Panelboard 100% Rated?

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I think the panel bus needs to be rated 125 amps or be rated for 100% use.

ARTICLE 215
Feeders

215.2 Minimum Rating and Size.

(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not
less than required to supply the load as calculated in Parts
III, IV, and V of Article 220. The minimum feeder-circuit
conductor size, before the application of any adjustment or
correction factors, shall have an allowable ampacity not
less than the noncontinuous load plus 125 percent of the
continuous load.

Exception No. 1: Where the assembly, including the overcurrent
devices protecting the feeder(s), is listed for operation
at 100 percent of its rating, the allowable ampacity of
the feeder conductors shall be permitted to be not less than
the sum of the continuous load plus the noncontinuous
load.

Exception No. 2: Grounded conductors that are not connected
to an overcurrent device shall be permitted to be
sized at 100 percent of the continuous and noncontinuous
load.

The size of the feeder circuit grounded conductor shall
not be smaller than that required by 250.122, except that
250.122(F) shall not apply where grounded conductors are
run in parallel.

Additional minimum sizes shall be as specified in
215.2(A)(2) and (A)(3) under the conditions stipulated.
Click to expand...


Now looking at Article 100

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.
Click to expand...

It sure seems like the panel buses are feeders.
 
iwire said:
I think the panel bus needs to be rated 125 amps or be rated for 100% use.
It sure seems like the panel buses are feeders.
Click to expand...

Bob I am not sure I agree but I disagree about the panel bus being a feeder. Here is why.

If the bus were a feeder and I ran a 100 amp conductor to a 200 MLO panel then I would have to upsize my egc proportionately. 250.122(B) I know that you know the section- it is for others. So I run NM cable to the panel and now I am in violation because of the bus. :)
 
ARTICLE 215
Feeders

215.2 Minimum Rating and Size.

(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not
less than required to supply the load as calculated in Parts
III, IV, and V of Article 220. The minimum feeder-circuit
conductor size, before the application of any adjustment or
correction factors, shall have an allowable ampacity not
less than the noncontinuous load plus 125 percent of the
continuous load.

Exception No. 1: Where the assembly, including the overcurrent
devices protecting the feeder(s), is listed for operation
at 100 percent of its rating, the allowable ampacity of
the feeder conductors shall be permitted to be not less than
the sum of the continuous load plus the noncontinuous
load.
Click to expand...

Wouldn't a fused switch (I think all are 100% rated, but I don't have proof) or 100% rated upstream OCPD make it okay to size the downstream conductor and panelboard for the continuous load plus the noncontinuous load? I only have 100A continuous, so 100A of wire and panelboard should be enough. Do you suspect that if the 100% rated main breaker were in the panelboard, the panelboard would have to have a special 100% rating to comply with "Where the assembly, including the overcurrent
devices ...."
 
ron said:
Wouldn't a fused switch (I think all are 100% rated, but I don't have proof) or 100% rated upstream OCPD make it okay to size the downstream conductor and panelboard for the continuous load plus the noncontinuous load? I only have 100A continuous, so 100A of wire and panelboard should be enough.
Click to expand...


I don't see how.


Do you suspect that if the 100% rated main breaker were in the panelboard, the panelboard would have to have a special 100% rating to comply with "Where the assembly, including the overcurrent
devices ...."
Click to expand...

That is exactly what I suspect.

Maybe Jim D. can jump in, he is a master of equipment and listings. :cool:
 
Panel bus is rated 100%, just like wire conductors are.
Have you ever heard of a code requirement that conductors be sized differently when being protected by a 100% rated breaker?

Fuses and circuit breakers are tested at 100%, but become 80% rated when they are installed into enclosures. 100% rated breakers usually require 'special' well ventilated enclosures. I have never seen 100% rated fusible switch smaller than Class L (800A).

