what is the SCCR of this circuit ??

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samvivi7

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Hey,

First: what resource or software do you guys use to calculate SCCR of a panel or circuit??

Second: Can anyone help identify what the SCCR would be for this circuit. i am trying to achieve a 65kVA.
SCCR1.jpg

Thanks for any help,
Sam
 
Let me just state that we can help you but you cannot use the company name for advertising. That is not allowed.
 
samvivi7 said:
Hey,

First: what resource or software do you guys use to calculate SCCR of a panel or circuit??

Second: Can anyone help identify what the SCCR would be for this circuit. i am trying to achieve a 65kVA.
View attachment 23339

Thanks for any help,
Sam
Click to expand...

Your question is a little non-specific. The way it works is everything in a power circuit has to have a SCCR. The smallest rating is what determines the overall rating, although some items that have a relatively low SCCR by themselves can have a much higher rating when combined with some other component.

Its also not real clear to me what you mean by a panel. If you mean a panelboard than the manufacturer would specify what it is based on the components you selected.

If the panel is a control panel, than UL508a would be used to evaluate its SCCR.

In your sketch, if the CB and xfmr are not part of the UL508a control panel than the engineer who came up with the circuit would need to put on his drawings what the maximum short circuit current is at the secondary of the transformer and it could not exceed the SCCR of the control panel.
 
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Dennis Alwon said:
Let me just state that we can help you but you cannot use the company name for advertising. That is not allowed.
Click to expand...

Hey Dennis thanks for the reply and are you referring to ******
if so i didn't know it wasn't allowed just signed up to these forums.
 
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  1. SCCR is measured in amps, not kVA. I'm going to assume you mean 65kA.
  2. Transformers do not have an SCCR and the PSCC (Prospective Short Circuit Current) of the primary does not pass through to the secondary.
  3. Anything on the load side of the transformer starts over anyway based on the Short Circuit current capability of the transformer secondary as a source. So what's the PSCC on the secondary of a 15kVA transformer at 400V? Not anywhere near 65kA, even if the primary side would be "infinite bus", which is is not. If that transformer were 10kVA or less for example, the PCSCC would be considered 5kA, so as long as the "control panel" components were rated for 5kA SCCR or more, you would be fine. Because it is over 10kVA you will have to determine the PSCC yourself and for that you need the transformer impedance. But just for S&G, let's assume it is 2% Z. That means at 2% of the primary voltage, you will get 100% current on the secondary, which on a 400V (assuming 3 phase) secondary is probably around 25A. So if you get 25A at 2% V, at 100% V you will get 50x the current. But that is STILL only going to be 1250A PSCC... basically irrelevant.
  4. The only thing in that lineup that matters then is the breaker and it is rated for 65kAIC, so your SCCR would be 65kA at the 480V side.
 
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petersonra said:
Your question is a little non-specific. The way it works is everything in a power circuit has to have a SCCR. The smallest rating is what determines the overall rating, although some items that have a relatively low SCCR by themselves can have a much higher rating when combined with some other component.

Its also not real clear to me what you mean by a panel. If you mean a panelboard than the manufacturer would specify what it is based on the components you selected.

If the panel is a control panel, than UL508a would be used to evaluate its SCCR.
Click to expand...

Hey petersonra,

i have two panels, my panel has a CB rated at 65kA with a transformer 15kVA which is feeding a second panel (third party vendor) rated at 5kA.
So, do i have to have a 65kA CB with a 65kA transformer and the sub panel rated at 65kA ?
 
I think you are using the term "SCCR" incorrectly, and it has me confused. There are two separate concepts that have a relationship with each other, but that are determined by very different means. What follows is an oversimplification of the two concepts.

Concept 1: How much current can a component withstand without being destroyed, or even if it is destroyed it won't start a fire or damage anything else? That is the Short Circuit Current Rating (SCCR) of the component. This value cannot be calculated, but rather is determined by the manufacturer. I suspect (others can explain further) that it is determined through experimentation. The SCCR of any given component has nothing to do with the SCCR of any other component.

Concept 2: How much current would be imposed on a component if a fault were to occur at its location? This depends on the energy source, the length and size of the conductors between the energy source and the component, and the presence of any intervening components. That is the Short Circuit Current Available (SCCA), and it is calculated by the designer of the distribution system.

