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#47128 - 01/10/05 08:35 PM Temperature ratings of circuit breakers
BigB Offline
Member

Registered: 03/31/04
Posts: 727
Loc: Tucson, AZ USA
I was under the impression all wiring device terminations (including circuit breakers) with ratings under 100 Amps must be treated as 60C terminals unless otherwise marked. I am looking at Spa instructions which call for a 50 amp circuit using #8 THHN/THWN. Using the 60C column only allows for 40 Amps. Are the instructions wrong or is it me?

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#47129 - 01/12/05 02:18 AM Re: Temperature ratings of circuit breakers
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
BigB...maybe 430.53(C)applies to your installation?

shortcircuit

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#47130 - 01/12/05 03:11 AM Re: Temperature ratings of circuit breakers
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Big B you are remebering only part of the code section.

Part of 110.14(C)(1)
 Quote:
(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(1) through (6).
(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:

(1)Conductors rated 60°C (140°F)

(2)Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used

(3)Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors

(4)For motors marked with design letters B, C, D, or E, conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity.


Look at your breakers, I would bet they are marked 60/75 C or just 75 C

[This message has been edited by iwire (edited 01-12-2005).]
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#47131 - 01/12/05 07:24 PM Re: Temperature ratings of circuit breakers
BigB Offline
Member

Registered: 03/31/04
Posts: 727
Loc: Tucson, AZ USA
That's just it iwire, the breaker offers no help. It is a GE THQL 2 pole 50 amp. There is a circle on it with "40C" printed inside the circle, which I think must indicate the ambient temperature it is calibrated at. I tried to research breaker specs but couldn't come up with the info.

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#47132 - 01/12/05 07:38 PM Re: Temperature ratings of circuit breakers
BigB Offline
Member

Registered: 03/31/04
Posts: 727
Loc: Tucson, AZ USA
OK I just went out to my truck and examined a bunch of breakers and sure enough, they do say 60/75C on most all of them. I had to get out a magnifying glass for some. I don't have that GE here, I wonder if I just didn't see the fine print.

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#47133 - 01/13/05 02:20 AM Re: Temperature ratings of circuit breakers
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
 Quote:
I had to get out a magnifying glass for some.


That and good lighting...it is frustrating to find the markings on some equipment.

Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#47134 - 01/13/05 03:18 AM Re: Temperature ratings of circuit breakers
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
If I wire a 12kw range in a dwelling with 8-3 copper romex and it hooks up to a 50 amp breaker...how is this OK if the copper wire amperage is 40 amps based on the 60C column?

shortcircuit

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#47135 - 01/13/05 03:39 AM Re: Temperature ratings of circuit breakers
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Big B said

 Quote:
#8 THHN/THWN


Which makes me think he is running a raceway so the 75 C rating could apply.

If it is NM then you are stuck with the 60 C rating.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#47136 - 01/13/05 04:54 AM Re: Temperature ratings of circuit breakers
shortcircuit Offline
Member

Registered: 06/27/04
Posts: 608
Loc: massachusetts
But romex comes with 90C rated conductors.This is confusing me here.Help me out?

shortcircuit

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#47137 - 01/13/05 07:26 AM Re: Temperature ratings of circuit breakers
sabrown Offline
Member

Registered: 12/12/02
Posts: 297
Loc: Ogden, Utah, USA
Look in 334.80 Ampacity. Ampacity of NM type cables shall be 60 degree with the 90 degree rating allowed for derating purposes.

Shane

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