Miniature Circuit Breakers B Curve / C Curve

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Saturn_Europa

Saturn_Europa

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Electrician Limited License NC, QMED Electrician
My organization works in countries primarily on the 400/230 50 hz standard. We use 2 pole miniature circuit breakers with a B curve. The B curve will trip the magnet part of the thermal magnet breaker in 3 to 5 times the current rating. C curves will trip at 5 to 10 times the current rating. We use B curve because we are often on generator power and 10 times the current rating of a 63 amp breaker will be a larger fault current then the genset can provide and cause a fire. Below is a link to a common breaker we use.

A9F76225 - Miniature circuit-breaker, Acti9 iC60N, 2P, 25 A, B curve, 6000 A (IEC 60898-1), 10 kA (IEC 60947-2) | Schneider Electric Egypt

Schneider Electric Egypt. A9F76225 - Miniature circuit-breaker, Acti9 iC60N, 2P, 25 A, B curve, 6000 A (IEC 60898-1), 10 kA (IEC 60947-2).
www.se.com www.se.com

We are setting up a project in Haiti on the US standard. Most of the electrical equipment in Haiti is residential US brands sent from Florida.

What is the trip curve of a Square D QO, 20A, 1 pole, 120/240VAC? I cant find much on trip curves for NEMA rated equipment.
I found this document but do not understand it:

Trip Curve: QO 20A 1P - No. 730-03 | Schneider Electric

Trip Curve: QO 20A 1P - No. 730-03
www.se.com www.se.com

In fact I had never heard of a B or C curve breaker until I started working over seas. Are off the shelf Homeline, QO, GE, Siemens, or Eaton residential breakers given a trip curve such as B, C, D, K and Z curves like MCBs are?

Any help would be appreciated.
 
That document from Schneider shows that the magnetic trip region is between 6 and a little over 10 times the breaker's nominal current rating.
 
We (North America) do not have selectable "trip curves" for our circuit breakers. You get what they give you. The Square D curve is similar to the C curve, but there is no other option.

But I think your reasoning for wanting to use a B curve is flawed by the way. Breakers are intended to protect the LOAD, not the source. The lower trip curve will not RESTRICT the current going to the load, it will just trip faster. If you are on a generator and there is a short circuit in the load, the breaker having a higher trip curve will not allow the generator to be damaged, the generator will just not HAVE the added short circuit current to feed to the short. The C curve breaker will still trip if there is a short circuit, it just might take a few milliseconds longer.
 
Saturn_Europa your heading for a bumpy road trying to mix international (IEC) standards and US standards.
Seems like your the AHJ and installer.
Sounds like an untrained person has been selecting equipment or suppliers for you to figure out how to install.
Its like mixing imperial and metric threads.
I would pick a 'system' and a standard and make it a requirement that all materials comply with that standard, which may not be what the bosses want to here..
Then document any variations you need from that standard, like the grounded circuit conductor color, voltages..
It does not matter which system you choose, its important to consistently use one for this project.
FWIW I think the last construction code that Haiti used was actually Canadian, so perhaps use the CEC.
And keep us posted, sounds like a cool project.
 
We are building a new hospital in Haiti. But we actually have a project there now. The city service is 120/240 60Hz. But a lot of the medical equipment is coming from Europe so they are running a separate generator with dedicated power lines for 220 volt 50 Hz equipment.

Its not ideal.

One standard is def the way to go :)


tortuga said:
Saturn_Europa your heading for a bumpy road trying to mix international (IEC) standards and US standards.
Seems like your the AHJ and installer.
Sounds like an untrained person has been selecting equipment or suppliers for you to figure out how to install.
Its like mixing imperial and metric threads.
I would pick a 'system' and a standard and make it a requirement that all materials comply with that standard, which may not be what the bosses want to here..
Then document any variations you need from that standard, like the grounded circuit conductor color, voltages..
It does not matter which system you choose, its important to consistently use one for this project.
FWIW I think the last construction code that Haiti used was actually Canadian, so perhaps use the CEC.
And keep us posted, sounds like a cool project
Click to expand...
 
Saturn_Europa said:
We are building a new hospital in Haiti. But we actually have a project there now. The city service is 120/240 60Hz. But a lot of the medical equipment is coming from Europe so they are running a separate generator with dedicated power lines for 220 volt 50 Hz equipment.

Its not ideal.

One standard is def the way to go :)
Click to expand...

Are frequency converters for supplying 50 Hz power from a 60 Hz city service an option you could use, so that you don't have to run a generator all the time?
One supplier of such equipment is linked below as an example. I have no experience with them.

https://50hz.com/
 
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