TCC Curve for Circuit Breaker

[Grouch1980]

I've searched and searched through Google, but cannot find the TCC curve for a Siemens Q3100 circuit breaker. It's a 3 pole, 100 amp circuit breaker. Can someone please help?

 

[lielec11]

I have access to this curve via SKM. Would a simple PDF diagram work?

 

[Grouch1980]

I have access to this curve via SKM. Would a simple PDF diagram work?

Yes, absolutely! Thank you.

 

[lielec11]

SKM has two versions, one labelled as Rev. 4, one as Rev. 6. I'm assuming it might be related to when the breaker was manufactured but I'm not certain. Both are on the attached file for reference.

 

[Grouch1980]

Thank you again. I'll probably refer to Revision 6.

 

[Grouch1980]

I have access to this curve via SKM. Would a simple PDF diagram work?

Would you also be able to provide the graph for Siemens Q3100H? It's similar, but with an AIC rating of 22k.

 

[lielec11]

They are the same curve just different rating.

 

[Grouch1980]

They are the same curve just different rating.

So I just extend the instantanous region on the right all the way out to 22k?

 

[jim dungar]

So I just extend the instantanous region on the right all the way out to 22k?

No.

The AIC rating does not affect the TCC at all.
The AIC is about the protective device not turning into shrapnel while it is clearing a fault.

You should always extend your instantaneous region up to the fault current 'flowing through' the protective device.

 

[Grouch1980]

Hmm. I was under the impression the right most line on a circuit breaker graph is its AIC rating. So if the rating is 65k, that right most line (the vertical boundary) will be at 65k.

 

[jim dungar]

Hmm. I was under the impression the right most line on a circuit breaker graph is its AIC rating. So if the rating is 65k, that right most line (the vertical boundary) will be at 65k.

Not always.
The AIC point might be where the curve 'ends', but many different AIC ratings may actually share the same TCC.

 

[Jraef]

All of the Siemens TCCs for the QP breakers are the same regardless of size.

Finding them on Siemens website is challenging though. I found them in the past, can’t any more.

 

[lielec11]

Hmm. I was under the impression the right most line on a circuit breaker graph is its AIC rating. So if the rating is 65k, that right most line (the vertical boundary) will be at 65k.

The right (or top) most lines are the actual clearing time of the breaker or fuse. For a fuse, the left/bottom lines are when the fuse actually starts melting, and the right/top is where it fully clears the fault.

For breakers, the left/bottom is where the device physically starts to unlatch/open, and the right/top are where the breaker is actually open and clears the fault.

 

[Grouch1980]

Not always.
The AIC point might be where the curve 'ends', but many different AIC ratings may actually share the same TCC.

But shouldn't the vertical boundary line all the way to the right always be at the AIC rating? Let's say I have a 22k AIC breaker. But the right most vertical boundary is at 15k...The curve stops at 15k. That seems like an inaccurate representation. If my calculated fault current is at 20k, the graph will show that the breaker is not sufficiently rated, since the 20k fault current is beyond the 15k line. Even though the breaker is 22k AIC.

 

[jim dungar]

But shouldn't the vertical boundary line all the way to the right always be at the AIC rating? Let's say I have a 22k AIC breaker. But the right most vertical boundary is at 15k...The curve stops at 15k. That seems like an inaccurate representation. If my calculated fault current is at 20k, the graph will show that the breaker is not sufficiently rated, since the 20k fault current is beyond the 15k line. Even though the breaker is 22k AIC.

The TCC curve is not required to show the AIC point of the device.
In reality a protective device begins clearing a fault well before its AIC rating, in fact if it is a current limiting device it must finish clearing well before its maximum.
Most breaker TCCs end up with a 'hockey stick' appearance that flattens out around 3 cycles regardless of the current value and are cut off where the manufacturer wants too. But this is only an issue where different AIC devices share a common trip element.

 

[lielec11]

But shouldn't the vertical boundary line all the way to the right always be at the AIC rating? Let's say I have a 22k AIC breaker. But the right most vertical boundary is at 15k...The curve stops at 15k. That seems like an inaccurate representation. If my calculated fault current is at 20k, the graph will show that the breaker is not sufficiently rated, since the 20k fault current is beyond the 15k line. Even though the breaker is 22k AIC.

The vertical line you're talking about is the value of the 3-phase bolted fault at the device and SKM (not sure of other software) will typically cut off any portion of the curve that is beyond the available fault current. The curve doesn't "stop" at 15kA like you say, but based on the system modeled there is no chance of that breaker seeing more than 15kA in that case.

I think you're trying to use TCC curves to check whether or not a breaker is sufficiently rated and this is incorrect. Curves are not used to validate short circuit/withstand ratings, but rather check for coordination and determine arc flash levels.

 

[wwhitney]

The curve stops at 15k. That seems like an inaccurate representation.

Sounds like the curve stopping at 15K means "this graph is silent on what happens above 15K" rather than "this device may blow up above 15K". So it's only inaccurate if you ascribe a meaning to the vertical boundary that it doesn't really have.

You are correct that if the AIC rating is 22K, then the graph could be extended out to 22K.

Cheers, Wayne

 

[jim dungar]

You are correct that if the AIC rating is 22K, then the graph could be extended out to 22K

It depends on where the TCC came from.
If the curve came from a software package, as you mentioned, it usually defaults to cutting off at the available fault current. The software is typically adjustable.
If the curve came from generic manufacturer literature, it will usually be cut off based on the manufacturer's policy. I know the old Square D FA (10kA @ 208V) and FH (65kA @ 208V) shared the same curve.

 

[wwhitney]

If the curve came from generic manufacturer literature, it will usually be cut off based on the manufacturer's policy. I know the old Square D FA (10kA @ 208V) and FH (65kA @ 208V) shared the same curve.

OK, the assumption that Grouch1980 and I have been making is that even if the published graph stops at 10kA, the FH breaker would trip in the same amount of time at any current between 10kA and 65kA. Is that correct?

If it is, seems like that means you can extend the graph for the FH breaker to the right all the way to 65 kA, as far as describing how the breaker acts.

Cheers, Wayne

 

[lielec11]

OK, the assumption that Grouch1980 and I have been making is that even if the published graph stops at 10kA, the FH breaker would trip in the same amount of time at any current between 10kA and 65kA. Is that correct?

If it is, seems like that means you can extend the graph for the FH breaker to the right all the way to 65 kA, as far as describing how the breaker acts.

Cheers, Wayne

Correct to an extent. The 10kA rated breaker may not interrupt a fault over 10kA at all (hence the rating). But yes if the curve and everything else about the breaker was the same, except one was 10kA and the other was 65kA, you can extend the instantaneous portion of the curve further to the right.