SER cable vs Conduit - Indoor subpanel ampacity/temperature questions
I am installing a 125 amp sub panel that will be about 40-45' away from the 200 amp main panel. Main panel is in the basement and the subpanel will be in the basement as well. The main panel is an older Siemens 200amp panel. I have purchased a 125amp feeder breaker (the panel does accept it, I checked with siemens) and I have also purchased the newer PN style 125 amp subpanel with CU bus bar. Links to these are below.
My plan was to run 1 1/2" PVC conduit and use #1 CU THHN wire for 2 hots and 1 neutral and also use a #6 CU for ground. I understand that THHN #1 CU wire is good for 75C. The breaker I bought and the subpanel are both 75C degree.
I started mapping out how I would run the conduit and when I started going into detail, I realized it wont be easy due to number of bends required to go around obstacles. It can be done, but its not going to be easy. Its going to require a 270 degree turn, then a pullbox, then another 270 degree turn.
At this point I told myself why bother with conduit, instead use 1-1-1-4 SER CU as its indoors and simply attach the cable to the joists as NEC allows this.
What I dont know is whether using this approach now forces me the use the 60C calculations which creates another problem in that now I need to use 1/0 CU wire. Another issue (not sure if it is an issue) is the feeder breaker I got says "75C wire" whereas the subpanel says "60/75 CU AL wire". Does this mean the breaker can only accept 75C wire and hence no SER cable?
Furthermore, doing some research I read something that says beginning 2014 NEC this 60C requirement was dropped from SER cables. Is this true?
- Conduit approach = 50 ft of 1 1/2 conduit + necessary 90/45/LBs + 50 ft of wire (1-1-1-6 CU) is exactly $370 ($1.80/foot for #1 cu and $0.60 for #6 cu)
- SER approach = 50 ft of 1-1-1-3 southwire CU is $368
So cost wise they are identical. And at these price points $100 more or less doesnt matter to me. What matters to me is the safe/long lasting solution but also something that has lower chance of something going wrong during install. I dont have experience with conduit this large so I dont know how hard it is to do this pull but I did several conduit pulls some quite long with lots of turns but they were all #12 (but several of them in one pull). To see the difficulty I did a simple test where I bought 3 feet of #1 wire (3 of them) and bought a few 45 and 90 degree pvc pipes and it doesnt look difficult at all. I can easily push 3 wires at the same time, although I’m sure in practice it might be harder.
I’m sure SER is significantly less work but I dont know about the ampacity/temperature calculation and furthermore I dont know how durable this cable is long term when you have moisture/water/etc dripping from floors above and hvac ductwork considered.
THHN wire is rated at 90C and the termination points on the breaker and panel are rated 75C. With SER cable you may only use the 60C degree column when the conductors are #10 or smaller and when installed in insulation per 2017 code. In your case it appears you are OK to use the 75C degree column.
I would also recommend running the cable through the joists rather than under them unless you already have other mechanicals (ductwork, plumbing, etc) under the joists. It will be a much cleaner install.
SER cable will last forever unless exposed to physical damage or some environment it is not designed to withstand. IF it was me, I would use SER.
The 1-1-1-3 Cu SER is what you need to use. As long as it's not installed within insulation it can be sized based on the 75 deg C column which is 130A. The #3 ground is what comes in the #1 Cu SER.
You do not want SEU or USE.
Do you really need 125A? The same size in aluminum is 100A and less than half the price. You can use #1/0 Al with a 125A breaker since there is no 120A breaker.
The 1-1-1-3 Cu SER is what you need to use. As long as it's not installed within insulation it can be sized based on the 75 deg C column which is 130A. The #3 ground is what comes in the #1 Cu SER. You do not want SEU or USE. Do you really need 125A? The same size in aluminum is 100A and less than half the price. You can use #1/0 Al with a 125A breaker since there is no 120A breaker.
Do I need 125A? I probably don't but I might and I would rather pay a bit more now than to rip this all apart or sacrifice other things down the line.
- I have plans to build a detached garage sometime in the future. While ideally I would like this garage to have its own 200A meter from the POCO, this might not be practical due to the location of my house and where the garage would be. POCO will not want to do this or will want me to pay for transformer which will be significant where I am (in NJ).
- With that said, it is likely that there will be a 3rd panel, sister to this 125A panel that will be a 100A subpanel but protected by a 80A feeder (so really 80A).
