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Old 01-28-2010, 11:32 AM   #1
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Chicago Conduit Rules


Chicago Conduit Rules

Summary: what is the max number of wires that can run in ½ and ¾ conduit in the City of Chicago. We wish to minimize impact on drywall and not drill holes for new conduit runs. I know rules here can be different; I’ve had a couple electricians come out and seem to be getting conflicting information. See details below.

Details: I live in the City of Chicago and my wife and I want to do some new lighting in our kitchen and living room (condo, less than 4 stories), plus add some circuits to isolate appliances (e.g. microwave is connected to ceiling light, etc.). We will be using a licensed electrician for the work and have already had two come out to provide quotes. I’m fairly handy around the house and know enough about electrical work to know that it’s best left to the pros. However, I like to double check methods / work / etc.

We want to add 4 new circuits. 3 will go into the kitchen and 1 in the living room. I believe all existing wiring is THHN, but not sure.

Kitchen: the conduit leading from the breaker box is ¾ inch rigid. This conduit has 3 hot 14AWG conductors and 2 14AWG neutrals (I believe the neutrals are 14AWG, might be 12). How many more conductors, if any, could we add to this conduit?

Living room: the conduit leading from the breaker box is ½ inch rigid. This conduit has 3 hot 14AWG and 2 14AWG neutrals (again, neutrals might be 12). We would like to add one 14AWG conductor to this conduit.

The feedback: one electrician told me we could likely NOT add any wire to the kitchen conduit (3/4 inch). Another one told me we could likely add a conductor to the living room conduit (1/2 inch). This seems contradictory to me. I don’t care who’s right (they both took just a brief look), I just want to know what’s the code compliant capacity of these conduits based on the existing conductors (after de-rating, etc.). If possible, I would like to use the existing conduit to run our new circuits to eliminate the need of tearing out drywall and running new pipe.

Bonus question: we have a ½ inch conduit running from the furnace near the breaker box to the thermostat next to the kitchen. The conduit carries only the low-voltage line from the thermostat to the furnace (I know it’s LV, because there is no j-box at the thermostat and the conduit is “open” at the furnace and the line runs out and wraps around the gas supply down to the furnace. This conduit would be perfect to run 2 (or 3) new circuits for the kitchen, since it runs into a crawl space next to the kitchen. However, my question is, is it okay to take the LV thermostat line out of the conduit and run it without conduit back to the furnace? Running the thermostat line without conduit could be easily done, since I ran a coax cable along the same path.

Any thoughts on these topics?

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Old 01-28-2010, 12:39 PM   #2
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Chicago Conduit Rules


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Originally Posted by Wrigleyville View Post
Chicago Conduit Rules

Summary: what is the max number of wires that can run in ½ and ¾ conduit in the City of Chicago. We wish to minimize impact on drywall and not drill holes for new conduit runs. I know rules here can be different; I’ve had a couple electricians come out and seem to be getting conflicting information. See details below.

That depends on the wire size you plan to pull and what wire is already in place. There is a table in the NEC that will give you a very good idea. You can read the NEC for free on the Internet.

NEC 2005, Table C.1 Maximum Number of Conductors or Fixture Wires in Electrical Metallic
Tubing (EMT) (Based on Table 1, Chapter 9)



Details: I live in the City of Chicago and my wife and I want to do some new lighting in our kitchen and living room (condo, less than 4 stories), plus add some circuits to isolate appliances (e.g. microwave is connected to ceiling light, etc.). We will be using a licensed electrician for the work and have already had two come out to provide quotes. I’m fairly handy around the house and know enough about electrical work to know that it’s best left to the pros. However, I like to double check methods / work / etc.

Good thinking.

We want to add 4 new circuits. 3 will go into the kitchen and 1 in the living room. I believe all existing wiring is THHN, but not sure.

Kitchen: the conduit leading from the breaker box is ¾ inch rigid. This conduit has 3 hot 14AWG conductors and 2 14AWG neutrals (I believe the neutrals are 14AWG, might be 12). How many more conductors, if any, could we add to this conduit?

It possible the conduit is ridged. But, I would put my money on it being EMT.

Living room: the conduit leading from the breaker box is ½ inch rigid. This conduit has 3 hot 14AWG and 2 14AWG neutrals (again, neutrals might be 12). We would like to add one 14AWG conductor to this conduit.

You have plenty room for another circuit. You could probably get 3 more circuits in that run if required. See the article on "conduit fill"above.

The feedback: one electrician told me we could likely NOT add any wire to the kitchen conduit (3/4 inch). Another one told me we could likely add a conductor to the living room conduit (1/2 inch). This seems contradictory to me. I don’t care who’s right (they both took just a brief look), I just want to know what’s the code compliant capacity of these conduits based on the existing conductors (after de-rating, etc.). If possible, I would like to use the existing conduit to run our new circuits to eliminate the need of tearing out drywall and running new pipe.

It depends on whats in the existing conduit. If the wire count does not exceed the NEC guidelines you can add as many as you like, but not to exceed the fill tables.
That is the beauty of conduit. You can add or remove wires as needed. In some cases you will need to run new conduit. If you have an attic or crawl space, you can limit the amount of drywall damage.



Bonus question: we have a ½ inch conduit running from the furnace near the breaker box to the thermostat next to the kitchen. The conduit carries only the low-voltage line from the thermostat to the furnace (I know it’s LV, because there is no j-box at the thermostat and the conduit is “open” at the furnace and the line runs out and wraps around the gas supply down to the furnace. This conduit would be perfect to run 2 (or 3) new circuits for the kitchen, since it runs into a crawl space next to the kitchen. However, my question is, is it okay to take the LV thermostat line out of the conduit and run it without conduit back to the furnace? Running the thermostat line without conduit could be easily done, since I ran a coax cable along the same path.

Common sense says you can run the low voltage cable without a conduit as long as it is not "Subject to Physical Damage". This should be discussed with the guy doing the job. After all, he is responsible for following the jurisdiction rules, not you. You could call the codes dept. and ask them your self if you like. Low voltage cables are not usually required to be in conduit. But who knows what they want in Chicago. To me its no different than a door bell circuit.

Any thoughts on these topics?
Please find the conduit fill tables in the online free NEC read only web page. This way you can determine how many wires and what size can be added.
Make sure the electrician gets a permit and has the job inspected. I have heard some real horror stories regarding Chicago.

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Old 01-28-2010, 01:50 PM   #3
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Chicago Conduit Rules


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Originally Posted by J. V. View Post
Please find the conduit fill tables in the online free NEC read only web page. This way you can determine how many wires and what size can be added.
Make sure the electrician gets a permit and has the job inspected. I have heard some real horror stories regarding Chicago.
I know for a fact (Spoke to many electricians hailing from Chicago) that in Chicago, no NM or BX (Armored cable) may be used. Everything must be in conduit. But I, too doubt if it's Rigid pipe. Unless the house is very old. I was told that a Double blade saw is used to insert the conduit on retrofits in Drywall. The reason for the ban on Armored Cable defies me. Here, in NYC, NM or exposed Armored Cable is illegal,too. But in neighboring Nassau County (Long Island), where there is a different AHJ, NM is permitted. Oh Yes. NM is permitted in NYC. Only for Temporary wiring in New Construction or Remodel!
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Old 01-28-2010, 01:54 PM   #4
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Originally Posted by spark plug View Post
I know for a fact (Spoke to many electricians hailing from Chicago) that in Chicago, no NM or BX (Armored cable) may be used. Everything must be in conduit. But I, too doubt if it's Rigid pipe. Unless the house is very old. I was told that a Double blade saw is used to insert the conduit on retrofits in Drywall. The reason for the ban on Armored Cable defies me. Here, in NYC, NM or exposed Armored Cable is illegal,too. But in neighboring Nassau County (Long Island), where there is a different AHJ, NM is permitted. Oh Yes. NM is permitted in NYC. Only for Temporary wiring in New Construction or Remodel!
This is an addendum to the previous post.; There could be some interesting situations where NYC and Nassau County border each other. For example, in the Far Rockaway section of Queens county, where, one side of the street has different rules than the other.
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Old 01-28-2010, 03:14 PM   #5
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Thanks to JV and Spark Plug for the helpful posts. Couple of follow up items:
- The condo is 1980 vintage.
- I’m sure you’re both right, my pipe is EMT. I was simply trying to designate between a fixed pipe versus flexible coming out of the breaker box. I really don’t know the difference between EMT and rigid (that’s for my electrician to figure out).
- I found the “Chicago” fill tables for conduit in the building codes, but they suggest something like 12 14AWG THHN in ½ inch and 22 14AWG THNN in ¾ inch max. That seems high to me, but I’ll just talk to the electrician about it. Looking at the holes in the breaker box, I couldn’t image cramming 12 wires into the ½ inch opening (or even the ¾ inch opening).
- FYI, Chicago code does allow for “Flexible metallic tubing” (18-27-349.4) and “Flexible metal conduit” (18-27-350.4), both electricians confirmed that. I don’t know how these differ from NM or BX. The code specifies that FMC can be used for “in existing walls, floors, ceilings, or partitions, where fishing is necessary.” I believe this code change happened around 1999/2000. I think new construction and remodels still require the fixed raceway (e.g. no flexible cable/conduit).
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Old 01-28-2010, 07:11 PM   #6
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Chicago Conduit Rules


try this site for allowable wire fill in conduit by NEC Code.
http://www.electrician2.com/calculat...alculator.html
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Old 01-28-2010, 07:49 PM   #7
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Chicago Conduit Rules


There are two tables you need to be aware of. One is fill table, how many wires will fit in a conduit. The other is derating. After nine wires you need to derate the amps they can carry. If you use MWBC (two hots share a neutral) then you have three wires for fill purposes but only two wires for derating purposes.

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