Is the # of tandem breakers limited by NEC?

[don_resqcapt19]

celtic,

Not in a panel...

Why not. If they are bundled for more than 24" you have to derate.
Don

 

[tallgirl]

LOL

Ok...lemme search my comp. for a "fine example".

EDIT:
Bad news.
The pictures I "had" were lost when the HD crashed in 8/04 (along with all the pics I had from '03 - '04)


I *could* remove my panel cover and take a shot of it.....

Okay, I'll put a homebrew in the fridge, get it nice and cold, then take a shot of me drinking it, and you can take the cover off your panel, and show me a pic of your handiwork. Sounds like a fair trade

But seriously -- I'd appreciate that. Or someone else who didn't have bad luck with a hard drive might share instead. And if y'all ever want personal tips on how to avoid losing everything (hint: USB connected 500GB disk drives are cheaper than tape backup these days ...), drop me a PM.

 

[celtic]

That was a '97 Gateway..I hadded a 30GB drive to use as the primary drive and left the 6GB as a back-up drive (internal). We went on vacation and when we returned home, I turned the comp and -poof- the HD was smoked. My brother is a techie and was successful in recovering most of the data...but not all.

I'm seeing him a few hours...I'll ask him if he recovered any jpegs from that range.

 

[tallgirl]

That was a '97 Gateway..I hadded a 30GB drive to use as the primary drive and left the 6GB as a back-up drive (internal). We went on vacation and when we returned home, I turned the comp and -poof- the HD was smoked. My brother is a techie and was successful in recovering most of the data...but not all.

I'm seeing him a few hours...I'll ask him if he recovered any jpegs from that range.

For your future reference, never leave a backup drive connected to a machine. I had a power supply blow up (no, really -- sounded like automatic weapons fire as the caps exploded one by one ...) and take out quite a few parts with it. I've also had HD controllers go buh-bye and take out multiple drives. That's why I suggested the USB connected drive. Or if you have a wirefull network, build a NAS box

USB and swappable enclosures are available at most computer geek stores. They have wires inside them, so I figure you guys can handle them

 

[celtic]

Right now I am using dual-layer dvd's as a back-up...the problem with is, if the HD should crap out, the dvd will need to be restored from another comp. runnibg the same burning software.

I'm thinking an external USB HD is the way to roll.

 

[tallgirl]

Right now I am using dual-layer dvd's as a back-up...the problem with is, if the HD should crap out, the dvd will need to be restored from another comp. runnibg the same burning software.

I'm thinking an external USB HD is the way to roll.

You have one of those products that creates its own propriety format backup?

If you're running Windows you should be able to recover using a floppy (I think Windows recovery still needs a floppy -- I've not had to recover a Windows box in ages), Windows native "backup" media and the installation CD.

You'll like the USB HD if you get one. You might even start making backups more often.

 

[dcspector]

celtic,

Why not. If they are bundled for more than 24" you have to derate.
Don

Don normally in a typical size panel the 24" is not a concern due to branching off of the "branch circuit conductors" to the individual ocpd,s when making up a panel. Hope I explained it correctly or.....what I meant.

 

[tallgirl]

Don normally in a typical size panel the 24" is not a concern due to branching off of the "branch circuit conductors" to the individual ocpd,s when making up a panel. Hope I explained it correctly or.....what I meant.

Greg, that might be the case for the conductors near whichever end they all enter, but a 24" bundle, especially if there is a main disconnect at the top which has to be traversed on the way up and out of the panel, doesn't seem all that unlikely.

That said, I was chatting with someone recently on the subject of Romex and ampacity, and he remarked that he thought most of the individual conductors INSIDE Romex were actually solid THHN. If that's correct, I'd assume the 40 amp starting value for #12 THHN (sorry, Code book is hiding somewhere in the house again ...) would be used for derating. So long as it isn't derated below 20A, which would require a hella bunch of bundled conductors, there shouldn't be a problem because of the 20A "small conductor" limit on #12.

(Okay, have at it -- I'm sure I said something wrong in that previous paragraph somewhere ...)

 

[iwire]

Julie, basically because of the small conductor rule you mentioned derating is not an issue on 14, 12 and 10 AWG until you bundle more than 9 current conductors together. After that things change.

FWIW where I live we have less restrictive derating rules.

 

[dcspector]

Julie....... picture individual conductors entering a panel "NOT ROMEX".......this would be a a load center Main breaker.... Grounds and grounded conductors to ground bars......hots to breakers as they fan out to their terminations do you see in a normal panel...... greater than 24" of bundling?

 

[celtic]

celtic,

Why not. If they are bundled for more than 24" you have to derate.
Don

Why do you have to derate?

Article please.

I need to "buy" some time to back my statement up....in the meantime, you show me where the NEC says bundeling in a panel IS a violation/requires derating.