- At the very least, this 125A panel will see the following concurrent loads : car lift (15A) + compressor (20A) + clothes dryer/washer (15A) + air fryer in kitchen (15A) + garage lights/outlets in garage (5A). These numbers are actual load numbers not crank or circuit sizes and it is likely for all of them to happen at the same time (although that same time frame is probably no more than a minute or so, but still). So you can see that at 75A potential load, I am already over 60% of the subpanel. I dont think given this going with 100A panel would be a good idea.
Questions about SER:
- Are there any special kind of connectors to attach this cable to the panels? Do I simply use a 1 1/2" NM-B connector or are there special ones? For example: https://www.homedepot.com/p/Halex-1-...5115/100207606
- Does the cable have to be sleeved inside the conduit as it drops from the ceiling to the plywood panel backing? From the main panel, it will leave from the bottom of the main and will have to run parallel to the length of the panel before it gets to the ceiling.
- Are there special rules as far as stripping these cables (outer sheathing) or simply use a sharp knife to get the outer stripped inside the panel and then remove the insulation of the inner wires in a similar fashion?
- Lastly, what type of hanger/straps do you recommend to attach them both perpendicular and also parallel to the joists? Can I use PVC conduit straps or do they need to special SER cable straps? Please see some options below:
The installation of SER is the same as NM-b. It only needs to be sleeved where it is subject to physical damage. PVC conduit straps can be use and clamping at panel entry is done by large NM clamps.
The cable connector you posted is correct. You will also need to install a plastic bushing as your wire is #4 or larger. Using a utility knife to remove the cable jacket is also correct.
The installation of SER is the same as NM-b. It only needs to be sleeved where it is subject to physical damage. PVC conduit straps can be use and clamping at panel entry is done by large NM clamps.
Thats good, but that means now I need a PVC sleeve from ceiling height to all the way to the bottom of the panel where it enters the main panel (so thats around 5' of vertical drop). Is it recommended to use a 90 degree or LB in these circumstances? I dont know how this stuff will bend inside that LB. For 1-1-1-3 SER, would I need a 2" PVC or 1 1/2" will do?
Originally Posted by Tolyn Ironhand
Actually, you are only at 30% (or so) because you have two hots available so you can balance the loads between them.
The cable connector you posted is correct. You will also need to install a plastic bushing as your wire is #4 or larger. Using a utility knife to remove the cable jacket is also correct.
Do you know what those plastic bushings look like? Is it one of these below? Do you thread this on top of the female connector inside the panel or instead of the metal female connector that threads on?
If using conduit down the wall and connecting to panel the NM clamp will not be necessary. Use a bushing on each end of conduit and staple cable close to where cable exiis the conduit at the ceiling. Using 2" conduit and either a type LL or LR conduit body for which ever way you need to turn. A LB type may also work depending on access to the cover.
That bushing is correct. You thread it on the connector after you install the locknut.
but that means now I need a PVC sleeve from ceiling height to all the way to the bottom of the panel where it enters the main panel
A cable that is running down a wall to a panel is not required to be sleeved if it is running along the wall surface or down a wall cavity. If it is running down a wall surface install some 2x4s or plywood down the wall to strap the cable to. Trying to install that cable through an LB or other conduit body will be quite difficult.
Thanks everyone for your responses. My panel is a little different please see attached pictures. Please ignore the white sump pump discharge pipe as that will be rerouted. Red lines is how the cable (or conduit) would have to be routed.
The top of the panel does have a knockout on the side but inside the panel is extremely crowded with a lot of conductors (lots of pigtail connections from potentially the time there was a smaller panel and the wires didnt reach). If I used that knockout, it will be very hard to bend #1 conductors and route them all the way to the bottom (the feeder breaker will be at the end of the panel) which is why I need to use the bottom.
I went to a few homedepots to see if I could find 1-1-1-3 SER cable (just to see how hard it is to bend it) and while I couldnt find that, I did find a 2-2-2-4 AL and it was very hard to bend. Not only that was a smaller gauge but also AL not CU. CU 1-1-1-3 would probably be difficult. I dont think its a good idea to bend 1-1-1-3 in any LB, even 2" one does not have enough radius. So if I have to do this conduit sleeve, it has to be 2x90 degree bent pipes (and a 45 degree on the ceiling to transition to the joists). Thats 225 degrees in a 1 1/2" PVC with 1-1-1-3 SER, not sure if its going to be easy. It may also look pretty ugly.
