Question on cabling for 50amp service
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Question on cabling for 50amp service
Greetings,
I just moved into an older home which had a bad swimming pool heat pump that we replacd. With the replacement heat pump in place, discovered that the circuit wiring is a bit too short.
There is 6/3 Romex running through a rigid and flexible pvc type conduit from the nearby dedicated subpanel. (See first picture) There is also 6/3 Romex run from the subpanel through rigid pvc up the wall of the house, through a LB-type conduit box into the attic and over to the main panel(see second picture).
I was going to run a longer replacement cable from the subpanel to the heat pump, but after doing some research, I’m not sure i can pull Romex.
Questions:
1) Can I run 6/3 Romex in the existing rigid and flexible conduit? Or do i need to use UF-B, or THHNs (red/black/white/green)?
2) Can i leave the existing cabling between the subpanel and main panel or should that be swapped out while I’m at it?
3) If the subpanel-to-main run needs to be replaced, is it a home run or does there need to be one kind of cable in the conduit outside and a different kind inside the attic, with the two meeting the LB box?
Thanks!
I just moved into an older home which had a bad swimming pool heat pump that we replacd. With the replacement heat pump in place, discovered that the circuit wiring is a bit too short.
There is 6/3 Romex running through a rigid and flexible pvc type conduit from the nearby dedicated subpanel. (See first picture) There is also 6/3 Romex run from the subpanel through rigid pvc up the wall of the house, through a LB-type conduit box into the attic and over to the main panel(see second picture).
I was going to run a longer replacement cable from the subpanel to the heat pump, but after doing some research, I’m not sure i can pull Romex.
Questions:
1) Can I run 6/3 Romex in the existing rigid and flexible conduit? Or do i need to use UF-B, or THHNs (red/black/white/green)?
2) Can i leave the existing cabling between the subpanel and main panel or should that be swapped out while I’m at it?
3) If the subpanel-to-main run needs to be replaced, is it a home run or does there need to be one kind of cable in the conduit outside and a different kind inside the attic, with the two meeting the LB box?
Thanks!
#3
You need to use UF-b or THHN/THWN for the portion that is outside even if in conduit. It is okay to put the UF-b in conduit although it is a pain to pull through conduit.
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Thanks joed and pattenp.
Between ufb and thhn, which is “thinner?” Reason being, the romex soesnt have a whole lot of room in the conduit as is. If either option is much thicker, i will probably need to instll new conduit.
which of course is its own brand of fun
Between ufb and thhn, which is “thinner?” Reason being, the romex soesnt have a whole lot of room in the conduit as is. If either option is much thicker, i will probably need to instll new conduit.
which of course is its own brand of fun
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Originally Posted by jmba0
1) Can I run 6/3 Romex in the existing rigid and flexible conduit? Or do i need to use UF-B, or THHNs (red/black/white/green)?
UF-B is for direct burial. Like with NM-B, it is not prohibited from being inside a conduit, but it is not designed for that purpose and it is nearly impossible to pull it through a conduit. The fill ratio would also need to be reduced because of temperature derating.
THHN is the ANSI designation for Thermoplastic High Heat Resistant Nylon Coated
THWN is the ANSI designation for Thermoplastic Heat and Water Resistant Nylon Coated.
Most single conductors are rated for both. Take a look at this product image. Notice how the packaging indicates this is THHN conductor, but if you zoom in on the wire itself it says THHN and THWN.

Originally Posted by jmba0
2) Can i leave the existing cabling between the subpanel and main panel or should that be swapped out while I’m at it?
Originally Posted by jmba0
3) If the subpanel-to-main run needs to be replaced, is it a home run or does there need to be one kind of cable in the conduit outside and a different kind inside the attic, with the two meeting the LB box?
If you use a metal work box for a junction box, make sure you ground it with a short pigtail and a green grounding screw. AHJ likes that.
Originally Posted by jmba0
Between ufb and thhn, which is “thinner?” Reason being, the romex soesnt have a whole lot of room in the conduit as is. If either option is much thicker, i will probably need to instll new conduit. which of course is its own brand of fun
I would definitely recommend leaving the existing conduit in place on the outside of your house. There is nothing wrong with it. Remove the existing Romex from the conduit and pull 4 THWN conductors (black, red, white, green).
Again, that's for the conduit on the outside of your house. The wire inside your house (a.k.a. in your attic) can be Romex. The Romex and THWN can meet within a junction box in your attic.
Last edited by electric_dummy; 05-04-19 at 10:58 PM.
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Glad to help. I wish you luck. Some more pertinant info that I forgot to mention.
You are using 6 AWG which is very dificult to work with. Your junction box should be at least a 6 inch square box.
You can’t bury the box in a wall or ceiling. It must remain accessible in your attic.
Your splices should use either the big blue wirenuts or a split bolt (electrical taped to insulate). More ideal but more expensive is a product called a Polaris that is already insulated.
Split Bolt

Polaris
You are using 6 AWG which is very dificult to work with. Your junction box should be at least a 6 inch square box.
You can’t bury the box in a wall or ceiling. It must remain accessible in your attic.
Your splices should use either the big blue wirenuts or a split bolt (electrical taped to insulate). More ideal but more expensive is a product called a Polaris that is already insulated.
Split Bolt

Polaris

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Thanks Electric_dummy!
I was thinking of using a 12x12in box (https://www.homedepot.com/p/12-in-x-...3713/202043349) since the larger guage wires are a pain and I figure there should be a little bit of a service loop in the box. The polaris connectors are nice, if expensive, but perfect for a simple job like this.
Thanks for the additional info!
I was thinking of using a 12x12in box (https://www.homedepot.com/p/12-in-x-...3713/202043349) since the larger guage wires are a pain and I figure there should be a little bit of a service loop in the box. The polaris connectors are nice, if expensive, but perfect for a simple job like this.
Thanks for the additional info!
#12
If you use THWN, the green ground wire can be #10 gauge on a 50 amp circuit. The ground wire on your 6/3 Romex is probably #10 as well.
Also, it's very likely the neutral can be downsized depending on the actual load, but in no case less than #10. Some local codes may be more strict on neutral downsizing than the NEC.
If the load is only a heat pump, a neutral may not even be needed.
Just letting you know in case four #6 wires poses a problem in the existing conduit.
Also, it's very likely the neutral can be downsized depending on the actual load, but in no case less than #10. Some local codes may be more strict on neutral downsizing than the NEC.
If the load is only a heat pump, a neutral may not even be needed.
Just letting you know in case four #6 wires poses a problem in the existing conduit.