Daisy-chained air conditioner disconnects

S

snakevargas

Active Member
I'm adding a mini split to a home with existing central air. The mini split's compressor will be located close enough to the main compressor that sharing the existing electrical would be enormously convenient. The existing central air has a 50 AMP breaker feeding 6-2 to a 40 AMP disconnect. The existing compressor's min circuit ampacity is 24.3A and its maximum overcurrent device is 40A. The mini split has a min circuit ampacity of 10A and a max fuse of 15A.
 
I've done a bit of research, but haven't found a definitive answer. Can I simply daisy chain from the existing 40A fused disconnect to a 15A fused disconnect for the mini-split?
 
State code is based on NEC 2014.
 
Thanks.
 
Does the mini split use 240 or 120?  If it uses 120, you'll need a new circuit anyway (6/2 has no neutral).
 
What do the instructions say?  I'll bet your central unit wants a dedicated circuit.  Maybe the mini-split does too.
 
I would be slightly concerned that both units starting at the same time might cause the 50A to trip.
 
And then how do you physically plan on doing this? 
 
Basically, you've got a 50A feed and want to make two drops off of it.
 
I assume your 40A disconnect is fused and not just a disconnect switch.
 
You'll need to connect to the feed side of the 40A disconnect to send to the 15A disconnect.
Does the 40A disconnect allow for multiple connections?
Since the feed side is protected by a 50A breaker, you'll need to continue to the 15A disconnect with 6/2 or THWN in conduit.
You might be able to pull it off as a tap and use smaller wire, but those are mainly done for certain types of loads (see NEC 210.19).
 
What you might consider is replacing the 40A disconnect with a small 2 slot subpanel.   A 40A breaker and a 15A breaker, then take off from there to non-fused disconnects for the units.
 
Or just run another circuit and remove all ambiguity.
 
The mini-split is 240V, no neutral required. It's an inverter compressor, which is supposed to have very low inrush at start.
 
My original plan was to see if I could wire double connections to the feed lugs of the disconnect. Yes, I realize this means checking the disconnect to see if it's marked as allowing double connection. Failing that would either require monster wire nuts or split bolts to accommodate the 6ga wire, which would eat up much space inside the relatively small disconnect box. I had considered the tap approach -- I would certainly be within 10 feet from disconnect to disconnect, but I would have to research the other conditions.
 
I like the subpanel approach. I was tossing that around as my backup if the daisy-chain approach was infeasible.
 
Adding another circuit is problematic due to the amount of house that needs to be traversed to get from the main panel to the air conditioner. Not impossible, as I've done similar already with this house, but it involves going up a wall, across the garage attic, down a wall, through a crawlspace that I don't physically fit in, and then outside through the foundation (or back up another wall for a short while).
 
Adding another circuit is problematic due to the amount of house that needs to be traversed to get from the main panel to the air conditioner. Not impossible, as I've done similar already with this house, but it involves going up a wall, across the garage attic, down a wall, through a crawlspace that I don't physically fit in, and then outside through the foundation (or back up another wall for a short while).
Click to expand...
 
 
Well then I suppose you can do this way eh?
 
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