Do I need to worry about conduit fill requirements for the sleeve or because its not a complete conduit system, it doesnt matter? I dont know if that cable will fit 1 1/2" PVC.
I really would like to stay way from 2" PVC, it will be very ugly looking much more than 1 1/2" PVC.
Please let me know given my panel, the SER needs to be in conduit from ceiling. Please note this is in the corner of my basement and behind furnace/HVAC unit. It is not easily accessible, but as per NM-B "subject to physical damage" rules, AHJ might not allow it.
On this note, is it a problem to place the 125A feeder breaker all the way to the bottom on the left handside? Does it have to be at the top? I read arguments that says it doesnt matter as voltage drop is so minimal but I also read heat rises up and this might overheat the entire stab. But I'm not sure if I'm overthinking this one.
Placing breaker at bottom is okay. I'd go without the conduit and do your best keeping the cable strapped to the wall, even placing a running board along side if possible.
Placing breaker at bottom is okay. I'd go without the conduit and do your best keeping the cable strapped to the wall, even placing a running board along side if possible.
Can you clarify what you mean by "keeping the cable strapped to the wall" and "running board along side if possible"?
There are set of studs attached to the masonry wall, then on top of these studs, there are 3 total 2'x4' (3/4" thick) plywood (2 of them are vertical, one of them is parallel below them). There is no wall there. I am attaching more pictures, maybe the initial set of pictures didnt really explain it well. There used to be only 1 plywood there (the one where main panel sits on), but I added the 2nd and 3rd one (brighter colored ones) because there was no room to work with).
Majority of the run will be on the ceiling, parallel to the natural gas line and the radon pipe. The conduit question is for the section when it drops from the ceiling, stapled on the plywood, adjacent to the main panel, all the way to the bottom of it.
I was trying to suggest a way to advert any issues over the protection of the cable by your inspector. That means running the cable on the wall surface either fastened directly to the wall surface or fastened directly to the plywood that the panel is mounted to. Also flanked by a running board if necessary. Edit: I was looking at the pictures on a cell phone and couldn't see that the plywood went as far as it did to the side. So fastening to the wall surface is not needed. You could use a piece of flex conduit for added protection.
Thank you. I havent seen flexible conduit that can fit this big cable before, maybe the electrical supply house nearby will carry it but homedepot/lowes here doesnt.
I was looking at the AL SER cable and cost is 1/3 of CU which is great. One question mark is the size of the conductors. Both the subpanel and the feeder braker has 2/0 as the largest conductor supported which I dont know if its a good idea or not. Usually when there is a range of supported values, I prefer to go with a value that falls within the middle of the range. Also I’m guessing 2/0-2/0-2/0-1 will be one heck of a cable to wrestle with, especially inside my overcrowded 30 year old main panel.
The cost difference between the two is $220 ($146 vs $364). The feeder breaker and subpanels I am using are in the first post. I have a #1 CU wire with me and believe me when I say this even that fits barely to that feeder breaker, I have no idea how 2/0 would fit and if it does, not sure how you can torque is as well.
Both subpanel and feeder breaker lists #3 to 2/0 as supported wire sizes. #1 is right in the middle.
I would relocate the small cable entering the panel at the top right in the concentric KO and install the feeder cable there. Then just run the new SER similar to the SER feeding the main panel.
That thing on top right is an old surge protector that is double tapped behind main lugs. The only way to remove it is to pull the meter, its not something I can do I’m afraid.
It predates my ownership of the house and by the looks of that thing, it must be a decade or more older. The problem is with the pandemic, its not very easy to coordinate with electricians to pull the meter out and disconnect that stuff, etc. I know this is not up to code but that stuff must have been there for so long, whats the worst that can happen? One electrician I approached made this sound too complicated (perhaps because its actually quite easy but his time is expensive) and that POCO had to pull the meter and then he comes and disconnects and POCO puts the meter back and its likely I am without power a day or two.
By the way this AHJ did two electrical permit approvals since I bought this house and both times have seen this panel open and never flagged that.
Here is a picture of that "lightning arrester". I did try to find it in google and came up empty. It doesnt say anything about installing it on a breaker, but does say "line" which perhaps means at the time this was installed, this installation was valid? Who knows. But I doubt this is impending doom because it has been there a long long time.
When the meter is pulled and these main lugs are loosened, is it a simple case of loosening them and removing these tiny wires and tightening back OR do you need to trim the main conductors as in cut them shorter in order to get newer bare AL surface, coat it with the paste, and retorque?
