Branch Circuit Installation Methods

[enginoak]

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?

 

[petersonra]

In general, I can't see any prohibition with what you are planning.

But I have no experience with hospitals. maybe there are special requirements there.

 

[76nemo]

Never heard that one before. Ask him about running #2 all the way to the devices due to voltage drop. Throw him a 20 recep and some #2 and ask him to terminate it.

As petersonra stated it's hard to say what "they" call for, it's "THEIR" call, I guess:roll:

 

[infinity]

Our maximum homerun consists of 16#10, 1#10 Ground in a 1" conduit.

What you're proposing is fine. However if this is 17-#10 THHN conductors in a 1" EMT then you have a raceway fill problem.

 

[enginoak]

Small Clarification

Small Clarification

Once I saw the little 'sketch' on the posting, it doesn't look like the one on my screen before I posted it.

To clarify, the two junctions boxes all the way to the left (fed by C and D) should actually be moved to the right so that they terminate at the junction box shown to the right of A. Sorry for the confusion!

 

[enginoak]

You are correct, that was my typo, the maximum is 15#10 current carrying conductors with 1#10 ground in a 1" conduit. Thanks

 

[Mulrooney]

your reviewer is wrong. keep asking for that specific code reference

 

[Cow]

Seems like kind of a weird installation practice to me?

Why wouldn't you just run a couple of 3/4's instead and save yourself from buying two different size wires plus the time it takes to splice them. Just seems like one more unnecessary splice......

How much are you really saving doing this?

 

[mcclary's electrical]

Seems like kind of a weird installation practice to me?

Why wouldn't you just run a couple of 3/4's instead and save yourself from buying two different size wires plus the time it takes to splice them. Just seems like one more unnecessary splice......

How much are you really saving doing this?

Very good point, but that's not his question,

I don't see anything wrong with the plan, and he won't find a section to cite that says you can't change wire sizes in the middle of a run, since it's a very common thing to do with lighting and long runs, as you get to the closer and closer to the end of the run, the wire gets smaller and smaller.

 

[BJ Conner]

Hospital Ckts

Hospital Ckts

I agree with the reviewer. Why complicate things? If I see a # 10 wire at the panel I want to see it at the device. I may see a short # 12 jumper at the receptical but I want to see a # 10 if thats what I saw at the panel.
I have worked on projects where we modified existing hospital rooms, it can be hard enough when people didn't try to complicate things.
If in two years you had to add a new circuit to each room how would you do it? If somebody else had to modify the what's he/she going to say about what they find? At any given time there's at least one crew of electricans working at one of the three hospitals around here.
Remember the KISS principle.

 

[zbang]

I agree with the reviewer. Why complicate things?

Doesn't matter, that's a design question, not code compliance (sort of like "I like to see it like this..."). You could go 8g off a 20a breaker, splice that to 5 feet of 1/0, splice back onto some 12g into a receptacle and it would be OK. Silly, but OK.

 

[enginoak]

Reply to COW Re: The Cost Savings

Reply to COW Re: The Cost Savings

The Electrical Contractor has quoted a $1.2 million savings to implement this method! This is a significant saving to our project.

 

[mcclary's electrical]

I agree with the reviewer. Why complicate things? If I see a # 10 wire at the panel I want to see it at the device. I may see a short # 12 jumper at the receptical but I want to see a # 10 if thats what I saw at the panel.
I have worked on projects where we modified existing hospital rooms, it can be hard enough when people didn't try to complicate things.
If in two years you had to add a new circuit to each room how would you do it? If somebody else had to modify the what's he/she going to say about what they find? At any given time there's at least one crew of electricans working at one of the three hospitals around here.
Remember the KISS principle.

It's nice to offer you opinion, but that's not what the op is looking for, and it doesn't quite matter what you'd "want to see"

 

[mcclary's electrical]

Doesn't matter, that's a design question, not code compliance (sort of like "I like to see it like this..."). You could go 8g off a 20a breaker, splice that to 5 feet of 1/0, splice back onto some 12g into a receptacle and it would be OK. Silly, but OK.

I agree

 

[BJ Conner]

It's nice to offer you opinion, but that's not what the op is looking for, and it doesn't quite matter what you'd "want to see"

His original entry said something about arguing with a plans examiner. Plans examiners can have opinions and usually do.
He gets my opinion just to illistrate how a plans examiner may be thinking. To bad but that life.
The Code is not a design tool.
I have done enough hospital work ( design -new and upgrades and construction) to know what owners and maintenance like. I talk to them before I start.
A design that meets code requirements can still be a piece of C _ _ _. I know of designers who didn't get invited back to bid on more work and couldn't understand why. Their first job was code compliant.
The best way to argue with any plans examiner or (inspector) is open the book to the part that shows you right , throw it on his desk and start yelling. You may win the battle but you loose the war.
What's your reaction when you take the cover off a box and it looks like a nest of snakes with 30 wire nuts thrown it? "Good work work, meets code requirements"?

 

[mcclary's electrical]

His original entry said something about arguing with a plans examiner. Plans examiners can have opinions and usually do.
He gets my opinion just to illistrate how a plans examiner may be thinking. To bad but that life.
The Code is not a design tool.
I have done enough hospital work ( design -new and upgrades and construction) to know what owners and maintenance like. I talk to them before I start.
A design that meets code requirements can still be a piece of C _ _ _. I know of designers who didn't get invited back to bid on more work and couldn't understand why. Their first job was code compliant.
The best way to argue with any plans examiner or (inspector) is open the book to the part that shows you right , throw it on his desk and start yelling. You may win the battle but you loose the war.
What's your reaction when you take the cover off a box and it looks like a nest of snakes with 30 wire nuts thrown it? "Good work work, meets code requirements"?

I don't think what the op is describing compares to snakes and wirenuts.

 

[Mgraw]

Personally I would not put 16 #10s in a 1" pipe as the OP stated but that is not the question. If the Electrical Plan Reviewer is from the permit office then I would say his only function is to determine if the plan is code compliant. It is. What else is there to debate?