10 on 40 amp

[crossman]

Then you would run in to the UL listing of the terminal size of the breaker and what is the minimum wire size for the terminals of a 100 amp breaker.

Well, I haven't seen the UL lsitings of every instantaneous trip breaker ever made, so I can't say whether a #10 could be attached or not. How about a 6" piece of #2 out of the breaker then kearnied to a #10?

Again, not saying it is practical, but it IS in the code.

 

[dhducati]

When considering voltage drop issues for cases like this, do you calculate based on the load current, the breaker size, or something else? I'm particularly wondering about voltage drop when the motor is starting.

 

[Sharpie]

We put Main Breakers at the load end of service conductors. IMO it's the same as what we're talking about with motors and such. If there's a fault on the service conductors, the utility fuses will blow. If it's a matter of over current, the panel's Main Breaker will trip and protect the wires that way.

We already do this all the time without thinking much of it.:roll:

 

[lmchenry]

Thanks for all the references and explanaiton. Just one more question. How do we know to handle the mca and the mcop independently? Is that just a given?
Remember that a package unit has more than just a motor load. The ocpd handles more than just a single motor. Infinity, Larry, and pierre had all spoke of this earlier but I still cant see the separation for this particular situation.

 

[infinity]

Thanks for all the references and explanaiton. Just one more question. How do we know to handle the mca and the mcop independently? Is that just a given?
Remember that a package unit has more than just a motor load. The ocpd handles more than just a single motor. Infinity, Larry, and pierre had all spoke of this earlier but I still cant see the separation for this particular situation.

The MCA number on the nameplate contains all of the information regarding the loads. The manufacturer will do a calculation by adding 25% to the largest motor load (usually the compressor) and then adding the other load(s) to it. This becomes the Minimum Circuit Ampacity. It would likely be the same number that you would come up with if you did the calculation yourself. Then they figure the MOCPD which will ensure that the unit will start and not nuisance trip the OCPD.

We're required to use the MCA and MOCPD when the information is provided on the nameplate. Take a look at 440.4(B) and 440.6.

 

[don_resqcapt19]

We put Main Breakers at the load end of service conductors. IMO it's the same as what we're talking about with motors and such. If there's a fault on the service conductors, the utility fuses will blow. If it's a matter of over current, the panel's Main Breaker will trip and protect the wires that way.

It is not likely that that utility fuses will blow for a fault on the service conductors. They are not normally sized to protect the transformer or the service conductors. Their main purpose is only to prevent a transformer fault from taking out the distribution feeder. Most service conductor faults will have to burn open to clear the fault.