Breaker tripping

[jim dungar]

It is a Type -SO. Sorry about the bad picture

Sorry, I meant the style of the breaker.

 

[jim dungar]

If my memory serves me correctly, Square D KA Frames do have adjustable trip.
If so, as Jraef, mentions, you can possibly adjust the trip to withstand the inrush.
I do not know what effect that might have on your system coordination.

The K family of breakers are in obsolesence. If this is a new I-Line panelboard it will probalby have Powerpact type H, which do not have adjustable magnetic settings, even up to 150A.

 

[Jraef]

If my memory serves me correctly, Square D KA Frames do have adjustable trip.
If so, as Jraef, mentions, you can possibly adjust the trip to withstand the inrush.
I do not know what effect that might have on your system coordination.

Your memory serves you well...

Tripping System
Square D? thermal-magnetic molded case circuit breakers have a permanent trip unit that contains a factory preset thermal trip element and a magnetic trip element in each pole. The thermal trip element is rms sensing. In circuit breakers with frame sizes greater than 100 ampere, the magnetic trip element is field adjustable. A single adjustment simultaneously adjusts the instantaneous trip point in each pole.

The mag trip on that breaker is adjustable from 625 to 1250A. For a transformer with 90A primary current, I'd have that set at 900A minimum, more if necessary. No mention in their data what the factory preset is. If in fact you are already at the maximum setting, you can use a higher rated breaker than what you have under many circumstances. You really need to read Article 450.3 as was previously mentioned.

 

[jim dungar]

Just my my data sheets.
In 2007, that transformer had an inrush of 10.04X. Since then Square D has tried to reduce the inrush, but as of 2009 this one is still at 10.0X (plotted at .1 sec).

So, like jraef said, your breaker needs to be have a minimum magnetic/instantaneous setting of 900A.

 

[Steve O]

I generally use 12X in my calculations for transformer inrush.

As the other members recommended, adjust the instantaneous dials on your Square D KC breaker to 4 (962.5A) to get inrush inside breaker INST curve.

 

[hurk27]

I located Square D's 2004 PDF that covers that breaker, and it does say it has a field ajustable mag pickup from 625 to 1250, but I can't find anything saying how to adjust it? as I see no ajustments on the breaker.

Here's the link to the PDF:
http://ecatalog.squared.com/pubs/Ci...uit Breakers/KA-KC-KH-KI/0601CT9101R12_03.pdf

 

[Steve O]

isn't there a small dial for magnetic adjustment on the lower left side of the breaker?

 

[brian john]

J

So, like jraef said, your breaker needs to be have a minimum magnetic/instantaneous setting of 900A.

Jim where did you get this from ? Sq D web site?

Second is this typical or worse case current. In field measurements I have generally seen 4-6 times, unless it is an out of phase transfer on a ATS.

 

[jim dungar]

Jim where did you get this from ? Sq D web site?

Second is this typical or worse case current. In field measurements I have generally seen 4-6 times, unless it is an out of phase transfer on a ATS.

These are the design specs for this particular (EE75T3H) transformer since 2009. Your Square D rep should be able to provide it to you.

 

[jim dungar]

I located Square D's 2004 PDF that covers that breaker, and it does say it has a field ajustable mag pickup from 625 to 1250, but I can't find anything saying how to adjust it? as I see no ajustments on the breaker.

Here's the link to the PDF:
http://ecatalog.squared.com/pubs/Ci...uit Breakers/KA-KC-KH-KI/0601CT9101R12_03.pdf

The adjustments for a K frame breaker are hidden by the wireway cover.

 

[dconrad]

Breaker tripping

Adjusted the breaker to setting 4, we had a power bump this week and breaker did not trip. So thanks for all the feed back guy's.

 

[tasdes104]

A simple miscalculation is always a disaster waiting for an incident

A simple miscalculation is always a disaster waiting for an incident

63 amp load inrush calculates to around 110 amps nominal, a weak breaker will always trip on the low scale. A 125 breaker low scale always defaults to 80% which is 100amps. This is lower than the calculated inrush, hence your nuisance tripping.

Another issue is that a fuse is rated different than a breaker for percentage of overload resistance.

 

[zog]

63 amp load inrush calculates to around 110 amps nominal, a weak breaker will always trip on the low scale. A 125 breaker low scale always defaults to 80% which is 100amps. This is lower than the calculated inrush, hence your nuisance tripping.

Another issue is that a fuse is rated different than a breaker for percentage of overload resistance.

Huh?

 

[jim dungar]

63 amp load inrush calculates to around 110 amps nominal, a weak breaker will always trip on the low scale. A 125 breaker low scale always defaults to 80% which is 100amps. This is lower than the calculated inrush, hence your nuisance tripping.

Another issue is that a fuse is rated different than a breaker for percentage of overload resistance.

Way to much confusing statements.

1. 63A is 63A. Without knowing the characteristics of the load, how can you estimate the inrush?
We have already established the inrush for this particular situation, a transformer, around 900A.

2. The possibility of a 'weak' breaker is almost non existent. A thermal magnetic breaker can only weaken through damage to its latching mechanism.

3. I have no clue what you mean by 'defaults to 80%'. Breakers are tested to 100% full load amps. Even in an enclosure, they are expected to carry 100% for at least 3 hours.

4. in this case the inrush currents are in excess of the full load amps, which means they are past the long time portion of the breaker's trip curve and therefore are not subject to any derating.

5. An fused switch and an enclosed circuit breaker pass the same UL testing. I have no idea what you mean by 'overload resistance'.

 

[davidr43229]

Another issue is that a fuse is rated different than a breaker for percentage of overload resistan

I 2nd that huh ?