Sizing wire for 40C Breaker
- Thread starter shills
- Start date
- Status
- Location
- Massachusetts
40 C is the ambient temp rating of the breaker, not the terminal rating.
The terminal ratings will be 75 C.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The 40? C that you're seeing is not the terminal temperature but the ambient temperature of the setting of the device. If not otherwise noted on the breaker I would use the 60? C ampacity in 310.16.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Bob, do even old FPE CB's have the 75? C rating?
- Location
- Massachusetts
I am not sure, but I doubt they where ever as low as 40C. 110.14 tells us they are at least 75C.
rated over 100 A).
Distribution and Control Equipment Terminations
Most terminals are suitable for use only with copper wire. Where aluminum
or copper-clad aluminum wire can or shall be used (some crimp terminals
may be Listed only for aluminum wire), there is marking to indicate
this. Such marking is required to be independent of any marking on terminal
connectors, such as on a wiring diagram or other visible location. The
marking may be in an abbreviated form, such as ??AL-CU.??
Except as noted in the following paragraphs or in the general Guide Information
for some product categories, the termination provisions are based on
the use of 60?C ampacities for wire size Nos. 14-1 AWG, and 75?C ampacities
for wire size Nos. 1/0 AWG and larger, as specified in Table 310.16 of
the NEC.
Some distribution and control equipment is marked to indicate the
required temperature rating of each field-installed conductor. If the equipment,
normally intended for connection by wire sizes within the range 14-1
AWG, is marked ??75C?? or ??60/75C,?? it is intended that 75?C insulated wire
may be used at full 75?C ampacity. Where the connection is made to a circuit
breaker or switch within the equipment, such a circuit breaker or
switch must also be marked for the temperature rating of the conductor.
A 75?C conductor temperature marking on a circuit breaker or switch normally
intended for wire sizes 14-1 AWG does not in itself indicate that 75?C
insulated wire can be used unless 1) the circuit breaker or switch is used by
itself, such as in a separate enclosure, or 2) the equipment in which the circuit
breaker or switch is installed is also so marked.
A 75 or 90?C temperature marking on a terminal (e.g.,or copper-clad aluminum wire can or shall be used (some crimp terminals
may be Listed only for aluminum wire), there is marking to indicate
this. Such marking is required to be independent of any marking on terminal
connectors, such as on a wiring diagram or other visible location. The
marking may be in an abbreviated form, such as ??AL-CU.??
Except as noted in the following paragraphs or in the general Guide Information
for some product categories, the termination provisions are based on
the use of 60?C ampacities for wire size Nos. 14-1 AWG, and 75?C ampacities
for wire size Nos. 1/0 AWG and larger, as specified in Table 310.16 of
the NEC.
Some distribution and control equipment is marked to indicate the
required temperature rating of each field-installed conductor. If the equipment,
normally intended for connection by wire sizes within the range 14-1
AWG, is marked ??75C?? or ??60/75C,?? it is intended that 75?C insulated wire
may be used at full 75?C ampacity. Where the connection is made to a circuit
breaker or switch within the equipment, such a circuit breaker or
switch must also be marked for the temperature rating of the conductor.
A 75?C conductor temperature marking on a circuit breaker or switch normally
intended for wire sizes 14-1 AWG does not in itself indicate that 75?C
insulated wire can be used unless 1) the circuit breaker or switch is used by
itself, such as in a separate enclosure, or 2) the equipment in which the circuit
breaker or switch is installed is also so marked.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I'm assuming that this is from the 2008 NEC. In the 1987 NEC there is no provision for 60/75? connections in 110-14. Since this is Federal Pacific equipment it likely predates the 1987 NEC so I wouldn't assume that it has a terminal rating of 75? based on the 2008 NEC. Just a thought.
- Location
- Massachusetts
I understand your point but I do not know of anything that says we cannot use todays code on yesterdays equipment.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It is an interesting point. If the breakers back then were only manufactured at 60C then using it at 75C would not be a good idea even if the code allows it now.
Is there magic when sizing a breaker?
This is the way I look at it.
I was of the opinion that breakers protect wire. The rated wire is sized to carry the calculated load with the various derating factors that may apply.
As such, you have to know what the non continuous and continuous loads are select a rated wire size that will care that load. If that ampacity wire is not standard select the next standard size. The select a breaker based upon the ampacity of the wire. If there is no standard breaker rating equal to the ampacity rating of the wire then you are allowed to select a breaker of the closest rating which is higher. If the wire ampacity is over 800a then you have to select the next standard breakers rating below.
In other words it is sizing the wire to carry the calculated load, selecting a breaker to protect the wire.
This is the way I look at it.
I was of the opinion that breakers protect wire. The rated wire is sized to carry the calculated load with the various derating factors that may apply.
As such, you have to know what the non continuous and continuous loads are select a rated wire size that will care that load. If that ampacity wire is not standard select the next standard size. The select a breaker based upon the ampacity of the wire. If there is no standard breaker rating equal to the ampacity rating of the wire then you are allowed to select a breaker of the closest rating which is higher. If the wire ampacity is over 800a then you have to select the next standard breakers rating below.
In other words it is sizing the wire to carry the calculated load, selecting a breaker to protect the wire.
Actaually 110.14 (C) was proposed based on that UL listing. The question is, was the information in the old green book the same as it is now.(white book) I think it was!, So if I am correct, it doesen't matter if it was pre 87 or post 87, the listing guide would have been in effect. Nobody read the guide so they included the info in the 87 NEC. (as I recall)
This building was built in 1974 and there are no markings indicating the terminal temperature rating of the terminals. I see the code reference 110.14(C)(1)(b) for breakers rated over 100A.
I also referenced code books all the way back to the 1964 NEC and found no reference for 40c terminations, only as low as 60C. Therefore I do believe that the larger equipment would have been rated for the at least 60C and probably 75C terminations.
I am going to use 110.14 and a remanufactured FPE breaker.
Thank You
I also referenced code books all the way back to the 1964 NEC and found no reference for 40c terminations, only as low as 60C. Therefore I do believe that the larger equipment would have been rated for the at least 60C and probably 75C terminations.
I am going to use 110.14 and a remanufactured FPE breaker.
Thank You
- Status