Conduit Size and Reduced Fittings.

[Industrial Toys]

Many flexible electrical tubing, or connectors for that matter are for 3/4" and larger. So code, tells you, to what extent you can fill the conduit. But many, for instance 3/4" fittings (or larger)go down to a 1/2" knockout. Same with bigger sizes still. How is that legal? Is there no temperature issue in that tiny opening, and basically if you can cram your wires through the hole, you are good?

I mean, basically, if you have a 1" liquitight conduit, shouldn't that go into a 1" Knockout?

Thanks

 

[RoyKing]

The answer is yes.

 

[Tractor Seabee]

A step drill is an easy way to turn a 1/2" KO into a 1" KO. Cast box, drill it out to fit a 1" Meyers hub. You may encounter a problem with box fill standard also. Get out he code book if you want to be absolutely legal. I have even seen places where someone used a plumbers reducer fitting.

Ron

 

[dieselcrawler]

The whole reason for conduit fill calculations are due to heat dissipation, and there are exemptions for short sections or 'chase nipples' and fittings likely fit this exemption in the eyes of the code.

 

[4get gto]

"But many, for instance 3/4" fittings (or larger)go down to a 1/2" knockout. Same with bigger sizes still. How is that legal? "

I have seen not many at all..
Usually the same size as the conduit. May be able to get special order but real special... I could be wrong..?

 

[JPRambo]

A conduit is 24" or longer and a Chase is less than 24". A Chase has different fill rating.

 

[Industrial Toys]

Thanks. I have punches, but usually start the hole with a step drill. GREAT invention! Less chance of you poking something with a longer drill bit as it rams through too.

I have seen many "larger" fittings that go down to 1/2" trade size. Even a 1" or so diameter connector for a heavy old style range cord, with a 1/2" threaded fitting.

Never even knew that about conduit and chase.

Many things like inverters have precious little room for connections and only have 1/2" knockouts. In fact some Zantrex (sp?) is beyond ridiculous! Not even room for wirenuts in the tiny connection cavity..

 

[CobyRupert]

The whole reason for conduit fill calculations are due to heat dissipation, and there are exemptions for short sections or 'chase nipples' and fittings likely fit this exemption in the eyes of the code.

There's really no heat dissipation issue in a short fitting. Remember, the conductors are copper or aluminum so any heat will distribute and not be localized.
However, I don't think OP's scenario fits technical definition of a nipple, so technically reducing fitting isn't to Code, but realistically its similar and AHJ won't care.

In addition to heat dissipation, the "fill" is also based on the geometry (of 1, 2 or multiple round wires in a round conduit) and ease of pulling wires through. So that cables are not damaged when pulling it in conduit. It also why cable pulls are limited to doing 360 degrees of bends.

That's why 1 wire can occupy 53% of the space in a conduit by Code (1 circle in another circle, that is: 1 wire in one tube)
but 2 wires (2 circles inside one big circle) are the worst & use a lot of conduit "diameter", but not much conduit "area".

With heat dissipation and pulling friction in mind, a short nipple where things are tighter packed doesn't add much pulling resistance compared to the rest of the conduit length. (This is similar to where you may need a #8 Awg conductor for voltage drop on a 20 amp circuit for a 400' run, but a 3' jumper of #12Awg at the end doesn't add much resistance. Or when you need a 1-1/2" water pipe to avoid pressure drop on a 400' run, but that 1/2" fitting at the end doesn't really add much restriction)

The National Electric Code's Chapter 9 tables list the maximum fill area each type of conduit (PVC, rigid metal, EMC, IMC, etc..) and size (3/4", 1", 2", etc..) is allowed for 1 wire (53%), 2 wires (31%), and over 2 wires (40%).

Note 4 of these tables states: "Where conduit or tubing nipples... (less than 24") ...are installed between...enclosures,...the nipples shall be permitted to be filled to 60%..."

 

[Industrial Toys]

Interesting. I also never knew about the 360 rule. But who would make that many bends and think they could make the pull?

Going into a narrow fitting would certainly press the conductors together causing the potential for heat buildup.

I have also wondered how one is supposed to connect larger conductors to satisfy voltage drop on long runs into a breaker? I have run into that a lot! Is one expected to make a J-Box at the panel?

 

[Tractor Seabee]

Four 90 degree bends is usually a tough pull, especially with max allowable conductors. I always try to stay with three and use a generous amount veener slickum. Friction becomes a real factor with rigid steel pipe.

Ron