wiring heat pump

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Old 09-24-08, 03:25 PM
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wiring heat pump

putting in new heat pump as part of addtion. the HVAC guy said I need to put new wire for air handler. the old heat pump air handler was on 50amp breaker, which I thought would be plenty. But the wire is SE 8-8-8. I need 6 wire, according to the HVAC guy. So is SE wire ok to use? I looked at connection to disconnect and it just has two wires and green grounding screw. Other options for wire type? NM OK? Is conduit needed for either of these? It will run in unfinished basement along/through joists (not along any concrete walls), then go up (in space next to old chimney that is not going to be used anymore-same place old wire ran) two floors and then in attic to the disconnect. run will be about 50ft. then will go from disconnect to air handler. 1.) is conduit needed anywhere in this run? 2.) what is best wire choice-type 3.) what gauge wire? HVAC guy said 6/2 but I thought might need 4/2 after looking at stickers shown below.

air handler label


aux heater label


for outdoor condenser unit, there is 10/2 UF-B wire on 30 amp circuit. unit rated at 23.4A per sticker. The wire runs along foundation into disconnect and then to unit. No conduit is used either in run to disconnect or from disconnect to unit. The wire never goes below ground. I thought you had to use conduit when running wire along foundation? I thought everything else OK except the conduit question.

condenser label


I need to run out and get the wire ASAP so any help apprecitated.

thanks

thanks
 
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Old 09-24-08, 04:35 PM
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For 60 amp circuit you will need to use #4 NM CU or #3 alum { this is imporat due the 2008 NEC. } { note this is sized per NEC code on 60C rating } and the SE and SER is the same catorgy on the tempture rating .,, Yes I know they do have much higher rating but the code say something else.,,

What you have now is 8-8-8 SE cable if this is alum it will only restricted to 30 amp but if this is copper verison it is good for 40 amp.


I do not know how common is the #3 Al SE cable in your area but other wise #4 SE CU is around otherwise the other option is run in conduit and run THHN's

But if you are on 2005 code then #6 CU SE cable or #6 NM will will work for this useage and yes the 6-2 W/G is avable in pretty good percentage of bigbox store { you may want check it ahead of the time to make sure they carry this }

For the breaker size it will have to be 60 amp you can not use smaller breaker due the heater size is there.


Now for outdoor unit the 30 amp breaker may hold ok for while but really it should be used with 35 amp breaker per nameplate info.

Merci,Marc
 
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Old 09-24-08, 04:54 PM
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Thanks Marc

I am pretty sure my county (Howard, Maryland) is NEC 2005. Seems odd that if on 2005 can use #6, but if on 2008 have to use #4? Am I interpreting your post correctly?

I guess I will have to call tomorrow to verify which version we are on.

Yeh, I knew that I needed 60amp for heater. I guess will have to buy one. Hopefully can find it.

wasn't sure about condenser. It said max fuse. so I thought that meant that you could use 30 since since it is not over 35 and 23.4/30 is 78%, so I thought that was OK. why don't they list min fuse or tell you exactly what to use? If use 35amp, you can still use 10-2? I thought 30amp was max for 10 gauge?

I guess conduit not needed along foundation. As for conduit to air handler, I certainly do not want to run THHN wires in conduit to the attic so will stick with either SE or CU.

thanks
 
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Old 09-24-08, 06:29 PM
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sorry, meant SE or NM (not Cu)
 
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Old 09-24-08, 06:47 PM
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Originally Posted by hammerash View Post
Thanks Marc

I am pretty sure my county (Howard, Maryland) is NEC 2005. Seems odd that if on 2005 can use #6, but if on 2008 have to use #4? Am I interpreting your post correctly?

I guess I will have to call tomorrow to verify which version we are on.
I think you are on 2005 but it will be wise idea to check it make sure you are on right cycle.

Originally Posted by hammerash View Post

Yeh, I knew that I needed 60amp for heater. I guess will have to buy one. Hopefully can find it.
60 amp two pole breaker is pretty common and you will find it almost any big box store and hardware unless you got one of the very old load centre.

Originally Posted by hammerash View Post
wasn't sure about condenser. It said max fuse. so I thought that meant that you could use 30 since since it is not over 35 and 23.4/30 is 78%, so I thought that was OK. why don't they list min fuse or tell you exactly what to use? If use 35amp, you can still use 10-2? I thought 30amp was max for 10 gauge?
The A/C and motor load have diffrent rules than standard circuit set up and they are very spefic in Art 430 and Art 440 .

As long the listing say both fuse and breaker you are fine with that part many A/C will list the min load amprange and max fuse so it mean we can wired by the min amprange and max fuse or breaker per listing.

Merci,Marc
 
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Old 09-24-08, 07:28 PM
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Marc

Whether 2005 or 2008 NM #6 cu is only rated at 55 amps. It would need to be #4 to carry the minimum ampacity (58.5) for 240 volts as I see things on both code cycles....have they changed something I'm not aware of... ?

SE cables were changed to the same as nm in 2008 using only the 60c column for ampacity of the conductors.Both NM and SE are rated 90C insulation which is probably going to be needed in order to connect to the heater.

Hammerhash....

wasn't sure about condenser. It said max fuse. so I thought that meant that you could use 30 since since it is not over 35 and 23.4/30 is 78%, so I thought that was OK. why don't they list min fuse or tell you exactly what to use? If use 35amp, you can still use 10-2? I thought 30amp was max for 10 gauge
The maximum fuse or inverse time breaker is 35 amps. The mimimum circuit amps is 23.4. this is obtained by taking 125% of the rla off the nameplate for the condensor compressor (17.9 amps) then adding that to the fla of the fan motor 1.1 which will give you the minimum circuit amps of 23.4.
Overcurrent and short circuit protection must be capable of handling the compressor starting current and is allowed to be a maximum of 175% the compressor rla of 17.9 amps. 1.75 x 17.9 = 31.3 amps next size up breaker (NEC 240.6) is 35 amps as stated as the maximum breaker on the nameplate.

