Amount of THNN wire in conduit

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torch0395

Member
Location
New York
Occupation
Pool technician
I started my electrical learning journey in pools where the main way of powering everything is through non metallic flexible pvc conduit or non metallic rigid pvc conduit with THHN wires. I was planning on wiring a subpanel where I need to pull 6 gauge THHN wires and am seeing a bunch of different charts on maxiumum number of wire gauge in conduit.

Does this apply to wires pulled separate in a conduit as I’ve always done?
 

tom baker

First Chief Moderator
Staff member
Wire fill limits always applies. Fill limit is based on number of wires that will fit, typically 40% cross sectional area of conduit, and derating ampacity over 3 wires due to heat dissipation.
Its a lot more than we can cover here. Go to mikeholt.com see if he has a video on this, or get a copy of his understanding the nec.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Most of the time it will be hard to put more wires in a conduit than is allowed. It can be done if you really try, but it is usually not worth the effort.

The code has some charts and tables that will tell you what you are allowed to do as far as how many wires can go in a conduit.

Just curious, are you a licensed electrician as well as being a pool technician?
 

Carultch

Senior Member
Location
Massachusetts
I started my electrical learning journey in pools where the main way of powering everything is through non metallic flexible pvc conduit or non metallic rigid pvc conduit with THHN wires. I was planning on wiring a subpanel where I need to pull 6 gauge THHN wires and am seeing a bunch of different charts on maxiumum number of wire gauge in conduit.

Does this apply to wires pulled separate in a conduit as I’ve always done?

The conduit fill tables give you the same information as if you did an area fill calculation. I.e. if you set up a spreadsheet with wire diameters and conduit diameters, that allows you to enumerate the area of the mix of wires within the conduit interior. The fill limits apply, regardless of what pulling mechanics and sequence of operation, you use for installation. The only time it doesn't apply, is if you are taking credit for the 60% nipple fill, for 2 ft and less lengths.

It represents about 75% diametral fill, which translates to a 40% area fill for 3 or more conductors. Since there is a 100% packing factor for a single wire, a single wire gets a 53% fill percentage. Two wires is a special case that requires a 31% fill limit, because two circles are inherently inefficient at packing in a circle. Diametral fill means if you pack the wires wall-to-wall, and draw a virtual circle around them. The ratio of that virtual circle's diameter to the inner raceway diameter, is what I'm calling "diametral fill".

The inner diameters of the various conduit types in any given trade size will vary slightly, so you may on occasion, get different answers for the maximum wires in different conduit types of the same trade size. IMC is the one with the largest interior diameter, while PVC schedule 80 is has the smallest interior diameter. If multiple conduit types are within any given run, the tightest conduit governs.
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
I started my electrical learning journey in pools where the main way of powering everything is through non metallic flexible pvc conduit or non metallic rigid pvc conduit with THHN wires. I was planning on wiring a subpanel where I need to pull 6 gauge THHN wires and am seeing a bunch of different charts on maxiumum number of wire gauge in conduit.

Does this apply to wires pulled separate in a conduit as I’ve always done?
Depends on the type of raceway, the wire size, and the number of wires.

Chapter 9 - C Tables work wonders if the wires are all the same size. Otherwise, you gotta find the area of each individual wire, add it up, and ensure it's not more than 40% (in most cases) of the internal area of the raceway.

More complicated than this, but essentially Chapter 9 - C Tables if all the same size, otherwise get out your calculator, lol.
 

torch0395

Member
Location
New York
Occupation
Pool technician
Most of the time it will be hard to put more wires in a conduit than is allowed. It can be done if you really try, but it is usually not worth the effort.

The code has some charts and tables that will tell you what you are allowed to do as far as how many wires can go in a conduit.

Just curious, are you a licensed electrician as well as being a pool technician?

its a gray area. We are not allowed to do “new” installs but you can work under another electricians license sometimes.

But we are allowed to replace and wire existing system setups.

But everyone in our industry does “new” installs all the time.

And pool electricians are generally awful and nobody wants to do the work. If you are in our industry you would understand the challenge.
 

torch0395

Member
Location
New York
Occupation
Pool technician
Most of the time it will be hard to put more wires in a conduit than is allowed. It can be done if you really try, but it is usually not worth the effort.

The code has some charts and tables that will tell you what you are allowed to do as far as how many wires can go in a conduit.

