SE cable installed indoors and insullation

Status
Not open for further replies.

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?
SE cannot be used more than a short distance inside if it is being used as a service conductors (upstream of the service disconnect/OCPD.)
Are you talking about a feeder that carries the whole dwelling load?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?

The 2014 requires that the feeder be sized at 83% of the entire load. According to the IN No. 1: adjustment factors would apply if the wiring method required it, such as SE cable within insulation.

Informational Note No. 1: The conductor ampacity may
require other correction or adjustment factors applicable to
the conductor installation.
 

Cletis

Senior Member
Location
OH
The 2014 requires that the feeder be sized at 83% of the entire load. According to the IN No. 1: adjustment factors would apply if the wiring method required it, such as SE cable within insulation.

Isn't that if it's over 12" of insulation ? Which would not be the case if just passing from outside to inside, in most cases .
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?

I think you are asking....can 310.15(B)(7) apply even if the SE Cable runs through an insulated wall from the exterior meter enclosure to the service equipment. If that is your question then yes, and as others have said all adjustments and corrections will apply.

FYI- 310.15(A)(2)Ex. can be applied to se cable even if some will disagree.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Isn't that if it's over 12" of insulation ? Which would not be the case if just passing from outside to inside, in most cases .


If you apply the exception that MTN mentioned then your overall SE cable conductor length would need to be 10' for the 12" embedded in insulation.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?

I believe the op is talking about ser. My guess anyway-- The answer may be yes and it may be no depending on which code cycle you are under. Generally thru insulation you need to use the 60C rating so it would not work, however it depends also on the length of the run and how much cble is in insulation. Look at 310.15(A)(2)
 

kwired

Electron manager
Location
NE Nebraska
OP only mentioned SE cable - this would include both SEU and SER unless he specifies otherwise.

Before 2014 NEC 310.15(B)(7) did not have any requirement to make ampacity adjustments, just select conductor size and go with it no matter what other adjustments may be otherwise required in other situations. With 2014 they did away with the table and went with the 83% ampacity otherwise required but the catch is you must also apply ampacity adjustments like you would any other conductor.

I think this is somewhat a bigger issue for conductors that may be on a rooftop where ambient temp can make a big difference in adjustment values. Otherwise most other instances you end up with same conductor size you did before 2014.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
OP only mentioned SE cable - this would include both SEU and SER unless he specifies otherwise.

Before 2014 NEC 310.15(B)(7) did not have any requirement to make ampacity adjustments, just select conductor size and go with it no matter what other adjustments may be otherwise required in other situations. With 2014 they did away with the table and went with the 83% ampacity otherwise required but the catch is you must also apply ampacity adjustments like you would any other conductor.

I think this is somewhat a bigger issue for conductors that may be on a rooftop where ambient temp can make a big difference in adjustment values. Otherwise most other instances you end up with same conductor size you did before 2014.

Actually I would argue that NEC 310.15(B)(7) did not have to make any mention about the adjustments and corrections because 310.15 already had that covered. I believe it was the notion that corrections and adjustments did not apply in which spawned the removal of the table along with attempting to simplify the idea of a "main power feeder".

We all know that an elevated ambient temperature does affect the ampacity of a conductor so to be honest with you I believe (I honestly do) that 310.15(B)(2) always applied and 310.15(B)(7) did not need to make mention of it. But so many people thought the table was a CATCH ALL that it was part of the debate to push for the change.

Just my thoughts on it...:D
 

kwired

Electron manager
Location
NE Nebraska
Actually I would argue that NEC 310.15(B)(7) did not have to make any mention about the adjustments and corrections because 310.15 already had that covered. I believe it was the notion that corrections and adjustments did not apply in which spawned the removal of the table along with attempting to simplify the idea of a "main power feeder".

We all know that an elevated ambient temperature does affect the ampacity of a conductor so to be honest with you I believe (I honestly do) that 310.15(B)(2) always applied and 310.15(B)(7) did not need to make mention of it. But so many people thought the table was a CATCH ALL that it was part of the debate to push for the change.

Just my thoughts on it...:D
So before the change how do you go about ampacity adjustments? all you had was a table that told you overcurrent protection level and a corresponding copper or aluminum cable that was acceptable to use at that overcurrent protection level, you were not in any way determining conductor ampacity, you didn't even need to consider conductor insulation rating, it was a same size fits all kind of situation, all that was different was they did recognize different sizes depending on if you used copper or aluminum.

Now you do exactly what you would do when sizing any other conductor. When you come up with a final ampacity you can just adjust it one more time to 83%.