Compressor motor branch circuit conductors do not have to follow the overcurrent for small conductors in subsection 240.4(D) but follow 240.4(G). This sends you to Article 440 parts III and IV. So for your condensor you can use #12 awg copper (ampacity 25 amps) as a minimum conductor on a maximum breaker or fuse of 35 amps. You can use a 30 if you want and see if it holds when the compressor starts. You can also use 10 awg copper if you want, you just have to have a conductor that will carry the load on the nameplate and not use a breaker less than the load required and don't go over 35 amps.

You must also consider voltage drop due to distance from the panel to the equipment in case an upsize in wire is needed. Maye you have already discussed this I'll have to look back in the thread....
 
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Old 09-24-08, 08:14 PM
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Originally Posted by Bruto View Post
Marc

Whether 2005 or 2008 NM #6 cu is only rated at 55 amps. It would need to be #4 to carry the minimum ampacity (58.5) for 240 volts as I see things on both code cycles....have they changed something I'm not aware of... ?

SE cables were changed to the same as nm in 2008 using only the 60c column for ampacity of the conductors.Both NM and SE are rated 90C insulation which is probably going to be needed in order to connect to the heater.
Thanks for bring it up to me Bruto but I used know the #6 cu can able size up with the next larger OCPD but typically most case #6 CU will useally run with 50's but for good pratice it will be much wiser to run #4 anyway .


To OP you may want to reread my last comment so to correct it and yes some store should stock #4 NM or #4 copper SE cable as well.

Merci,Marc
 
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Old 09-25-08, 07:51 AM
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thanks for the help. I mentioned the 50ft to air handler in case voltage drop would be an issue. Is that far enough to matter? I tried to look at some tables and didn't think 50ft would be a problem. I think probably 50ft to condenser also, although I may cut hole in concrete to give a more direct route. Big boxes didn't have any 4-2. Starting calling around electrical supply and really having hard time finding it. Only found it at one place (type SE) but far drive. One place told me that they don't make 4-2 NM. I guess I am taking a drive later today. hope for decent weather as I don't have any heat right now!
 
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Old 09-25-08, 08:20 AM
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Aluminum #3 or #2 SER is common however be sure the heater does not require copper conductors.

50 feet is no issue for voltage drop.
 

Last edited by Bruto; 09-25-08 at 10:39 AM.
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Old 09-25-08, 08:55 AM
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I guess just have extra insulated conductor is use SER, correct? If I need #4 Cu, wouldn't I need bigger if use Al? I think will just go and get the #4 Cu SE. At $2.68/ft I probably should verify my measurements!
 
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Old 09-25-08, 10:36 AM
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If I need #4 Cu, wouldn't I need bigger if use Al?
Yes... my apologies .... remember to use 60C column of the table for the ampacity of nm and se.

You can look around here to see what is generally available to most suppliers.

http://www.southwire.com/processChan...4c026564RCRD#1


I guess just have extra insulated conductor is use SER, correct?
YES
One place told me that they don't make 4-2 NM.
Very rare but 4-3 is made.
 

Last edited by Bruto; 09-25-08 at 11:00 AM.
  #12  
Old 09-25-08, 02:21 PM
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got #4 SEU. Now have to get wife to help me pull it down from attic! Thanks guys.
 
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Old 09-27-08, 06:30 AM
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Working with #4 in the tight confines of the disconnect at the heat pump was no fun, but got it done and had unit up and running to test yesterday. Thanks to all. Question I have is why is the wire going from disconnect to the unit so small? Looks like maybe #8. Per the labels, it needs 60Amps with the auxillary heat unit.
 
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Old 09-27-08, 07:34 AM
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Originally Posted by hammerash View Post
Working with #4 in the tight confines of the disconnect at the heat pump was no fun, but got it done and had unit up and running to test yesterday. Thanks to all. Question I have is why is the wire going from disconnect to the unit so small? Looks like maybe #8. Per the labels, it needs 60Amps with the auxillary heat unit.
Manufactuerers use wiring in close proximity to the heating element and therefore are required to use high heat insulation, This allows them to use a smaller wire with the same ampacity as the supply conductors you ran to the unit. You will see the same thing on your cooking appliances...like ranges and cooktops.

SE Type U would not have been my choice other than you do not have the extra conductor in that as in SER . I would have ran thhn in conduit. Style U Se cable as you used has a concentrically braided bare 'neutral' over the two hot conductors so you are kinda mis-applying the intended application though it will work. Generally speaking we only use style U for 3 wire service entrances now days.
 
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Old 09-27-08, 09:56 AM
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thought about running THHN in conduit, but it would have been a lot harder to run the conduit. thanks for all your help and explanations. I enjoy learning WHY something is done a certain way. Your explanations certainly make me respect what you guys do-the NEC seems like it is pretty darn complicated.
 
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Old 09-27-08, 07:48 PM
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Originally Posted by hammerash View Post
thought about running THHN in conduit, but it would have been a lot harder to run the conduit. thanks for all your help and explanations. I enjoy learning WHY something is done a certain way. Your explanations certainly make me respect what you guys do-the NEC seems like it is pretty darn complicated.
In rereading my last reply I may have made you feel that you used the SEU incorrectly that was not what I meant to say. SEU type cables that have all circuit conductors insulated are allowed for branch circuit wiring to use the bare for equipment grounding purposes only.

My point was the cable is more preferably used for service entrance. What you used it for was fine.
 
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