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Verifying series rated breakers on a TCC plot

Verifying series rated breakers on a TCC plot

Verifying series rated breakers on a TCC plot

(OP)

I understand now adays its easy to just reference manufacturers breaker data to find breakers that are series rated.  But just to verify this theoretically how can you plot two breakers on a TCC and verify that they are series rated?  Can you somehow look at the let-thru of the upstream breaker?  

For instance is you are trying to manually verify if two breakers are series rated without having any manufacturers data to tell you so.

RE: Verifying series rated breakers on a TCC plot

You can't.  The TCCs really don't provide any information that is going to help you.  Everything is occurring in the instantaneous region of the both TCCs.

The only data that has any value is the manufacturer's test data for series ratings.  

I suppose if you wanted to spend a few years studying plasma physics and the nature of arcs, a predictive theory could be developed.  But testing is required because there is presently no other reliable method.  Since the applicable codes currently require a tested combination, the theory would be of limited value anyway, even if it was realistic.

 

David Castor
www.cvoes.com

RE: Verifying series rated breakers on a TCC plot

(OP)
dpc

Thanks thats kind of what I thought.

So I guess that you cannot use series ratings for breakers between different manufacturers.

The following comment out of the NEC was what had me wondering weather or not there could be any manual verification but it sounds like there cannont be.

"The operating parameters of the existing overcurrent protection equipment dictate what can be done in a field-engineered protection scheme.
Compatibility with series rated systems will in all likelihood be limited to circuit breakers that (1) remain closed during the first  1/ 2 cycle of a fault and (2) have an interrupting rating that is not less than the let-through current of an upstream protective device (such as a current-limiting fuse)."

These comments seem to indicate that there can be a field engineered soulution implemented.

RE: Verifying series rated breakers on a TCC plot

This may be the hidden joker;
"have an interrupting rating that is not less than the let-through current of an upstream protective device (such as a current-limiting fuse)."
I believe that this statement implies that if you want to use a circuit breaker with an interrupting rating less than the let through current of the upstream device the combination must be tested.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Verifying series rated breakers on a TCC plot

(OP)
waross

Just out of curiosity how can you verify what the let-through current of the upstream breaker will be for a given fault current?

RE: Verifying series rated breakers on a TCC plot

The spec sheet. More applicable for current limiting fuses than breakers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Verifying series rated breakers on a TCC plot

Quote:

So I guess that you cannot use series ratings for breakers between different manufacturers.
Not only that, but you cannot do it even for breakers of the SAME manufacturer if they have not been tested, IN SERIES COMBINATION, by the manufacturer. Each mfr will have a list of specific breakers they offer with Series Ratings. You cannot deviate from that list.

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RE: Verifying series rated breakers on a TCC plot

That statement in the NEC was added to allow a PE to assume responsibility for the safety of a "series rating" that had not been tested.  It was, I think, intended as a sop for the old "up-over-down" die-hards and maybe the fuse manufacturers.   

If manufacturers will not take responsibility for these types of installations, it's hard to see what could justify a PE assuming this liability.  

At any installation, the owner can basically do whatever he wants and then deal with the consequences if there are any. There is really no one out there enforcing this stuff in an existing facility -- until someone gets injured.

 

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