Up sized conductors

[Stepisnikhvac]

I have a quick question. We're changing out a old heat pump, the new unit is 30amp from the old 50amp. Customer thinks the over sized wire will tax the breaker. I told him it won't and that I can prove in the code book. Now I can't find the reference wher you can up size wire as long as you don't go back down. Cops so far is all I can find and ungrounded conductors in 250.122b called increased in size. Can anyone help with the reference? Thank you.

 

[charlie b]

Now I can't find the reference where you can up size wire as long as you don't go back down.

That you are not going to find. The design process does not work that way. You first determine the amount of current that the load will draw, then you select a wire that can handle that much current, and finally you select a breaker that is capable of protecting that size wire against overcurrent. If a load only draws 30 amps, you can use a wire that can handle 50, or 100, or 700 amps, if you wish. Not a good investment, I agree, but also not a code problem. Also, if the wire can handle 100 amps, you are allowed to protect it with a 50 amp breaker. Again, a bit of overkill, but not a code problem.

In your case, however, I would look at the manufacturer's documentation for the new unit. It is likely to include a value for MOCP (maximum overcurrent protection). If it says that the MOCP is 30, or 35, or 40, or 45, then you can't use the existing 50 amp breaker.

Oh, and if a circuit needs a wire of, let us say, #8, you can install #8 wire for part of the run, then connect it to a larger #6 for part of the run, and connect it to another #8 at the end of the run. Nothing says "you can't go back down."

Also, the article you cited, 250.122, does require you to use a larger ground wire, if you are using larger "hot conductors" than are needed for the circuit. At that point, it might be best to call in an electrician to help with the install.

 

[growler]

Now I can't find the reference wher you can up size wire as long as you don't go back down.

I think what you are trying to say is that you can use a larger conductor than required by code but you can not use a smaller coductor than required by code.

The code does not specify the size of conductor to be used. The code will only give you the "minimum" size conductor allowed.

For a job like this get a permit and let the inspector answer these questions for the customer. This will let the customer know they have a code compliant installation.

The customer probably thinks he should get new wiring out of the deal. Looking for a reason.

 

[Dennis Alwon]

As long as the larger wire is listed to be used under the lugs of the breaker then there is no issue. Heck, tell the owner you would be happy to change the wire and explain what it will cost him.

 

[ptonsparky]

I would use the oversized wires without blinking or make the owner blink with the price of new.