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HPWC SER vs Romex Wire?

SureValla

Member
Mar 15, 2016
626
422
Shelton, CT
I'm all set to get my HPWC installed and was planning on using romex wire. That is until I came upon SER cable. It seems like its just as safe and easy to use but costs less. Seems like I should switch no? Can anyone elaborate on the differences between these two cables?

For reference:
2-3 NM-B | $6.74/ft | 2-3 W/G NM-B Wire Black
2-2-2-4 SER | $6.29/ft | 2-2-2-4 Copper SER Service Entrance Cable

I am installing a 90 amp breaker, 75 ft of cable. Yes I know the M3 can only take 48amps but I am planning for a second tesla in the future with a second HPWC
 

Craig-Tx

Member
Aug 1, 2016
112
142
Fort Worth, TX
I'm all set to get my HPWC installed and was planning on using romex wire. That is until I came upon SER cable. It seems like its just as safe and easy to use but costs less. Seems like I should switch no? Can anyone elaborate on the differences between these two cables?

For reference:
2-3 NM-B | $6.74/ft | 2-3 W/G NM-B Wire Black
2-2-2-4 SER | $6.29/ft | 2-2-2-4 Copper SER Service Entrance Cable

I am installing a 90 amp breaker, 75 ft of cable. Yes I know the M3 can only take 48amps but I am planning for a second tesla in the future with a second HPWC

Standard Disclaimer - I'm not a professional... seek advice... etc.etc.

It seems that SE cable is frequently used in Branch circuits and is permitted per NEC 338.10 (check with local authorities for your area...)
You may also look for other electrical supply as you don't need 3 conductor for the HPWC, it doesn't need a neutral connection.
For NM-B, you only need 2-2 with ground or 2-2-4 SER. If you can locate that (if they make it) it could save a lot in copper.
 
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Craig-Tx

Member
Aug 1, 2016
112
142
Fort Worth, TX
You only need two conductors for HPWC. I would do it with THHN and conduit. Would be about the same price and safer.
For 90A can't you use 3ga even for a 75ft run?
For Romex (NM-B) and SER cable used in insulation, you must size the cables per the 60 degree ampacity limits. 2 AWG limit at 60 deg is 95 amps.

THHN and Conduit is always a great idea when possible. I can't speak to the OP's situation, but when I ran my circuit, I had to cut about 8 holes in sheetrock to fish about 75 feet of romex to where I wanted it. No possible way without LOTS of sheetrock distruction to run conduit.
 

SureValla

Member
Mar 15, 2016
626
422
Shelton, CT
For Romex (NM-B) and SER cable used in insulation, you must size the cables per the 60 degree ampacity limits. 2 AWG limit at 60 deg is 95 amps.

THHN and Conduit is always a great idea when possible. I can't speak to the OP's situation, but when I ran my circuit, I had to cut about 8 holes in sheetrock to fish about 75 feet of romex to where I wanted it. No possible way without LOTS of sheetrock distruction to run conduit.
Thanks yeah not looking to exceed 95amp as I'm only going to have a 90amp breaker.

I'm looking to avoid the hassle of running conduit. I just don't get why you'd ever use nm 2-2 with ground when 2-2-4 ser is cheaper
 

Daniel in SD

Well-Known Member
Jan 25, 2018
6,594
9,378
San Diego
Thanks yeah not looking to exceed 95amp as I'm only going to have a 90amp breaker.

I'm looking to avoid the hassle of running conduit. I just don't get why you'd ever use nm 2-2 with ground when 2-2-4 ser is cheaper
If you're not making a bunch of turns it's really not that bad. You don't even have to fish it. I was able to push 3ga wire through 1 inch conduit no problem.
I can't imagine fishing 2ga romex through studs!
 

Craig-Tx

Member
Aug 1, 2016
112
142
Fort Worth, TX
Wasn't thinking of running through studs I was think of using large plastic staples. I.e. GARDNER BENDER Cable Staple,1-1/2In,Plastic,Serv E,Pk2 - 6LVG1|GSE-402 - Grainger
Depending on your scenario, you may not be able to pass an inspection if you go this route.
Romex (and likely SER) cable cannot be exposed. It must be protected from physical damage. I believe it may be acceptable in garages above a certain height (i.e. near the ceiling) but not likely at the height of your HPWC.
 

SureValla

Member
Mar 15, 2016
626
422
Shelton, CT
Depending on your scenario, you may not be able to pass an inspection if you go this route.
Romex (and likely SER) cable cannot be exposed. It must be protected from physical damage. I believe it may be acceptable in garages above a certain height (i.e. near the ceiling) but not likely at the height of your HPWC.

Wire will be run along joists in basement then up inside wall to the rear entry of the HPWC so never exposed to physical damage
 
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eSpiritIV

Member
Mar 24, 2016
434
229
Portland, OR
For Romex (NM-B) and SER cable used in insulation, you must size the cables per the 60 degree ampacity limits. 2 AWG limit at 60 deg is 95 amps.

