115v/20amp Mini Split on Larger Breaker

[ardpub]

I'm planning to install a small minisplit unit in a detached office, re-routing power from an existing 250v AC plug on a 50amp breaker. Even though this is a dedicated circuit, I'm assuming it would be inadvisable to use the existing 50amp breaker, even if I use a lower amperage fused service disconnect? Is it pretty straightforward swapping the 50amp breaker for a 20amp? Assuming the wire gauge is sufficient to carry 50 amps (or at least the 30 amps the plug is rated for), there shouldn't be any issues with oversizing the cable for a 20amp, right?

The unit is a MRCOOL DIY Gen-3 12,000 BTU 22 SEER, Model# DIY12-HP-115B25. The manual covers several size units so doesn't specify the max breaker size but I'm assuming its a 20amp--don't have the unit yet.

Another option would be to simply re-route power from the standard edison plug that is adjacent to the 250v AC plug but it's on a shared 20amp branch with all the other outlets in the room so I fear I'd risk tripping the breaker when the AC is running full in addition to other devices on that branch.

 

[wyliesdiesels]

Theres a number of possible issues here.

A 240v outlet does not need a neutral. Was a neutral ran anyways and left in the box?

If no neutral, what type of wire was ran? If NM-b then one wire will be white and youre fine.

Another issue is the oversized conductors creates an issue with the required larger ground wire. If NM-b, the ground wire is #10 and that would be too small since the other conductors only needed to be #12 originally. This means the ground wire would need to be #6 just like the ungrounded conductors.

Your option in this scenario is to put a small subpanel in the location then run a circuit for the AC.

 

[ardpub]

Theres a number of possible issues here.

A 240v outlet does not need a neutral. Was ran anyways and left in the box?

If no neutral, what type of wire was ran? If NM-b then one wire will be white and youre fine.

Another issue is the oversized conductors creates an issue with the required larger ground wire. If NM-b, the ground wire is #10 and that would be too small since the other conductors only needed to be #12 originally. This means the ground wire would need to be #6 just like the ungrounded conductors.

Your option in this scenario is to put a small subpanel in the location then run a circuit for the AC.

Thanks for your reply. That's what I was afraid of. I think its #10 NM-b. Guess I'm looking at either using the existing 20amp breaker or calling an electrician, as I'm not really comfortable working in the panel.