80% vs 100% breaker

[electrofelon]

So I know that you cant just buy a "100% breaker" and throw it in and use it on a continuous load at its rating - it needs to be a manufacturer approved/tested panelboard and breaker combination. But is there anything different about the breaker itself? Is a 100% breaker have an elevated thermal trip curve to help prevent "nuisance" tripping? Say for example I have electrical equipment in an area of high ambient temperature and am having occasional tripping at even around 80%. Would a 100% breaker be less likely to trip under these same circumstances?

 

[templdl]

So I know that you cant just buy a "100% breaker" and throw it in and use it on a continuous load at its rating - it needs to be a manufacturer approved/tested panelboard and breaker combination. But is there anything different about the breaker itself? Is a 100% breaker have an elevated thermal trip curve to help prevent "nuisance" tripping? Say for example I have electrical equipment in an area of high ambient temperature and am having occasional tripping at even around 80%. Would a 100% breaker be less likely to trip under these same circumstances?

A 100% breaker is actually no different than an 80% breaker if simply swapped out. If you do not apply a 100% breaker per its UL listing to be applied at 100% the it can only be used as an 80% breaker as anyways. To understand the please get a hold of a 100% tasted breaker,s instruction sheet. You will find that their intended use is to possibly save of the use of conductor because the conductor size is based upon 100% of the continuous load plus 100% of the continuous load intead of the 80%/100% rule. When sizng the conductor using this method depending upon where the computed load ends up you can end up with a smaller tasted conductor which can save money. But in order to do so the conductor must have a 90degC rating. It is only then that you can apply a 100% rated breaker. In addition the 100% breaker must be mounted is an enclosure that is suitable to be used for a 100% breaker.
But read the instruction ufor the breaker.
As previously stated a 100% rated breaker physically and electricaslly is no different than an 80% breaker except it will have an electronic trip unit. Even 80% and 100% rates breakers both having electronic trip units will be identical except for how they are UL listed, tested, and labeled for use. The 100% breaker is specifically tested with 90degC rated cable for temperature rise to assure that the breaker when it is applied at 100% rating will not exceed a given temperature rise at its terminations.

 

[kwired]

So I know that you cant just buy a "100% breaker" and throw it in and use it on a continuous load at its rating - it needs to be a manufacturer approved/tested panelboard and breaker combination. But is there anything different about the breaker itself? Is a 100% breaker have an elevated thermal trip curve to help prevent "nuisance" tripping? Say for example I have electrical equipment in an area of high ambient temperature and am having occasional tripping at even around 80%. Would a 100% breaker be less likely to trip under these same circumstances?

I don't think you are likely to find a 100% breaker for the typical "loadcenter" panelboards (the ones that you purchase with panelboard, cabinet, maybe a choice of covers, all in one packge that usually use a plug on style breaker). You may find them in some commercial/industrial panelboards that usually use a bolt on style breaker, but are more likely yet to run into them in individual breakers with lugs on input and output like is used in motor control centers, industrial panels, etc.

 

[Jraef]

I don't think you are likely to find a 100% breaker for the typical "loadcenter" panelboards (the ones that you purchase with panelboard, cabinet, maybe a choice of covers, all in one packge that usually use a plug on style breaker). You may find them in some commercial/industrial panelboards that usually use a bolt on style breaker, but are more likely yet to run into them in individual breakers with lugs on input and output like is used in motor control centers, industrial panels, etc.

I may be wrong, but I don't think you can get any panel board or switchboard that can have a 100% rated FEEDER breaker, only the main and maybe a sub feed breaker. Basically you can't get a 100% rating on a breaker that is wedged in between other breakers, you need air flow around all sides.

The only visible difference in the breakers themselves is sometimes just the lugs, because as mentioned you end up having to use 90C conductors, but basic lugs are 75C. So at Siemens for instance, we used copper lugs on 100% rated breakers. Internally though, larger frames sometimes have different power path components to dissipate the heat better. Also, 100% rated breakers existed before electronic trips, but calibration is simpler to attain it with ETUs now, so is has become that way on new breaker designs.

 

[jim dungar]

I may be wrong, but I don't think you can get any panel board or switchboard that can have a 100% rated FEEDER breaker...

Square D I-Line branch breakers are available with 100% ratings. These breakers are identified by having a "C" in the 9 position of their catalog number, so there is likely something slightly different in their construction.

 

[kingpb]

Square D I-Line branch breakers are available with 100% ratings. These breakers are identified by having a "C" in the 9 position of their catalog number, so there is likely something slightly different in their construction.

I agree; albeit typical panelboard you will be hard pressed unless you go to IEC equipment, which as all 100% rated.

