SER cable

Status
Not open for further replies.
N

nizak

Senior Member
What size AL cable is required to feed a 100 amp sub panel?

This is a residential application.

I say 1/0, another electrician on site says he has always uses #1 and has never been turned down for it on an inspection.

Thanks.
 
It really depends on what code cycle you are under and whether or not the ser is rated 75C or 60C . Look at 338.10(B)(4). Another factor is whether or not the ser is powering the entire load of the dwelling

(4) Installation Methods for Branch Circuits and Feeders.
(a) Interior Installations. In addition to the provisions of
this article, Type SE service-entrance cable used for interior
wiring shall comply with the installation requirements of Part
II of Article 334, excluding 334.80.
Where installed in thermal insulation the ampacity shall be
in accordance with the 60°C (140°F) conductor temperature
rating. The maximum conductor temperature rating shall be
permitted to be used for ampacity adjustment and correction
purposes, if the final derated ampacity does not exceed that for
a 60°C (140°F) rated conductor
Click to expand...


This is from the 2014
310.15(B)(7) said:
(7) 120/240-Volt, Single-Phase Dwelling Services and
Feeders. For one-family dwellings and the individual
dwelling units of two-family and multifamily dwellings,
service and feeder conductors supplied by a single-phase,
120/240-volt system shall be permitted be sized in accordance
with 310.15(B)(7)(1) through (4).
(1) For a service rated 100 through 400 A, the service
conductors supplying the entire load associated with a
one-family dwelling, or the service conductors supplying
the entire load associated with an individual dwelling
unit in a two-family or multifamily dwelling, shall
be permitted to have an ampacity not less than 83 percent
of the service rating.
(2) For a feeder rated 100 through 400 A, the feeder conductors
supplying the entire load associated with a onefamily
dwelling, or the feeder conductors supplying the
entire load associated with an individual dwelling, unit
in a two-family or multifamily dwelling, shall be permitted
to have an ampacity not less than 83 percent of
the feeder rating.
(3) In no case shall a feeder for an individual dwelling unit
be required to have an ampacity greater than that specified
in 310.15(B)(7)(1) or (2).
(4) Grounded conductors shall be permitted to be sized
smaller than the ungrounded conductors, provided that
the requirements of 220.61 and 230.42 for service conductors
or the requirements of 215.2 and 220.61 for
feeder conductors are met.
Click to expand...
 
This application is not a service conductor or a feeder.
It is a sub panel being installed in a relatively large home. Loads supplied will be bathrooms, bedrooms, lighting, floor heat, general purpose receps, furnace, whirlpool tub, etc.
 
@75 degrees C #1 Al is rated for 100 amps, @65 degrees C Al is rated for 85 amps, next size up rule would be 90 amps. So as Dennis stated it depends on whether you use the 60 or 75 degree ampacity, a factor which is different under several code cycles.
 
infinity said:
@75 degrees C #1 Al is rated for 100 amps, @65 degrees C Al is rated for 85 amps, next size up rule would be 90 amps. So as Dennis stated it depends on whether you use the 60 or 75 degree ampacity, a factor which is different under several code cycles.
Click to expand...

Can you use the 75 column?, I know with romex we must use the 60 degrees column.
 
infinity said:
@75 degrees C #1 Al is rated for 100 amps, @65 degrees C Al is rated for 85 amps, next size up rule would be 90 amps. So as Dennis stated it depends on whether you use the 60 or 75 degree ampacity, a factor which is different under several code cycles.
Click to expand...

So what determines the temperature? The manufacturing of the wire or the lugs on the subpanel? Or something else?
 
jaylectricity said:
So what determines the temperature? The manufacturing of the wire or the lugs on the subpanel? Or something else?
Click to expand...
In this situation, it's pretty much the "something else" that being the restrictions of 338.10 which varies depending on the specifics of the install and the Code cycle as mentioned.
The manner in which it is addressed varies between the '05,08,11 and '14 Codes.
In certain situations you are required to terminate at the 60° rating.
 
Fairly new around here and to the electrical trade but the company I am with uses 2-2-2-4 SER to feed 100A sub panels in houses. I have always wondered if that was right but it passes inspection every time
 
augie47 said:
In this situation, it's pretty much the "something else" that being the restrictions of 338.10 which varies depending on the specifics of the install and the Code cycle as mentioned.
The manner in which it is addressed varies between the '05,08,11 and '14 Codes.
In certain situations you are required to terminate at the 60° rating.
Click to expand...
And the number of SER failures under any of these code cycles and the ones before them is?.....?.....?....
 
jhawkbb said:
Fairly new around here and to the electrical trade but the company I am with uses 2-2-2-4 SER to feed 100A sub panels in houses. I have always wondered if that was right but it passes inspection every time
Click to expand...

It may be compliant if that subpanels has the entire load of the dwelling. For instance, if you have a 200 amp service and panel that feeds the subppanel as well as other loads then the #2 is not compliant.
 
Dennis Alwon said:
It may be compliant if that subpanels has the entire load of the dwelling. For instance, if you have a 200 amp service and panel that feeds the subppanel as well as other loads then the #2 is not compliant.
Click to expand...

Ok so I have two examples:

#1) 200A underground service to meter. Went out the back of the meter to a 200A garage panel. Panel in garage has the circuits for the upstairs of the house as well as a 100A breaker with 2-2-2-4 SER going to a 100A panel in basement where the downstairs circuits go. This example would be non compliant?

#2) 200A overhead service to meter on a shed with a raintight 200A feed thru panel. 100A breaker with 2-2-2-4 SER out the back to a 100A panel for the shed then we fed the 200A house panel from the feed thru of the raintight panel. This is a situation where the SER was sized properly because the shed panel will serve the whole load of the shed?
 
jhawkbb said:
Ok so I have two examples:

#1) 200A underground service to meter. Went out the back of the meter to a 200A garage panel. Panel in garage has the circuits for the upstairs of the house as well as a 100A breaker with 2-2-2-4 SER going to a 100A panel in basement where the downstairs circuits go. This example would be non compliant?
Click to expand...
Violation. Should be a 90A breaker max.
#2) 200A overhead service to meter on a shed with a raintight 200A feed thru panel. 100A breaker with 2-2-2-4 SER out the back to a 100A panel for the shed then we fed the 200A house panel from the feed thru of the raintight panel. This is a situation where the SER was sized properly because the shed panel will serve the whole load of the shed?
Click to expand...
Violation. 310.15(B)(7) is limited to dwelling units. 90A breaker again.
 
Or, depending on the Code cycle and the AHJ, even a 80 amp breaker.
In neither case are you "serving all loads that are associated with the dwelling unit" (a shed is not a dwelling unit albeit occasionally used as one in my area) so the 100 amp rating in 310.15(B)(7)- '11 is not valid.
The installs you describe may well fall under the 60° 338.10 rule where the #2 SE could have a 75 amp rating (if installed in insulation) thus limiting your OCP to the next standard size. 80 amp.
As ActionDave notes, 90 amp breaker at best, possibly an 80.
 
Last edited:
Status
Not open for further replies.
Top