Elevator Controller SCCR

[petersonra]

My point is 240.86 does NOT require a tested combination for SCCR of a downstream device. That section is for two OCOD's in series.

As it is, I see no NEC prohibition against using a properly selected CL fuse (no PE required) to reduce the fault current for SCCR purposes. I actually don't have a dog in the fight - If this isn't an "accepted" method, then the NEC needs to tell me it's not.

Just how would you properly select the current limiting fuse? And just who would have to accept it to make it an acceptable solution?

Conceivably, you might be able to use current limiting fuses in combination with some kind of circuit breaker for instance in series if you put it in a UL508a panel and used it as your feeder source.

Based on the charts and UL508A though that describe how you can do this it's not going to help you for much more than 30 or 60 amp circuits.

 

[electrofelon]

Just how would you properly select the current limiting fuse? And just who would have to accept it to make it an acceptable solution?

.

The charts from the manufacturer.

Let me turn it around and say what NEC section would you cite? Perhaps the NEC needs to provide a definition for "available fault current" and state exactly what methods are acceptable.

 

[mayanees]

The charts from the manufacturer.

Let me turn it around and say what NEC section would you cite? Perhaps the NEC needs to provide a definition for "available fault current" and state exactly what methods are acceptable.

They have.
Fault Current, Available (Available Fault Current).
The largest amount of current capable of being delivered at a point on the system during a short-circuit condition. (CMP-10)
Informational Note:
A short-circuit can occur during abnormal conditions such as a fault between circuit conductors or a ground fault. See Informational Note Figure 100.1.

Informational Note Figure 100.1 Available Fault Current.

And ...
240.86 Series Ratings.
Where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an approved overcurrent protective device having a higher rating, the circuit breaker shall meet the requirements specified in 240.86(A) or (B), and (C).

I agree with Jim Dungar that the downstream device can't have contactors that are rated for less than what's available downstream of the contractor, so each application needs to be looked at and blessed, by a PE per 240.86(A) and only for existing installations.

 

[electrofelon]

They have.
Fault Current, Available (Available Fault Current).
The largest amount of current capable of being delivered at a point on the system during a short-circuit condition. (CMP-10)
Informational Note:
A short-circuit can occur during abnormal conditions such as a fault between circuit conductors or a ground fault. See Informational Note Figure 100.1.

Informational Note Figure 100.1 Available Fault Current.

And ...
240.86 Series Ratings.
Where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an approved overcurrent protective device having a higher rating, the circuit breaker shall meet the requirements specified in 240.86(A) or (B), and (C).

I agree with Jim Dungar that the downstream device can't have contactors that are rated for less than what's available downstream of the contractor, so each application needs to be looked at and blessed, by a PE per 240.86(A) and only for existing installations.

Sorry I meant a "better" definition . Yes but the definition dances around whether using a CL fuse is acceptable. It doesn't say using a transformer or reactor is acceptable either. You can come to my job and say my properly selected CL fuse isn't acceptable and I'll come to your job and say the current limiting reactor you used isn't acceptable.

Again, we are not talking about 2 OCPDs in series, 240.84 does not apply.

 

[electrofelon]

: The use of CLFs appears to be a contentious topic on this forum and elsewhere.

I don't know what you are talking about

 

[jim dungar]

Sorry I meant a "better" definition . Yes but the definition dances around whether using a CL fuse is acceptable. It doesn't say using a transformer or reactor is acceptable either. You can come to my job and say my properly selected CL fuse isn't acceptable and I'll come to your job and say the current limiting reactor you used isn't acceptable.

Again, we are not talking about 2 OCPDs in series, 240.84 does not apply.

A current limiting reactor is impedance which is recognized in 110.10 as one thing to be considered when determine the available fault current.

The NEC does not describe how available Short Circuit Current should be calculated. It does say Listing requirements for industrial control panels, elevator controls, and HVAC control panels need to be followed. There is no fuse manufacturer with a published short circuit analysis procedure, like Eaton's point to point method, that includes their fuse performance.

