100% Rated Breakers

[charlie b]

I am reviewing a project for which the designers believe all breakers 100 amp and above should be rated 100%. I can't get them to tell my why. The facility serves a cybersecurity function. The first two levels of distribution are switchgear, but the requirement appears on one-lines that show switchboards and distribution panels. Questions:

1. Any reasons that 100% rating is a good idea?
2. Any reasons (other perhaps than cost) that it's a bad idea?
3. What might be the difference in cost (in dollars or in percent)?
4. Does "100% Rated" mean, for example, that you could place 200 amps of continuous load on a 200 amp 100% rated breaker?

 

[infinity]

Does "100% Rated" mean, for example, that you could place 200 amps of continuous load on a 200 amp 100% rated breaker?

I believe that is correct. At 100% continuous there is no need to apply the 80% limit. I'm not sure that small breakers above 100 amps have the 100% rating.

 

[jim dungar]

I believe that is correct. At 100% continuous there is no need to apply the 80% limit. I'm not sure that small breakers above 100 amps have the 100% rating.

You can get 100% rated trip units down to just about any value you want, however I believe you will rarely find them in frame sizes smaller than 250A with electronic trip.

The physical size of the breakers and the amount of enclosure air flow needed for cooling usually means 'branch circuit' panels could become prohibitively large and expensive. Distribution panels are not as affected.

 

[charlie b]

Thanks Rob and Jim. But can anyone give me reasons for 100% rated breakers to be good or bad ideas?

 

[jim dungar]

Thanks Rob and Jim. But can anyone give me reasons for 100% rated breakers to be good or bad ideas?

Purely a design choice. As you have noticed the advantages of smaller OCPD and conductors disappears as the amp rating of the circuit goes down.Eventually simply b sizing the circuit at 125% becomes more cost effective. In the old days, the dollar savings on the installed pipe and wire was often the deciding factor with the OCPD and increased enclosure size being tradeoffs.

 

[MyCleveland]

Hello Charlie
Please add "SEMI"....your still at it.

I asked the great and powerful Oz for you.
Oz stated...
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Incorporating 100% rated circuit breakers into an electrical system design, especially for a critical facility like a cybersecurity function building, offers several advantages:

Maximizes Equipment Use: Standard circuit breakers are typically rated for 80% of their maximum current-carrying capacity. A 100% rated breaker can handle the full load continuously without derating, allowing you to fully utilize the capacity of the electrical system and equipment. This can lead to more efficient designs, reducing the need for additional equipment.

Space Optimization: Since 100% rated breakers allow for full load utilization, the designer can avoid oversizing panels and other equipment. This reduces the physical space required for electrical infrastructure, which is crucial in facilities with constrained space or high equipment density.

Cost Efficiency: By utilizing breakers that allow continuous operation at full capacity, the designer can avoid having to install multiple breakers or oversized electrical panels. This can help reduce overall equipment costs and labor during installation.

Critical Load Support: In cybersecurity or other critical facilities, ensuring continuous operation of key systems (like data centers, network security appliances, or servers) is crucial. 100% rated circuit breakers can support uninterrupted power for these high-demand loads, ensuring reliable performance under peak conditions.

Enhanced Safety and Compliance: Some applications or local codes may require 100% rated circuit breakers for certain types of equipment or environments. Using these breakers can ensure compliance with relevant electrical codes and safety standards, which is especially important in facilities handling sensitive data.

Thermal Management: 100% rated breakers are designed to better handle the heat generated by continuous full-load operation. In a cybersecurity building, which might house servers or other heat-sensitive equipment, thermal management is critical. These breakers help in ensuring that the electrical system operates within safe thermal limits.

By choosing 100% rated circuit breakers, the designer ensures that the building’s electrical system is more efficient, reliable, and capable of supporting critical loads without requiring excess capacity or additional components.
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My thought leans toward "Critical Load Support". They simply do not want outages.
Can you share how they addressed the service conductor sizing...assuming it is underground. How are they dealing with 100% load factor?

 

[don_resqcapt19]

...

By choosing 100% rated circuit breakers, the designer ensures that the building’s electrical system is more efficient, reliable, and capable of supporting critical loads without requiring excess capacity or additional components.
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My thought leans toward "Critical Load Support". They simply do not want outages.
Can you share how they addressed the service conductor sizing...assuming it is underground. How are they dealing with 100% load factor?

Not sure how it is more efficient as the I²R losses will be higher when you use the conductor at 100% of its ampacity as opposed to 80%. Also don't see how a switch to 100% breakers makes the system more reliable.

 

[jim dungar]

Incorporating 100% rated circuit breakers into an electrical system design, especially for a critical facility like a cybersecurity function building, offers several advantages

Sounds like this was written by some sales group that benefits from 100% equipment.
They do not provide and data or examples to support their conclusions.

 

[MyCleveland]

Sounds like this was written by some sales group that benefits from 100% equipment.
They do not provide and data or examples to support their conclusions.

Just sharing for Charlie what Oz's (ChatGpt) response would be. Would never recommend relying on it.

Ask it a few SCC calc questions and see the responses.

 

[charlie b]

Hello Charlie
Please add "SEMI"....your still at it.

True. Done. Thanks.

 

[dkidd]

It may be backing into it, but I think that selective coordination may be a driving issue. You generally need instantaneous settings.

 

[infinity]

I've never seen them being used so IMO they're not very practical. If these are so much better than a standard breaker operating at 80% continuous you would see them everywhere.

 

[petersonra]

The only time I have used them is when I would have to otherwise go to the next frame size. There can be a big difference in space used sometimes. If space is tight, a smaller MCCB might be what is needed. In any case, it really rarely matters since you rarely run into situations where even 80% breakers see 80% for any length of time. Most of they time they see 50% or less.

 

[jim dungar]

It may be backing into it, but I think that selective coordination may be a driving issue. You generally need instantaneous settings.

This is independent of whether the long time setting is at 80% or 100%, as it does not impact the short time and instantaneous portions of the device's operating curve.

 

[jim dungar]

Just sharing for Charlie what Oz's (ChatGpt) response would be. Would never recommend relying on it.

Ask it a few SCC calc questions and see the responses.

This is part of the problem with AI, seemingly verbose answers with little substance.

Charlies question asked for "good or bad ideas" the submitted answer supplied unsubstantiated opinionated 'good' points.

AI is only 'a' tool, it is not 'the' tool. Someday, probably, this will change.

 

[hillbilly1]

I have used them only once, it was for an office complex that had existing 200 amp services, and I think the engineers wanted to squeeze more out of the existing services. The complex was a large insurance call center that originally was twelve spaces, but they took over the entire building.