When the meter is pulled and these main lugs are loosened, is it a simple case of loosening them and removing these tiny wires and tightening back OR do you need to trim the main conductors as in cut them shorter in order to get newer bare AL surface, coat it with the paste, and retorque?
I have never seen one of those on a panel before, but I would say you could just reconnect them, coat them with paste, and retorque.
I'm not suggesting you do this, but I would take a pair of well insulated diags plus using appropriate rubber gloves and snip the wires right at the lugs. Then install a new surge protector on a breaker.
So I went to buy a sample SER cable today. First of all, no one sells CU SER, any size, anywhere here (NJ). I called 4 electrical supply houses, they all said the same thing that they dont stock this, heck they wont even get it for me. Great. Then I said OK, let me see what AL looks like. Obviously I have to go to 2/0 to get 125A at 75C (1/0 does give me 120 and it would work if I did prove on load calculation, but I dont want to cut corners and I want to get 125A). So I got 4 feet of it just to see if it will fit on the feeder breaker and the panel lugs. It does fit but really barely. Also 2/0 SER is huge as I m sure you guys know. There is no way it will fit into a 1 1/2” PVC (unless its straight) and even 2” might be tough. On the positive side, 2/0 conductors are easier to bend than #1 CU.
Not sure what to do, I dont know if I can come to terms with a huge 2-3” conduit. Its also not possible the 2/0 SER will fit into any knockout but the one at the bottom of the panel. So even if I were to remove that old lightning arrester, it wont help me with the 2/0 SER.
Cost is funny at $2.10/ft vs $1.80/ft for just single #1 CU conductor. But still, all the positives are pointless if I cant use it due to the massive conduit sleeve I will need.
(1/0 does give me 120 and it would work if I did prove on load calculation, but I dont want to cut corners and I want to get 125A
They do not make a 120 amp breaker so you allowed to go up to the next size which is 125 amps. You are fine with 1/0 AL. (240.4(B)) There is no way your load calculation will come even close to 120 amps.
1) What is allowed : There is no breaker at 120A so can support next breaker
vs
2) What is physically allowed : A wire can support the amperes it is physically able to carry without overheating. In the case of 1/0 cable, that is 120A. So in the unlikely event (today but who knows in 10 years), I draw 125A, I am overheating that wire.
The important factor is I am not getting paid to do this (no offense to licensed electricians). Where the difference between 1/0 vs 2/0 might make a big deal on dozens of jobs in a year (and exponentially higher labor cost due to larger conduit etc), this is my own house and I have infinite amount of time (to some extent lol) and I will only do this once and never again (hopefully if I dont screw up).
Also as I mentioned earlier, I have plans to build a detach garage which will have its own subpanel that will be fed from this 125A panel (which is why I am going to 125 vs 100). That second run will be another 100-120ft, at those lengths, I would rather not go smaller wire (does it not make sense?).
I also dont know how vastly different 1/0 vs 2/0 would be, maybe at most 10 mils?
Question: I see a knockout that is more easily accessible but it is smaller (its diameter measures 1.79”, so i m guessing thats 1 3/4”). I’m assuming this is for 1 1/4” conduit and 1 1/2” will not fit. Assuming conduit fill rules do not apply for sleeved conduits, if I used this particular knockout, I can get away with single 90 degree wide angle elbow. Are there any issues having 2/0 SER be inside 1 1/4” conduit? It will be about 4’ of vertical run and a 90 degree elbow.
I agree with both PCboss, Pattenp, and myself that I previously posted. The cable is not subjected to physical damage when run along the building surface.
1/0 aluminum is allowed on a 125 amp breaker for the reasons I mentioned before. The wire inside is actually rated for 135 amps as SER cable is rated for 90 degrees C. You are limited to 75 degrees due to the termination points. Realistically the wire could carry 150 amps or more without the insulation degrading to the point of failure but that is why the code limits it to the ratings it does. Its not like the wire is fine at 120 amps but at 125 amps the wire bursts into flames. That's not how it works. The code ALWAYS errors on the side of safety.
On a side note if you go with 2/0 aluminum you can go with a 150 amp breaker even though it is rated at 135 amps at the 75 degree column.
thanks guys. I just got off the phone with our inspector and he has agreed that conduit is not necessary as well. I am relieved! Can you review the attached pictures to confirm this is the right NM-B connector and the right plastic bushing? Do I use the plastic bushing on top of the metal nut or in place of the metal nut? This connector is 1 1/4" size. There is a 1 1/2" but that is too big. There is also SE - Service Entry specific connectors but those have flat bottoms due to 2 conductors and I dont think appropriate for the 4 wire SER cable. It would be good if there was a chart somewhere that breaks down supported cable sizes (mine is 1.18" diameter) relative to the connectors, maybe there is but I couldnt find it.
