100% Rated Main Breaker?

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mbrooke

mbrooke

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When would someone use a 100% rated main breaker? What are the advantages of a 100% rated main? And what makes it 100% rated as apposed to any other "normal" main breaker? Feed form the padmount is 5 sets of 4 500kcmil in 4 inch conduit.
 

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So basically, the 100% breaker allows us to not derate the conductors for continuous loads and thus saves on conductor costs?

Is it just me or would anyone else get nervous running a breaker at 100% ? I have had breakers trip at 80% in some high ambient temp situations.
 
ron said:
It depends on whether the standard rated breaker would cause you to go to the next size after doing your load calculation and if the 100% rated breaker was available in the equipment and was worth the extra cost.


https://iaeimagazine.org/magazine/2016/07/19/100-vs-80-choosing-the-right-ocpd-solution/
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If the calculated load were near 1600 amps continuous and they were instead using a standard breaker at 80% then wouldn't everything need to be bumped up to 2000 amps meaning the conductors, main CB and switchboard?
 
electrofelon said:
So basically, the 100% breaker allows us to not derate the conductors for continuous loads and thus saves on conductor costs?

Is it just me or would anyone else get nervous running a breaker at 100% ? I have had breakers trip at 80% in some high ambient temp situations.
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Yes you can use a smaller conductor because you can use 100% of load instead of 125% of load. Also this 125% only applies to continuous load (for standard breakers) when selecting conductor ampacity needed.

I was always told a major reason they require 125% for standard device is because the device sinks some of the heat it produces into the conductor - and it is for the termination temp rating more then anything. 100% breakers supposedly don't depend on conductor as a heat sink is one of their major differences over a standard device.
 
kwired said:
Yes you can use a smaller conductor because you can use 100% of load instead of 125% of load. Also this 125% only applies to continuous load (for standard breakers) when selecting conductor ampacity needed.

I was always told a major reason they require 125% for standard device is because the device sinks some of the heat it produces into the conductor - and it is for the termination temp rating more then anything. 100% breakers supposedly don't depend on conductor as a heat sink is one of their major differences over a standard device.
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Isn't there also something about 90*C terminations on the breaker?
 
electrofelon said:
IIRC, you are still restricted to 75 degree terminations. 100% breakers, again IIRC, require 90 degree rated conductors used at 75 degrees (mostly an academic requirement these days).
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Maybe thats what I was thinking of.


In terms of the breakers, I remember someone saying they are exactly like regular breaker, just with provisions for air flow, cooling and spacing.
 
kwired said:
I was always told a major reason they require 125% for standard device is because the device sinks some of the heat it produces into the conductor - and it is for the termination temp rating more then anything. 100% breakers supposedly don't depend on conductor as a heat sink is one of their major differences over a standard device.
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That is correct on 125%. By requiring the breaker to be rated at 125%, or limiting the load to 80%, in effect you are increasing the size of the conductor, which creates a heat sink.
 
tom baker said:
That is correct on 125%. By requiring the breaker to be rated at 125%, or limiting the load to 80%, in effect you are increasing the size of the conductor, which creates a heat sink.
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Perhaps, but I am willing to debate that as the CEC doesn't require up-sizing the wire.
 
The 90 deg versus 75 is academic, because I don't think you can buy 75 deg insulation anymore in these ampacities. As always, applied at 75 deg column, derated from 90 deg column if needed.

The 100% rated breakers are tested to have adequate airflow etc permitting 100% loading without tripping and the conductors get sized at the handle rating.

1600A of continuous load, no problem, and only 1600A worth of wire. Yeah!

The breaker and enclosure (whole assembly) need to be listed for 100% continuous operation.

Sometimes it is a freebee, such as UL 1558 SWGR with power breaker are always 100% rated breakers
 
mbrooke said:
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In terms of the breakers, I remember someone saying they are exactly like regular breaker, just with provisions for air flow, cooling and spacing.
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Yes, sort of. The issue is that you cannot buy a "100% rated" breaker as a component and install it yourself in the field. Unless you ARE the switchgear OEM, the ONLY way you can buy a 100% rated breaker is in an ENCLOSED piece of gear where the ENTIRE ASSEMBLY is tested and listed for 100% current. So a Main CB on a switchboard is a perfect example; you don't order a switchboard, then order a 100% rated breaker to put inside of it, you order a switchboard WITH a 100% rated main breaker; they have to be listed together. In addition, you will never find a FEEDER breaker in a switchboard or panelboard that is 100% rated. You have to move up to switchGEAR where each breaker is inside of its own cubicle to get that.

