Disconnect or OCPD

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jwatts

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Feeding an assortment of molding presses on 480 and 240 systems. All press feeds originate from the corresponding panels. Each of the machines have a breaker built into it. The AHJ wants to know the AIC rating of the integral breakers. I explained that the breakers on the machines are nothing more than a disconnecting means, and the OCPD's are the 3 pole breakers in the corresponding panels. He disapproves this citing article 670 of the 2005NEC. I can not seem to find any issues with our proposed setup in this article.
 
Is the machinery equipped with an OCPD as the disconnect or is the disconnect just a switch?

If the disconnect is an OCPD then it will have an AIC rating and must either be rated above the available fault current or be series rated with the next upstream OCPD.

If the disconnect is not an OCPD then it must have a short circuit current rating (SCCR) that meets or exceeds the available fault current at the machine.

Chris
 
I agree with the inspector, in principal. I would also cite 110.9,for protective devices, and 110.10, for equipment.
 
Coordination

Coordination

Is a circuit breaker fed by a smaller/faster OCPD a disconnect since it will never operate for overcurrent? For example, if I have a 200A MCB main in a panel but feed it with a 100A MCB, is the 200A MCB a breaker or disconnect? It will never operate on current.

Or, is the very presence of a thermal or magnetic element mean the device must be an OCPD. (Is a wire an EGC or load carrying, depends on its use!)
 
beanland said:
Is a circuit breaker fed by a smaller/faster OCPD a disconnect since it will never operate for overcurrent? For example, if I have a 200A MCB main in a panel but feed it with a 100A MCB, is the 200A MCB a breaker or disconnect? It will never operate on current.

Or, is the very presence of a thermal or magnetic element mean the device must be an OCPD. (Is a wire an EGC or load carrying, depends on its use!)
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110.9 deals with devices intended to interrupt fault currents, 110.10 deals with everything intended to 'tolerate' fault currents. So, regardless of its function, the device in the equipment must be rated for the fault current available at its line side terminals.
 
It appears to me that Art 670 and Art 409 are applicable.
There is similar wording in both that would lead me to require more than you inspector is requesting.


670.3 Machine Nameplate Data.
(A) Permanent Nameplate. A permanent nameplate shall be attached to the control equipment enclosure or machine and shall be plainly visible after installation. The nameplate shall include the following information:
(1) Supply voltage, number of phases, frequency, and full-load current
(2) Maximum ampere rating of the short-circuit and ground-fault protective device
(3) Ampere rating of largest motor, from the motor nameplate, or load
(4) Short-circuit current rating of the machine industrial control panel based on one of the following:
a. Short-circuit current rating of a listed and labeled machine control enclosure or assembly
b. Short-circuit current rating established utilizing an approved method
FPN: UL 508A-2001, Supplement SB, is an example of an approved method.
(5) Electrical diagram number(s) or the number of the index to the electrical drawings
 
I guess I don' understand why the machine breaker rating is needed. IF the AIC rating of the panelboard in which it is fed from has an AIC rating exceeding the potential from the utiltiy..... the machine would be protected. Also, if the panelboard is actually at the end of an extensive distribution system which includeds the Gear, distribution panels, as well as a 225 kva transformer..... would the potential fault at this panel be significantly lower considering all of the resistance the fault would have to pass through prior to reaching my panels and then machines?
 
jwatts said:
I guess I don' understand why the machine breaker rating is needed. IF the AIC rating of the panelboard in which it is fed from has an AIC rating exceeding the potential from the utiltiy..... the machine would be protected.
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Just because the upstream OCPD has an AIC rating that is greater than what the system can supply at that point does not mean that the downstream devices don't have to have an AIC rating equal to or greater than what the system can supply at that point on the circuit.
Also, if the panelboard is actually at the end of an extensive distribution system which includeds the Gear, distribution panels, as well as a 225 kva transformer..... would the potential fault at this panel be significantly lower considering all of the resistance the fault would have to pass through prior to reaching my panels and then machines?
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The device at the equipment only has to have a rating equal to the maximum amout of fault current that the system can supply to that equipment. The feeder conductors and transformers will provide a signicificant reduction in available fault current as compared to what is available at the service equipment.
 