Most panelboard and switchboard bussing is sized based on UL heat rise tests and not on density (Amps/in?).
 
jim dungar said:
Panel bus is rated 100%, just like wire conductors are.
Have you ever heard of a code requirement that conductors be sized differently when being protected by a 100% rated breaker?
Click to expand...

No, but I have heard of having to size the conductors at 125% for continuous loads, so that step is already done.

Lets say I have exactly 100 amps of continuous load.
  • I need a 125 amp standard breaker or a 100 amp 100% breaker
  • I will need 125 amp 'wire' conductors with either breaker unless my 'assembly' meets exception 1
  • It seems the panel buss would have to be 125 amp rated as well as they are feeders unless my 'assembly' meets exception 1
 
Would you agree that the grounded conductor can be 100% rated? If so, then half the panel is addressed. All that remains are the main buses, and I don't know how to convince anyone about the rating of those being rated for continuous use at their listed ampacity.
 
iwire said:
No, but I have heard of having to size the conductors at 125% for continuous loads, so that step is already done.

Lets say I have exactly 100 amps of continuous load.
  • I need a 125 amp standard breaker or a 100 amp 100% breaker
  • I will need 125 amp 'wire' conductors with either breaker unless my 'assembly' meets exception 1
  • It seems the panel buss would have to be 125 amp rated as well as they are feeders unless my 'assembly' meets exception 1
Click to expand...
The key to a 100%-rated application of a 100%-rated breaker therefore lies in meeting the condition of exception 1. Refer to following documentation...

http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=225062
http://ecatalog.squared.com/pubs/Circuit Protection/0600DB0101.pdf
 
Wow, according to the pdf's that Smart posted there only appears to be, at least for Sq. D, switchboards that are rated 100%. This seems to prevent use of any other enclosure at 100%. Am I gathering that info correctly?
 
The references posted by Smart are written for breakers only. Also,The Square D one is almost 9 years old, some 100% rated branch breakers may now be installed in some of theirs I-Line panels.

The PDF does say "switchboards' are not listed as either 100% or 80%, instead they are listed for what devices can be installed in them.

Some FAQs for Square D
QuestionDoes the NQOD panel have a 100% neutral?
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AnswerThe neutral is rated 100% as standard.

QuestionCan a 100% rated Powerpact H frame Main breaker be factory installed into a NQ panelboard
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AnswerNo, NQ interiors and boxes are not able to accept these breakers with 100% rating feature

QuestionIs the I-Line busway 100% rated?
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AnswerYes. The I-Line busway is rated to allow 100% of the current to flow continuously.

Bussing is similar to wire, it is typically applied at 80% unless its protective device is 100% rated.
You can also see that in the conductor selection procedure shown in both manufacturers' examples.
 
iwire said:
No, but I have heard of having to size the conductors at 125% for continuous loads, so that step is already done.


Lets say I have exactly 100 amps of continuous load.
  • I need a 125 amp standard breaker or a 100 amp 100% breaker
  • I will need 125 amp 'wire' conductors with either breaker unless my 'assembly' meets exception 1
  • It seems the panel buss would have to be 125 amp rated as well as they are feeders unless my 'assembly' meets exception 1
Click to expand...

Bob,
I've not seen an "assembly" that includes the breaker, enclosure and a particular wire brand. In your example, I think the wire ampacity is okay at 100A with the 100A 100% rated breaker.


What do you think?
 
ron said:
Bob,
I've not seen an "assembly" that includes the breaker, enclosure and a particular wire brand. In your example, I think the wire ampacity is okay at 100A with the 100A 100% rated breaker.


What do you think?
Click to expand...
Not Bob (thankfully :D), but in this discussion we can't just say a wire ampacity of 100A or a 100A 100%-rated breaker without elaborating. Ultimately the 100%-rated breaker being utilized at its 100% rating requires the wire be to be of the 90?C insulation type (or better) but the ampacity is based on the 75?C column ampacity of the same size. Additionally, the enclosure listing or minimum size requirements must be met. Only when all three conditions are met is the feeder 100% rated for continuous load.
 
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