Example: with 100 amp overcurrent device, ambient temp of 140F, 90C insulation, for some reason we have 4-6 current carrying conductors in the raceway supplying a feeder or service that complies with 310.15(B)(7) requirements allowing reduced conductor size-

Before 2014: Look at table, 4 AWG copper or 2 AWG aluminum is the size - no adjustments needed, don't care what temp rating of terminations are, don't care what temp rating of conductor insulation is, don't care if high ambient, or if more then 3 current carrying conductors are in raceway for some reason.

After 2011: conductor minimum ampacity needs to be 100 x 83% so we need a conductor sized like we normally size any other conductor and it needs to have final ampacity of at least 83. So we go with 83 x 1.25 (recriprocal of .8) adjustment for number of conductors in raceway and x 1.41 (recriprocal of .71) for ambient temp correction adjustment.

This leaves us with needing 146 amp conductor @ 90C for insulation - we still need a bare minimum of 83 amps for termination temp likely at 75C.

75C termination could require as little as 4 copper or 2 aluminum which is all the old method went by to come up with values in the old chart.

But after adjustments we need 90C conductor that is greater or equal to 146 - 1/0 copper or 2/0 aluminum. This is larger of two values and is minimum size needed for the application.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
I would argue (and not sure why I am) that when you selected 4/0 AL from 310.15(B)(7) that you treated the internal conductors as you would in NM-B and use the 90 degree value as given in 310.15(B)(16) and then made the adjustment. The application without the table is no different in my opinion.

In the 2011 NEC you can choose your conductor (if applicable) per 310.15(B)(7) and then if you had to apply any adjustments or corrections as specified in 310.15(B) then you would do so accordingly. The size from the chart to me was just a starting point. I actually sat in on the discussions regarding this at the ROC in Redondo Beach, CA and I never got the sense that they did not feel 310.15(B) applied. That was part of the reasons for the change to make sure the message was clear that it did apply.

Prior to 2014, I would have selected an applicable conductor per 310.15(B)(7) and if any of the conditions in 310.15 apply I would then have to go to the relevant ampacity value in 310.15(B)(16) and do it just like any other cable would. I just now that thermal dynamics are going to take place and blindly choosing a CATCH ALL was not the intent.

But again.....we can agree to disagree...I'm ok with that as I am quite happy with how the 2014 NEC made it clear.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
IMO the old Table 310.15(B)(7) did not make prevision for ampacity adjustment. Common sense did but the NEC did not.
 

kwired

Electron manager
Location
NE Nebraska
I would argue (and not sure why I am) that when you selected 4/0 AL from 310.15(B)(7) that you treated the internal conductors as you would in NM-B and use the 90 degree value as given in 310.15(B)(16) and then made the adjustment. The application without the table is no different in my opinion.

In the 2011 NEC you can choose your conductor (if applicable) per 310.15(B)(7) and then if you had to apply any adjustments or corrections as specified in 310.15(B) then you would do so accordingly. The size from the chart to me was just a starting point. I actually sat in on the discussions regarding this at the ROC in Redondo Beach, CA and I never got the sense that they did not feel 310.15(B) applied. That was part of the reasons for the change to make sure the message was clear that it did apply.

Prior to 2014, I would have selected an applicable conductor per 310.15(B)(7) and if any of the conditions in 310.15 apply I would then have to go to the relevant ampacity value in 310.15(B)(16) and do it just like any other cable would. I just now that thermal dynamics are going to take place and blindly choosing a CATCH ALL was not the intent.

But again.....we can agree to disagree...I'm ok with that as I am quite happy with how the 2014 NEC made it clear.

Please tell me how you would have made adjustments to the conductors in my example a couple posts back prior to the 2014 NEC.

from (B)(7) in 2011: "For individual dwelling units of onefamily,two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(7), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor."

It never mentions ampacity at all, it just says in different words "these size conductors are permitted to supply the entire dwelling load if the service or feeder rating is XXX according to the table".

For 100 amp example it does not in any way indicate that 4 AWG is considered a 100 amp conductor it just says 4 AWG is permitted to be used if all conditions that apply to (B)(7) are met.

It also isn't now saying that a 4 AWG is a 83 amp conductor, it is saying that if you are running a 100 amp circuit (that meets (B)(7) requirements of course) you can assume for conductor sizing purposes you need an 83 amp conductor.
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
Prior to 2014, I would have selected an applicable conductor per 310.15(B)(7) and if any of the conditions in 310.15 apply I would then have to go to the relevant ampacity value in 310.15(B)(16) and do it just like any other cable would. I just now that thermal dynamics are going to take place and blindly choosing a CATCH ALL was not the intent.

