Series ratings of GEAR?

[jraef]

Has anyone heard of two different types of GEAR being "series rated"? A claim was made by a salesperson for a company that makes MCCs and Switchgear that the must be given the order for both because the MCCs are "series rated" at 100kA with the switchgear. The data sheets for the MCCs clearly state that the MCCs are rated for "only" 65kA. I was not given the one-line diagram so I don't know what the actual available fault current is yet, but I called BS on this. I know what series rating of circuit breakers and fuses is and how it works, and I know that in the panelboard/load center world the manufacturers will often series rate their panels for use behind a specific circuit breaker up stream or used as a main to get a higher overall rating. But i also know that to attain that, they must test them in series with very specific components installed and it's a destructive testing process, so it is only done for high volume applications like residential / commercial panels where they sell thousands and thousands of them every year. I've never heard of this concept extending into primary type gear like LV MCCs fed by Switchgear. I'm saying that the Switchgear might be rated for 100kA even if you only need 65kA because that's getting to be fairly common now, but I don't think anyone has gone through the extreme expense of series rating an entire MCC lineup so that you can use a 65kA rated MCC in a system capable of 100kA by using the same manufacturer's switchgear. My bet is that the MCCs are rated for 65kA because the AFC is <65kA at the MCC terminals, not because there is any "series rating" with the up stream gear.

But I've been out of the Switchgear business for a decade or more now, so is there something new out there that I'm not aware of?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[dArsonval]

Engineering [specs] come from any place.

A nuclear power plant wants a spare motor delivered exhibiting no moisture content.

That's fine. We'll store 'em in controlled tents until they are ready for service.

There are certain specifications called out by engineering departments that fall into [a] place...
Not-Known-to-Man.

Recalling... how absolutely no scratch marks of any kind were allowed on shafts of rebuilt motors
for the United States Navy.

Fine. We can do this.

It's impossible to know if these specifications called for... are related to life safety, or toward the advancement of human civilization.

It doesn't really seem to matter. It's what the customer requests.

People in business... do the best they can.

The rest of us... [for the most part] strive to go along with the program.

John

 

[dpc]

This is not a concept I'm aware of, Jeff. Never heard of it.

Dave

 

[che12345]

Dear Mr jraef

Q1. ... Has anyone heard of two different types of GEAR being "series rated"? A claim was made by ....
A1. Reference Google: " series rating of circuit breakers " shows the following....:
a) See Wikipedia " ... in the US, UL certifies equipment ratings..."
b) See NEMA " ....series ratings, it is practical? "
c) See EC&M " ... 2005 NEC changes 204.86 on series ratings..."
A1.1 See IEC 60947-2 Annex A " coordination under short-circuit conditions between a CB and another SCPD..."

Q2. ....claim was made by a salesperson for a company that makes MCCs and Switchgear that (he) the must be given the order for both because the MCCs are "series rated" ....
A2. the claim is relevant/valid if he has document as evidence to show that the [up-stream and the down-stream] CBs had been tested [together in a combination] per IEC or complied with NEC/UL requirements, see above A1. b) and c). See also above A1.1.

Q3. ... I've never heard of this concept extending into primary type gear like LV MCCs fed by Switchgear.
A3. This is widely practiced, where the up-stream CB is located in the switchgear and the down-stream CB is located in the MCC, in two separated/different locations.
A3.1 See above A1.1 for more detail.

Che Kuan Yau (Singapore)

 

[dpc]

che12345,

You're talking about series rating of circuit breakers, not equipment. Pretty sure jraef is well aware of series rating of MCCBs - in fact he says so in his post.

 

[che12345]

Dear Mr dpc

1. No standards called for two separate (gears/boards) or ASSEMBLYs to be subjected to "series rated" testing to qualify for "series rated" requirement.

2. a)If the up-stream ASSEMBLY is tested and rated equal to or higher than the up-stream CB rating, and
b)with the down-stream ASSEMBLY tested and rated equal to or higher than the down-stream CB rating, and
c) when they are installed with the up-stream and the down-stream CBs which are tested in combination which fulfilled the "series rated" requirements, then
there is [no] issue. The two ASSEMBLYs fulfilled the "series rated" conditions.

3. However, even if both the up-stream and the down-stream ASSEMBLYs are tested to higher ratings; but if they are [not] installed with the [tested "series rated" combination of two (particular) breakers]; the "series rated " does [not] exist. The two ASSEMBLYs [do not] fulfilled the "series rated" conditions.

4. This illustrates how the ASSEMBLY is involved besides the CB, to qualify for the "series rated" requirements.

Che Kuan Yau (Singapore)

 

[LionelHutz]

I'm pretty sure this is a North America question where UL or CSA would apply, meaning IEC standards are useless.

jraef - You need to specify what standard applies.

Ask for proof of what is claimed.

I haven't heard of it being done, but I suppose it's possible the switchgear and MCC's use a few common frame breakers which meant that series testing the possible combinations wasn't that difficult.

It sounds like you're saying the site has <65kA available, so the 65kA gear would be fine. So, telling stories that the 65kA gear becomes 100kA wouldn't cause issues once installed, but would rather just be a spec game being played.

 

[jraef]

Well, the tactic worked. The user became fearful and gave them the project because of that issue, which I still think is a red herring. So because they made the decision before I could get a chance to talk to them, we were never provided with the data necessary to make a cogent argument.

But at least now I have had an opportunity to educate our sales team about not accepting things at face value and challenging statements like this by at least pressing for a chance to investigate it. It's a shame really, because now that person at the end user is going to believe this is an issue and likely it will end up in a future tender specification, making other people scratch their heads and say "Where the heck did they come up with that notion?"


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden