125% ocpd calculation

[Djelite]

Why would you size a ocpd at 125% after sizing conductors at 125%? Dont you size the ocpd to 100%(continous) of the calculated conductor load (125%+100%)

 

[petersonra]

Why would you size a ocpd at 125% after sizing conductors at 125%? Dont you size the ocpd to 100%(continous) of the calculated conductor load (125%+100%)

most circuit breakers are not designed for 100% continuous load and might trip.

i don't know what you mean by "125%+100%".

 

[Djelite]

If you sized the conductor at 125% continous load and the breaker is sized to that wire size isnt the ocd sized to 100% of the calculated load of 125

 

[petersonra]

If you sized the conductor at 125% continous load and the breaker is sized to that wire size isnt the ocd sized to 100% of the calculated load of 125

i am not quite sure what you are trying to get at.

sizing of the conductors for the required ampacity is similar to but not the same as sizing the OCPD for the calculated load.

 

[Djelite]

You dont size the wire at 125 percent then size the ocd at 125 percent too , right?

 

[petersonra]

You dont size the wire at 125 percent then size the ocd at 125 percent too , right?

The rules are not exactly the same, but usually if you do this it works out OK.

 

[wwhitney]

Say 40A continuous load and 50A non-continuous
Then 100A ampacity of conductors
And 100A breaker (not 125A)

Cheers, Wayne

 

[petersonra]

Say 40A continuous load and 50A non-continuous
Then 100A ampacity of conductors
And 100A breaker (not 125A)

Cheers, Wayne

I am not sure what the OP is getting at. If I had a panel with 40 A continuous loads, AND 50 A non-continuous loads, I think I would do more than 100 A, just because I don't want to get caught short on capacity when the customer wants to add something.

 

[wwhitney]

I am not sure what the OP is getting at. If I had a panel with 40 A continuous loads, AND 50 A non-continuous loads, I think I would do more than 100 A, just because I don't want to get caught short on capacity when the customer wants to add something.

My reading is that the OP was concerned that the breaker should be 125A in my example, which is not correct.

Future headroom is a separate, design issue.

Cheers, Wayne

 

[petersonra]

My reading is that the OP was concerned that the breaker should be 125A in my example, which is not correct.

Future headroom is a separate, design issue.

Cheers, Wayne

I am not sure what his point is.