Question for the electricians

[MNBobcat]

I have a 30 amp fuseable disconnect box to install on the outside of my house for a ductless mini-split air-conditioner. It looks to me like the mini-split only requires a 20 amp, 220 circuit. I got to thinking that I don't think I should use a 30 amp fuse with wire rated for only 20 amps. So is it okay to put 20 amp fuses in the 30 amp box? I'm pretty sure it is but I hate to assume so I thought I would ask.

Please let me know if you're a licensed electrician or a DIYer if you reply.

Thanks!

 

[RNeumann]

The fuse should be at the panel and the "disconnect" is located by the condenser.

 

[RNeumann]

GE 6 Amp 24-Volt Non-Fuse Metallic AC Disconnect-TFN6RCP - The Home Depot

This is all you need. It's "rated" for 60amps but all it does is disconnect power at the unit for ease of service- which is code. As stated above- the fuse/breaker that protects the line is at the panel where the 20amp wire originates.

 

[Budweiser John]

The name plate on the AC unit will call out the full load amp draw.
Do not protect a 20 amp circuit with a 30 amp breaker.
If the disconnect you intend to use is the old style plug fuse type toss it and purchase the correct amperage breaker which if used out doors must be rated for exterior use and properly grounded.
B. John
Retired licensed builder

 

[RNeumann]

GE 6 Amp 24-Volt Non-Fuse Metallic AC Disconnect-TFN6RCP - The Home Depot

This is all you need. It's "rated" for 60amps but all it does is disconnect power at the unit for ease of service- which is code. As stated above- the fuse/breaker that protects the line is at the panel where the 20amp wire originates.

Edit- the "link" above is dropping the "0"s. It is 240v and 60a- not 24 and 6

 

[MNBobcat]

I already have the fuseable disconnect bought, which I got from an HVAC supply place, and I'm not going to return it.

 

[JPRambo]

Use the disconnect as is. It only going to be used as a service disconnect. Use a 20 amp breaker in/at the beginning of the circuit and you're good to go.
Electrician 35 years.

 

[jaxs]

I think you have a handle on what can and can't be done,all info so far is correct but I will say it different. Breaker/fuse "protect's"wire and devices DOWNSTREAM. Wire rated for more amps than fuse is exceptable and safe. Your mini-split will be protected and happy as long as there is correct amp fuse ANYWHERE in circuit. One common mistake is 30amp fuse feeding 10 guage wire that has been tapped with 12 guage wire then fused with 20amp breaker at END OF 12ga wire before power enter's appliance/outlet.
Retired building maintenance engineer.

 

[Passattdi]

Yep found that many places a wanna be electrician did work at my facility. All fixed now.

 

[buickanddeere]

I have a 30 amp fuseable disconnect box to install on the outside of my house for a ductless mini-split air-conditioner. It looks to me like the mini-split only requires a 20 amp, 220 circuit. I got to thinking that I don't think I should use a 30 amp fuse with wire rated for only 20 amps. So is it okay to put 20 amp fuses in the 30 amp box? I'm pretty sure it is but I hate to assume so I thought I would ask.

Please let me know if you're a licensed electrician or a DIYer if you reply.

Thanks!

The fuses or breaker in the supply panel are only for short circuit protection of the entire circuit and system supply. thermal protection of the conductors and thermal protection of the motor is provided by the motor thermal protection/overloads.
For example . It is Perfectly fine to use a 70amp breaker on #10 R90 wire rated for 35 amps load if supplying a motor with thermal protection. 70 amp breaker prevents nuisance tripping when the motor starts with the normal inrush current of 5 to 13 times greater than normal fuel load amps.

 

[MNBobcat]

What I was planning on doing is putting a 20 amp 220 breaker in the panel. Then run 12/2 romex to the 30 amp fused disconnect. Put 20 amp fuses in the disconnect. Color code the white wire to red using red tape. I don't believe a neutral is needed. Just the 2 hot wires and ground. Sound about right?

 

[jaxs]

Work's for me. For what it's worth,the 20 amp breaker at breaker panel will protect everything and meet code regardless what's in the disconnect. It isn't necessary to discard 30 amp fuses and buy 20 amps to replace them. Doesn't hurt either.

 

[RNeumann]

What I was planning on doing is putting a 20 amp 220 breaker in the panel. Then run 12/2 romex to the 30 amp fused disconnect. Put 20 amp fuses in the disconnect. Color code the white wire to red using red tape. I don't believe a neutral is needed. Just the 2 hot wires and ground. Sound about right?

