Published X/R Ratios

[Grouch]

Because the MFG did not provide you with any literature to state you can use a CL fuse to raise your SCC rating in combination with the CL fuse you are Helically Wound.

What do you mean by 'helically wound'?

Assume your SCC at the unit is 4.7K and your calc yields an X/R of 2.
Local 10K rated OCPD.
Here I would say you now must use your MF adjustment to see if you fall below 5K...I leave the math to you.

Not following... so you're saying to calculate the MF adjustment at the unit. What text X/R ratio am I using at the unit?

The equation is MF = (I asym @ X/R calculated) / (I asym @ X/R tested).

I use the calculated 4.7k and x/r of 2 to calculate the numerator.
I use the tested 5k and x/r of what?? to calculated the denominator?

And then I run the same calculation at the OCPD serving the unit you're saying, further upstream from the unit?

 

[MyCleveland]

What do you mean by 'helically wound'?

Not following... so you're saying to calculate the MF adjustment at the unit. What text X/R ratio am I using at the unit?

The equation is MF = (I asym @ X/R calculated) / (I asym @ X/R tested).

I use the calculated 4.7k and x/r of 2 to calculate the numerator.
I use the tested 5k and x/r of what?? to calculated the denominator?

And then I run the same calculation at the OCPD serving the unit you're saying, further upstream from the unit?

Your first ?…You have a tool box full of things that end with DRIVER. Now delete the driver and add ed.
Reference was where you have equipment installed and the AFC is above its rating and you can do nothing to fix it.

Recall I stated I was not sure my advice was sound.
No one commented on the examples or added any advice on how to address a situation of adjusting the AFC for a high X/R ratio.

If you have been following other thread about using CL fusing to address equipment with low SCCRs…I made an attempt to contact UL and even register on the web site but they are asking for info I cannot provide.
My goal was to look over some equipment product standards to see if they have an assigned X/R for various SCC values…5k, 10k, etc.

I was making an assumption that for a given SCC value I could use the same X/R values from the table 1 for OCPDs.

I believe your question needs addressing but cannot give you an answer.

Are you willing to try an communicate with UL on this?

 

[Grouch]

Your first ?…You have a tool box full of things that end with DRIVER. Now delete the driver and add ed.
Reference was where you have equipment installed and the AFC is above its rating and you can do nothing to fix it.

I have no idea what this means. Are these SKM terms? I don't have SKM... yet.

Are you willing to try an communicate with UL on this?

Never did that. No idea who to reach out to.

 

[Grouch]

If you have HVAC equipment with an SCCR value of 5k, for example... does the HVAC equipment have test X/R ratios? How does one calculate a multiplying factor to see if the asymmetrical component of your calculated short circuit affects the HVAC equipment?

Can anyone confirm how to do this?

 

[MyCleveland]

Can anyone confirm how to do this?

Have been trying multiple sources today with no luck yet.

I tried someone that TEACHES SCC calculations first and received a disappointing response.....
"I don’t recall seeing this but it makes sense as a test setup needs to define both the short circuit current and amount of x and r that results in the current.
I would contact the manufacturer like Eaton, Schneider etc. to see if they can tell you what is used."

With that, I have reached out to TWO different manufacturers. No idea if I will get a response from either.
I am now the nail instead of the hammer.

I am also trying to get the question to one of the major SCC calc program tech support engineers.

You are a specifing engineer yes? Reach out to your sales support and request they run the question by the companies design department.
I would place the request with the two vendors you work with the most.

Please let us know what the response is.

 

[Grouch]

I tried someone that TEACHES SCC calculations first and received a disappointing response.....
"I don’t recall seeing this but it makes sense as a test setup needs to define both the short circuit current and amount of x and r that results in the current.
I would contact the manufacturer like Eaton, Schneider etc. to see if they can tell you what is used."

wow... I appreciate your reaching out!

With that, I have reached out to TWO different manufacturers. No idea if I will get a response from either.
I am now the nail instead of the hammer.

I am also trying to get the question to one of the major SCC calc program tech support engineers.

You are a specifing engineer yes? Reach out to your sales support and request they run the question by the companies design department.
I would place the request with the two vendors you work with the most.

Yes I am. Let me see if I can reach out to someone.

 

[MyCleveland]

wow... I appreciate your reaching out!

Yes I am. Let me see if I can reach out to someone.

