the downstream OCPD.

unsaint33 said:
...

I appreciate all your replies. I hope I can get the answer as to why.
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Me too. That sentence above wasn't added by accident, but I honestly can't imagine what substantiation was provided and how anyone could have been convinced by it. Has there been a thread on the history of that?
 
jumper said:
Jag, I have no idea what you just said.
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Then keep re-reading it until you get one? :lol:

Sorry, I'm not sure how to say it better. It's related to this though...

unsaint33 said:
...
But nobody seems to be able to actually explain why the different level of protection although both conductors are protected against overload by the same OCPD...
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jaggedben said:
Gotcha on the citation. It's still a rather baffling entry, in that by definition tap conductors can have an upstream OCPD 'upsized' by practically any number of sizes. One is left to dope out by process of elimination that it must refer to the downstream OCPD.



Me too. That sentence above wasn't added by accident, but I honestly can't imagine what substantiation was provided and how anyone could have been convinced by it. Has there been a thread on the history of that?
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That section is not referencing the OCPD upstream of the tap conductor, it is saying that you cant use 240.4(B) for the OCPD where the tap conductor ends.

If you want to supply an 80 ampere load with a tap conductor, you could not use a #4 copper conductor and terminate it in a 90 amp OCPD. The tap conductor has to have an ampacity of at least that of the OCPD that it terminates in.
 
packersparky said:
That section is not referencing the OCPD upstream of the tap conductor, it is saying that you cant use 240.4(B) for the OCPD where the tap conductor ends.

If you want to supply an 80 ampere load with a tap conductor, you could not use a #4 copper conductor and terminate it in a 90 amp OCPD. The tap conductor has to have an ampacity of at least that of the OCPD that it terminates in.
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We know that Packs

The question is why if the loads are equal...
 
infinity said:
For example if you had 2 sets of 500 Kcmil THHN conductors (380*2=760 amps) feeding equipment with a load calculation value of 760 amps or less those conductors are considered adequately protected even when you use the next standard size OCPD of 800 amps.
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Correct me if I'm wrong please......... but if your load calculations were 761 amps - 800 you would not be able to do this.
 
jumper said:
Jag, I have no idea what you just said.
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packersparky said:
That section is not referencing the OCPD upstream of the tap conductor, it is saying that you cant use 240.4(B) for the OCPD where the tap conductor ends.
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Okay, I'll try again...

My thought process on first reading that section goes like this:

- I'm imagining a 100A tap to a 200A feeder.
- "The provisions of 240.4(B) shall not be permitted for tap conductors."
- Whadya mean? My 200A OCPD is already way oversized beyond what 240.4(B) permits! Why even say that?!
- oooooooh, you must mean the other OCPD. The 100A one that only protects them from overload, not fault. (It might help if you actually said that.)
- ...and I cannot imagine a scientific justification for making that rule. Either 240.4(B) is okay for preventing overload, or it isn't.
 
jaggedben said:
Okay, I'll try again...

My thought process on first reading that section goes like this:

- I'm imagining a 100A tap to a 200A feeder.
- "The provisions of 240.4(B) shall not be permitted for tap conductors."
- Whadya mean? My 200A OCPD is already way oversized beyond what 240.4(B) permits! Why even say that?!
- oooooooh, you must mean the other OCPD. The 100A one that only protects them from overload, not fault. (It might help if you actually said that.)
- ...and I cannot imagine a scientific justification for making that rule. Either 240.4(B) is okay for preventing overload, or it isn't.
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hmmm.. interesting.. tomorrow my friend.
 
So I did some research last night, down the rabbit hole.

It seems that "The provisions of 240.4(B) shall not be permitted for tap conductors" was added in 2005. (240.21(B) as we know it only dates to 1999.)

What gets me is that the original proposal was rejected. The substantiation said something about transformer secondaries, I still think it had no merit but I'll have to reread it again. But the CMP didn't reject it on technical merit. Their reason was "240.21(B) already says that". And then, somehow through the comment period they were convinced that an extra sentence warranted being added as a clarification. But it seems nobody seriously questioned if the previously existing language made technical sense. So I think it really is a case of "because that's what the code says".
 
