Series Rated panel

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Rai136926

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I have a project where I need to install a transformer and a panel. The panel which feeds the transformer is a series rated panel. My question is the new panel which is fed from the new transformer does it have to be series rated? Can this panel be fully rated?
 
I don't see any reason it couldn't be either.

What's on the primary side of the transformer doesn't have any effect on the ratings on the secondary side of the transformer.

And in general, having a series rated panel doesn't have any effect on what is installed downstream (as long as everything downstream is rated for the available fault current at its downstream location).
 
Rai136926 said:
I have a project where I need to install a transformer and a panel. The panel which feeds the transformer is a series rated panel. My question is the new panel which is fed from the new transformer does it have to be series rated? Can this panel be fully rated?
Click to expand...

You never have to series rate panels. it is a option to reduce equipment costs.
You can always fully rate.
 
Rai136926 said:
I have a project where I need to install a transformer and a panel. The panel which feeds the transformer is a series rated panel. My question is the new panel which is fed from the new transformer does it have to be series rated? Can this panel be fully rated?
Click to expand...

Series rating means the downstream/branch breakers can take credit for the KAIC rating of the upstream/main breakers/other OCPD, even though the downstream/branch devices have a lower KAIC rating. This way your branch breakers and subpanels can have lower ratings (thus cheaper equipment), while your devices closest to the source carry the full rating and interrupt the fault before it gets to the downstream devices. Series ratings apply to a combination of two OCPDs that are tested together to make sure the higher rated device coordinates to trip before the downstream device catastrophically fails.

Typically, a product family of breakers, will be series rated with a certain fuse class. An example is Square D's QOB breakers with 10 KAIC series rated with Class J fuses at 200 KA. The panelboard with QOB breakers can therefore be anywhere downstream of the disconnect fused with Class J fuses, and the system is capable of up to 200 kA of fault current. Another example you might see, is one breaker product family series rated with another breaker family, within the same manufacturer. Few (if any) series rated combinations will mix breaker manufacturers.
 
You would need the specifics on your particular transformer. According to the charts on this site
http://www1.cooperbussmann.com/library/docs/epr_booklet.pdf you may be looking at 23k +/- . (see Chart Pg 9)
That's high enough to warrant your investigating the transformer (impedance) and calculating your particular situation. If you are 22k or less, a series rated panel in commonly available.
 
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augie47 said:
You would need the specifics on your particular transformer. According to the charts on this site
http://www1.cooperbussmann.com/library/docs/epr_booklet.pdf you may be looking at 23k +/- . (see Chart Pg 9)
That's high enough to warrant your investigating the transformer (impedance) and calculating your particular situation. If you are 22k or less, a series rated panel in commonly available.
Click to expand...


A typical 75 kva 480 to 120/208 has an impedance between 3.5 and 5.5 - at least every one that I have seen. I am not saying there are zero exceptions, but very likely AIC not an issue. Agree though, always check transformer.
 
electrofelon said:
A typical 75 kva 480 to 120/208 has an impedance between 3.5 and 5.5 - at least every one that I have seen. I am not saying there are zero exceptions, but very likely AIC not an issue. Agree though, always check transformer.
Click to expand...

Keep in mind that the fault current calculation tool hosted on this website, makes the assumption that the primary voltage and primary fault current are infinite. Obviously they are not, but the function takes off to a cruising altitude (i.e. asymptote) as these two parameters get large, and making that assumption is practical for a worst case scenario. If this is a medium voltage to utilization voltage transformer, it is a good assumption. But if it is a utilization voltage to utilization voltage transformer, it is probably a lot more fault current than there really is.


Here are the details of the complete formula, where you can apply primary voltage and primary side available fault current (if known):
http://forums.mikeholt.com/showthread.php?t=171709
 
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