Feeding MCB Panel

[Alwayslearningelec]

If a panel has a particular size MCB and the total connected load is obviously lower do you still need to have wiring rated for MCB size regardless of connected load?

 

[infinity]

No. It would need to be sized according to the OCPD ahead of the feeder.

 

[don_resqcapt19]

The size of the conductor will be no less than the rating of the upstream OCPD. The OCPD at the panel just becomes a switch if it is smaller then the feeder overcurrent protector. Note this assumes we are not talking about a service panel.

 

[jap]

If a panel has a particular size MCB and the total connected load is obviously lower do you still need to have wiring rated for MCB size regardless of connected load?

If you don't size the wiring to the capability of the MCB's OCPD, what's going to protect the wiring?

JAP>

 

[jim dungar]

If you don't size the wiring to the capability of the MCB's OCPD, what's going to protect the wiring?

JAP>

The protective device at the begining/source of the conductors, or the rules in 240.21(B).

 

[jap]

I don't think he's talking about an upstream overcurrent protection device.

I think he's asking if you have a panel that's drawing 30 amps but has a larger Main can you size the wiring to the main at 30 amps.

I say no.

JAP>

 

[don_resqcapt19]

If a panel has a particular size MCB and the total connected load is obviously lower do you still need to have wiring rated for MCB size regardless of connected load?

Is this panel the service equipment? If not, how does it get its power?

 

[jim dungar]

I don't think he's talking about an upstream overcurrent protection device.

I think he's asking if you have a panel that's drawing 30 amps but has a larger Main can you size the wiring to the main at 30 amps.

I say no.

JAP>

Conductors need to be protected at their source except when following the rules in 240.21(B).

Services are the only exceptions in which case utility rules come into play

 

[jap]

Is this panel the service equipment? If not, how does it get its power?

That's the question we need to know the answer to 1st.

JAP>

 

[infinity]

I don't think that this is a service, so if the panel is 225 amps with a 225 amp main but the calculated load is 100 amps then a 100 amp feeder can supply the panel.

 

[jap]

I don't think that this is a service, so if the panel is 225 amps with a 225 amp main but the calculated load is 100 amps then a 100 amp feeder can supply the panel.

I still don't understand where you all are coming up with a "Feeder" based on the OP"s opening statement.

What if this is a service panel directly behind a meter where the Main is the one and only OCPD?

How could you size the wire feeding the 225amp main breaker from the meter at only 100 amps ?

JAP>

 

[infinity]

I still don't understand where you all are coming up with a "Feeder" based on the OP"s opening statement.

What if this is a service panel directly behind a meter where the Main is the one and only OCPD?

How could you size the wire feeding the 225amp main breaker from the meter at only 100 amps ?

JAP>

It not being a service is an educated guess.

 

[Little Bill]

I still don't understand where you all are coming up with a "Feeder" based on the OP"s opening statement.

What if this is a service panel directly behind a meter where the Main is the one and only OCPD?

How could you size the wire feeding the 225amp main breaker from the meter at only 100 amps ?

JAP>

Because the OP used the words "Feeding" in his title. That, to me, indicates a feeder.

 

[Alwayslearningelec]

Source OCPD feeding MCB panel. I referring to the MCB in the panel in this scenario . So your saying wire needs to be sized to the OCPD at this source in this scenario? This is not a service .

 

[infinity]

Source OCPD feeding MCB panel. I referring to the MCB in the panel in this scenario . So your saying wire needs to be sized to the OCPD at this source in this scenario? This is not a service .

Yes, feed a 225 amp panel with a 60 amp ocpd and #6 conductors if the calculated load is 60 amps.

 

[Alwayslearningelec]

Yes, feed a 225 amp panel with a 60 amp ocpd and #6 conductors if the calculated load is 60 amps.

So to be clear, except for service , when feeding from source OCPD to another panel OCPD the feeder/wire size needs to be sized to the source OCPD and the calculated load your feeding obviously can’t be higher than the source OCPD?

 

[infinity]

So to be clear, except for service , when feeding from source OCPD to another panel OCPD the feeder/wire size needs to be sized to the source OCPD and the calculated load your feeding obviously can’t be higher than the source OCPD?

Short answer yes.

 

[jap]

So to be clear, except for service , when feeding from source OCPD to another panel OCPD the feeder/wire size needs to be sized to the source OCPD and the calculated load your feeding obviously can’t be higher than the source OCPD?

Usually it's not looked at as "I'm going to use this size breaker and need this size wire", it's usually looked at as "I'm going to use this size wire and need this size OCPD to protect it".

JAP>

 

[jap]

Because the OP used the words "Feeding" in his title. That, to me, indicates a feeder.

"Feeding" is simply a much simpler way to say "I'm going to extend wiring from one source to another..

"Feeding" should never be confused with our definition of "Feeders", Taps, Branch Circuits and Service Conductors.

JAP>

 

[Little Bill]

"Feeding" is simply a much simpler way to say "I'm going to extend wiring from one source to another..

"Feeding" should never be confused with our definition of "Feeders", Taps, Branch Circuits and Service Conductors.

JAP>

Thanks professor!
I never hear anyone saying "I'm feeding my 200A service"
I hear "I'm feeding my xxxA subpanel" or "I'm feeding my stove circuit with ..."