Is a facilities device AIC rating somehow implied?

[Ugly]

I've been tasked with integrating our system, a collection of various equipment on a network of branch circuits, into a facility currently being designed/built. I will be supplied with, presumably code compliant, power drops we can tap into for our system power. I need to choose downstream breaker panels, breakers, conductors etc.

I have been supplied with the following information about the upstream devices: line voltage and circuit breaker trip values.

Since I wasn't given the AIC rating of the upstream devices by the facility designer I'm wondering if it is somehow implied.

Is it safe to assume an installations power delivery devices AIC rating, and thus what required ratings our systems devices should meet or exceed, based on something like standard practice peculiar to facility power requirements, it's voltage, locale, etc?

I suspect I don't have enough info and need to talk ask the facility designer but figured I'd run it past this esteemed panel of experts first since I'm new.

 

[augie47]

"this esteemed panel of experts" .... Boy, are easily fooled

IMHO, there is very little you can assume given the up-stream device.
Even if you know the AIC rating of the immediate upstream OCP device, it might be series rated and your load components are not likely to be (series rated).
Considering there is little limitation as to the AIC and your loads might have a withstand rating of 5k or less, you need far more information.

In a system of any size, an engineering study is probably needed especially if there is a possibility of motor contribution.

As a rule of thumb, locally the AHJs ask for documentation for any service/feeder 400 amp or higher.

 

[skeshesh]

"this esteemed panel of experts" .... Boy, are easily fooled

That certainly made me laugh Gus. While I consider many on this forum to be some of the most knowledgeable engineers, technicians and professionals in the trade, this forum is certainly open to the less experienced and knowledgeable (myself included).

I agree with Gus's comments. Even when using series rated breakers, it is necessary for a qualified engineer to calculate the fault current available at the location of each of your equipment. I advise against trying to complete the selection on your own without input from an experienced electrical engineer who can verify the results.

Having said that, the way you would go about this is calculate the available currents at the location of equipment. A simple approach is to begin with the source transformer, assuming an infinite bus and using the transformer impedance to estimate the available fault current at the secondary. Afterwards you generate a single line diagram of all the feeders, distribution equipment, motors, transformers, etc. You will need the size of the cables as well as the length to determine the network impedance. A point to point calculation would allow you to determine available fault current at various locations in the network. Based on these values you can proceed to select the AIC rating of your devices and equipment.

 

[Ugly]

"this esteemed panel of experts" .... Boy, are easily fooled

Relative to this limited point of view it doesn't take much, I'll admit. However, the answers given were sufficiently dazzling to propagate the illusion forward.

Thanks for posting folks.

 

[augie47]

Relative to this limited point of view it doesn't take much, I'll admit. However, the answers given were sufficiently dazzling to propagate the illusion forward.

Thanks for posting folks.

anybody have a dictionary I can borrow ?

 

[Ugly]

...to stir the pot a little.

Is it reasonable for a product manufacturer, like us, to offer a product, like ours, with a single fixed AIC rating for all customers regardless of what the customers power tap capacity happens to be? Keeping in mind our system will typically require major site rewiring for already existing facilities.

Would facility development personel have reasonable solutions for accomadating a product of arbitrary AIC rating like I think I'd like to make ours?

Maybe this is why the facility development manager didn't supply AIC requirements, ie they jplan to accomadate our equipment?

I'd like to distance our product from the burden of accomadating varying facility capacities and locale code requirements, etc. but it also shouldn't be a huge deal for our customers to deal with.

 

[skeshesh]

...to stir the pot a little.

Is it reasonable for a product manufacturer, like us, to offer a product, like ours, with a single fixed AIC rating for all customers regardless of what the customers power tap capacity happens to be? Keeping in mind our system will typically require major site rewiring for already existing facilities.

Would facility development personel have reasonable solutions for accomadating a product of arbitrary AIC rating like I think I'd like to make ours?

Maybe this is why the facility development manager didn't supply AIC requirements, ie they jplan to accomadate our equipment?

I'd like to distance our product from the burden of accomadating varying facility capacities and locale code requirements, etc. but it also shouldn't be a huge deal for our customers to deal with.

Wow, you're asking a very broad question. I feel almost inclined not to comment so as not to steer you in the wrong direction, so please realize that my comments are ver general and will not by any means cover all the cases you may face.
First of all a lot more detail about the nature of the equipment is needed so we can establish an understanding of where its used, and where in an electrical system it will connect to. The scale of the electrical system, though not the only parameter, has a lot of bearing on your available fault. In addition, generally speaking, the further upstream closer to the source of your service (i.e. utility transformer, generator), the higher the available fault. Electrical systems vary greatly, and if your product is a speciality product used in unique plants, there's a greater than you will run into less than conventional systems and have to deal with complications.
One point you need to keep in mind is that it is not likely that the facility electrical system will be hugly modified to accomodate your equipment. Other methods may be used to limit the fault current at the location of your equipment or further upstream and reduce the minimum AIC rating required, but the system itself will no be modified. Provide a bit more detail about the product and where it's used and more accurate advice may be provided.

 

[jim dungar]

First, understand the terms:
AIC = Ampere Interrupting Capacity: the amount of fault current that a protective device can safely interrupt. This is only applicable to protective devices. See NEC article 110.9.

SCCR = Short Circuit Current Rating: the amount of fault current that equipment can tolerate until a protective device operates. See NEC article 110.10. Similar terms include withstand rating and bus bracing.

SCA = Short Circuit Amps: The amount of fault current available at a location.

Now the concepts.
You do not need to know the AIC of upstream protective devices.

A system designer needs to be able to provide the SCA at each piece of equipment, as the impedance of branch circuit wiring can have a large impact.

An equipment designer is responsible for providing an accurate and realistic SCCR, for their equipment (i..e per UL508A).

 

[Ugly]

skeshesh,

This product is, what will probably always be under a half million or so watts, lighting system with 20hp or less motors w/ controllers to move them around. It's in a an industrial lab environment and we generally do the whole lab but in this case I'm just working on the lighting.

Jim,

The definitions are indeed helpful. Thank you. I apologise for likely having butchered apropriate terminology.

My confusion comes from not knowing where the line is drawn between what is system level and what is equipment level design. How does responsibility correctly get delegated?

It would seem my product has elements of both. It seems a bit system level in that it has multiwire branches protected by overcurrent devices we provide. Equipment level in that it all works together to perform a single function. How does one distinguish the difference in cases like this?

It would seem desirable to attempt to classify ourselves as equipment designers if I'm understanding your post. I think we would then only be left responsible for supplying manufacturer documentation detailing SCCR for components under scrutiny. Since I've been choosing off the shelf devices this shouls be a mtter of rounding up the documentation from the manufacturers.