cant find code

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Its a manufacture rating on the most part. Some breakers are rated 100% but many are not.
 
All breakers can be loaded 100% for 179 min 59 sec

Roger
 
So then what is the specs I have seen that state 100% rated and 80% rated where does this come into play?
 
treyp3 said:
So then a 20a breaker is permissable for a 19a load but why 3 hours? If I had a 15a 4 hour load would the 20a breaker not be ok, ie 15 x 125% = 18.75.
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Yes, the 20A breaker is OK for a 15A continuous load.

A 20A breaker is permissible for a 20A non-continuous load. A 20A breaker is permissible for a 16A continuous load. A 20A breaker is OK for a 10A continuous and 7.5A non-continuous load on the same circuit, etc.
 
Sierrasparky said:
So then what is the specs I have seen that state 100% rated and 80% rated where does this come into play?
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I don't think (I could be wrong) that there is such thing as an 80% rated circuit breaker. The breaker is designed to carry 100% of its rating for infinite time under ideal test conditions. However, the conditions of its installation are such that heat will affect the breaker, so the NEC dictates the application of the breaker at 125% of continuous load plus 100% of non-continuous load.

The use of a breaker at its 100% for continuous loads is dictated by the Assembly, including the breaker be "listed" for operation at 100%. The assembly would be tested to ensure that the heat from the continuous 100% loading for be safely dissipated.

I'm sure some of the UL experts in the forum could explain this better.
 
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david luchini said:
Yes, the 20A breaker is OK for a 15A continuous load.

A 20A breaker is permissible for a 20A non-continuous load. A 20A breaker is permissible for a 16A continuous load. A 20A breaker is OK for a 10A continuous and 7.5A non-continuous load on the same circuit, etc.
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Thanks David. That is how I see it, but Ive heard this 80% thing time and again and I was begining to doubt myself. I must have spent an hour in the code book trying to prove myself wrong, and have not been able to. If someone else can show me where it says otherwise please do.
 
treyp3 said:
So then a 20a breaker is permissable for a 19a load but why 3 hours? If I had a 15a 4 hour load would the 20a breaker not be ok, ie 15 x 125% = 18.75.
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Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.
 
This is about the closest thing to an answer to the OP question that I find.

210.20 Overcurrent Protection.

Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
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9.1.2.13 of UL Standard 489
9.1.4.4 of UL Standard 489

100% rated needs cabinet volume and venting, bus, listed for 100% - and conductor 100% rated. It may save $ if bus size and conductor savings etc. are there.
Probably more of a UL issue and in the case of a continuous load.
 
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Finite10 said:
9.1.2.13 of UL Standard 489
9.1.4.4 of UL Standard 489

100% rated needs cabinet volume and venting, bus, listed for 100% - and conductor 100% rated. It may save $ if bus size and conductor savings etc. are there.
Probably more of a UL issue and in the case of a continuous load.
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I seldom see them but I understand some (probably most new units nowadays) that are rated 100% have electronic tripping devices instead of thermal trip devices. That would make a difference in heat produced and management of that heat.
 
The standard thermal magnetic breakers we use are rated 100% non-continuous or 80% continuous.

The following from the UL white book.

CIRCUIT BREAKERS, MOLDED-CASE AND
CIRCUIT-BREAKER ENCLOSURES (DIVQ)

USE
This category covers circuit breakers and circuit-breaker enclosures
designed to provide service-entrance, feeder or branch-circuit protection in
accordance with ANSI/NFPA 70, ‘‘National Electrical Code’’ (NEC).
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Unless otherwise marked, circuit breakers should not be loaded to exceed
80% of their current rating, where in normal operation the load will continue
for three hours or more.
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From the NEC we can get the definition of continuous load.

Continuous Load. A load where the maximum current is
expected to continue for 3 hours or more.
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Thanks iwire, I have one of those white books back at my desk. So far I've reviewed the cover thoroughly.

I guess the smaller breaker frame and space savings from reduced equipment size is a money consideration. I have no idea how much more the 100% stuff costs.

Square D has 100% equipment, "Power Line" IIRC? Probably Schneider and others too. Anyhow, it all has to be 'listed'.
 
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