Busbar ampacity

[arrail.thomas]

Whats the maximum amapacity of 3"×3/4 copper busbar. And code reference it'd applicable

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[electrofelon]

Whats the maximum amapacity of 3"×3/4 copper busbar. And code reference it'd applicable

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Under what standard or rules are you working under? IMO Under the NEC we can't make CCC out of busbars.

Edit: Although, 366.23 does state the ampacity of copper bus bars in auxiliary gutters shall be 1000A/sq in and that is a pretty common rule of thumb you hear out in the wild.

 

[roger]

Whats the maximum amapacity of 3"×3/4 copper busbar. And code reference it'd applicable

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See article 366.23(A)

Roger

 

[petersonra]

Under what standard or rules are you working under? IMO Under the NEC we can't make CCC out of busbars.

Edit: Although, 366.23 does state the ampacity of copper bus bars in auxiliary gutters shall be 1000A/sq in and that is a pretty common rule of thumb you hear out in the wild.

It seems to me that if the code indicates the ampacity of copper bars in a gutter is a certain value, that strongly implies you can use them in a gutter that way.

I am inclined to agree that absent some other dispensation that one cannot use bus bars as part of an installation, although they can be part of equipment.

However, I would point out this gem. Applies to over 1000V only.

110.36 Circuit Conductors. Circuit conductors shall be
permitted to be installed in raceways; in cable trays; as metalclad
cable Type MC; as bare wire, cable, and busbars; or as Type
MV cables or conductors as provided in 300.37, 300.39, 300.40,
and 300.50. Bare live conductors shall comply with 490.24.

 

[electrofelon]

It seems to me that if the code indicates the ampacity of copper bars in a gutter is a certain value, that strongly implies you can use them in a gutter that way.

I am inclined to agree that absent some other dispensation that one cannot use bus bars as part of an installation, although they can be part of equipment.

However, I would point out this gem. Applies to over 1000V only.

If you look at 366.6, indoor metal auxiliary gutters are not required to be listed so apparently I could homebrew one of those. I would like to emphasize that we are talking article 366 here and doesn't grant us universal permission to make and use copper bus bars.

 

[Jraef]

You need context. The ampacity of busbar inside of equipment, like switchgear, will be different than something like bus duct or busbar in a gutter, because part of the current rating has to do with allowable temperature rise above ambient, which then relates to how it dissipates heat into its surrounding space.

 

[petersonra]

If you look at 366.6, indoor metal auxiliary gutters are not required to be listed so apparently I could homebrew one of those. I would like to emphasize that we are talking article 366 here and doesn't grant us universal permission to make and use copper bus bars.

I am inclined to agree on that point. I am not sure how you would convince an inspector though that your homebrew busbar system was braced properly for the available short circuit current. Having said that, there does not appear to be any NEC requirement at all to brace conductors to take the available short circuit current. It is a curious omission.

 

[Sahib]

If you look at 366.6, indoor metal auxiliary gutters are not required to be listed so apparently I could homebrew one of those. I would like to emphasize that we are talking article 366 here and doesn't grant us universal permission to make and use copper bus bars.

A home made set of busbars is unlikely to have been tested for fault withstand capacity and may be too poorly brazed against short circuit currents. Oh! Bob already made my point and much better at that.

 

[Jraef]

A home made set of busbars is unlikely to have been tested for fault withstand capacity and may be too poorly brazed against short circuit currents. Oh! Bob already made my point and much better at that.

You probably meant "braced", not "brazed" I think...

 

[jim dungar]

Having said that, there does not appear to be any NEC requirement at all to brace conductors to take the available short circuit current. It is a curious omission.

What about 110.10?

 

[petersonra]

What about 110.10?

presumably you are referring to this part of 110.10

110.10 Circuit Impedance, Short-Circuit Current Ratings, and
Other Characteristics. The overcurrent protective devices, the
total impedance, the equipment short-circuit current ratings,
and other characteristics of the circuit to be protected shall be
selected and coordinated to permit the circuit protective devices
used to clear a fault to do so without extensive damage to
the electrical equipment of the circuit.

Note it does not say anything about conductors here - just equipment. It does not appear to me that the term "equipment" includes conductors.

Equipment. A general term, including fittings, devices, appliances,
luminaires, apparatus, machinery, and the like used as a
part of, or in connection with, an electrical installation.

 

[infinity]

What does home brewed or bracing have to do with the OP? Sounds to me like a test or homework question.

 

[electrofelon]

What does home brewed or bracing have to do with the OP? Sounds to me like a test or homework question.

I think it is relevant. If the question was specific to article 336, I would be content giving a simple answer. If not I think we need to know more about the context of the question. Busbar ampacity is not so simple. There is more information in this older thread:

http://forums.mikeholt.com/showthread.php?t=52182

 

[jim dungar]

presumably you are referring to this part of 110.10

Note it does not say anything about conductors here - just equipment. It does not appear to me that the term "equipment" includes conductors.

The definition you quoted said "and the like used as a part of, or in connection with, an electrical installation", why wouldn't conductors meet this definition?
Also, the definition says "including" a list of items, it does not say limited to this list.

 

[arrail.thomas]

This is not spelling out anything bit a gutter.

See article 366.23(A)

Roger

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[roger]

This is not spelling out anything bit a gutter.

No, it tells you how to calculate the ampacity of a bussbar and is the only place in the NEC that you will find anything about it.

The current carried continuously in bare copper bars in sheet metal auxiliary gutters shall
not exceed 1.55 amperes/mm2 (1000 amperes/in.2) of cross
section of the conductor. For aluminum bars, the current carried
continuously shall not exceed 1.09 amperes/mm2 (700
amperes/in.2) of cross section of the conductor

With that said you specifically asked for a code reference and I gave it to you.


Roger

 

[Kinexis]

Whats the maximum amapacity of 3"×3/4 copper busbar. And code reference it'd applicable

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it would be designated by the manufacturer(which could be you if you make them in your garage)


110.2
110.3(a)(b)and (c)
110.8

i think there might be a reference to bus bar sizes in grounding somewhere



https://stormpowercomponents.com/resources/ampacity-tables/quick-copper-busbar-design-selector

 

[arrail.thomas]

No, it tells you how to calculate the ampacity of a bussbar and is the only place in the NEC that you will find anything about it.



With that said you specifically asked for a code reference and I gave it to you.


Roger

So... 198 amps ....if im doing the math right.

1000A/(3×3/4)^2=197.53

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[infinity]

So... 198 amps ....if im doing the math right.

1000A/(3×3/4)^2=197.53

If you're using Rogers code section, 3*3/4=2.25 square inches. 2.25*1000=2250