Any responses?

 

[Grouch]

Any responses?

I'll be on it this coming week.

 

[Grouch]

Any responses?

No response yet. I'm checking with a manufacturer. They did respond, but only that they have to check with their engineering team.

 

[MyCleveland]

No response yet. I'm checking with a manufacturer. They did respond, but only that they have to check with their engineering team.

Hope they get back with you.

I have had zero success.

Had question sent in to TWO SCC calc program tech support....crickets for a response.

Only response from a gear rep was rambling about Arc-Flash and IEEE 1584 commentary....refuses to discuss over the phone.

Waiting on one last attempt, but do not hold your breath.

I did find in the IEEE Violet Book where they indicate Bus Duct is required to be tested at X/R of 4.9, but no minimum ampacity of the Bus Duct is provided.

 

[MyCleveland]

I think every short circuit test has a specific X/R ratio, otherwise it would be hard to replicate tests on a consistent basis. I agree the only X/R adjustment values I have seen are for OCPDs.

Jim

Staying on the topic of equipment SCC test circuit PF or X/R rating.

This specifically revolves around UL 98: Switches, Enclosed.
I requested from a gear manufacturer the SCC Test Circuit PF requirements and here is what I was provided....

from UL 98. "Switches, Enclosed"
NOTE: Data NOT in table format
d) The test circuit requirements shall be as follows:
For an ac circuit, the power factor of the circuit shall be 0.45 to 0.50 lagging for a circuit of
0 to 10000 amps, except the power factor shall be 0.85 to 0.95 lagging for fuses rated 100A or less.
0.25 to 0.30 lagging for a circuit of 10001 to 20000 amps, and
0.15 to 0.20 lagging for circuits over 20000 amps.

I placed the data into the following table....
- Power factor of Test Circuits -
Test circuit in amperes Power Factor X/R
10000 or less 0.45 - 0.50 1.9845 - 1.7321
10001 - 20000 0.25 - 0.30 3.8729 - 3.1798
over 20000 0.15 - 0.20 6.5912 - 4.8989

Special Case: Fusible Switches Rated 100A or LESS
10000 or less 0.85 - 0.95 0.6197 - 0.3287

My assumption here is the PF test circuit data applies to both NON-Fused & Fused disconnects.

Question 1:
Do you agree with my table arrangement?

Question 2:
Any idea of why the special case for 100A (& smaller) fusible disconnects was added?

Question 3:
If I have a 100A or smaller fusible switch, that according to this table has a test X/R of 0.3287, and I install a R or J class fuse.
I believe the R & J have a test circuit X/R of 4.9.
In a SCC analysis, which X/R value gets applied at the switch, 0.3287 or 4.9?

 

[jim dungar]

Question 1:
Do you agree with my table arrangement?

Sounds reasonable, but I have confirmed anything.

Question 2:
Any idea of why the special case for 100A (& smaller) fusible disconnects was added?

Maybe because there are many devices whose contacts are closed manually, like pull out style switches.

Question 3:
If I have a 100A or smaller fusible switch, that according to this table has a test X/R of 0.3287, and I install a R or J class fuse.
I believe the R & J have a test circuit X/R of 4.9.
In a SCC analysis, which X/R value gets applied at the switch, 0.3287 or 4.9?

The calculation for available short circuit amps does not use the individual device X/R values.
I believe it is the 'Device Evaluation' module that would compare a device's SCCR and X/R to the calculations. Check with the software company.

 

[MyCleveland]

The calculation for available short circuit amps does not use the individual device X/R values.

Sure it does Jim...example would be checking to make sure a MCCB has not been over-dutied.
UL 489 spells out the test cct PF (X/R) for various SCC ranges.
If a CBer is evaluated to have a HIGHER than tested X/R at the fault point it must be derated per IEEE Violet Book.

My struggle is how to evaluate when TWO components are combined at the fault point...which component X/R takes precedent.

 

[jim dungar]

Sure it does Jim...example would be checking to make sure a MCCB has not been over-dutied.

That is not part of the actual short circuit calculation.
What you describe is an evaluation which uses the results of the short circuit calculation and the performance/ratings of an OCDP.

My struggle is how to evaluate when TWO components are combined at the fault point...which component X/R takes precedent.

Evaluate each device individually. If either one 'fails' you have a condition that needs to be addressed.