THHN and Conduit is always a great idea when possible. I can't speak to the OP's situation, but when I ran my circuit, I had to cut about 8 holes in sheetrock to fish about 75 feet of romex to where I wanted it. No possible way without LOTS of sheetrock distruction to run conduit.


Craig is correct. SER cable should only be used for "service entrace" per the cable type, and as he said, you have to use the lower ampacity tables at 60 degrees. running single conductors of THHN in conduit is the way to go! In the long run a few bucks wont hurt you to go with the appropriate wire.
 

SureValla

Member
Mar 15, 2016
626
422
Shelton, CT
Craig is correct. SER cable should only be used for "service entrace" per the cable type, and as he said, you have to use the lower ampacity tables at 60 degrees. running single conductors of THHN in conduit is the way to go! In the long run a few bucks wont hurt you to go with the appropriate wire.

my desire to go without conduit is not due to cost (in fact romex will cost more) its actually to make the install easier. Its very easy to fish the cable where it needs to go so I don't see having to change it in the future as being an issue at all.
 

voip-ninja

Give me some sugar baby
Mar 15, 2012
4,124
4,694
Colorado
You only need two conductors for HPWC. I would do it with THHN and conduit. Would be about the same price and safer.
For 90A can't you use 3ga even for a 75ft run?

I think it is smarter to just run all four wires (three conductors and neutral) that way the circuit can be repurposed for another application later, if needed... rather than spending time and money having to run the circuit again.

If you run all four wires you can also terminate to a new sub-panel, run the HPWC from that and run something else from the rest of it.
 
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voip-ninja

Give me some sugar baby
Mar 15, 2012
4,124
4,694
Colorado
Depending on your scenario, you may not be able to pass an inspection if you go this route.
Romex (and likely SER) cable cannot be exposed. It must be protected from physical damage. I believe it may be acceptable in garages above a certain height (i.e. near the ceiling) but not likely at the height of your HPWC.

It meets code for it to run in basement rafters where it is technically exposed as long as any gaps across drywall or open space are bridged with building structure such as 2x4 studs that the romex is attached to.
 

SureValla

Member
Mar 15, 2016
626
422
Shelton, CT
I think it is smarter to just run all four wires (three conductors and neutral) that way the circuit can be repurposed for another application later, if needed... rather than spending time and money having to run the circuit again.

If you run all four wires you can also terminate to a new sub-panel, run the HPWC from that and run something else from the rest of it.

exactly, I was planning on capping the neutral wire inside the HPWC. Would I also cap it inside the main panel or should that be connected to the neutral bar?
 

mongo

Well-Known Member
May 3, 2017
13,126
39,989
Michigan
Craig is correct. SER cable should only be used for "service entrace" per the cable type, and as he said, you have to use the lower ampacity tables at 60 degrees. running single conductors of THHN in conduit is the way to go! In the long run a few bucks wont hurt you to go with the appropriate wire.

SER is fine for branch circuits, it just has extra features (such as UV resistance) that make it usable for service connections. https://www.dli.mn.gov/ccld/PDF/eli_bulletin_cable.pdf

It meets code for it to run in basement rafters where it is technically exposed as long as any gaps across drywall or open space are bridged with building structure such as 2x4 studs that the romex is attached to.

For this size of cable, the bridging is not required.
National Electrical Code 2011
Chapter 3 Wiring Methods and Materials
Article 334 Nonmetallic-Sheathed Cable: Types NM, NMC, and NMS

II. Installation
334.15 Exposed Work.

(C) In Unfinished Basements and Crawl Spaces. Where cable is run at angles with joists in unfinished basements and crawl spaces, it shall be permissible to secure cables not smaller than two 6 AWG or three 8 AWG conductors directly to the lower edges of the joists. Smaller cables shall be run either through bored holes in joists or on running boards.

exactly, I was planning on capping the neutral wire inside the HPWC. Would I also cap it inside the main panel or should that be connected to the neutral bar?

Connect at panel, prevents it from picking up induced voltages and prevents issues down the road if the HPWC is replaced.

Have you looked at flexible metal conduit? I used it for a hot tub run (inside section). You can pre-install the THHN, then rout the whole thing. 1 in. Flexible Reduced Wall Aluminum Conduit, 50ft or 500ft
 

cmaster

Member
Dec 4, 2014
240
76
United States
You can use #2 SER Aluminum then connect a disconnect switch (100A) from the circuit breaker. Next, from the disconnect switch, use #4 COpper to HPWC. It meets the NEC spec.

How do I know? An electrician gave me a quote with that job. I did it myself.
 

voip-ninja

Give me some sugar baby
Mar 15, 2012
4,124
4,694
Colorado
exactly, I was planning on capping the neutral wire inside the HPWC. Would I also cap it inside the main panel or should that be connected to the neutral bar?

According to the electrician I spoke with you should terminate the neutral lead at the circuit breaker side.
 
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