That connector is okay. You do need to use the locking ring. I'm not aware that a bushing is required on a NM connector. The edges of the connector should be rounded and not sharp. You can use the bushing if it fits.
Sorry, I was mistaken and Pattenp is correct. A bushing is required for raceways but not for cables if the connector is rounded and not sharp. You can still use it though.
I have a question regarding neutral/ground lug addition to my main panel. This is an older Siemens panel with only neutral bus bars (both sides) which are bonded to the panel. There is a metal brace that connects left to right.
With that said, I need 2 lugs to connect the 1/0 AL neutral wire and #1 ground wire. All the siemens neutral kits I found online has the orientation of these lugs parallel to the bus bars. This obvious takes up tremendous space if I have to insert these big wires perpendicular to the regular orientation of how other neutral/ground wires go to these bus bars.
Are there different neutral/ground lug kits that dont have this problem? What is usually done in these cases/recommended approach?
The lug has tangs on the side that insert into the holes of the buss bar making the lug mounted on the side of the bar making the connection hole perpendicular to the bar. The tang spacing may not fit your bar. 7f8cd29e715b8bf1ad84fbc1471fa692.pdf (alliedelec.com)
The last one you posted has a plastic wire guide that comes with it.
I haven't read anything in this thread to believe you need anything close to 125 amps, but that's your decision. I would just go with a 100 amp breaker and appropriately sized feeder.
#2 is the one that came today, #1 is still days away. I bought both of them because I didnt know how small the small one is considering my neutral is 2/0.
I tried it on my panel and unfortunately it doesn't fit. My main panel (ITE Siemens) has its neutral screws far distant. In other words, distance between neutral screw holes is too much. The newer panels have their screw spacing much less. In fact, when I tried the neutral lug on my 125A Siemens sub panel, it fit like a glove. But you can see from the pictures that there is no way make these fit in the main panel.
What are my other options at this point? Why isn't there a simple cube like lug that you can orient in any way you want?
Do I need to buy a separate neutral/ground bus bar and mount it to the case? If I do this though, is the panel board considered a good bond and is okay to mount the neutral and ground wires on this new bar that will not be connected to the actual bus bars thats on the main panel?
Note : The first two pictures showing the neutral lug is on the new panel. I have attached these as reference to show how the screw spacing is different between new vs old panel.
Looking to mount a powerful LED indirect flood lamp in a boathouse. I would aim this up to the underside of the roof and attach it o a permanent box, fed by pvc conduit. The lamp is designed for hard mount using 1/2" threaded fittings. Asking if there is a smart way for ON/OFF, that doesn't require an additional box at a lower level. I can find only replacement pull chain switches, nothing I would call suitable for permanent wiring.
Same house I've had, built in 78, but the room in question was a former garage, professionally converted mid 80's, and a new garage forms the new back wall of the room (front of the garage). The construction was well done, and its only been that past few years that one outlet has been troublesome. Simply put, they dont get used.
[b]The problem[/b]: The plug in tester says Open Neutral (outlets B, C, D), and as I test backwards (upstream) to where the first drop in voltage is, I get 62v.
Power comes in on the right side here, into a GFCI outlet A (tests ok, volts 110), but that outlet does not feed downstream. It is fed off [b]spice S[/b] in the GFCI box[b]. [/b] 110v incoming at that splice and headed into the wall to outlet B and downstream.
12' away is [b]outlet B [/b]on an interior wall. 60v there. <-- [u]the problem[/u].
Outlets C, D have been removed from the circuit (for testing purposes) which are fed from stab connectors from outlet B.
It seems I am headed for drywall destruction to uncover any root cause of voltage drop. This building material (drywall, studs, etc) are not damaged in any way. It's beyond me how something could happen in the wall.
Perplexed, and poised with a hammer in hand.
[img]https://cimg2.ibsrv.net/gimg/www.doityourselft.com-vbulletin/661x339/open_05d41022429dfde31b979c1088ecfb6e25d44745.jpg[/img]
01-16-21, 12:31 PM
SER cable vs Conduit - Indoor subpanel ampacity/temperature questions