In ANSI, you have to typically get into some switchboards, MCC's, LV switchgear and so forth before 100% is generally the norm.

 

[Jraef]

Square D I-Line branch breakers are available with 100% ratings. These breakers are identified by having a "C" in the 9 position of their catalog number, so there is likely something slightly different in their construction.

Well there you go. Learned something new today.

 

[templdl]

There still seems to be a belief that 100% rated beakers are magically superior to 80% rated breakers. Remember that breakers protect wire, wire is sized to carry the calculated load. Normally the wire size is based upon 125% of the continuos load plus 100% of the non continuous load. The wire size must carry that calculated load based upon 75degC rated wire and then protected by a common breaker.
But there is the exception where you are allowed to size the wire based upon 100%+100% which then provides the possible opportunity to use a smaller wire size. BUT, the wire used must have a 90degC rated insulation but the actual wire size is based still based upon 75degC.
To do so a 100% rated breaker can be used only if that 100% rated beaker is applied per the application instructions.
As such simply replacing an 80% rated breaker with a 100% rated breaker is not that simple. It is all about the wire size and how the size is calculated and the insulation class required.
If I can recall correctly this is address is the NEC art 210.20 Over current protection and the exception for calculating the continuous and noncontinuous loads used to size the wire.
I did make an incorrect reference to 80%/100% and 100%/100% in my previous post which should have been 125+100% vs 100%+100% used to size the wire.
It is all about being allowed to apply a smaller wire size which can reduce the cost of wire providing that the OCPD is rated and applied for the application. The is certainly not a matter that 100% breakers are superior to those that are 80% rated but is how the 100% rated breaker is allowed to be applied at 100% of its rating.
If you can verify that the installing the 100% rated breaker meets its application requirements to assure that the panel is rated for it and the wire has already been sized for a 100% application then there should be no issues. But please varify that the existing wire has been correctly sized for 100% and that the 100% rated breaker in fact can be installed per its listing.

 

[Carultch]

There still seems to be a belief that 100% rated beakers are magically superior to 80% rated breakers. Remember that breakers protect wire, wire is sized to carry the calculated load. Normally the wire size is based upon 125% of the continuos load plus 100% of the non continuous load. The wire size must carry that calculated load based upon 75degC rated wire and then protected by a common breaker.
But there is the exception where you are allowed to size the wire based upon 100%+100% which then provides the possible opportunity to use a smaller wire size. BUT, the wire used must have a 90degC rated insulation but the actual wire size is based still based upon 75degC.
To do so a 100% rated breaker can be used only if that 100% rated beaker is applied per the application instructions.
As such simply replacing an 80% rated breaker with a 100% rated breaker is not that simple. It is all about the wire size and how the size is calculated and the insulation class required.
If I can recall correctly this is address is the NEC art 210.20 Over current protection and the exception for calculating the continuous and noncontinuous loads used to size the wire.
I did make an incorrect reference to 80%/100% and 100%/100% in my previous post which should have been 125+100% vs 100%+100% used to size the wire.
It is all about being allowed to apply a smaller wire size which can reduce the cost of wire providing that the OCPD is rated and applied for the application. The is certainly not a matter that 100% breakers are superior to those that are 80% rated but is how the 100% rated breaker is allowed to be applied at 100% of its rating.
If you can verify that the installing the 100% rated breaker meets its application requirements to assure that the panel is rated for it and the wire has already been sized for a 100% application then there should be no issues. But please varify that the existing wire has been correctly sized for 100% and that the 100% rated breaker in fact can be installed per its listing.

Given Breaker A, which is an 80A breaker rated at 100% in its application, and breaker B which is a 100A breaker with a standard rating. What is the difference between the two? How do I design a feeder size differently around them in their respective applications?

 

[kwired]

Given Breaker A, which is an 80A breaker rated at 100% in its application, and breaker B which is a 100A breaker with a standard rating. What is the difference between the two? How do I design a feeder size differently around them in their respective applications?

One also needs to factor in whether you are supplying continuous or non continuous loads, which is what will make the difference in size of conductor allowed.

Remember we don't generally say I want a 100 amp feeder and then match the load to that, but instead we determine what the load is and then determine minimum size conductor and overcurrent protection needed, but may decide to factor in some extra capacity for future loads in some instances and in others we will limit a particular circuit to only supply specific load(s).

So if you have a 80 amp load - you can supply it with a minimum of 80 amp conductor and 80 amp overcurrent device but if that 80 amp load is continuous and you are not using a 100% rated breaker you need to increase conductor ampacity and overcurrent protection by a factor of 1.25 and will need a minimum of 100 amp conductor and 100 amp device.

