3 level series rated systems

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Gustav

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Assuming that I am using
- Fuse RK5 with 400A = Fuse1
- Circuit Breaker with 200A and 65kA interrupt rating = CB1
- Circuit Breaker with 100A and 65kA interrupt rating = CB2

I need to establish a series rated system starting at the fuse1 and than connected downstream first the breaker CB1 for section 1 and than second CB2 as branch outlet. Of course Section Breaker CB1 will have several parallel breakers as well as the CB2.

I do have series rated documents for Fuse1 to CB1 and Fuse 1 to CB2, which are showing that both breakers individually are series rated with the fuse for up to 150kA@480V.

Would an AHJ or Inspector allow me to use this individual series rated reports to establish this a.m. 3-level series rated system?
Or do we have to do a series rating test with official report for exact this 3 level arrangement.

I do also know that I have to observe the motor contribution if available.

Thanks
Gustav
 
Would an AHJ or Inspector allow me to use this individual series rated reports to establish this a.m. 3-level series rated system?
Or do we have to do a series rating test with official report for exact this 3 level arrangement.
Click to expand...
Gustav,
I know of no Series Rating where 3 overcurrent protective devices have been rated.
 
David,

well looking to applications as I know them in Europe and Latin America.
The machinery is connected to the main power system. This is often an Busway System having a fused tap off box (400A; RK5) with 150kA r.m.s

Inside the industrial control panel there is a molded case circuit breaker as main disconnecting means and some branch circuit breakers. All circuit Breakers do have the same interrupt rating, i.e. in my example 65kA.

Per UL 508A we need to put an SCCR value on the panel.
The NEC requires that all involved fuses and Circuit breakers are series rated.

This leads to a three level series rating.

Thanks
Gustav
 
would you be at liberty to tell us what type of equipment you are desiging..like wood processing equipment, food processing equipment ect...it would help us to understand the concepts..
 
It's metal forming (like bending, cutting) or molding injection machines a.s.o.
I am delivering the Breakers (UL489) and control gear (UL508) to these manufacturers and they are picking on me to have such rated produtcs.
 
Gustav said:
David,
Inside the industrial control panel there is a molded case circuit breaker as main disconnecting means and some branch circuit breakers. All circuit Breakers do have the same interrupt rating, i.e. in my example 65kA.

Per UL 508A we need to put an SCCR value on the panel.
The NEC requires that all involved fuses and Circuit breakers are series rated.

This leads to a three level series rating.
Click to expand...

The NEC does not require series ratings of any devices. Series ratings are always optional.

NEC 409 and UL508A require you to tell your customers what short circuit rating your equipment has. It is up to the customer to design the electrical system so that your equipment can be used.

The only three level series ratings I have seen have been limited to "residential" service entrance equipment.
 
jim dungar said:
The NEC does not require series ratings of any devices. Series ratings are always optional.
Click to expand...

I am referring to NEC 240.86
(A) very expensive, due to the fact that each state or maybe City requires a local listed engineer,
(B) thats where I am referring to
(C) has to be observed

jim dungar said:
It is up to the customer to design the electrical system so that your equipment can be used.
Click to expand...

This works only in limited cases, because the customer does have the need for an certain amount of power and the respective transformer delivers its certain amount of short circuit current. This would lead to the effect, that the customer would wind up some 100 feet of cable to reduce the short circuit current, which he mostly not will do.

Thanks
Gustav
 
Gustav said:
I am referring to NEC 240.86
Click to expand...

110.9, 110.10, and 409.110(3) are mandatory. 240.86 is an optional method for use with circuits breakers in order to comply with 110.9.
 
Per your email, you mentioned a Circuit breaker as the main form of disconnect within the Industrial Control panel. I suspect it is non current limiting. In all probability there is some form of power distribution block also. The max SCCR rating that you can get is 10k, per UL508A guidelines. If I were you, I would change out the Circuit breaker to a current limiting overcurrent protection device. Additionally you can not use the 400amp fuse in the bussway system to determine your SCCR of the your Industrial control panel, unless the operator can turn off the power directly from that bussway system device. American Auto companies ARE using the bussway device as a means with chains attached to the bussway system device (switch) as a means to turn on & off the machine.
I do have series rated documents for Fuse1 to CB1 and Fuse 1 to CB2, which are showing that both breakers individually are series rated with the fuse for up to 150kA@480V
Click to expand...
Again Series rating is between 2 components, not 3. You can not use the Series rating of Fuse 1 to CB1 and Fuse 1 to CB2 and apply it to 3 components.
Just my $.02
 
Gustav said:
Assuming that I am using
- Fuse RK5 with 400A = Fuse1
- Circuit Breaker with 200A and 65kA interrupt rating = CB1
- Circuit Breaker with 100A and 65kA interrupt rating = CB2

I need to establish a series rated system starting at the fuse1 and than connected downstream first the breaker CB1 for section 1 and than second CB2 as branch outlet. Of course Section Breaker CB1 will have several parallel breakers as well as the CB2.

I do have series rated documents for Fuse1 to CB1 and Fuse 1 to CB2, which are showing that both breakers individually are series rated with the fuse for up to 150kA@480V.

Would an AHJ or Inspector allow me to use this individual series rated reports to establish this a.m. 3-level series rated system?
Or do we have to do a series rating test with official report for exact this 3 level arrangement.

