- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is the rating of the protective device or the 'bussing' size, depending on which code section you are using.
80% vs 100% breaker
- Thread starter electrofelon
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It is the rating of the protective device or the 'bussing' size, depending on which code section you are using.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
With IEC breakers, who is it that they get away with 100% ratings? ID imagine with panel boards full of breakers with loads running over 3 hours heat build up might be a problem?
I'm not sure that they are getting away with anything. Are they UL listed as 489?
mbrooke
Batteries Included
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- United States
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- Technician
No clue, but all the IEC breakers appear to be 100% rated. In BS7671 they don't even do the whole 80% thing.
Carultch
Senior Member
- Location
- Massachusetts
Code section? Do you mean code version? Or do you mean that it depends on what kind of equipment it is, and thus what NEC chapter/section applies?
So in NEC2014, if I have an 800A panelboard busbar protected by a 700A main, does it qualify as 800A and more?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Which section, or more specifically what article and paragraph, of the NEC2014 are you looking at?
110.26(C)(2)
240.4(B)
240.6(B)
240.6(C)
I am guessing your answer is in 240.6(C).
IEC breakers shall also be derated as per ambient temperature and IP degree of enclosure. The difference is that the derating factor is up to breaker fabricator and panel builder rather than the electrical code.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
I like that type of thinking. But in a standard install how would the electrician know what the panel maker wants. What is typical?
kwired
Electron manager
- Location
- NE Nebraska
In general and having nothing to do with whether device is 100% rated or not, if the overcurrent device is a fixed setting or has max setting of 700 amps then you essentially have to supply such panel with 700 amps worth of conductor ampacity, but are able to have less as long as you still have ampacity greater or equal then the connected load and round up to next standard overcurrent device, but that changes once you go over 800 amp level.
What is not as clear is if you have a 800 amp fuseholder but only a 700 amp fuse. Some will say it can easily be replaced with an 800 amp fuse and that you still need to supply the fuse holder with an 800 amp conductor - but most will say as long as the 700 amp fuse is present the thing is considered a 700 amp circuit, feeder, service ...
Most of us don't carry 800 amp fuses around and swap with 700's on an existing install on a regular basis, but this does happen on 15-30 and 35-60 amp circuits more often. They do make fuse reducing fittings as well for when you have a 60 amp fuse holder but want to install a 20 amp fuse for whatever reason. In that case it is the load side protection that is usually more important, but you could IMO run 20 amp conductor as both supply and load conductors to a (60 amp fused switch with fuse reducers) service disconnecting means that supplies only a single load requiring 20 amp conductors/overcurrent protection.
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