I appreciate everyones explanations and help on this topic. I must say that I had never once looked at article 670 until this point, or ever had this issue with an inspector. My problem is this. Some of the machines have AIC ratings listed on the breakers that are less than the values provided by the utility company. How would I resolve this issue? I suppose a resolution would be to have a fault study done to actually show the available fault current at the end equipment. I am certian this is pricey and would prefer to avoid this avenue. Would I have any other options in regards to resolving my issue of the OCPD provided with the machine having an AIC less than that which is required?
 
jwatts said:
I appreciate everyones explanations and help on this topic. I must say that I had never once looked at article 670 until this point, or ever had this issue with an inspector. My problem is this. Some of the machines have AIC ratings listed on the breakers that are less than the values provided by the utility company. How would I resolve this issue? I suppose a resolution would be to have a fault study done to actually show the available fault current at the end equipment. I am certian this is pricey and would prefer to avoid this avenue. Would I have any other options in regards to resolving my issue of the OCPD provided with the machine having an AIC less than that which is required?
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You've hit on a big deal that's been brewing for some time now, ever since the 2005 code came out. But a lot of AHJs and different jurisdictions have been slow to start enforcing it, either because they had to thoroughly learn it themselves, or they wanted to give people time (or both). Lately I've seen an increase in enforcement here in California on new installations or additions to existing systems that were previously grandfathered in. It's getting to the point where I see people avoiding upgrades to old systems because they don't want to trigger the re-evaluation.

There are now PEs around here making a living just doing these studies and coming up with engineered solutions, i.e. current limiting fuses, reactors, added transformers etc. Most AHJs are not buying off on contractors just throwing stuff together, they need to see a PE stamp on it.

If you have a good relationship with your AHJ he may accept a carefully documented study from you and a plan of action if it turns out you have too much at the panel, but I don't think he is under an obligation to accept your solution. An alternative would be to take the panels to a UL508 shop to have them engineered under UL508 Supplement SB and labeled by them at an SCCR in excess of what you have available at the terminals. it might be less expensive than the PE route, hard to say.
 
jwatts said:
I appreciate everyones explanations and help on this topic. I must say that I had never once looked at article 670 until this point, or ever had this issue with an inspector. My problem is this. Some of the machines have AIC ratings listed on the breakers that are less than the values provided by the utility company. How would I resolve this issue? I suppose a resolution would be to have a fault study done to actually show the available fault current at the end equipment. I am certian this is pricey and would prefer to avoid this avenue. Would I have any other options in regards to resolving my issue of the OCPD provided with the machine having an AIC less than that which is required?
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If you know the available fault current at the service, it is not too difficult to do some simple calculations to find the available current at the line side of of your equipment. It does not take a lot of conduit and wire to drop the available fault current. Bussmann has free software to do simple calculations. There are also a number of online calculators that will also let you calculate the available current at the line side of your equipment.
 
jwatts said:
My problem is this. Some of the machines have AIC ratings listed on the breakers that are less than the values provided by the utility company. How would I resolve this issue?
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When I was designing control panels for textile lines, we weaseled out of the issue by having our panel markings say "Feed to this panel must be limited to 65kAIC" or whatever value our main breaker was rated. The customer accomplished this 2 ways, via current limiting fusing or by an impedance study of the supplying transformer and wiring ... or more commonly by ignoring it.

We used the Mag-Gard product which was rated 65kA at 480, or 22kA at 600 in well over 95% of our panels which were almost always multiple (3-20) small (1-15HP) motor. The utility feed was almost always over our rating, but both customer owned transformers and/or switchgear and/or feeder likely did limit it to our specifications. It was not unusual on 600V jobs for us to put a fused disconnect in, either in addition to the main breaker or in lieu of it. My boss (I was REAL GREEN at power back then, not much better now ... controls is my speciality) had some understanding of series ratings.
 
