100% ocpd

[templdl]

This is a copy of an Eaton document which should help in the understanding of the application:
http://www.eaton.com/ecm/groups/public/@pub/@eaton/@ee/documents/content/ap01200008e.pdf

In addition, this is an excellent in MC&M writen by Jim Pauley Manager, Industry Standards, and Sandi Young is Circuit Breaker Product Specialist with Square D Co., Lexington, Ky. and Cedar Rapids, Iowa respectively:

http://ecmweb.com/mag/electric_sizing_circuit_breaker/

Insidently, there are no 90degC lugs available for MCCBs.
Siemens says this:
Q: Does Siemens have breaker lugs rated for use with 90 Deg C wire?
A: The short answer is no - nor does any other breaker manufacturer. However, 90 Deg C insulated wire CAN be used IF it is sized per the 75 Deg ampacity column in the NEC tables. In fact, with most of Siemens 100% rated circuit breakers, 90 Deg. Cable is required, but it must be sized per the 75 Deg ampacity.

I trust that this addresses some of the myths about this unusual device.

 

[SG-1]

This is a copy of an Eaton document which should help in the understanding of the application:
http://www.eaton.com/ecm/groups/public/@pub/@eaton/@ee/documents/content/ap01200008e.pdf

First, thank you for the information.
The Eaton document page 4 (Table 3 Results) states that you can use smaller conductors with 100% rated devices.

This is not correct.

 

[mull982]

If a terminal is rated for 75deg C you can use 90deg wire and derate the wire based on the 90deg C column as long as the final derating is lower then the value listed in the 75deg C column.

Am I correct in my understanding here?

Why is 75deg C chosen for breaker terminations? Is this due to the rated heat rise of the breaker? So when doing an IR scan on a breaker should a red flag go up for any temps over 75deg C?

 

[jim dungar]

Am I correct in my understanding here?

Why is 75deg C chosen for breaker terminations? Is this due to the rated heat rise of the breaker? So when doing an IR scan on a breaker should a red flag go up for any temps over 75deg C?

The lug pads, lugs, and conductors, act as heat sinks for the OCPD (both breakers and fused switches). The actual temperature rating of the entire connection will be lower than 75?.

 

[templdl]

SG-1,
Let's see,
With an 80 degC device you size the cable based upon 125% of the continuous load plus 100% if the non continuous load. The cable is sized based upon this ampacity. Is that correct?

Then, if one would like to apply a 100% rated device you would size the cable based upon 100% of the continuous load plus 100% of the non continuos load. I my book the ampaciry would be less based upon the fact that you have 80% less amperes for the contiuous amps. When added to the non continuous amps the equates to less amps. Less amps commonly means that a smaller cable size can be used. Is that correct? Or am I missing something here?

 

[Leestarkweather]

Square D Series H & J frame CB's are Available 100% rated

Square D Series H & J frame CB's are Available 100% rated

Just did a project 2 months ago. Existing 200A 1=Phase Sites, with Murray Meter/TB Unit and 2P 200A 240V Main CB in Separate Enclosure. Over the last 10 years the loads at the (8) identical sites grew to exceed 160A, with some sites at 180+ amps. Customer wanted to squeeze 18 months more out of all sites before either moving or upsizing to 400A Services (BIG $$).

Bought 16 Sq D. 2P 200A (600V) 100% Rated CB's (1 for Utility MCB and 1 for Generator Output CB). Had to have special 3R CB boxes made to provide required cubic inches. Replaced 10 year old 3/0 CU THWN/THHN wire with new 3/0 CU THWN-2 rated wire (rated 90 degree C in wet locations), about 40 total feet per site. Now customer can load up to (200A) 100% continuous load (all sites are UPS loads plus AC's that run almost constantly), and squeek by for another 18 months.

The CB's are available (7-10 lead time) in 2P or 3P down to 15A and up to 250A. Not electronic trip, must use 90 degree C wiring sized at 76 degree rating.

Check it out. It may be applicable to your job.

 

[SG-1]

Obviously, my blondness asserting itself !!

Obviously, my blondness asserting itself !!

SG-1,
Let's see,
With an 80 degC device you size the cable based upon 125% of the continuous load plus 100% if the non continuous load. The cable is sized based upon this ampacity. Is that correct?