210.19(A)(1) and 215.2(A)(1) both say nearly same thing for minimum size of conductor, 210.20(A) and 215.3 both say nearly same thing for minimum size of overcurrent protection for branch circuits and feeders, service conductors however are to be able to carry the load as calculated from art 220 according to 230.23(A), and 230.31(A). But overcurrent protection for service conductors can be a little more complex then it is for feeders or branch circuits and is covered by 230.90.

 

[Carultch]

One also needs to factor in whether you are supplying continuous or non continuous loads, which is what will make the difference in size of conductor allowed.

Remember we don't generally say I want a 100 amp feeder and then match the load to that, but instead we determine what the load is and then determine minimum size conductor and overcurrent protection needed, but may decide to factor in some extra capacity for future loads in some instances and in others we will limit a particular circuit to only supply specific load(s).

So if you have a 80 amp load - you can supply it with a minimum of 80 amp conductor and 80 amp overcurrent device but if that 80 amp load is continuous and you are not using a 100% rated breaker you need to increase conductor ampacity and overcurrent protection by a factor of 1.25 and will need a minimum of 100 amp conductor and 100 amp device.

210.19(A)(1) and 215.2(A)(1) both say nearly same thing for minimum size of conductor, 210.20(A) and 215.3 both say nearly same thing for minimum size of overcurrent protection for branch circuits and feeders, service conductors however are to be able to carry the load as calculated from art 220 according to 230.23(A), and 230.31(A). But overcurrent protection for service conductors can be a little more complex then it is for feeders or branch circuits and is covered by 230.90.

So given a continuous 80A load on an 80A fully rated breaker, would I use exactly the same conductor ampacity as I would use, if I were to connect the same load to a 100A standard rated breaker?

 

[kwired]

So given a continuous 80A load on an 80A fully rated breaker, would I use exactly the same conductor ampacity as I would use, if I were to connect the same load to a 100A standard rated breaker?

No. 80 amp continuous load on a 80 amp 100% breaker can be on 80 amp conductor. (must be 4 AWG minimum copper @ 75C)

80 amp continuous load on a standard breaker you must multiply the load by 1.25 and that is base for minimum size conductor and also minimum size overcurrent device - which gives you 100 amps minimum for both. (must be 3 AWG minimum copper @ 75C)


ADD: but a 80 amp non continuous load doesn't require to add the 1.25 factor no matter which breaker type is used and it can be a 80 amp conductor and 80 amp breaker.

 

[electrofelon]

A 100% breaker is actually no different than an 80% breaker if simply swapped out.

But that doesnt make sense. The breaker must be different. Say I have breaker A a regular 80% breaker, and breaker B a 100% breaker. Say the panelboard is tested/approved to be compatible with the 100% breaker used at 100%. There must be a difference in the two breakers, unless its a case of the manufacturer putting a different label on the same breaker and charging more. Either the trip characteristics are different, or the 100% breaker somehow dissipates more heat, or both.

I don't think you are likely to find a 100% breaker for the typical "loadcenter" panelboards

Square D I-Line branch breakers are available with 100% ratings.

I suspected I-line had them. I was generally referring to larger frame breakers like I-line or 200-400 bolt on breaker like you might find in say a Siemens P4. Does anyone know if any are available in the QOB series?

 

[templdl]

Given Breaker A, which is an 80A breaker rated at 100% in its application, and breaker B which is a 100A breaker with a standard rating. What is the difference between the two? How do I design a feeder size differently around them in their respective applications?

What you are trying to do is to optimize the cost of your installation.Compare the cost of your cable based upon the 125%_+100% rule. Remember the is all is your load is in fact continuous then the cable is sized to carry 125% of that. The the breaker is sized to protect the cable. Since your cable is sized based upon 125% of the load and the wire has been sized to carry that load the breaker selected is by default is applied at 80% of its rating at a maximum. If you follow this procedure the issue of an "80% rated breaker" is a non issue.
Should you consider optimizing your design by applying a 100% rated breaker then simply us 100% of the continuous load plus 100% of the non continuous load to size your wire. In doing so it is not uncommon for your to be able to a smaller wire to save on cost. BUT, you must use a 90degC rated cable but allied as if it were 75degC. To protect the cable you MUST now use a breaker the is UL listed for 100%. In doing so the 100% breaker MUST be installed per its instructions for it to be used at 100% of its rating.
Keep in mind that you must evaluate the savings but you also can't ignore that 100% rated breakers do cost most.
There even may be s possibly for you to step down a frame size when using a smaller conductor which can save on cost.
If you are designing a distribution system around using 100% rated devices it may make you more competitive.
Another trick is to design your system based upon series rated devices which gives you the opportunity to use devices with a lower kaic rather than more expensive fully rated devices.
If the specs does take exception the using 100% rated and series rated devices then this may allow you to be more competitive than those who design their systems conventionally and use fully rated devices.
Remember that both breakers that are applied at 80% and 100% are identical except for their UL listing. 100% rated breakers will have a solid state trip units. But simply by having a solid state trip unit does not mean that it can be a 100% as it must by UL listed for 100%.