My issue is there are a number of injector presses that are equiped with a OCPD. These breakers integral to the machines, have an AIC that is less than the available fault value given to us by the utility contractor. The iowner is building a new faciltiy and is relocating his machines from the old to the new. In the old building, I am certain nothing was inspected because when I did a walk through, I nearly had a heart attack at the electrical system. Now these older machines are being relocated to a new facility where the AHJ is EXTREMELY thorough. I guess my only solution is to prove that the AIC ratings of the existing OCPD on the machines is capable of withstanding what ever the fault value will be at the actual equipment. My only problem is that if a fault study is required, this wouldn't be able to be completed until my distribution system is installed. I am hesitant to procede with the electrical system because what if after everything is installed and tested, our machines don not meet the minimum AIC......what would I do then?
 
UL Listing on Breakers

UL Listing on Breakers

Did some research and need some clarification. If a breaker in a injection press does not have a UL489 stamp, meaning it wasn't tested to be a "circuit breaker", then the device can not be considered a circuit breaker. It would be considered to be a supplematary protector from what I have found. Since these "supplemantary protectors" were installed as part of the press, they would be designed for the machines needs? So in my opinion, the AIC rating on these "supplemantary protectors" is useless, since AIC ratings only apply to OCPD. Any thoughts to support or refute this would be greatly appreciated.
 
jwatts said:
.So in my opinion, the AIC rating on these "supplemantary protectors" is useless, since AIC ratings only apply to OCPD. Any thoughts to support or refute this would be greatly appreciated.
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You are wrong.
AIC ratings, as required by 110.9, apply to all devices intended to interrupter fault current.
UL does have AIC ratings for supplementary overcurrent protective devices, so 110.3 would require you to use them.
 
Thanks for pointing that out Jim. I am just having a hard time grasping the fact that most of the machines I am feeding have a smaller OCPD in the panelboard than the protection provided with the machine. The breakers in the machines should never operate on current since the OCPD supplying them is smaller.
 
the simplest solution is to just remove the offending Cb from the panels and install a fused disconnect in its place.

you can screw around with this kind of stuff forever.

I would point out that even if the CB met the requirements the rest of the panel probably does not since no one cared about it until someone found a way to make money off it.

there are tens of millions of control panels out there that don't meet the requirements. there is a lot of money to made by "fixing" them.

in many cases it will be cheaper to replace the panels than to "fix" them.
 
Let's simplify.

Each of your presses require marking on their face per 670.3(4) that declares their Short-Circuit-Current-Rating (SCCR). This is rated at the top of the machine disconnect which in your case you've declared to be the internal breakers. As to the machine, that's all your inspector has to know about the interrupting capability. If you don't have the permanent nameplate with the SCCR then you have to fix that problem first and foremost.

Your utility company has given you a rating for your facility. In all likelihood that rating is well above the SCCR on the machine.

The laziest way to meet that is to presume no current drop. Instead install combination fuse banks. Two sets, of say Bussmann fuses, used in series will reduce the rating required for the machine. These could be installed outside the machine. Or replace the both the panel breakers and the internal breakers with the fuse sets. The combination will often drop the requirements below 10kA.

If you go with the combination then the machine is dual rated on the SCCR. The rating on the nameplate is the SCCR without knowing the upstream fuses in the panel. It becomes a valid install when the fuses are used in combination. You should label the panel and the machine for the required fuses as "No Substitution".
 
petersonra said:
How does having 2 fuses in series solve the problem. I can't say I ever heard of that one.
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Bussmann LPS-RK1-600SPI
600A current limiting fuse
SCCR 300kA with 23,200A let-through current

Current limiting fuses reduce the SCCR requirement. The umbrella limits stand unless the vendor tests the specific pair in series. Bussmann tests theirs in series.
 
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