Reading that again I guess you maybe answered my question, but I think doing that basically eliminates any reduction of conductor size that is permitted by (B)(7) and is pointless to even look at (B)(7) if you know you will have adjustments to make - you end up with same size conductor as you would if (B)(7) never existed.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
As Dennis can confirm, I had a terrible time with 310.15(B)(6) vs 338.10 in the '08 & '11.
Now '14 has "straightened all that out"... except in my feeble mind...
No doubt this is what you guys have been discussing, but I got lost in the maze.

Help clarify for me... before I have to start enforcing '14...
Some specific questions......:

310.15(B)(7) ('14) allows us to apply a 83% factor to the "service ampere rating".
From that wording, I assume that is 83% of the OCP size not the computed load.
Correct ?

'14 references this to "service and feeder conductors" (Note: I am looking at a '14 Draft..hopefully there were no significant changes in the final publication)
There is no mention of "whole house feeders", so can the 83% be applied to ANY feeder or only "whole house" feeders ?

So, on a 200 amp service we need a conductor with a 166 amp ampacity . That ampacity would be the computed ampacity after any adjustment factors from 310.15(B)(2) correct ?

In the case of SE (SER) cable in insulation, 338.10 would still limit us the 60? ampacity after all is said and done (ignoring 310.15(A)(2) for discussions sake)
Correct ?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
If you want a 200 amp conductor then you need to take 200 amps and multiply it times 83%-- 166 amps. Now you need a conductor rated 166 amps after all ampacity adjustments are made.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
In the case of SE (SER) cable in insulation, 338.10 would still limit us the 60? ampacity after all is said and done (ignoring 310.15(A)(2) for discussions sake)
Correct ?

That is correct. If the ser is in insulation then you would need to use 60C ampacity. So for a ser alum feeder that is doing the entire load of the dwelling at 200 amps and run thru insulation, then we need to look at 310.15(B)(16) at 60? C . For this install we would need a 250 KCM cable (170 amps) because that is higher than 83% of 200 amps. 4/0 would only be good for 150 amps.

Also take note that they finally did away with 215(A)(4) which caused all that controversy. So now there is no question that the service conductors could be 4/0 but the feeder may have to be 250 KCM.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
As Dennis can confirm, I had a terrible time with 310.15(B)(6) vs 338.10 in the '08 & '11.


Well actual you had the right thought on it all and your thinking on it is what the 2014 is now saying. The problem was in the past the wording wasn't there to support what you and many of us assumed would be what they meant. Now there is no question IMO
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Well actual you had the right thought on it all and your thinking on it is what the 2014 is now saying. The problem was in the past the wording wasn't there to support what you and many of us assumed would be what they meant. Now there is no question IMO

I hate to fight that battle again. :D
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
IMO the old Table 310.15(B)(7) did not make prevision for ampacity adjustment. Common sense did but the NEC did not.

Dennis..now you know I am going to disagree here with this statement.

Firstly, in the 2014 NEC the mention to Adjustments and Corrections is referenced in an "informational note" and is not applicable to the NEC. Second, since it is an information note which is just giving direction, the lack of such a note in the 2011 NEC has no less of an impact.

We all know that if you place a conductor in an elevated ambient location or have more than 3 CCC's bundled together (in the case of a feeder, in a multifamily dwelling were 310.15(B)(7)(2) complies) then you have to make adjustments or corrections where applicable....the thermal dynamic principles did not just APPEAR in the 2014 NEC. In fact, nothing in 310.15(B)(6) or when changed to (B)(7) excluded the requirements of those thermal dynamics in 310.15(B). If it did not exclude them then they MUST apply.

So we can argue the intent all day, but it is clear that in the 2014 NEC, section 310.15(B)(7) the only mention to these dynamics are in an information note which means that the CMP-6 was saying "Hey code users, Thermal Dynamics do apply here" and so it is not something new in the 2014 NEC, the informational not is new just as a guide post telling you to be aware.

So it is not really a "common sense" issue, it was a code issue that 310.15(B) and it's various requirements do apply.

Personally they could have achieved the same thing by placing the 2014 NEC, 310.15(B)(7) Informational Note #1 as just a "note" to the old table and served the same purpose but alas...they table is gone and it should stay gone in my opinion.
 
Status
Not open for further replies.
Top