Distribution & Terminal Block SCCR on ICP

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iLeKtRiKoS

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AB, Canada
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Electrical designer & estimator
Need assistance & clarification for evaluating the SCCR of an ICP. Below are the flow of the circuit and the components SCCR/IR.

Main CB (50 CB(50kA) - PDB - SPD (200 kA) - Comb. Controller (50 kA) - TB's

Question 1: Can I use the main CB-IR for the PDB-SCCR? thought that the PDB is protected by the main CB, or should I use a default value of 10kA for the PDB-SCCR since the main CB and PDB are not listed?

Question 2: Should I include the TB's after the combination controller for SCCR evaluation of a control panel? Again, I was under the impression that the combination controllers are protecting the TB's, so I can exclude the TB on the evaluation.

I used PDB because this will be use for a group of motors with a typical sizes.
 
Best bet usually is to see if you can get rid of the pdb entirely. Most mccb manufacturers have what are called distribution lugs you can buy. Usually six openings so unless you have more than six motors you don't need a pbd at all.

Usually you can't use unlisted or unrecognized parts in a ul508a ICP because the SCCR is dependant on you following all the other rules in the standard.

Terminals usually are relatively low in SCCR unless there are current limiting fuses upstream.

Very few if any pdbs have high sccrs unless there is a current limiting fuse upstream. There are a handful that are listed with high sccr if you use a specific mccb upstream.
 
petersonra said:
Best bet usually is to see if you can get rid of the pdb entirely. Most mccb manufacturers have what are called distribution lugs you can buy. Usually six openings so unless you have more than six motors you don't need a pbd at all.

Usually you can't use unlisted or unrecognized parts in a ul508a ICP because the SCCR is dependant on you following all the other rules in the standard.

Terminals usually are relatively low in SCCR unless there are current limiting fuses upstream.

Very few if any pdbs have high sccrs unless there is a current limiting fuse upstream. There are a handful that are listed with high sccr if you use a specific mccb upstream.
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Hi Petersonra, thanks for the insight.
I do understand that, in that case, I will be using the default SCCR for the distribution and terminal blocks from SB4.1 (10kA) for evaluations since they are UL listed.

You mentioned the current limiting fuse. What if I used a current limiting breaker for my main CB, will that increase the SCCR of PDB & TB downstream accordingly base off the Ip(Peak) of the main CB?
 
iLeKtRiKoS said:
Hi Petersonra, thanks for the insight.
I do understand that, in that case, I will be using the default SCCR for the distribution and terminal blocks from SB4.1 (10kA) for evaluations since they are UL listed.

You mentioned the current limiting fuse. What if I used a current limiting breaker for my main CB, will that increase the SCCR of PDB & TB downstream accordingly base off the Ip(Peak) of the main CB?
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Read carefully what it says about putting a current limiting CB in the feeder circuit in the supplement that describes evaluating SCCRs. SB4.3.4. The few times I have tried using a CL fuse or CB it does not help much, especially over 60 A.

I usually just do not put terminals in power circuits. They don't bring much to the table. Just another place something can fail, and electricians are notorious for causing such failures by over torqueing because they mistakenly think tighter is better. No reason the motors cannot be wired directly to the overload blocks or contactors, depending on what you have.
 
petersonra said:
Read carefully what it says about putting a current limiting CB in the feeder circuit in the supplement that describes evaluating SCCRs. SB4.3.4. The few times I have tried using a CL fuse or CB it does not help much, especially over 60 A.

I usually just do not put terminals in power circuits. They don't bring much to the table. Just another place something can fail, and electricians are notorious for causing such failures by over torqueing because they mistakenly think tighter is better. No reason the motors cannot be wired directly to the overload blocks or contactors, depending on what you have.
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Sometimes I have terminal blocks provided for motor leads, and sometimes I use receptacles. I understand the use of terminal lugs with multiple holes on the breaker, but that might require me to have more wire spacing.

In short, I cannot exclude the PDB & TB for evaluation and think that the main CB and combination controller will protect the PDB & TB accordingly when faults occur.
 
iLeKtRiKoS said:
Sometimes I have terminal blocks provided for motor leads, and sometimes I use receptacles. I understand the use of terminal lugs with multiple holes on the breaker, but that might require me to have more wire spacing.