So to revisit this, here is the original submission in the 2005 Report on Proposals:

Submitter: Phil Simmons, Simmons Electrical Services
Recommendation:
Revise existing Section 240.21(B) as follows:
(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in
240.21(B)(1) through (5). The provisions of 240.4(B) shall not be permitted for conductors that are tapped.
Substantiation:
This proposal is intended to clarify the issue of whether these conductors that do not have overcurrent
protection where they originate are required to be not less than the rating of the device or overcurrent
protection they terminate in. Since the tapped conductors or conductors on the secondary of a transformer do
not have overcurrent protection where they originate, it seems logical that they should not be permitted to
round up to the next standard size as provided in 240.4(B). A more logical approach seems to be that the
subject conductors must have an ampacity not less than the rating of the device or overcurrent protection
they terminate in.
Panel Meeting Action: Reject
Panel Statement:
The present text in 240.21(B) meets the submitter's intent. See, for example, 240.21(B)(1)(1)b. The provisions of 240.4(B) are not
permitted for tapped conductors.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
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So the red part is the entire technical justification for this. It 'seemed logicial' to someone. I have to grant that evidently it seems logical at first to a lot of people. But it just isn't logical at all if you think it through in depth and consider some examples.

Note that the blue part, the panel's response, does not address whether it is logical or not. It's clear from the report on comments that the CMP decided to interpret the previously existing language as prohibiting the application of 240.4(B), and then make that explicit. One commenter wanted to essentially reverse the decision, by adding "The next higher standard overcurrent device shall be permitted to be used in accordance with 240.4(B)". The CMP rejected this sentence not on any technical logic, but because "The panel advises the submitter that the provisions of 240.4(B) are not permitted for tap conductors." Put another way, if that commenter had gotten is input in as an initial proposal with a sound technical argument, this whole thing might have gone the other way.

There you have it. Sometimes things get added to the code for flimsiest of reasons.
 
infinity said:
You're correct that the conductors after the tap may be a feeder and when they are they're protected just like any other feeder. Up to 800 amps if the conductor ampacity doesn't correspond to a standard OCPD size in 240.6 then you can go up to the next larger standard size but the calcuated load on those feeder conductors still cannot exceed the ampacity of the feeder conductors.

For example if you had 2 sets of 500 Kcmil THHN conductors (380*2=760 amps) feeding equipment with a load calculation value of 760 amps or less those conductors are considered adequately protected even when you use the next standard size OCPD of 800 amps.
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I am also confused about same scenario , I Have Load of 600 Amp (Load is Chiller Units , and at Nameplate it is mentioned that OCPD should be 800Amp) , The ampacity of Cable is 882 amp , but once i apply the de-rating factor the ampacity is reduced to 740 amp. Can i use 800 amp CB and is it accepted as per codes. If yes, please mention the Code reference.
 
mohsan514 said:
I am also confused about same scenario , I Have Load of 600 Amp (Load is Chiller Units , and at Nameplate it is mentioned that OCPD should be 800Amp) , The ampacity of Cable is 882 amp , but once i apply the de-rating factor the ampacity is reduced to 740 amp. Can i use 800 amp CB and is it accepted as per codes. If yes, please mention the Code reference.
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You didn't say if they are tap conductors.

Under the NEC...
If they are not tap conductors, you can do that.
If they are tap conductors, you cannot.
 
Thank you for response ..

They are not Tap conductors.. but if cable is overloaded till 780 amp and 800 amp breaker will not trip.. i am just confused how to justify that..



Sent from my SM-J700F using Tapatalk
 
jaggedben said:
Why not? Because we are making a legalistic argument that the language of 240.21 contradicts 204.4(B)? I admit that I haven't thought about it before and that the language is open to interpretation. (Although I would argue that for other than 10ft taps the language is open to still invoking 204.4(B).)

In that case I'm fairly confident that there is no good reason for the difference. Just code language that says what it says, and probably not intended to produce that result.
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The specific reference to 240.4(B) was added to 240.21 a few cycles back because code users were not following the previous language. The previous language required that the tap or transformer secondary conductor have an ampacity not less than the OCPD at the end of that conductor. It is clear that the result was intended when they added the reference to 240.4(B), but not sure of why it needs to be that way.
There may be information in the ROP and ROC for that change that would say why this is a requirement.

Edit...I posted before I read that you had found the ROP...I guess you need to be looking to the TCRs and TCDs from when the rule was written that required the tap or secondary conductor to have an ampacity not less than the rating of the OCPD at the load end of that conductor. I have no idea of when that went into the code.
 
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