coolingelectricalheating
I'm getting ready to install a mr. Cool 24k mini split. The Electrical in the instructions is pretty vague. Just want to double-check that I'm correct on how I'm going to install it.
Inside my main breaker box gets a double pole 30 amp breaker. Then I run 10-3 to and outdoor a/c fuse box with two 25amp fuses in it. Then I run a whip cable into outdoor unit. Does that sound right? Thanks
In the US, it's required that manufacturers include the following items on condensing unit's nameplate (NEC 440.4(B)):
You'll simply use the minimum supply circuit conductor ampacity value from the name plate, and NEC 2011 Table 310.15(B)(16) through Table 310.15(B)(19) to determine the proper conductor size.
As for the branch-circuit short-circuit ground-fault protection, you'll have to select one less than or equal to the maximum rating listed on the nameplate. However, you'll have to choose a device with a high enough rating to handle the inrush current, so you'll want to choose a device close to this value.
To answer your questions directly...
A 30 ampere breaker is the wrong one, if the nameplate lists 25 as the maximum rating of the branch-circuit short-circuit and ground-fault protective device.
For 25 amperes, you're likely correct to use 10 AWG cable.
Usually the disconnect is not fused, and simply functions as a safety disconnect. You'll just have to make sure the disconnect is rated for greater than 25 amperes, and the appropriate voltage.
For a typical 240V tank style water heater you will need a 30A/240V circuit. No neutral is required.
You CAN use the white wire as a hot going to the breaker for a straight 240V circuit such as this. You just need to mark it as a hot conductor with a permanent marker or such. You can use any typical hot color such as black, red or blue. You DO NOT need to use a red wire.
Now....you ask "Can I install the red line to a second hot breaker". This implies there is a red wire in the cable. If this is the case then yes, you must use the red and you can just cap off the white in the water heater since it is not used.
You CANNOT simply use a "second hot breaker". You MUST use a two-pole breaker for a 240V circuit as previously mentioned.
Best Answer
Air conditioners don't quite follow the same rules as everything else out there
Due to the fact that hermetic air conditioning compressors invariably have overload protection built-in, the circuit breaker on an air conditioner circuit doesn't need to protect against a motor overload condition, just a short circuit. Hence, the NEC lets you size wiring and protection for an air conditioner based on the Minimum Circuit Ampacity and Maximum Overcurrent Protection Device figures quoted by the manufacturer and listed on the nameplate, instead of using the general branch-circuit wire sizing rules. (These figures obey rules found in NEC Article 440.)
In particular, according to the brochure's specifications for your unit, it has a Minimum Circuit Ampacity of 18A and a Maximum Overcurrent Protection Device of 30A. So, you could run 10/2 or 12/2 NM to the disconnect, since the unit has no use for a neutral wire, then run a prefab 1/2" flex whip kit (1/2" LFNC with 3x 12AWG) from a non-fusible pullout disconnect down to the outdoor unit. (The signal cable on these units is an integral part of the lineset, so it is routed with that instead of traveling up the flex whip.)
If you need a service receptacle at the unit, 12/4, 12/2/2, or 10/4 NM can be used instead, with the black and white wires used for the service receptacle and the red and blue (or white/red taped black, red, or blue) wires used for the 240V circuit to the air conditioner. In all of these cases, you'll be using a THQL2130 or THQP230 (30A, 2 pole) breaker for the air conditioner circuit; while one could use a 25A breaker instead, that may lead to difficulty down the road (namely, false trips due to a hard starting compressor). The service receptacle circuit, if present, is then connected to a general lighting circuit in the panel using wirenuts and 12AWG THHN pigtails to avoid a double tap on the breaker, by the way.