In short, I cannot exclude the PDB & TB for evaluation and think that the main CB and combination controller will protect the PDB & TB accordingly when faults occur.
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It may not meet the requirements of UL508a though, and if you don't meet them all you can't list it, and if you can't list it, it is pointless to worry about SCCR.
 
petersonra said:
It may not meet the requirements of UL508a though, and if you don't meet them all you can't list it, and if you can't list it, it is pointless to worry about SCCR.
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Yeah, that makes sense to me. So to clarify my questions, I need to include the PDB and TB using their default value as per table SB4.1 and comply with UL508A so I can list my panel?
 
iLeKtRiKoS said:
Yeah, that makes sense to me. So to clarify my questions, I need to include the PDB and TB using their default value as per table SB4.1 and comply with UL508A so I can list my panel?
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If you insist on putting a PDB and TBs in a power circuit the answer is yes UNLESS you can find some documentation from the manufacturer that says otherwise. There are some PDBs that have higher than the standard ratings even without CL fuses. Since I don't put TBs in power circuits, I don't know if there are any TBs that have SCCRs above the default rating without CL fuses because it does not matter to me.

Keep in mind you cannot list an ICP. Only a NRTL such as UL or CSA can do that. If you are part of UL's UL508a ICP program, they will let you apply the sticker under their procedures but it is still listed by UL.

Just a few examples.


Look at page 3 of this spec. It tells you what SCCRs are available based on various classes of fuses (100 kA), several different brands/models of MCCBs (14-65 kA), and none of the above (10 kA). Note in this particular case only conductors with ultrasonically welded insulation can use the MCCBs listed and get the higher SCCR. If you don't use the right wire, you are back to 10 kA.


This one is only 10 kA regardless of what fuses or MCCBs you use, because it says so on page 1.


Look at page 2 of this spec. Note that for certain sizes and types of conductors, there is a SCCR that is higher than the default. Its not real useful unless you need big conductors, but its available. But otherwise it is 10 kA.

You will need to look at and read very closely what the manufacturer's documentation actually says.


This one is for a typical AB terminal. Note there is no rating for anything other than 480 wye or 600 wye with specified CBs. There is a 100 kA rating with CL fuses of the specified types and ratings.

But if you wanted to for instance use it at 208 Wye with a CB there is no SCCR for that, or for that matter any rating for delta systems using CBs, so the default would apply.

Incidentally, if I had to guess, I would guess that the chart provided is incomplete and that you can indeed use it at 240 Delta or 208 wye. But you would need to hunt down the documentation to prove that. Since AB updated their web site a few months ago, there are a crap load of errors and omissions like this.
 
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petersonra said:
If you insist on putting a PDB and TBs in a power circuit the answer is yes UNLESS you can find some documentation from the manufacturer that says otherwise. There are some PDBs that have higher than the standard ratings even without CL fuses. Since I don't put TBs in power circuits, I don't know if there are any TBs that have SCCRs above the default rating without CL fuses because it does not matter to me.

Keep in mind you cannot list an ICP. Only a NRTL such as UL or CSA can do that. If you are part of UL's UL508a ICP program, they will let you apply the sticker under their procedures but it is still listed by UL.

Just a few examples.


Look at page 3 of this spec. It tells you what SCCRs are available based on various classes of fuses (100 kA), several different brands/models of MCCBs (14-65 kA), and none of the above (10 kA). Note in this particular case only conductors with ultrasonically welded insulation can use the MCCBs listed and get the higher SCCR. If you don't use the right wire, you are back to 10 kA.


This one is only 10 kA regardless of what fuses or MCCBs you use, because it says so on page 1.


Look at page 2 of this spec. Note that for certain sizes and types of conductors, there is a SCCR that is higher than the default. Its not real useful unless you need big conductors, but its available. But otherwise it is 10 kA.

You will need to look at and read very closely what the manufacturer's documentation actually says.


This one is for a typical AB terminal. Note there is no rating for anything other than 480 wye or 600 wye with specified CBs. There is a 100 kA rating with CL fuses of the specified types and ratings.

But if you wanted to for instance use it at 208 Wye with a CB there is no SCCR for that, or for that matter any rating for delta systems using CBs, so the default would apply.

Incidentally, if I had to guess, I would guess that the chart provided is incomplete and that you can indeed use it at 240 Delta or 208 wye. But you would need to hunt down the documentation to prove that. Since AB updated their web site a few months ago, there are a crap load of errors and omissions like this.
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@petersonra Thank you so much for all your input. Highly appreciated!
 
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