80% Loading on circuit breakers - Applicable to European made circuit breakers? 1

[NickParker]

Is the 80% loading rule on a circuit breaker applicable to European made circuit breakers? I think this rule is more common in NEC land. How about this rule in Europe? If this rule is not followed, are the breakers manufactured to different standards in different countries?

 

[waross]

It is an approval issue, Nick.
It is 80% for continuous loading, unless approved for 100% loading. In NEMA land you can use IEC breakers if they are approved for use in NEMA land and for the loading that they are approved for.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jraef]

There is no "80% rule", that's just how it ends up. ALL breakers are rated to carry 100% of their design amps, the difference is in the way they are used.

Conductors for continuous loads must be sized at 125% of the rated load. Then because breakers are sized to protect those conductors, the breaker ENDS UP carrying no more than 80% of their rated amps (80% is the inverse of 125%). If you put a breaker in a switchboard or panelboard, it is NEXT TO other breakers that all generate heat. Standard circuit breakers cannot exceed a maximum of 50°C temperature rise at the wire terminal connection at 100% rated current in 40°C in open air. So because the panel manufacturers know that the breakers are never going to have to carry more than 80% of their load continuously, the panel design uses that fact with regard to spacing and temperature rise of the equipment as a whole. (That by the way is why when you buy a "100% rated" breaker, it is always in a stand-alone enclosure or cubicle with no other breakers or power devices in the same space.)

How does that apply to IEC breakers used here in North America? None of this changes based on the origin of the breakers. If the GEAR is listed with those breakers inside, then they will END UP being used at 80% capacity just like any other switchboard or panelboard mounted breaker. If the gear is NOT listed to use them, you can't use them anyway, regardless of being at 80% or 100% of their rating. If you are building a custom control panel with breakers in them, you will be bound by the same temperature rise requirements of the breakers in your equipment design, so unless it is in OPEN AIR, the same constraints are put on you. Here in North America, those are reflected in design standards like UL or CSA. Are the IEC rules based on the same principles? I believe they are, but that is best answered by those more familiar with IEC.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[che12345]

Dear Mr NickParker
N. " Is the 80% loading rule on a circuit breaker applicable to European made circuit breakers? I think this rule is more common in NEC land. How about this rule in Europe? If this rule is not followed, are the breakers manufactured to different standards in different countries? "
C1. In Europe, IEC 60947-2 covers (ACB and MCCB) . These circuit-breakers are tested in [free air]. They are assigned with [rated uninterrupted current I_u at 40 ⁰ C. Therefore, these breakers can be loaded to 100%.
C2.

 

[davidbeach]

They cannot be loaded to 100%, continuously, if installed where the NEC applies.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[che12345]

Dear Mr NickParker
N. " Is the 80% loading rule on a circuit breaker applicable to European made circuit breakers? I think this rule is more common in NEC land. How about this rule in Europe? If this rule is not followed, are the breakers manufactured to different standards in different countries? "
C1. In Europe, IEC 60947-2 covers (ACB and MCCB) . These circuit-breakers are tested in [free air]. They are assigned with [rated uninterrupted current I_u at 40 ⁰ C. Therefore, these breakers can be loaded to 100%.
C2. Attn: When these breakers are installed inside the switchboard where the [inside] temperature > 40 ⁰ C, a de-rating factor shall be observed. The factor may varies between different ratings. Refer to the manufacturers' published data.
C 3. Refer to IEC 60364-x-xx [Electrical installation of buildings] for installation details. See also IEC 60364-5-51 on [External influences] e.g. Code AA6 etc.
Che Kuan Yau (Singapore)

 

[RedSnake]

There is two IEC standards one fore households IEC 60898-1 and one for industry IEC 60947-2.

Exactly how this two are different when it comes to temperature I do not know, at the moment.

In most small / low Amp applications this cable standard are used as guideline.

Cablearea______________Continuous loads___________Overcurrent fuse ____________Short-circuit fuse

Swedish households are always fitted with C-10, 6kA, 1,5 mm2 it is norm, all premade panels are fitted with them.
At work we are not allowed to use less then 10kA.
Proper calculations are mostly only made in special cases ex. extrem cable lengths etc, high Amp applications and to decide the SC breaking capacity.

Best Regards A



“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[RedSnake]

I can't say I know how NEC applies.
But if the cable must stand får 125% of the breaker amp, which is understandable you don't want the cable to become a fuse. So with a 10A breaker you need a cable that can take 12,5 A.

EU
But if a have a 10 A CB (+40C) and a 1,5 mm2 copper cable max amp 15 A, Max fuse 13A (+40 C)
Then I have In=10 A continuous load and the cable can take 150%.
Not sure this makes sense.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Kiribanda]

All overcurrent devices are designed and tested at 100% of their nameplate current
rating in OPEN AIR. As a result, that continuous current rating is printed
on the device nameplate. When an overcurrent device such as a molded case circuit breaker
(MCCB) or fuse is applied in an ASSEMBLY, it must be sized at 125% of the
continuous load due to restricted cooling inside the assembly. This applies to UL489 MCCBs too.
So 100% rated MCCBs are also in the market but must be mentioned in the name plate.
But this doesn't apply to PCBs.

The Rated Current (In) for IEC60947-2 MCCBs & IEC60898 mcbs are all assigned by the
manufacturer. It is true that per IEC these MCCBs and mcbs can be used up to +40deg C
ambient. But still if one installed a set of these MCCBs and mcbs in a typical
TPN/4P/100A/Flushed type consumer unit enclosure, nobody knows the operating temperature
inside this enclosure. In most cases what happens is since these MCCBs & mcbs are always
oversized, they will NEVER TRIP even the inside temperature of the enclosure reaches 40deg C.