large breakers
- Thread starter shaw0486
- Start date
- Status
I'll take a stab from a lay person's viewpoint.
1 part is simple maufacturing standarization. From a production/warehousing standpoint it' logical to mfg the brekers in "steps" the same as fusible switches.
The larger frame breakers are also designed to handle larger fault currrent, disapaiting the heat as required when they open.
I assume mfg desing based on ability to carry the load and handle the fault curent. The breakers also have to meet standards for NEMA and testing labs such as U.L.
The frame size is somewhat determined by the fault current the breaker must handle and then the "trip" size is selected for that frame basesd on the circuit (wire) ampacity. That ability to hande the fault current isi why you have 100 amp breakers you can hold in your hand along with ones it takes both hands to hold.
is that close breaker/engineering guys ??
1 part is simple maufacturing standarization. From a production/warehousing standpoint it' logical to mfg the brekers in "steps" the same as fusible switches.
The larger frame breakers are also designed to handle larger fault currrent, disapaiting the heat as required when they open.
I assume mfg desing based on ability to carry the load and handle the fault curent. The breakers also have to meet standards for NEMA and testing labs such as U.L.
The frame size is somewhat determined by the fault current the breaker must handle and then the "trip" size is selected for that frame basesd on the circuit (wire) ampacity. That ability to hande the fault current isi why you have 100 amp breakers you can hold in your hand along with ones it takes both hands to hold.
is that close breaker/engineering guys ??
nope. frame is basically physical size, trip is ampacity.
Your 1200 amp frame breaker could have a trip from 100 amps thru 1200.
Some "trip" sizes are factory set, some interchangable (often "plug-in" )and some adjustable.
You choose the frame mostly to fit the switchgear and for it's interrupting capacity (10,000 AIC, 22,000, 65000, etc. for example) and the trip to protect the circuit.
Your 1200 amp frame breaker could have a trip from 100 amps thru 1200.
Some "trip" sizes are factory set, some interchangable (often "plug-in" )and some adjustable.
You choose the frame mostly to fit the switchgear and for it's interrupting capacity (10,000 AIC, 22,000, 65000, etc. for example) and the trip to protect the circuit.
zog
Senior Member
- Location
- Charlotte, NC
The frame size is the continious current capabillity o fthe breaker. that rating is based on heat dissapation ability of the breaker that is affected by the size of the frame (and several other factors) hence the name.
Interuption rating (or Isc) is the max amount of current the breaker is capable of interupting at the systems voltage and with a inst or short time delay trip. T
hese ratings have nothing to do with at what current level the breaker will trip, but it can be confusing becase the INST and ST trip is on the nameplate (See pic) however if you look closely that is the interuption rating.
Interuption rating (or Isc) is the max amount of current the breaker is capable of interupting at the systems voltage and with a inst or short time delay trip. T
hese ratings have nothing to do with at what current level the breaker will trip, but it can be confusing becase the INST and ST trip is on the nameplate (See pic) however if you look closely that is the interuption rating.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Think of fuse sizes. Small cartridge fuses go up to 30a; large cartridges up to 60a. Small blade-type fuses go up to 100a, medium up to 200a, etc.shaw0486 said:
They do the same thing with breaker sizes. Imagine having to use a 200a-size breaker for a 20a circuit. Larger sizes need greater contact area, too.
zog
Senior Member
- Location
- Charlotte, NC
LarryFine said:
Not sure how this relates to the question any more than different size fries. The question is based on a confusion of the meaning of a rating, the same answer I posted applies to even a little 400A MCCB.
- Status