Working with EE on Cost effective Series Rated Systems

[Aledrell]

So I recently reconfigured an EE design su it would be more cost effective. Got 200a class j-fuses at the SES which run the MLO panelboards with typical QP 10,000kaic rated siemens breakers. I had to ask the engineer if for the panel AIC calcs as they need to be listed on the panels boards. One panel came in with high 35kaic rating. So I asked the EE if I need to install a MB with an AIC higher than this for safety and proper series rating.
His response to me was that I needed to check with the breaker manufacturer.
Shouldn’t I just tell home that I’m using siemens products x,y, and z and have him sign off that it’s safe. Isn’t this his job?
Below is the calcs he sent me and the manufacturer info. The way I read this, I need to add a QJ2H MB to panel A and then the combination with the j fuses and standard qp breakers would provide a 42kaic protection rating?
My supplier tells me I’m protected up to 100kaic bc that’s the rating of the SES fuses. I think he’s wrong. Give me your thoughts. Thx as always.

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[brantmacga]

His response to me was that I needed to check with the breaker manufacturer.
Shouldn’t I just tell home that I’m using siemens products x,y, and z and have him sign off that it’s safe. Isn’t this his job?

My supplier tells me I’m protected up to 100kaic bc that’s the rating of the SES fuses. I think he’s wrong. Give me your thoughts. Thx as always.

Only the manufacturer can provide you with a series rating approval.

The supplier salesperson is literally the last person I would ever look to when asking “will this work?”


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[paulengr]

In series rating quite often the situation is that the downstream device has a rating where it can withstand a higher current than it can interrupt. This sounds goofy but it is normally the case. So as long as the upstream device OR the current considering current limiting of both the devices is less than the withstand and the upstream device opens first, it will be series rated. But series ratings are a lot of trouble to test so they are pretty rare. Most of the time what I more commonly see is backup fuses where fuses are built into the breaker.

Plus the cost goes up significantly but if you are just looking at upgrading to 48 or 65 kA it’s not that much for upgraded breakers and there is no incentive for the manufacturer to do series rating tests. Series rating is more common for 100 kA ratings. So there’s just no money in it for them.

Look up for instance the old “Tri break” breakers that have backup fuses built into the breaker.

Might also want to look at a current limiting breaker for a main. Similar to fuses these work by using a hairpin arrangement to reduce the fault current to a manageable level.

Alternatively why not just go up on transformer impedance or install reactors? This directly reduces the available fault current. So if you are at say 40 kA with 5% impedance you could just add 1% reactors and take it down to 33 kA inexpensively;

 

[augie47]

I guess this will end up being a learning lesson for me. But based on the manufacturer series rating sheet you posted, I would agree with you.
It appears with the Class J fuse and the QJ2H main the 10k QP branch breakers would be acceptable.

 

[hmspe]

"Shouldn’t I just tell home that I’m using siemens products x,y, and z and have him sign off that it’s safe. Isn’t this his job?"

That absolutely is not the engineer's job. In some states the engineer could lose his license for doing what you suggest. In addition, "signing off" means the engineer assumes liability for the change. I think the engineer's response was entirely reasonable.

 

[petersonra]

"Shouldn’t I just tell home that I’m using siemens products x,y, and z and have him sign off that it’s safe. Isn’t this his job?"

That absolutely is not the engineer's job. In some states the engineer could lose his license for doing what you suggest. In addition, "signing off" means the engineer assumes liability for the change. I think the engineer's response was entirely reasonable.

I think it would be ok to ask for his professional opinion on it. It would not be unreasonable for him to charge for that opinion.

 

[electrofelon]

"Shouldn’t I just tell home that I’m using siemens products x,y, and z and have him sign off that it’s safe. Isn’t this his job?"

That absolutely is not the engineer's job. In some states the engineer could lose his license for doing what you suggest. In addition, "signing off" means the engineer assumes liability for the change. I think the engineer's response was entirely reasonable.

IMO yes that is absolutely his job, to select proper series and SCCR ratings of equipment (in general that is, I dont know the specific details of his scope of work on this of course).

 

[electrofelon]

So I recently reconfigured an EE design su it would be more cost effective. Got 200a class j-fuses at the SES which run the MLO panelboards with typical QP 10,000kaic rated siemens breakers. I had to ask the engineer if for the panel AIC calcs as they need to be listed on the panels boards. One panel came in with high 35kaic rating. So I asked the EE if I need to install a MB with an AIC higher than this for safety and proper series rating.
His response to me was that I needed to check with the breaker manufacturer.
Shouldn’t I just tell home that I’m using siemens products x,y, and z and have him sign off that it’s safe. Isn’t this his job?
Below is the calcs he sent me and the manufacturer info. The way I read this, I need to add a QJ2H MB to panel A and then the combination with the j fuses and standard qp breakers would provide a 42kaic protection rating?
My supplier tells me I’m protected up to 100kaic bc that’s the rating of the SES fuses. I think he’s wrong. Give me your thoughts. Thx as always.


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I am a bit confused. First I am not entirely clear what you have. Is this a 230.40 exception 2 setup with each of several 200's feeding the panelboards?
Second, you are mixing up AIC rating and SCCR rating. Note that that panelboard label is giving the SCCR of the panelboard not AIC. Third, I just checked my siemens series rating chart, and I am not seeing a series rating for a class J to a QP breaker.

 

[jim dungar]

The way I read this, I need to add a QJ2H MB to panel A and then the combination with the j fuses and standard qp breakers would provide a 42kaic protection rating?

The chart you posted has columns for 3 devices in series.
You need to find a 'row' that contains a 'not used' in one of the cells, because you currently have only two devices in series.
In your case there is no row that has just a fuse and QP combination.

I agree you need to add the feeder, or main, breaker.

 

[Aledrell]

So I recently came across this series rating chart put out by Siemens. And if I’m reading it correctly my supplier was right and the SCCR rating of a 200a j fuse and qp is 100kaic?


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[jim dungar]

So I recently came across this series rating chart put out by Siemens. And if I’m reading it correctly my supplier was right and the SCCR rating of a 200a j fuse and qp is 100kaic?

The first chart you posted was for three devices in series.
The second chart was for two devices in series.

Use the one appropriate for your installation.

 

[Aledrell]

The first chart you posted was for three devices in series.
The second chart was for two devices in series.

Use the one appropriate for your installation.

Curious how it’s considered a three tier series if it says “none used” in one of the columns....isn’t that essentially a two tier?


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[electrofelon]

So I recently came across this series rating chart put out by Siemens. And if I’m reading it correctly my supplier was right and the SCCR rating of a 200a j fuse and qp is 100kaic?


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I have seen this chart before and it's rather confusing - I don't really understand what it applies to. It mentions several switchboards
(I'm not familiar with Siemens switchboards) and then below it "panel board S1". I don't know what an S1 panel board is, if this is outdated or what. Also I think this is giving SCCR of a panel board not AIC. As I said, the series rating chart I have doesn't show a J to QP series rating, maybe it's not complete I don't know.

 

[jim dungar]

Another thing to be careful with is the voltage rating for the chart. I am surprised the system isn't also listed
120/240 usually means it is for a single phase system 1PH 3W.
240V might mean it is applicable for any voltage up to 240V L-L such as 1PH 3W, 3PH 3W, and 3PH, 4W.

At least that is what I have seen on UL Listed charts from other manufacturers.

 

[Aledrell]

Problem Solved....turns out fuses are class T jnnl fuses not class J. So my supplier was correct 100kaic sccr rating. I illustrated it on the matrix.

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