Then, if one would like to apply a 100% rated device you would size the cable based upon 100% of the continuous load plus 100% of the non continuos load. I my book the ampaciry would be less based upon the fact that you have 80% less amperes for the contiuous amps. When added to the non continuous amps the equates to less amps. Less amps commonly means that a smaller cable size can be used. Is that correct? Or am I missing something here?

I stand corrected. Obviously, my blondness asserting itself !!

Again !!

Given a few more days to think about it, I may have figured it out.

What was tripping me up was that the load ( device using the energy ) had not changed & the 1.25 % was because of the breaker.

What do you mean by a 80 degree C device ?

Therefore, the 100% rated OCPD is better able to cool itself.

 

[templdl]

SG-1,

I'm glad that you are normal like me. There are all too many who think that they are better than others and take pride in themselves by speaking down to others.
And that 80deg C device? Interesting enough when you only have a 100% load you must size the wire based upon 125% of the continuous load. The cable must carry that computed load. Then you size the breaker based upon the rating of the cable which would be a minimum of 125% of the continuous load.
When the breaker is applied at a minimum of 125% of the continuous load then you can say that it is applied at 80% of the continuous load. Thus it is an 80% rated device.
When sizing a breaker based upon this procedure the breaker should never see more that 80% of its rating continuously.
Remember that breakers protect wire and wire is sized to carry the load.

 

[kwired]

SG-1,

I'm glad that you are normal like me. There are all too many who think that they are better than others and take pride in themselves by speaking down to others.
And that 80deg C device? Interesting enough when you only have a 100% load you must size the wire based upon 125% of the continuous load. The cable must carry that computed load. Then you size the breaker based upon the rating of the cable which would be a minimum of 125% of the continuous load.
When the breaker is applied at a minimum of 125% of the continuous load then you can say that it is applied at 80% of the continuous load. Thus it is an 80% rated device.
When sizing a breaker based upon this procedure the breaker should never see more that 80% of its rating continuously.
Remember that breakers protect wire and wire is sized to carry the load.

I am not trying to speak down at anyone, just telling what I know to be true, sometimes I get corrected when I thought I knew something but didn't. I am not familiar at all with 100% rated devices but the information I give is what I understand as why we have to use 125% for standard devices.

You are on the right track with this. The reason for sizing at 1.25% for continuous load is because the conductor acts as a heat sink for the overcurrent device. You ever notice failing conductor insulation within first few inches of overcurrent device if there is an undersized conductor installed, that is because that will be the hottest operating point along that conductor. The conductor itself may be able to handle the load but was not sized for the termination temperature. 100% rated devices do not depend on conductor as heat sink in the same way as regular devices.

 

[templdl]

I was not implying that you were talking down to me. My feeble attempt to compliment your honesty in asking a question was misunderstood.
I believe that the testing is conducted requiring 4' of rated wire on each side of the breaker. The terminals on the breaker remain rated at 75degC as they are on the 80degC rated breakers.So I think we can agree that the 80% and 100% rated breakers would be the same at that point. To be honest I have never thought about asking the design engineers that I had once worked with why they required that the breakers be tested and listed using 90degC rated wire when the 75degC terminations remained the same as on the 80degC devices. It may be that they wanted to cover their back side by requiring the 90degC insulation for the possibility of 75degC being exceeding at some point in the routing of the cable.
Other than what one of the other gentlemen pointed out that SqD had a 100% non electronic breaker available which I wasn't aware of. Electronic trip breakers do not derate with temperature as non electronic trip units do. Thus electronic trip units are capable of addition temperature rise that would often cause non-electronic breaker to and nuisance trip but still not exceed the 75degC limitations of the terminals. But as you pointed out it may exceed 75degC at a give distance from the breaker. This may make sense but it is only my speculation.
Bottom line is that it certainly would be beneficial to know just what UL489 test procedures were different between the 80% and 100% rated breakers to cause the requirement for the 90degC rated wire.
Becasue I don't have the pipeline to the design engineers I once knew anymore it is very likely that I may never know the reason.

 

[kwired]

As I have said I am not familiar with 100% devices and not sure if I have ever seen one, but I can easily see something with electronic trip not requiring derating for continuous load vs. a thermal trip device. If a thermal trip device is to have a 100% rating it would need to have a way of dissipating or compensating for additional heat for continuous load at 100%.