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Temperature ratings of circuit breakers #47128
01/10/05 11:35 PM
01/10/05 11:35 PM
B
BigB  Offline OP
Member
Joined: Mar 2004
Posts: 721
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?

Work Gear for Electricians and the Trades
Re: Temperature ratings of circuit breakers #47129
01/12/05 05:18 AM
01/12/05 05:18 AM
S
shortcircuit  Offline
Member
Joined: Jun 2004
Posts: 608
massachusetts
BigB...maybe 430.53(C)applies to your installation?

shortcircuit

Re: Temperature ratings of circuit breakers #47130
01/12/05 06:11 AM
01/12/05 06:11 AM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Big B you are remebering only part of the code section. [Linked Image]

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
Re: Temperature ratings of circuit breakers #47131
01/12/05 10:24 PM
01/12/05 10:24 PM
B
BigB  Offline OP
Member
Joined: Mar 2004
Posts: 721
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.

Re: Temperature ratings of circuit breakers #47132
01/12/05 10:38 PM
01/12/05 10:38 PM
B
BigB  Offline OP
Member
Joined: Mar 2004
Posts: 721
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.

Re: Temperature ratings of circuit breakers #47133
01/13/05 05:20 AM
01/13/05 05:20 AM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
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. [Linked Image]

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Temperature ratings of circuit breakers #47134
01/13/05 06:18 AM
01/13/05 06:18 AM
S
shortcircuit  Offline
Member
Joined: Jun 2004
Posts: 608
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

Re: Temperature ratings of circuit breakers #47135
01/13/05 06:39 AM
01/13/05 06:39 AM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
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
Re: Temperature ratings of circuit breakers #47136
01/13/05 07:54 AM
01/13/05 07:54 AM
S
shortcircuit  Offline
Member
Joined: Jun 2004
Posts: 608
massachusetts
But romex comes with 90C rated conductors.This is confusing me here.Help me out?

shortcircuit

Re: Temperature ratings of circuit breakers #47137
01/13/05 10:26 AM
01/13/05 10:26 AM
S
sabrown  Offline
Member
Joined: Dec 2002
Posts: 302
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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