#4 AL OCP

[Sberry]

The customer replaced the house panel with a larger panel with 125A bus 3 years ago during a remodel, re-using the existing #4AL feeder.

That makes the alum wire bad?

 

[GarwoodV6]

I've only ran across a few houses with aluminum wiring in branch circuits, and they all had problems. I avoid aluminum like the plague.

 

[Sberry]

Branches are different. Often highly cyclical loading at larger currents, take kitchen counter circuits. Used to be they could be served by a 15A general, they were overloaded regardless of the wire,,, the alum didnt help and was not as forgiving of sloppy workmanship.

 

[GarwoodV6]

Sberry, I suppose not. Call me paranoid; I just have very little experience when it comes to using Al conductors. I just want to get the aluminum ampacity and OCP limits down pat for when I do run across it.

 

[Sberry]

Seems like we keep reaching to specific scenarios to jump to a general conclusion.

 

[GarwoodV6]

And yes, this is a feeder. And it appears now that it is definitely safe to put #4AL on a 60A CB.
I remember the spiral wrapped stranded neutral and assume that that ID's it as SE cable. Am I wrong to assume this? The wire is from 1974.

Has AL SE cable always been rated at 75* C?

 

[curt swartz]

And yes, this is a feeder. And it appears now that it is definitely safe to put #4AL on a 60A CB.
I remember the spiral wrapped stranded neutral and assume that that ID's it as SE cable. Am I wrong to assume this? The wire is from 1974.

Has AL SE cable always been rated at 75* C?

Sounds like SEU cable. If that is the case your feeder is only 3 wires (2-insulated and 1- bare) The cable needs to be replaced with a 4 wire cable.

 

[GarwoodV6]

I did commercial electrical construction for 30 years so conductor insulation temp ratings, conduit fill de-rating, etc. is nothing new to me... for copper.

Aluminum wiring in residential applications is unfamiliar territory for me.

I take this case as a teaching moment about AL residential wiring practices for future cases, and to overcome my nervousness about AL wiring in smaller (less than 100A) circuits.

In this specific case, the homeowner really does need to upgrade the house panel feeder, especially with all the add-ons to the house.

 

[GarwoodV6]

Sounds like SEU cable. If that is the case your feeder is only 3 wires (2-insulated and 1- bare) The cable needs to be replaced with a 4 wire cable.

Yes it is 3-wire, which never should've been used in this application. (Residential electricians in 1974). I told the homeowner that It needs to be 4 wire when the main panel was replaced last fall, and that it needs to have the neutrals isolated from the grounds on a separate ground bar at the sub-panel.

 

[GarwoodV6]

The 70A question came up when it came to feeders smaller than 100A in residential applications, and the old rule about treating them as if they are only rated to 60* C regardless of the actual insulation rating on the wire type used. SE cable is rated for 75*C applications, but if I understand what I've read, NEC doesn't allow it to be on a 70A breaker... that's what I'm seeking clarification on.
Sometimes the deeper you dive into the NEC, the more confusing it becomes.

 

[Tulsa Electrician]

Addressing your direct question. Assuming the #4 AL SE has 75° conductors and the terminations are rated 75° (both highly likely siktuationsP), the cable can be used at it's 75° ampacity of 65 amps and, if the actual load does not exceed 75 amps, it can be protected by a 70 amp breaker (assuming the panel buss in rated that high)

Did you mean 65 amps?

 

[letgomywago]

The 70A question came up when it came to feeders smaller than 100A in residential applications, and the old rule about treating them as if they are only rated to 60* C regardless of the actual insulation rating on the wire type used. SE cable is rated for 75*C applications, but if I understand what I've read, NEC doesn't allow it to be on a 70A breaker... that's what I'm seeking clarification on.
Sometimes the deeper you dive into the NEC, the more confusing it becomes.

When the terminations are not written down you need to assume 60° till 100 amps. Is this what you're thinking about? If so almost all breakers and modern panels have 75° rated and identified lugs.

 

[augie47]

Did you mean 65 amps?

yes//typo

 

[GarwoodV6]

When the terminations are not written down you need to assume 60° till 100 amps. Is this what you're thinking about? If so almost all breakers and modern panels have 75° rated and identified lugs.

No, I know about the terminations and these all are 75*C... SE cable ampacity rating as a residential sub-panel feeder is the question: is it limited to 60* ampacity in this case even though the SE cable insulation is rated higher? Much of the posts I have read here indicate SE is treated thr same as NM-B at 60* C rating only

The run in this case is through the garage attic, breezeway, house attic, and down into an interior wall in the laundry room. Apparently the code has been modified beginning in 2008, going back & forth several times on this. Trying to sort through all the nuances and contradictions in the Code has given me headaches and doubts as to whether or not the 75* ampacity column applies to SE in this case.

 

[tom baker]

Yes code has gone back and forth

 

[letgomywago]

No, I know about the terminations and these all are 75*C... SE cable ampacity rating as a residential sub-panel feeder is the question: is it limited to 60* ampacity in this case even though the SE cable insulation is rated higher? Much of the posts I have read here indicate SE is treated thr same as NM-B at 60* C rating only

The run in this case is through the garage attic, breezeway, house attic, and down into an interior wall in the laundry room. Apparently the code has been modified beginning in 2008, going back & forth several times on this. Trying to sort through all the nuances and contradictions in the Code has given me headaches and doubts as to whether or not the 75* ampacity column applies to SE in this case.

2017 2020 and 2023 say if it's bigger than 10awg you're good with 75° so long as the conditions allowing it are followed

 

[GarwoodV6]

2017 2020 and 2023 say if it's bigger than 10awg you're good with 75° so long as the conditions allowing it are followed

Thanks! That makes sense.
Now- does that apply to NM-B larger than 10awg?
What about original NM? I was taught that it was only rated to 60* regardless of awg size.

 

[letgomywago]

Thanks! That makes sense.
Now- does that apply to NM-B larger than 10awg?
What about original NM? I was taught that it was only rated to 60* regardless of awg size.

Nmb is always 60 for ampacity but 90 for derating purposes. This is no matter the size or conditions.

 

[GarwoodV6]

2017 2020 and 2023 say if it's bigger than 10awg you're good with 75° so long as the conditions allowing it are followed

Thanks for the confirmation.
Now I know that I can size SE cable off the 75* column after derating for distance & ambient temperature, and terminal & eqpt. rating.
So that means this 4awg AL SE can be protected by a 60A breaker without falling into the "upsize OCP" category from 55A 60*C rating.

I'm still pressing the owner to replace this feeder to 100A. He has added a lot of additional loads to the house panel over the years, and this will will also get the grounds and neutrals split out like they should be.

 

[GarwoodV6]

Nmb is always 60 for ampacity but 90 for derating purposes. This is no matter the size or conditions.

That explains why SE is often seen on residential HVAC & large appliances. It allows smaller wire than NM provided the lugs and eqpt are rated at 75*C and ambient temp derating is in line.