I do also know that I have to observe the motor contribution if available.

Thanks
Gustav
Click to expand...

Perhaps it is a confusion of terms and what the customer is loking for that the devices connected in SERIES COORDINATE with each other, eg. the trip CURVES do not overlap.:cool:
 
Gentlemen,

thanks for all of your input, but unfortunately things are not getting clear enough

1. Maschine builder insists on using inverse time circuit breakers for Main Disconnecting means as well as for Branch circuits.
His opinion:
- the service and maintenance do have an easier way in case of an overload tripping to restart the maschine.
- Using fuses would need to replace with the prober fuse, means spare parts have to be available
- Circuit Breakers do not getting old, i.e. fuses are getting old and the trip curves are moving towards faster trip, which may lead to a lost coordination
- etc...

2. Local AHJ insists on fulfilling the NEC 240.86

Well I understand that the UL508A only covers the entire panel and nothing more - okay.
But what happens if you write on the panel an SCCR value of 100kA, because your panel only withstands 100kA in the case that you have to connect it to a power distribution which has on the line side of the power distribution fuse 120kA. Would that be okay?
Or how ist this topic solved in the US?
The IEC would have some engineering consideration to do so - avoiding hundreds of tests - and it works without major damage or injuries.

One of you wrote that the NEC 240.86 is NOT mandatory - is this anywhere in the NEC stated for the use to convince this AHJ?

PDB - we do not use them, we just connect directly to the main disconnecting means, it is suitable for field wiring anyway (it is UL489)

Thanks
Best regardds
Gustav
 
Gustav,
Maschine builder insists on using inverse time circuit breakers for Main Disconnecting means as well as for Branch circuits
Click to expand...
This is acceptable, however per UL508A, will "Let-through" most to all the available fault current, so there is no possible way for you to rate your panel at 100k. Again you need some form of "Current-Limitation" at the Disconnect.
Using fuses would need to replace with the prober fuse, means spare parts have to be available
- Circuit Breakers do not getting old
Click to expand...
Understandable, however properly sized, this will not happen to fuses, until a problem occurs and OSHA says you can not randomly reset a circuit breaker 1910.334, but since this is going overseas, you may not care.....However you want UL508A, is the AHJ asking for this?
The IEC would have some engineering
Click to expand...
Are you designing to EN60204-1?
Colorcoding of wire is alittle different than UL508A
Sorry, I mean not to confuse you , but to gain a bbetter understanding of your situation.
Just my $.02
 
Gustav said:
One of you wrote that the NEC 240.86 is NOT mandatory - is this anywhere in the NEC stated for the use to convince this AHJ?
Click to expand...

NEC 409 requires equipment to be labled with an SCCR. UL508A is an accepted method of determining an SCCR.
NEC 110.09 and 110.10 effectively say that equipment can not be used if the available system fault current is greater the the SCCR of the equipment.
NEC 240.86 says series ratings MAY be used as a method to allow circuit breakers to be applied on systems that exceed their AIC rating.

Gustav, this is not your problem.
The customer wants you do provide a solution to his problem (and I will bet he wants it for free).

The normal steps are:
1. Equipment manufacturer determines an SCCR and labels the equipment. At this point the manufactrer is done.
2. The available short circuit fault current (SCA) is determined for the location where the equipment will be installed.
3. If the available SCA is in excess of the SCCR of the equipment the INSTALLER has three choices: lower the SCA, take advantage of 240.86, or replace the equipment.

You have told your customer that 240.86 can not be applied to your present equipment. The only option left is to rebuild your equipment or have the available fault current lowered.
 
Well, of course we tried to push this topic back to the customer, but he said (similar)
".. well you're right ... we did not clearly specify .... but now we need .... series rated systems .... fuse to breaker 1 to breaker 2.."

The AHJ told to the final user that the NEC 240.86 has to be applied, not me.

What it wonders me, this might not be the first case in the US ? or is a fault level higher than 65kA@480V very seldom?
In IEC countries we do need to go up to 50kA@415V and sometimes up to 100kA for special industrie.
How is this than done in the US normally?
Do really the final user reduce the available Short Circuit current by using longer cables to the machinery or by reducing the amount of feeding transformers simultaneously?
 
Gustov,
What it wonders me, this might not be the first case in the US ? or is a fault level higher than 65kA@480V very seldom?
In IEC countries we do need to go up to 50kA@415V and sometimes up to 100kA for special industrie.
How is this than done in the US normally?
Do really the final user reduce the available Short Circuit current by using longer cables to the machinery or by reducing the amount of feeding transformers simultaneously
Click to expand...
We spoke on the phone earlier this morning, and thank you for that.
GM, Ford, Honda are all asking for 65K SCCR equipment. The 1st Auto manufacturer to reduce this is Cyrsler, do to 30amp & 60 amp drops being used driving down the amount of available fault current, due to the size of the wire & length of run ( 20'-30'). They are at 25K
Your application of 140,000amps available is very high. Something we seldom see over here.
We spoke of using an isolation transformer within your Industrial Equipment to "Choke" that to something more manageable.
Gustovs' application using conventional means (current limiting fuses or breakers) will not work, due to the excessive available fault currents, given to him.
Just my $.02
 
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