Singlepole is tripping the main

[tom baker]

Typical miscoordination of breakers issue. Age doesn't matter, it's all about how they are designed by the manufacturer. The attached picture shows why the main may have tripped before the 15A breaker. The areas that are shaded red and blue represent the sensing boundary of each breaker. Basically, if a fault happens anywhere within those boundaries the breaker will see it and trip. The chart reads amperage on the x-axis vs. time in seconds on the y-axis. So for example, point (1000, 0.1) means that there was a fault of 1000 amps that lasted for 0.1 seconds. Remember, whichever breaker gets its boundary crossed by the fault current first will trip. If the fault crosses both breakers boundaries at the same time then either of them may trip first.

Nice dwg thanks for taking the time on that

 

[mbrooke]

It must be hell to find problems everywhere you look.

What does your remark have to do with RJ's question? :blink:

 

[mbrooke]

What are the mag trip ratings of both the 60 & 15A ocpd ?

Please keep in mind the nrtl's seem to not care.......

~RJ~

Well, they have cared...

But, what models are you interested in?

QO 15:

http://static.schneider-electric.us...it Breakers/QO-QOB Circuit Breakers/730-2.pdf


2 pole QO 15:

http://static.schneider-electric.us...it Breakers/QO-QOB Circuit Breakers/730-4.pdf


QO 60:

http://static.schneider-electric.us...it Breakers/QO-QOB Circuit Breakers/730-6.pdf

Although on others it varies, older single pole breakers often have trip curves that look like the 60amp shown here.

 

[mbrooke]

What are the mag trip ratings of both the 60 & 15A ocpd ?

Please keep in mind the nrtl's seem to not care.......

~RJ~

And, GE:

older single pole 15s:

http://apps.geindustrial.com/publib...ent Curves|GES-9884|PDF&filename=GES-9884.pdf

Newer single pole 15s:

http://apps.geindustrial.com/publib...|GES-9886B|PDF&filename=GES-9886B_v2 9-09.pdf

2 pole 60s:

http://apps.geindustrial.com/publib...t Curves|GES-6203B|PDF&filename=GES-6203B.pdf


When an older single pole 15 is used the 60 tripping first is almost a given.