Frame/Trip or Load

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Alwayslearningelec

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ATS schedule says 400A and draw out breaker say trip of 300A and frame indicates 400A.

You size conductors to the frame or trip setting?
 

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horsegoer said:
ATS schedule says 400A and draw out breaker say trip of 300A and frame indicates 400A.

You size conductors to the frame or trip setting?
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Size per the drawings which should be sized per the trip setting. The frame is just the max rating of the device.


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horsegoer said:
ATS schedule says 400A and draw out breaker say trip of 300A and frame indicates 400A.

You size conductors to the frame or trip setting?
Click to expand...

By default it’s the frame, but if you have a way to restrict the settings adjustment of the trip unit it can be the pickup. See 240.6(B) and (C).


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horsegoer said:
So you could set the trip to max @ 400A?
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Technically yes, as long as the conductors are protected. But you shouldn’t just change the trip from what is shown on the drawing. Any changes need to be approved by the Engineer of Record. It’s his design not yours.
 
In my opinion it depends on if the breaker is an adjustable trip breaker and you set it down from 400 amps to 300 amps, or if you physically change a rating plug to change the trip point.

If it is adjustable trip, you apply the rules in 240.6(B) and (C).

If it has a rating plug to change the trip rating, then you treat it just like a 400 amp fusible disconnect with 300 amp fuses...you provide wire for 300 amps.
 
don_resqcapt19 said:
In my opinion it depends on if the breaker is an adjustable trip breaker and you set it down from 400 amps to 300 amps, or if you physically change a rating plug to change the trip point.

If it is adjustable trip, you apply the rules in 240.6(B) and (C).

If it has a rating plug to change the trip rating, then you treat it just like a 400 amp fusible disconnect with 300 amp fuses...you provide wire for 300 amps.
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What's the diff between the two....adj trip or rating plug? Thanks
 
horsegoer said:
What's the diff between the two....adj trip or rating plug? Thanks
Click to expand...
Take a look at those Sections in the NEC. One is restricted access, one is not.
Keep in mind the conductor selected may have taken other factors into consideration such as ambient and voltage drop,
If it's not an adjustable trip, it would be no different than a 400 amp fusible disconnect (standard size) with 300 amp fuses.
 
horsegoer said:
What's the diff between the two....adj trip or rating plug? Thanks
Click to expand...
A rating plug is a physical change...you remove the 400 amp one and replace it with a 300 amp one.
Adjustable trip devices have dials that you set to change the trip point.
 
I doubt that this is really an adjustable trip breaker. Could just be a 300 amp breaker that is the size of a 400 amp frame.
 
infinity said:
I doubt that this is really an adjustable trip breaker. Could just be a 300 amp breaker that is the size of a 400 amp frame.
Click to expand...

The drawing calls for an LSIA device, so it’s adjustable.


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