Circuit to AC unit -- romex in conduit?

Reply

  #1  
Old 07-24-10, 01:53 PM
kish2554's Avatar
Member
Thread Starter
Join Date: Jan 2010
Location: Fort Worth, TX
Posts: 46
Received 0 Votes on 0 Posts
Circuit to AC unit -- romex in conduit?

I am in the process of remodeling my bathroom and currently, the 220 circuit feeding my air conditioner disconnect runs from the main breaker panel down, then horizontally through the studs along the exterior wall to where it exits just behind where my new shower stall will be. Personally, I'm not comfortable having a 220 volt circuit running between the water pipes and I'd like to relocate it to the exterior of the house. Plus, seeing as I've replaced almost all the circuits in the home already, leaving an old cloth-covered wire to feed my air conditioner seems like something foolish to do. Anyways, my question is, can I install a piece of 10/2 + ground romex in watertight conduit on the exterior of the house from the circuit breaker panel to the disconnect? It's a small air conditioner and only requires a 30 amp 220 volt circuit. The reason I'm asking is the main panel is on the inside of an exterior wall about 15 feet from the air conditioner. If I run individual wires, I'd have to make multiple conduit bends to get it in the wall and up into the panel. If I use romex, I can stub the conduit into the wall and simply use romex for about 1 foot where it would then enter the panel. Running romex in conduit seems to be a touchy subject and some say it's fine and others say it's not. Running new romex on the interior through the wall to the disconnect would require me to tear out two walls and I'm not going to do that.
 
Sponsored Links
  #2  
Old 07-24-10, 02:07 PM
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 4,793
Received 36 Votes on 35 Posts
Code-wise, if the wire is running outside (inside or out of conduit), it needs to be water resistant - either UF-B or THWN. There's no code-reason not to run 10/2 UF-B out of the panel, into a conduit sleeve, and then to the disconnect.

Some would recommend keeping it conduit the whole way and use individual THWN (THHN) wires, but either way is code-compliant.
 
  #3  
Old 07-24-10, 02:16 PM
kish2554's Avatar
Member
Thread Starter
Join Date: Jan 2010
Location: Fort Worth, TX
Posts: 46
Received 0 Votes on 0 Posts
Thank you for your input. I couldn't see why using romex would be wrong because I'm only running one circuit. Just overkill, you know? It's still 3 wires and a ground, so it should be up to code. The conduit will be watertight, so that part will suffice.
 
  #4  
Old 07-24-10, 04:51 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,493
Received 33 Votes on 25 Posts
Sorry, but that is strictly forbidden.

First of all, there is no such thing as "watertight" conduit. All conduit will collect water inside if from no other source than condensation. "Romex" cable (technically called type NM cable) is NOT listed for use in damp or wet spaces and an outdoors conduit is definitely considered to be a wet space.

Perhaps you can cut a hole directly through the back of your circuit panel and using a nipple and conduit LB fitting get the conduit in the proper position for the run to the A/C disconnect. Then you could use type THHN/THWN insulated wires in the conduit.

BTW, there is nothing wrong in running the type NM cable near water piping as your described existing condition.
 
  #5  
Old 07-24-10, 07:51 PM
kish2554's Avatar
Member
Thread Starter
Join Date: Jan 2010
Location: Fort Worth, TX
Posts: 46
Received 0 Votes on 0 Posts
I probably should have mentioned...the circuit in use is a 30 amp 220v. The wire currently in wall is 12/2. Yes, the same wire used for 110v 20 amp circuits. Although it does work, it gets warm, and (first of all let me say I did NOT run it -- it was here when I bought the house) isn't up to code. Anyways, assuming I do run conduit end to end with non-romex wire (4 10gauge wires), what size conduit would I need? I can bend 1/2" conduit, but not 3/4". Any suggestions?
 
  #6  
Old 07-24-10, 09:15 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,493
Received 33 Votes on 25 Posts
Any type of 1/2 inch conduit will hold 4 #10 conductors with type THHN/THWN insulation. Outside I prefer to use PVC conduit with all glued joints although EMT with compression fittings is acceptable. Are you certain that you need four conductors? Most A/C condensing units are straight 240 volts.

Also, you need a 120 volt receptacle within 25 feet of the A/C condensing unit. Since it is an outside receptacle it needs an "in use" (bubble type) cover.

If the conduit will be in an area where it is "subject to damage" then if you use PVC it must be schedule 80. In 1/2 inch size the schedule 80 is limited to a maximum of four THHN/THWN conductors whereas EMT can have five conductors. If you need to install the 120 volt receptacle also then running five conductors through the single conduit makes sense. Pre-made 45 and 90 degree bends in PVC are easily available and if you need a different bend then a heat gun carefully used will get you where you need to go.
 
  #7  
Old 07-24-10, 09:24 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
Post deleted.
....................
 
  #8  
Old 07-25-10, 07:38 AM
Member
Join Date: Aug 2009
Location: Northern California
Posts: 130
Received 0 Votes on 0 Posts
Am I missing something here? If the existing circuit is ran with 12/2, why are you saying that you will run 4 #10? It's a 220 volt circuit so you would only need 2 hots and a ground.

Unless you do need the 120 volt receptacle, in which case furd's 5 conductors would be correct...

