Series rated systems

Status
Not open for further replies.
B

buck

Member
Location
California
Have view posts here on occasion and have been impressed with the knowledge.That being said,can anyone explain in simple terms the requirements for series rated systems or direct me to some handy and easy to understand information?Does Mike Holt have any booklets about this subject?
Is it indeed a fact that all equipment is to be from same mfg?
Thanks all, for your help
 
Re: Series rated systems

basically series rating is used to avoid using devices with high interrupting rating. For example if a system was 100K, instead of using 100K breakers, you could use a combination(UL listed) of a fuse(or circuit breaker) and branch circuit circuit breakers(or downstream breakers) with lower interrupting rating to meet the requirements. Thats how I understand it.
 
Re: Series rated systems

The key word us UL "recognized component rating" as indicated by bwyllie. It is possible to have 100ka available at 240v where the upstream breaker has a rating of 100kaic and the down stream breakers may have ratings as low as 10kaic. To be able to do this the over current protective devices must be tested for series connected protection of the power distribution system. You must consult the breaker manufacturers catalog for OCPDs that meet this testing requirement.
There are also fuse/circuit breaker series combinations. Again, you must consult the manufacturers catalog for products that can be applied in this manor.
 
Re: Series rated systems

Thanks guys for your responses.I had an electrician install a Siemens panel and step down XFMR downstream of a GE series rated system and I told him it wouldn't be acceptable due to different MFG's.Is this what you understand to be true? He also stated, due to the "seperately derived" system of the new XFMR he could use a different MFG panel and XMFR.
Any help here?Thanks
 
Re: Series rated systems

This is the way I would interpret your question:
To be series combination rated the OCPDs on the line side of the Xfmr must be UL "recognized component rating" that are tested with one another usually all from the same manufacture. Since you have a separately derived system on the secondary of the transformer you would have to establish the available fault current at the secondary and then are able to use OCPDs that are UL "recognized component rating" supplied by another manufacture based upon that fault current.
 
Re: Series rated systems

Thanks for the info,but aren't we baseing the AIC rating on the utility co. supply? So a downstream seperately derived system would still be based on the utility?
 
Re: Series rated systems

Get Bussmann's SPD booklet.
It is downloadable if you don't want to wait to receive one.

It has formula(s) ( 1? and 3? ) for deterimning the ASCC on the secondary side of a ( second transformer ) SDS when the ASCC on the primary side is known.

gwz2

[ November 17, 2003, 03:13 PM: Message edited by: gwz2 ]
 
Re: Series rated systems

Thanks to all you guys,especially gwz2,I downloaded the Bussman info--best stuff I've ever come across and explains exactly what I was looking for.
Thanks again
 
Re: Series rated systems

Buck,
Basically, I am not aware of a series rating that includes a transformer.
I would suggest that the transformer itself isn't series rated with regards to the available fault current on the load side of the transformer. All the series ratings get you is the coordination of the OCPDs from the service entrance to the last OCPD on the line side of the transformer. The question is what is the available fault current of the secondary side of the transformer? With out documentation as to what the actual fault current available at the xmr pri. one would have to assume the maximum and start out from scratch with applying the OCPDS on the secondary.
 
Re: Series rated systems

Hey thanks for the response templdl, good info.
Does anyone have AIC ratings for typical standard size XFMR primaries? Would be handy for future reference.Thanks
 
Re: Series rated systems

Don't know about your area.

The local Poco will supply chart(s) of their tranformer maximum [actually the transformers with the lowest Percent Impedance ( %Z )] Fault Currents when requested.

It does not seem to be information that they give with-out a request.

For every installation that I question the Available Short Circuit Current (ASCC) at their transformer secondary, I call the local Poco and ask what size transformer they will be using at "that" site and for the Fault Current. They have always quoted what their chart indicates.

On one installation several years ago they quoted the values and when inspecting for a Service Release they had already set the transformer. It had a %Z two one-tenths less, I think it was 1.4 quoted and 1.2 installed, than the quoted value figure, thus boosting the ASCC several thousand amps.
Luckily the contractor had used equipment that met the higher ASCC values.

gwz2

[ November 19, 2003, 02:36 PM: Message edited by: gwz2 ]
 
Status
Not open for further replies.
Top