In that 100% listing, the breaker testing procedure may have (usually have been) listed using 90C rated conductors, but you cannot use the conductors at their 90C ratings, you must still use them at their 75C ratings. So it changes nothing with regard to the conductors if you are already using 90C insulation.
 
Jraef said:
Yes, sort of. The issue is that you cannot buy a "100% rated" breaker as a component and install it yourself in the field. Unless you ARE the switchgear OEM, the ONLY way you can buy a 100% rated breaker is in an ENCLOSED piece of gear where the ENTIRE ASSEMBLY is tested and listed for 100% current. So a Main CB on a switchboard is a perfect example; you don't order a switchboard, then order a 100% rated breaker to put inside of it, you order a switchboard WITH a 100% rated main breaker; they have to be listed together. In addition, you will never find a FEEDER breaker in a switchboard or panelboard that is 100% rated. You have to move up to switchGEAR where each breaker is inside of its own cubicle to get that.

In that 100% listing, the breaker testing procedure may have (usually have been) listed using 90C rated conductors, but you cannot use the conductors at their 90C ratings, you must still use them at their 75C ratings. So it changes nothing with regard to the conductors if you are already using 90C insulation.
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Any idea of the extra cost an 100% breaker scheme?
 
mbrooke said:
Any idea of the extra cost an 100% breaker scheme?
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At 1600A? Probably significant compared to a 2000A breaker used at 80%, because for some mfrs that's a frame size and classification change. But it really depends on that issue. So for example if a mfr doesn't offer a 1600A frame MCCB and would give you a 2000AF ICCB with a 1600A rating plug, then there is no difference in price.

But that said, 1600A is the upper typical limit of "Molded Case Circuit Breakers" (MCCBs) listed under UL489. There are also UL 489 listed "Insulated Case Circuit Breakers" (ICCB) from some mfrs, but they have pretty much gone by the wayside as a separate design in that most mfrs now just sell you a "lighter duty" Power Breaker with a UL 489 listing, instead of a UL 1066 listed Power Circuit Breaker (PCB). PCBs and ICCBs are almost always going to be 100% rated, but they are typically a lot more expensive than MCCBs.
 
Jraef said:
Yes, sort of. The issue is that you cannot buy a "100% rated" breaker as a component and install it yourself in the field. Unless you ARE the switchgear OEM, the ONLY way you can buy a 100% rated breaker is in an ENCLOSED piece of gear where the ENTIRE ASSEMBLY is tested and listed for 100% current. So a Main CB on a switchboard is a perfect example; you don't order a switchboard, then order a 100% rated breaker to put inside of it, you order a switchboard WITH a 100% rated main breaker; they have to be listed together. In addition, you will never find a FEEDER breaker in a switchboard or panelboard that is 100% rated. You have to move up to switchGEAR where each breaker is inside of its own cubicle to get that.

In that 100% listing, the breaker testing procedure may have (usually have been) listed using 90C rated conductors, but you cannot use the conductors at their 90C ratings, you must still use them at their 75C ratings. So it changes nothing with regard to the conductors if you are already using 90C insulation.
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Jraef, I question some of this. First I have a hard time believing that I cant get and use 100% breakers for feeders or branch circuits in panelboards. For example. L frame breakers for I line are available in 100%. Also, I understand it is the Assembly that needs to be 100% rated, but I imagine that manufacturers have approved combinations and I could add a 100% breaker to an existing panelboard if it met the requirements for space, other breakers, etc. Correct me if I am wrong, this is somewhat assumed from what I see in manufacturers breaker and panelboard catalogs....
 
Jraef said:
At 1600A? Probably significant compared to a 2000A breaker used at 80%, because for some mfrs that's a frame size and classification change. But it really depends on that issue. So for example if a mfr doesn't offer a 1600A frame MCCB and would give you a 2000AF ICCB with a 1600A rating plug, then there is no difference in price.

But that said, 1600A is the upper typical limit of "Molded Case Circuit Breakers" (MCCBs) listed under UL489. There are also UL 489 listed "Insulated Case Circuit Breakers" (ICCB) from some mfrs, but they have pretty much gone by the wayside as a separate design in that most mfrs now just sell you a "lighter duty" Power Breaker with a UL 489 listing, instead of a UL 1066 listed Power Circuit Breaker (PCB). PCBs and ICCBs are almost always going to be 100% rated, but they are typically a lot more expensive than MCCBs.
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Ok- here comes the dumb question, but what is the difference between modeled case, insulated case and power circuit breakers? What are minimum and max for each?
 
kwired said:
Never installed one but seem to recall reading you typically must use 90C conductor selected from 75C ampacity table.
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Looked around, You're right:


s-l1600.jpg
 
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