ryan_618 said:One disadvantage to series ratings is that they can't be selectively coordinated.
Because on a series system you are depending on the upstream device to open. That is the opposite of selective coordination.Mike01 said:Why can't selective coordination be achieved thru series rating??
ryan_618 said:Jim, if the fault current was that low, it wouldn't be a series rated system. The breakers would be fully rated if the fault current is only 2K. If the fault current one inch away from the breaker is over the fully rated value of the circuit, you have a series rated system. How do you selectively coordinate it if you are depending on the upstream device to open?
* I need to add a note here that I am not an expert on this, but what I am saying seems like logic to me.
ryan_618 said:Jim, if the fault current was that low, it wouldn't be a series rated system. The breakers would be fully rated if the fault current is only 2K. If the fault current one inch away from the breaker is over the fully rated value of the circuit, you have a series rated system. How do you selectively coordinate it if you are depending on the upstream device to open?
* I need to add a note here that I am not an expert on this, but what I am saying seems like logic to me.
winnie said:In the example that Jim gave, if the fault downstream of the 20A breaker were to happen _inside_ the panel, and were to be some sort of bolted fault (the forklift driver smashes the panel, and the 12ga wire gets pinched into the neutral bus), then the fault current might approach the maximum available at that feeder. This would presumably exceed the rating of the 20A breaker, and IMHO all bets are off as to which breaker would open first.
-Jon
Let's see... Fork through the panel, and it only hits the one #12. Okay, that could happen. Add: the panel has critical equipment on it. Ok. The main trips along with the 20A branch cause it's series rated equipment.ryan_618 said:And that would be a lack of coordination. ...
Uhhh... I don't know. Take a look at post 12 by Ryan Jackson, quoting winnie(Jon) in post 10.ryan_618 said:I don't recall reading anything about forklifts. What am I missing?...
Okay. My, translation is: your concern is for lack of coordination for critical panels where the fault is in the panel or very close (low impedance) to the panel. Is that close to what you are thinking?ryan_618 said:... I was thinking more along the lines of a fault due to someone working in an energized panel creating a fault in the panel, or, more likely, a fault in a box close to the panel.
Jon is correct here. This is why the Breaker people and Fuse people submit these combinations to UL to achieve a higher AIC rating. Both Overcurrent devices are intended to open at the same time, which means you loose selective coordination.In a series rated system, you are depending upon the _combination_ of the upstream device and the downstream device to open in the event of a fault which may exceed the capability of the downstream device
This is to reinforce Ryans point.One disadvantage to series ratings is that they can't be selectively coordinated
I was reading so much into the fault I wasn't looking at what caused it. Sorry.coulter said:Uhhh... I don't know. Take a look at post 12 by Ryan Jackson, quoting winnie(Jon) in post 10.
carl
davidr43229 said:Jon is correct here. This is why the Breaker people and Fuse people submit these combinations to UL to achieve a higher AIC rating. Both Overcurrent devices are intended to open at the same time, which means you loose selective coordination.
This is to reinforce Ryans point.
Truth be known, even with fully rated systems you can not achieve Selective Coordination, due to the instantious region within the breaker (.01)
People generally use a Series Rated system to save money, until they have a fault and the mains trip out and they fully understand what series rated systems really mean then. It's a trade-off, you get what you pay for.
Just my $.02