UL has special 'umbrella' fuses which it uses in its listing process partly to accommodate the fact fuses types and brands may be changed in the field.

 

[electrofelon]

A current limiting reactor is impedance which is recognized in 110.10 as one thing to be considered when determine the available fault current.

The NEC does not describe how available Short Circuit Current should be calculated. It does say Listing requirements for industrial control panels, elevator controls, and HVAC control panels need to be followed. There is no fuse manufacturer with a published short circuit analysis procedure, like Eaton's point to point method, that includes their fuse performance.

UL has special 'umbrella' fuses which it uses in its listing process partly to accommodate the fact fuses types and brands may be changed in the field.

Ok so what is this for? It's from cooper Bussmann:

How to Use the Let-Through Charts
Using the example given, one can determine the pertinent let-through data for
the KRP-C-800SP amp Low-Peak fuse. The Let-Through Chart pertaining to
the 800A Low-Peak fuse is illustrated.
A. Determine the PEAK let-through CURRENT.
Step 1. Enter the chart on the Prospective Short-Circuit current scale
at 86,000 amps and proceed vertically until the 800A fuse
curve is intersected.
Step 2. Follow horizontally until the Instantaneous Peak Let-Through
Current scale is intersected.
Step 3. Read the PEAK let-through CURRENT as 49,000A. (If a fuse
had not been used, the peak current would have been
198,000A.)
B. Determine the APPARENT PROSPECTIVE RMS
SYMMETRICAL let-through CURRENT.
Step 1. Enter the chart on the Prospective Short-Circuit current scale
at 86,000A and proceed vertically until the 800A fuse curve is
intersected.
Step 2. Follow horizontally until line A-B is intersected.
Step 3. Proceed vertically down to the Prospective Short-Circuit
Current.
Step 4. Read the APPARENT PROSPECTIVE RMS SYMMETRICAL
let-through CURRENT as 21,000A. (The RMS
SYMMETRICAL let-through CURRENT would be 86,000A if
there were no fuse in the circuit.)

 

[electrofelon]

And why does the NEC plop this definition of CL fuse right in the beginning of 240? Why are they trying to trick me?

Current-Limiting Overcurrent Protective Device. A device that,
when interrupting currents in its current-limiting range,
reduces the current flowing in the faulted circuit to a magni‐
tude substantially less than that obtainable in the same circuit if
the device were replaced with a solid conductor having comparable impedance.

 

[petersonra]

And why does the NEC plop this definition of CL fuse right in the beginning of 240? Why are they trying to trick me?

Current-Limiting Overcurrent Protective Device. A device that,
when interrupting currents in its current-limiting range,
reduces the current flowing in the faulted circuit to a magni‐
tude substantially less than that obtainable in the same circuit if
the device were replaced with a solid conductor having comparable impedance.

they are not tricking you. read carefully what it actually says.

 

[Strathead]

According to the document I quoted, a 200A RK1 fuse has a let through of less than 3000 A RMS. "Clearing time: less than 1 ⁄2 cycle when fuse is in it’s current-limiting range (beyond where fuse curve intersects A-B line)." In what way is that not an acceptable method of limiting the current to less than 5000 amps?

https://www.eaton.com/content/dam/e...through-charts-current-limitations-charts.pdf

 

[Strathead]

They have.
Fault Current, Available (Available Fault Current).
The largest amount of current capable of being delivered at a point on the system during a short-circuit condition. (CMP-10)
Informational Note:
A short-circuit can occur during abnormal conditions such as a fault between circuit conductors or a ground fault. See Informational Note Figure 100.1.

Informational Note Figure 100.1 Available Fault Current.

And ...
240.86 Series Ratings.
Where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an approved overcurrent protective device having a higher rating, the circuit breaker shall meet the requirements specified in 240.86(A) or (B), and (C).

I agree with Jim Dungar that the downstream device can't have contactors that are rated for less than what's available downstream of the contractor, so each application needs to be looked at and blessed, by a PE per 240.86(A) and only for existing installations.