Technically yes- USA 220v split phase doesn't need a neutral.

Taping the white wire with red tape on both ends is common practice. However it sounds like you are going to be putting romex in conduit and have the romex in an exterior location. Both no-nos. The wire in conduit should, per code, be rated for such use. If you do this you will have the correct coloring as well.

 

[MNBobcat]

The Romex for the majority of the run won't be in conduit. I do have a 1 1/2" PVC chase pipe run from the basement to the attic and I'll run the romex through that to the attic and then drill down through the top plate and fish the wire down the wall to the disconnect box.

My understanding is that romex can't be run in conduit in any location that could be wet but that indoors is okay as long as the conduit is sized correctly?

jaxs - The 30 amp fused disconnect didn't come with the fuses so I have to buy them anyway, Otherwise, I'd have used 30 amp fuses and a 20 amp breaker.

Technically yes- USA 220v split phase doesn't need a neutral.

Taping the white wire with red tape on both ends is common practice. However it sounds like you are going to be putting romex in conduit and have the romex in an exterior location. Both no-nos. The wire in conduit should, per code, be rated for such use. If you do this you will have the correct coloring as well.

 

[RNeumann]

The Romex for the majority of the run won't be in conduit. I do have a 1 1/2" PVC chase pipe run from the basement to the attic and I'll run the romex through that to the attic and then drill down through the top plate and fish the wire down the wall to the disconnect box.

My understanding is that romex can't be run in conduit in any location that could be wet but that indoors is okay as long as the conduit is sized correctly?

Code does provide for protection of the Romex (NM cable) in conduit in dry locations. So the indoor conduit is close to code....technically it would need to be for the protection of the wire. So basically that part is ok.

My comment was in relation to the exterior wire and conduit. Both rigid and flexible.

 

[GregbkH]

The 30 amp disconnect is rated for a max. of 30 amps. It is OK to use 20 fuses in it for a 20 amp circuit.

I ran a 20 amp 240 volt circuit for my mini-split. I used 10-3 w/ground romex on the inside because the run was getting long (voltage drop). When I went to the outside of the building I installed a splice box and spliced 12 awg thwn wires to the 10 awg romex for the final 8 feet to the disconnect. I ran a neutral and capped it off (wire nut) in the disconnect enclosure in case of future need.

Anytime a raceway is installed for electrical it must be rated for electrical. Meaning you can't use pvc water pipe etc. You must use an electrical raceway.

Master electrician.

 

[MNBobcat]

Hi Greg,

I was thinking about going 10 gauge for the same reason. I was going to measure the run today and then check the voltage drop charts and see if I needed to up-size. I never run 14 gauge wire for anything because 12 gauge isn't much more expensive and it gives me options if I ever need the ampacity. So I have a lot of 12 gauge on hand. 10 gauge I'd have to run to Menards and get. The compressor only needs a little over 14 amps. I'll probably end up using 10 gauge like you, just because I always over engineer everything.

Originally the run was only going to be about 30 feet from the panel. But I can't get access to pull the line because the basement is finished. The area where I thought I had access isn't going to work. Also, I want to mount the panel high enough to be clear of snow so going to the attic and then fishing a line through the stud cavity to the outside wall location will give me the best mounting option.

The PVC chases (I installed 3 when I remodeled the kitchen) were put in place a few years back when I had the walls open so that if in the future I ever needed to run something from the basement to the attic I had an easy way to do it.

I was thinking about it this morning and it came to me that I have an alternative path to the attic. I installed a bathroom on the second floor and I have not yet boxed in and sheet rocked where I ran the drain for the toilet between floors. I already have a couple of electrical lines (GFCI breakers) ran next to the drain pipe for a whirlpool tub I'm installing in a bedroom. So right now it will be easy to run the wire for the A/C using that path and I can save the PVC chases for something else down the road.

The 30 amp disconnect comes with a 4 foot whip to connect from the panel to the compressor. I didn't look to see if the wire was included in the whip. But I have spools of 12 gauge THHN and I'll use that if I need to. I wired about 30 fluorescent lights in my pole building, all through electrical conduit screwed to the metal ceiling, so I have a lot of THHN left over.

Thanks for the info on the fuses. I assumed that it would be fine but I always double check everything because I don't like mistakes so I thought it best to ask.