Just curious, are you a licensed electrician as well as being a pool technician?

here are the 4 (#6 awg) wires in 3/4” conduit it is only a 1-2 foot run to a 50 amp subpanel. Some charts I saw didn’t allow this but I think they have more than enough room to “breathe”.
 

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tom baker

First Chief Moderator
Staff member
here are the 4 (#6 awg) wires in 3/4” conduit it is only a 1-2 foot run to a 50 amp subpanel. Some charts I saw didn’t allow this but I think they have more than enough room to “breathe”.
Respectfully, its not what you think, but what the NEC allows. Wire fill tables have been in the NEC for a long time and are based on research. Knowing how to calculate wire fill and derating is basic to being an electrician. Mike Holt has material on this subject, he may have some You Tube video's.
 

torch0395

Member
Location
New York
Occupation
Pool technician
Respectfully, its not what you think, but what the NEC allows. Wire fill tables have been in the NEC for a long time and are based on research. Knowing how to calculate wire fill and derating is basic to being an electrician. Mike Holt has material on this subject, he may have some You Tube video's.

All the calculators I found didn’t include flexible liquid tight which is what I’m using above. But the calculator posted actually has it as an input which is great.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Just curious, are you a licensed electrician as well as being a pool technician?

its a gray area. We are not allowed to do “new” installs but you can work under another electricians license sometimes.

But we are allowed to replace and wire existing system setups.

But everyone in our industry does “new” installs all the time.

And pool electricians are generally awful and nobody wants to do the work. If you are in our industry you would understand the challenge.

I'm more than a little concerned here. Pool electrical wiring is a very serious business, more so than most other areas because there are a lot of things that must be done to make the pool and area safe that aren't found anywhere else. Pool electrical done by an unknowledgeable person can very easily cause someone to die.

You sound like a nice guy and all that, but from what you said here I can tell that you have no business doing electrical work, particularly involving pools.

We have a couple of guys here (@Mystic Pools for instance) that do pool work and are licensed ECs. So I don't understand what you are saying about the pool industry where you are. I can only speculate that it's the company you work for that low balls the electrical with the employees doing the work.

-Hal
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I'm more than a little concerned here. Pool electrical wiring is a very serious business, more so than most other areas because there are a lot of things that must be done to make the pool and area safe that aren't found anywhere else. Pool electrical done by an unknowledgeable person can very easily cause someone to die.

You sound like a nice guy and all that, but from what you said here I can tell that you have no business doing electrical work, particularly involving pools.

We have a couple of guys here (@Mystic Pools for instance) that do pool work and are licensed ECs. So I don't understand what you are saying about the pool industry where you are. I can only speculate that it's the company you work for that low balls the electrical with the employees doing the work.

-Hal
1000% agree, I've super highlighted your statement above, as important information any reading post in future to see.
OP must be upstate, I've run across these types all the time and had more than one argument over equapotential bonding, not connecting all in range required by code, and no electrical inspection, comment coming from workers "this is how we do it". Been called in after a new install with homeowner reporting an "electrical tickle" or a "little shock" on a particular pool part. These pool guys seem to have idea the hazard they are creating, but not sure what to do about these "types" that seem to be allowed to do this work upstate, no licensing required here. And like you said they will underbid installation when a "real" electrician is involved on installation team.
 

Mystic Pools

Senior Member
Location
Park Ridge, NJ
Occupation
Swimming Pool Contractor
1000% agree, I've super highlighted your statement above, as important information any reading post in future to see.
OP must be upstate, I've run across these types all the time and had more than one argument over equapotential bonding, not connecting all in range required by code, and no electrical inspection, comment coming from workers "this is how we do it". Been called in after a new install with homeowner reporting an "electrical tickle" or a "little shock" on a particular pool part. These pool guys seem to have idea the hazard they are creating, but not sure what to do about these "types" that seem to be allowed to do this work upstate, no licensing required here. And like you said they will underbid installation when a "real" electrician is involved on installation team.

Totally agree with both statements by Hal and Fred B.

Pool wiring takes experience. You can't just wing it. There are even some posters on this forum who don't want to tackle pool wiring.
I applaud them that are willing to say no to this work, while others do, without the knowing all the requirements and codes.

I do work in both NJ and NY. In the Hudson Valley in New York, Woodstock area and the like. There is no licensing required and a 3rd party inspector is hired directly by the contractor. In fact, some of these rural towns require no licensing for any trade. Free for all. One day an electrician, next day a plumber, carpenter, logger.... you get the picture.


Stories about "electrical tickle" or "little shock" is really scary. This unfortunately does happen nationwide.
 
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