But we are not using "a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an approved overcurrent protective device having a higher rating" We are using an OCPD on the load side of a circuit breaker that has a higher rating. 240.86 does not apply to what we are talking about.

 

[electrofelon]

they are not tricking you. read carefully what it actually says.

Go ahead and enlighten me.

 

[mayanees]

But we are not using "a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an approved overcurrent protective device having a higher rating" We are using an OCPD on the load side of a circuit breaker that has a higher rating. 240.86 does not apply to what we are talking about.

... and I agree that a passive downstream device like a bus or terminal will see a current reduction when downstream of a current limiting fuse as determined by the let-through charts you presented.

 

[jim dungar]

Ok so what is this for? It's from cooper Bussmann:

How to Use the Let-Through Charts

It can be used for conductors and similar components.
It should not be used, in the field, to protect components subject to Listing which included a SCCR, like contractors and VFDs have.

Again, I refer to the Eaton/Bussman article about complying with the 2017 NEC.

Even though they make current limiting fuses, I don't believe either Mersen or Littelfuse promote the Up, Over, and Down methodology to the extent that Bussmann does.

 

[Strathead]

It can be used for conductors and similar components.
It should not be used, in the field, to protect components subject to Listing which included a SCCR, like contractors and VFDs have.

Again, I refer to the Eaton/Bussman article about complying with the 2017 NEC.

Even though they make current limiting fuses, I don't believe either Mersen or Littelfuse promote the Up, Over, and Down methodology to the extent that Bussmann does.

Since, if the code doesn't prohibit it, then it is allowed, what in the 2017 NEC makes in non-compliant? I must keep repeating that I'm not well informed on this, and that is why I am continuing to ask for further clarification. The other rub is, if this so clearly a matter of modifying the equipment to satisfy the max overcurrent, then why isn't it a major step in ALL MEP DESIGN PLANS?

 

[jim dungar]

Since, if the code doesn't prohibit it, then it is allowed, what in the 2017 NEC makes in non-compliant? I must keep repeating that I'm not well informed on this, and that is why I am continuing to ask for further clarification. The other rub is, if this so clearly a matter of modifying the equipment to satisfy the max overcurrent, then why isn't it a major step in ALL MEP DESIGN PLANS?

The NEC says you must follow a device's listing requirements. If the listing requirements include the use of an upstream fuse, like many non-fused disconnects, then you are good to go.

The NEC requires you to determine the available SCA at a device. But the NEC doesn't tell you specifically how to perform this type of analysis, just like it doesn't tell you how to actually bend conduit, so you must use other resources. I know of no short circuit analysis methodology, including the one from Bussman, that includes the performance of protective devices.

This is not a matter of doing anything in the field, except applying equipment per its listing. It is a matter of the MEP designed plans including the available SCA and then having manufacturers supplied appropriately listed equipment.

The big problem I see is equipment, like HVAC and elevators, being ordered by people that ignore the electrical specification portions of the project. It doesn't help that available short circuit studies are often not performed until after equipment is on site and installed.

 

[electrofelon]

I know of no short circuit analysis methodology, including the one from Bussman, that includes the performance of protective devices.
.

But arnt the let thru charts exactly that, or am I misunderstanding? They seem to be quite clearly stating "if x and y and z, then the resulting max let thru current is...."

 

[petersonra]

But arnt the let thru charts exactly that, or am I misunderstanding? They seem to be quite clearly stating "if x and y and z, then the resulting max let thru current is...."

I think at least part of the answer is that the charts only reflect the performance of the fuse itself. It does not reflect what happens when you add dynamic impedance into the mix.

 

[jim dungar]

But arnt the let thru charts exactly that, or am I misunderstanding? They seem to be quite clearly stating "if x and y and z, then the resulting max let thru current is...."

Not if the equipment listing does not include an upstream fuse.
Have you looked at what other manufacturers say about using these curves?

 

[electrofelon]

Not if the equipment listing does not include an upstream fuse.

. Can you elaborate? I don't understand what you mean.

Have you looked at what other manufacturers say about using these curves?

No . Do they say something different than Bussmann?