 

[tallgirl]

Why do you have to derate?

Article please.

I need to "buy" some time to back my statement up....in the meantime, you show me where the NEC says bundeling in a panel IS a violation/requires derating.

Show me where bundling inside a panel is different from bundling outside a panel. And 310.15 (B) (2) doesn't say "except inside a panel" -- inside a panel is either inside a raceway or not inside a raceway, and those are the only two categories I see listed.

 

[tallgirl]

Julie, basically because of the small conductor rule you mentioned derating is not an issue on 14, 12 and 10 AWG until you bundle more than 9 current conductors together. After that things change.

Yeah, that's why I'm thinking it might be an issue -- if one is dealing with a 42 slot panel (not a 30 slot panel, but something with 42 actual slots ...), they're going to have up to 21 (or so ...) conductors they might want to bundle from where they enter the top of the panel, past the main disconnect, until they've used up 12 (21 - 9 = 12) conductors. And I'm betting that could be over 24".

FWIW where I live we have less restrictive derating rules.

That's because the ambient temperature there is mostly frozen solid

Julie....... picture individual conductors entering a panel "NOT ROMEX".......this would be a a load center Main breaker.... Grounds and grounded conductors to ground bars......hots to breakers as they fan out to their terminations do you see in a normal panel...... greater than 24" of bundling?

See my response to Bob. Perhaps not common, but it would certainly seem possible, especially if it's uncommon enough that people don't take it into consideration.

And my comment about Romex wasn't specifically about Romex, it was asking what the insulation is on the wires inside Romex. It was just a random question from an earlier discussion that happened somewhere else.

 

[dcspector]

...................................zip ties................Yep!

 

[dnem]

On the issue of the 24" max for bundling inside the panel, are you guys counting
A) the total number of inches that the conductors are running in the same direction between the first zip tie and the last zip tie
or
B) the total number of inches that the conductors are in contact with the zip ties

I've always looked at B. . So with quarter inch wide zip ties you could put on 96 zip ties side by side before you reach the 24" limit.

The only thing I ever look for is if they tape the wires together and continue the tape encapsulation for longer than 24" or zip tie / tape / bundle more than 9 conductors which drops the ampacity to 50% [Table310.15(B)(2)(a)].

David

 

[dnem]

That said, I was chatting with someone recently on the subject of Romex and ampacity, and he remarked that he thought most of the individual conductors INSIDE Romex were actually solid THHN. If that's correct, I'd assume the 40 amp starting value for #12 THHN (sorry, Code book is hiding somewhere in the house again ...) would be used for derating. So long as it isn't derated below 20A, which would require a hella bunch of bundled conductors, there shouldn't be a problem because of the 20A "small conductor" limit on #12.

90? calc starting temp yes, 334.80, but only 30a for 12gauge, Table310.16

Julie, basically because of the small conductor rule you mentioned derating is not an issue on 14, 12 and 10 AWG until you bundle more than 9 current conductors together. After that things change.

Yeah, with the exception of 10gauge which becomes an issue after 6 bundled

Table310.15(B)(2)(a)
7-9 = 70% derating
10-20 = 50% derating

Table310.16
14gauge, 240.4(D) 15a breaker, 25a x 70% = 17.5a, still 15a breaker, 25a x 50% = 12.5a
12gauge, 240.4(D) 20a breaker, 30a x 70% = 21a, still 20a breaker, 30a x 50% = 15a, 15a breaker
10gauge, 240.4(D) 30a breaker, 40a x 70% = 28a, 25a breaker, 40a x 50% = 20a, 20a breaker

David

 

[don_resqcapt19]

celtic,

I need to "buy" some time to back my statement up....in the meantime, you show me where the NEC says bundeling in a panel IS a violation/requires derating.

This section covers the issue.

310.15(B)(2)(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

Don

 

[tallgirl]

Don,

I think the issue is "what does 'maintaining spacing' mean?" This is why I think that wire looms are the way to go -- they "maintain spacing" while at the same time maintaining neatness.

 

[rokefuller]

You won't find this in the NEC, past or present.

The requirements, that control, first, whether tandems can be installed at all, and, second, on which poles and how many poles, are published by the manufacturer.

Careful examination of a panel's bus diagram (pasted inside, or on, the panel, if present) will tell a lot.

I had come to the conclusion that this was the case. I evidently had installed some panels when I was younger that had those manufacture's guidelines and that stayed in the back of my mind. Thank's to all who responded.

 

[celtic]

celtic,

This section covers the issue.

Don

310.15(B)(2)(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

Is a panel a raceway?

Raceway.
An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.

I didn't check the 615 hits I got for a "raceway" in my NECH to see all the "additional functions as permitted in this Code." , but a panel is NOT "expressly for holding wires, cables...".