The relationship between these two concepts is that a component's SCCR is required to be at least as high as the SCCA at the component's location.

 
samvivi7 said:
Hey petersonra,

i have two panels, my panel has a CB rated at 65kA with a transformer 15kVA which is feeding a second panel (third party vendor) rated at 5kA.
So, do i have to have a 65kA CB with a 65kA transformer and the sub panel rated at 65kA ?
Click to expand...

After the Transformer a new SCCR is established.
 
samvivi7 said:
. . . my panel has a CB rated at 65kA. . . .
Click to expand...
That is neither an SCCR nor an SCCA. That is an AIC - an acronym that has several possible meanings. I prefer "Amps Interrupting Capability," but other choices are available. It refers to the amount of current that can pass through the breaker's metal contacts without heating them up so severely that they melt together, forever thereafter preventing the breaker from opening.

 
charlie b said:
That is neither an SCCR nor an SCCA. That is an AIC - an acronym that has several possible meanings. I prefer "Amps Interrupting Capability," but other choices are available. It refers to the amount of current that can pass through the breaker's metal contacts without heating them up so severely that they melt together, forever thereafter preventing the breaker from opening.
Click to expand...

Forgot the fireball and mushroom cloud emoji. :)
 
okay.

i am confused :? all i know is, if i am building a panel who's name plate should read SCCR: 65kA.
i need to have all my CB's (feeder circuit) rated at 65kA
and all other component should also be rated at 65kA if they are part of the feeder circuit.
some are excluded per S.B 4.2.1 (i.e filters reactors ..etc)
Also, as i understand if i have transformer which doesn't have SCCR and is excluded per UL S.B 4.2.1
anything after a transformer should not affect my the SCCR rating of the panel.

do i make sense or do i have this completely wrong ??
 
samvivi7 said:
okay.

i am confused :? all i know is, if i am building a panel who's name plate should read SCCR: 65kA.
i need to have all my CB's (feeder circuit) rated at 65kA
and all other component should also be rated at 65kA if they are part of the feeder circuit.
some are excluded per S.B 4.2.1 (i.e filters reactors ..etc)
Also, as i understand if i have transformer which doesn't have SCCR and is excluded per UL S.B 4.2.1
anything after a transformer should not affect my the SCCR rating of the panel.

do i make sense or do i have this completely wrong ??
Click to expand...

If you are building a panel whose name plate should read SCCR: 65kA,
then all the breakers in the panel should have a 65kA rating or greater.
 
samvivi7 said:
i have two panels, my panel has a CB rated at 65kA with a transformer 15kVA which is feeding a second panel (third party vendor) rated at 5kA.
So, do i have to have a 65kA CB with a 65kA transformer and the sub panel rated at 65kA ?
Click to expand...

You need to be very careful with your terminology. There are several things that need to be considered and they all sound similar, partly because they are all expressed in thousands of Amps, typically as kA.

The Short Circuit Amps (SCA) or short circuit current available is the amount of current that can flow into a bolted fault condition. The starting SCA is often provided by the utility and then re-calculated at various points in the distribution system, such as after a length of conductor or a transformer. All equipment must be rated to handle the amount of SCA at its line side terminals. This value is may be calculated in the field. SCA is really what most people are asking for.

Amps Interrupting Capacity (AIC) is a rating unique to protective devices that interrupt fault current, like breakers and fuses. This value is determined by the manufacturer based on testing. Devices should be selected so that their AIC exceeds the available SCA.

Short Circuit Current Rating (SCCR) is the amount of fault current that a piece of equipment is rated to tolerate until a protective device operates clearing the fault. This value must be provided by the equipment manufacturer. There is no universal method for determining it in the field. Each type of equipment may get its SCCR value in a different manner. Panelboards, switchboards, disconnect switches, and motor control centers, may have a maximum tested/listed value with a label that limits its actual rating based on the field installed devices. An automatic transfer switch may have different tested SCCRs depending on the specific device protecting it. Control panels, like those built to UL508A, may have an SCCR calculated by the registered assembly shop, although many simply use the UL default value of 5kA.
 
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