2 #10 hots, 1 #10 ground and 2 #14 or #12 for the 120 volt receptacle.
 
  #9  
Old 07-25-10, 10:00 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 10,239
Received 40 Votes on 32 Posts
Whether the #12 conductors to the a-c unit are right or wrong is dependent upon the minimum circuit ampacity (MCA) of the unit, which can be determined by the full load amps of the unit. The 30 amp breaker might be correct even if #12 conductors are all that is required on the circuit, it depends on the maximum overcurrent protection (MOCP) listed for the unit. Regardless, #10 conductors should be more than adequate. Considering the age of the house, the unit was probably changed at least once and could have been replaced with a larger unit requiring a higher amperage circuit. The a-c guy who changed the unit should have caught the fact that a higher amperage circuit was required, if it is required.
 
  #10  
Old 07-26-10, 05:34 PM
kish2554's Avatar
Member
Thread Starter
Join Date: Jan 2010
Location: Fort Worth, TX
Posts: 46
Received 0 Votes on 0 Posts
Okay, well, the house originally had 50 amp 220v service, which has since been upgraded and I'm not sure what the old or original air conditioner required, but the new one installed just before I bought the house is a 2 ton Goodman, which says minimum circuit size 18.2 amp and maximum circuit size 30 amp on the rear plate. I am planning on installing some outdoor electrical receptacles in the near future, but at the moment, just want to be sure that the AC wiring is up to spec so I can finish the bathroom. The reason I wanted to run 4 10 gauge wires was for L1, L2, neutral and ground. Now I've read mixed reviews on running a ground and a neutral for 220, but is that just overkill? As for the location of the AC unit to the power panel, here's a rough example:

[]
bathroom []
[][][][][][][][][][][ PANEL ][][][][][][]
[][][][][][][][][][][][[][][][][][][][][][] These signify wall

[ AC ]

It's located approx 8 feet down, just on the outside of the bathroom window. The existing wire runs down from the panel about a foot, then turns and goes horizontally through the exterior wall to where it exits into a disconnect for the AC just behind the shower in the bathroom. I want to stub a conduit out from below the panel, then run it on the exterior in a similar fashion. I simply don't want to have the wire behind a cemented up custom built shower.
 
  #11  
Old 07-26-10, 07:12 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 10,239
Received 40 Votes on 32 Posts
What is the FLA on the plate? I have a really hard time believing you need a 30 amp circuit for a 2 ton unit unless it is very old and inefficient. You said it was new just before you bought the house, how many years ago was that? IF it is a very old unit, a new unit could pay for itself in 5 years.
 
  #12  
Old 07-27-10, 02:35 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,984
Received 35 Votes on 30 Posts
Air conditioners do not need a neutral. Your unit is fine with the #12. You said the minimum circuit ampacity required is less than 19 amps. Your breaker at 30 amps allows for the startup current which is higher than running current.
 
  #13  
Old 07-29-10, 12:15 AM
kish2554's Avatar
Member
Thread Starter
Join Date: Jan 2010
Location: Fort Worth, TX
Posts: 46
Received 0 Votes on 0 Posts
Alright, thanks for the input everyone. I appreciate it.
 
  #14  
Old 07-30-10, 04:16 PM
Member
Join Date: Jul 2006
Location: Near Philly
Posts: 559
Received 0 Votes on 0 Posts
Someone explain to me why 12 g wire is ok with a 30 a breaker please. If 12 g is rated for 20 amps and the breaker for 30 amps, wouldn't the wire overheat if a short condition existed before the breaker might trip? WOuldn't 10 g be a better choice if a 30 amp breaker is being used?
 
  #15  
Old 07-30-10, 04:57 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,984
Received 35 Votes on 30 Posts
The smaller than normal wire is appropriate for loads like air conditioner compressors. The wire is sized for the running load. The breaker is sized to allow for the high startup currents needed without tripping.
 
  #16  
Old 07-30-10, 05:21 PM
Member
Join Date: Jul 2006
Location: Near Philly
Posts: 559
Received 0 Votes on 0 Posts
PC,
I understand the point you are making. I don't think it answers my question on a short situation though does it?
 
  #17  
Old 07-30-10, 05:24 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 10,239
Received 40 Votes on 32 Posts
In a situation with a short circuit, the breaker will trip immediately regardless of whether the wire is #12 or #10.
 
  #18  
Old 07-31-10, 07:44 AM
mukansamonkey's Avatar
Member
Join Date: Nov 2007
Location: Indianapolis
Posts: 120
Received 0 Votes on 0 Posts
A note to the thread opener: Use schedule 80. 80 should be sunlight resistant, 40 normally isn't. 80 just generally more durable.

And this was more or less stated, but just to be clear: Use UF instead of NM because NM isn't properly water-resistant. Calling it Romex doesn't really specify which one of those it is.

And a note to bob22: 12ga THHN is actually rated for 30 amps in 310.16, the big chart of ampacities. Because it's too easy for small gauge to end up in situations where it overheats (think under insulation in a badly ventilated attic), article 240.4(D) limits it to 20 amps... except for a set of specific cases. The very first case is Air-conditioning and refrigeration. Which sends you to 440 part III and IV, an easy dozen paragraphs that need to be read to get the numbers right.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: