[curiousB]

I am relocating some wiring for a couple of 25 year old AC units on my home. Each compressor unit is protected with a 30A 2P breaker and 8AWG wiring for the two hot lines and a 10AWG conductor for ground (all inside EMT to the disconnect then flexible liquidtite to the compressor unit).


I was wondering why 8AWG on a 30A circuit? Just an abundance of caution by the original installer? The wire length (THHN/THWN) is 30-40' so not extraordinarily long. Or is this just considered proper practice for these types of loads? Up rate the wire gauge to minimize voltage drop?


Just trying to understand why the 8AWG on 30A....

 

[HandyAndyInNC]

I would choose #8 or even #6. less resistance, means less current. Use Ohm's law formula to see. Nothing wrong with going larger, or above minimal code.

 

[curiousB]

I would choose #8 or even #6. less resistance, means less current. Use Ohm's law formula to see. Nothing wrong with going larger, or above minimal code.

Yes but blindly chasing lower resistance without regard to cost is wasteful. On a 30A circuit if pulling the full 30A and 8AWG for 40' that is 1.5V drop on 240v or 0.628%, hardly anything. Shrink wire to 10AWG and drop increases to 2.4V or 1% still very small.


Just wondering if it is to do with startup peak current where draw might be well above 30A for a few seconds. Or was this just a super conservative installation.

 

[brric]

Much ado about nothing. Probably should consider replacing 25 year old units with modern more efficient equipment.

 

[Wiredindallas]

Likely when the house was built the unit pulled more power than today's units so the breaker size was reduced to properly protect the new unit. Bigger wire is good, Just not mandatory.

 

[jbfan]

I would choose #8 or even #6. less resistance, means less current. Use Ohm's law formula to see. Nothing wrong with going larger, or above minimal code.

And possibly create a code violation.
Bigger is not always better and and the increase in material cost far outweigh any perceived benefits.

 

[Jim Port]

I would choose #8 or even #6. less resistance, means less current. Use Ohm's law formula to see. Nothing wrong with going larger, or above minimal code.

No reason to go above what the data plate calls for. You could have #12 and a 40 amp breaker and be code compliant. The above is just a waste of money.