240.86(c) nec 2017 version series rating

[hhsting]

first reaction
second reaction
third reaction at the end


Well so its not easy you all only see post thats 2% of what is being submitted. What happen if you actually where in my position

But I like to add:

Sorry! Thats what I have on plans but I really appreciate all of your help as much as possible, response and patience.

 

[xptpcrewx]

Can one use breakers in system that are series rated and fully rated and ignore the NEC 2017 section 240.86(c)?

You can't ignore rules in the code although they may be rendered not applicable. In this case, the objective is to account for situations where both series rated devices are not "truly" in series as determined by their fault sources, and hence need to interrupt an additional portion of the fault currents without aid from the other device.

Keep in mind, this type of rating system applies to the branch currents seen by the protective devices and not the fault current at the bus. Also note that its a bit trickier to apply multiplying factors to the branch current to account for asymmetry when performing the device evaluation.

I think the question relates to whether or not “series ratings” are bidirectional or not. Ie if a 22kA breaker is series rated with a 65kA breaker at 42kA, if the 22kA breaker is UP stream, does the series rating still hold true?

I don't see why not.

But more importantly, do the rules on series ratings expressly state that the lower rated device must be downstream of the higher one, or just “in series” with it? I don’t know.

They don't. IMO upstream/downstream are ambiguous terms because what may be considered downstream for normal operation could be considered upstream in terms of fault generation... I believe the original series rating concept was called "Cascade" systems/ratings.

 

[Jraef]

You can't ignore rules in the code although they may be rendered not applicable. In this case, the objective is to account for situations where both series rated devices are not "truly" in series as determined by their fault sources, and hence need to interrupt an additional portion of the fault currents without aid from the other device.

Keep in mind, this type of rating system applies to the branch currents seen by the protective devices and not the fault current at the bus. Also note that its a bit trickier to apply multiplying factors to the branch current to account for asymmetry when performing the device evaluation.


I don't see why not.


They don't. IMO upstream/downstream are ambiguous terms because what may be considered downstream for normal operation could be considered upstream in terms of fault generation... I believe the original series rating concept was "Cascade" systems/ratings.

I just added however that it is indeed unidirectional, the definition states it as the downstream device rating being increased by virtue of the upstream device.

 

[xptpcrewx]

I just added however that it is indeed unidirectional, the definition states it as the downstream device rating being increased by virtue of the upstream device.

It says connected on the load side not downstream. But I take your point on the intent.
(what about a tie breaker, which side is line/load?)

 

[Jraef]

It says connected on the load side not downstream. But I take your point on the intent.
(what about a tie breaker, which side is line/load?)

You’re right, it does use Line and load, not upstream and downstream.

Why would you need series ratings on tie breakers?

 

[jim dungar]

As it happens often, too much junk has been added making this thread hard to follow.

Very simply
If devices are fully rated you can ignore any series ratings as they are not applicable by the definition of 'series rating'.

Series ratings are tested combinations that work at a fault current, it is not a limitation on the full rating of any single device.

 

[xptpcrewx]

You’re right, it does use Line and load, not upstream and downstream.

Why would you need series ratings on tie breakers?

For some older systems where series rated systems might/could be employed like secondary spot networks with a tie breaker but no main breakers. I suppose Line and Load can be considered as being on both sides simultaneously?

 

[DrSparks]

As it happens often, too much junk has been added making this thread hard to follow.

Very simply
If devices are fully rated you can ignore any series ratings as they are not applicable by the definition of 'series rating'.

Series ratings are tested combinations that work at a fault current, it is not a limitation on the full rating of any single device.

That's how I see it. Technically, any main breaker with a higher withstand than a lesser branch breaker should provide protection at the AIC rating of the upstream breaker. I don't know how this could work both directions (and I don't mean current flow.. AC duh) as a branch breaker would never be called to interrupt current to an upstream breaker. I mean I suppose it's possible but not design intent.

Series ratings as the gentleman said are combinations tested in a lab. The studies are paid for by manufacturers, so you're unlikely to see series ratings across brands!

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