 

[kwired]

But that doesnt make sense. The breaker must be different. Say I have breaker A a regular 80% breaker, and breaker B a 100% breaker. Say the panelboard is tested/approved to be compatible with the 100% breaker used at 100%. There must be a difference in the two breakers, unless its a case of the manufacturer putting a different label on the same breaker and charging more. Either the trip characteristics are different, or the 100% breaker somehow dissipates more heat, or both.







I suspected I-line had them. I was generally referring to larger frame breakers like I-line or 200-400 bolt on breaker like you might find in say a Siemens P4. Does anyone know if any are available in the QOB series?

My understanding has always been that with standard breakers the reason we need to increase conductor by 125% over the actual continuous load is because the conductor is a "heat sink" to some degree for heat developed within the breaker. 100% rated breakers either don't develop as much heat (which would make sense for electronic vs thermal sensing) or the breaker is just designed to dissipate that heat in a different manner - as some have mentioned there were 100% rated breakers before the electronic ones appeared.

 

[templdl]

But that doesnt make sense. The breaker must be different. Say I have breaker A a regular 80% breaker, and breaker B a 100% breaker. Say the panelboard is tested/approved to be compatible with the 100% breaker used at 100%. There must be a difference in the two breakers, unless its a case of the manufacturer putting a different label on the same breaker and charging more. Either the trip characteristics are different, or the 100% breaker somehow dissipates more heat, or both.







I suspected I-line had them. I was generally referring to larger frame breakers like I-line or 200-400 bolt on breaker like you might find in say a Siemens P4. Does anyone know if any are available in the QOB series?

The breakers that I represented as an breaker applications engineer we not different. 100% rated breakers all had a solid state electronic trip unit the same a conventional breaker that has a solid state trip unit. The electronics as well as the construction of both breakers was identical. The only difference was that the 100% breakers were specifically tested based upon their use at 100% with the 90degC rated cable applied at 75degC to assure that it stays within the allowable temperature rise. Yes, then the manufactured charges for the 100% rating. We called it functional pricing.
It would cost the manufacture was too much to specifically design a breaker based upon 100%. Manufacturing wise the standard breaker has the capability to be applied at 100% but additional tests are performed to allow for the 100% rating.
This is based upon the manufacturer that I worked for as a breaker applications and sales engineed. I can't say if other manufactures do the same.

 

[jim dungar]

I suspected I-line had them. I was generally referring to larger frame breakers like I-line or 200-400 bolt on breaker like you might find in say a Siemens P4. Does anyone know if any are available in the QOB series?

QO/QOB does not have 100% rated breaker.
There is no practical reason to have these smaller branch circuit breakers with 100% ratings.

The 100% rating allows for smaller or fewer conductors and physically smaller breakers which hopefully results in less overall expense.
In my experience it is easier to show the trade offs using a 780A continuous load fed by an 800A equipment versus 1000A equipment.

 

[kwired]

QO/QOB does not have 100% rated breaker.
There is no practical reason to have these smaller branch circuit breakers with 100% ratings.

The 100% rating allows for smaller or fewer conductors and physically smaller breakers which hopefully results in less overall expense.
In my experience it is easier to show the trade offs using a 780A continuous load fed by an 800A equipment versus 1000A equipment.

I think he is saying the breaker may cost you more then you save in reduced conductor cost(if you even save anything) if only using this on a 20 amp circuit

 

[jim dungar]

I think he is saying the breaker may cost you more then you save in reduced conductor cost(if you even save anything) if only using this on a 20 amp circuit

That is why there is no practical reason to be justifying 100% vs 80% cost savings when your breakers are in the same frame size and the potential conductor and conduit differences are minimal.
This often occurs between the 800A to 1200A size. Above 800A the conductors can not be 'rounded up' which often requires more runs and NEC110.26 clearance and access may become issues.

 

[Carultch]

That is why there is no practical reason to be justifying 100% vs 80% cost savings when your breakers are in the same frame size and the potential conductor and conduit differences are minimal.
This often occurs between the 800A to 1200A size. Above 800A the conductors can not be 'rounded up' which often requires more runs and NEC110.26 clearance and access may become issues.

In NEC110.26, there are rules for 800A and more, and rules for 1200A and more. Is this amperes of overcurrent device, or is this amperes of operating current?

If you have a 1000A fuse in a 1200A disconnect, is that still less than 1200A?