I am having a 'disagreement' with an Electrical Plan Reviewer about an installation that we are proposing for a new Acute Care Hospital.
We have proposed a design that collects a number of branch circuits feeding a series of rooms and these are feed from a 'local' junction box. Next we connect several of these 'local' junction boxes to a larger 'homerun' junction box. From the 'homerun' junction box to the panelboard we have a large 'bundled' group of conductors.
Our maximum homerun consists of 16#10, 1#10 Ground in a 1" conduit. This homerun is then split up into a series of smaller runs going to the 'local' junction boxes as noted above. These smaller feeds are limited to 4#12, 1#12 ground in a 3/4" conduit.
This is a construction method we have used before with no issues raised by the inspectors. However on this particular project, the reviewer says that the code "does not allow us to change wire sizes in the middle of a branch circuit". However, he hasn't been able to give us a Code reference for his decision.
Some particulars of the installation:
Code in effect is 2005 NEC.
Circuit breakers are 20A/1P and are listed and marked 60/75 Degree C.
Both the #10 and #12 conductors are protected by the 20A/1P breaker
Conductors are type THHN.
Neutrals are all considered to be current carrying conductors.
Conductor ampacity derating calculations are based on the 90 degree C column in Table 310.16.
We have addressed voltage drop to his satisfaction.
We have addressed the sizing of these 'oversized' junction boxes to his satisfaction.
His only comment is that "if you start out with #10 conductors you have to carry them through to the last device". Our position is that we provided the #10 conductors in the bundled homeruns to satisfy the derating requirement and then dropped back to #12 conductors when the fill no longer required the 50% derating.
In the 'sketch' below, [J] indicates a junction box and the conduit runs are noted with letters as follows:
A =12#10, 1#10 Ground, 1"C
B, C, D = 4#12, 1#12 Ground, 3/4" C
[J]
l
l
C
l
Homerun to Panel l
<-------------A---------[J]------B--------[J]
l
l
D
l
l
[J]
By the way, someone may question the value and constructability of this installation. We have a very large and experienced electrical contractor on our project in a Design Assist capacity. They have reviewed this design and totally support it from both a cost and construction point.
Is anyone aware of a Code requirement that we are missing or has anyone experienced this situation before?
We have proposed a design that collects a number of branch circuits feeding a series of rooms and these are feed from a 'local' junction box. Next we connect several of these 'local' junction boxes to a larger 'homerun' junction box. From the 'homerun' junction box to the panelboard we have a large 'bundled' group of conductors.
Our maximum homerun consists of 16#10, 1#10 Ground in a 1" conduit. This homerun is then split up into a series of smaller runs going to the 'local' junction boxes as noted above. These smaller feeds are limited to 4#12, 1#12 ground in a 3/4" conduit.
This is a construction method we have used before with no issues raised by the inspectors. However on this particular project, the reviewer says that the code "does not allow us to change wire sizes in the middle of a branch circuit". However, he hasn't been able to give us a Code reference for his decision.
Some particulars of the installation:
Code in effect is 2005 NEC.
Circuit breakers are 20A/1P and are listed and marked 60/75 Degree C.
Both the #10 and #12 conductors are protected by the 20A/1P breaker
Conductors are type THHN.
Neutrals are all considered to be current carrying conductors.
Conductor ampacity derating calculations are based on the 90 degree C column in Table 310.16.
We have addressed voltage drop to his satisfaction.
We have addressed the sizing of these 'oversized' junction boxes to his satisfaction.
His only comment is that "if you start out with #10 conductors you have to carry them through to the last device". Our position is that we provided the #10 conductors in the bundled homeruns to satisfy the derating requirement and then dropped back to #12 conductors when the fill no longer required the 50% derating.
In the 'sketch' below, [J] indicates a junction box and the conduit runs are noted with letters as follows:
A =12#10, 1#10 Ground, 1"C
B, C, D = 4#12, 1#12 Ground, 3/4" C
[J]
l
l
C
l
Homerun to Panel l
<-------------A---------[J]------B--------[J]
l
l
D
l
l
[J]
By the way, someone may question the value and constructability of this installation. We have a very large and experienced electrical contractor on our project in a Design Assist capacity. They have reviewed this design and totally support it from both a cost and construction point.
Is anyone aware of a Code requirement that we are missing or has anyone experienced this situation before?