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# How to determine the size of FMC

## How to determine the size of FMC

#1
03-19-24, 02:58 PM
Member
Join Date: Jan 2022
Location: United States
Posts: 22
How to determine the size of FMC

Hi,

Is there a method to determine the diameter (inside) of a flexible metal conduit? The conduit already has wires of various gauges going through it, and I'd like to pull more wires through it. But I don't know what the diameter of the conduit is, and I need to know so I can calculate the fill ratio with the current wires before pulling more wires.

It looks to be either a 1-1/4" or 1-1/2" FMC. It might even be 2" FMC

So, I took a piece of 12-gauge solid wire and wrapped it around the conduit, marked it where it met, then straighten it out and measured it. The wires measured to about 5-7/8" in length.

Okay, thank you for your input!

Gregory

#2
03-19-24, 03:05 PM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 27,978
The diameter is the circumference divided by pie. d = c/π Or, you can cheat and use an online calculator.

#3
03-19-24, 05:34 PM
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,451
FMC is sized by inside diameter.

Based on what you posted..... no jacket.... that's 1-1/2" which is roughly 1.75" OD.
2" would be approx 2.2" OD.

#4
03-19-24, 11:22 PM
Member
Join Date: Jan 2022
Location: United States
Posts: 22
Thank you to both Pilot Dane and PJmax for your input! Using the calculation that Pilot Dane provided, I was able to determine that it is 1-1/2", confirming what PJmax stated (based on my input).

Time for wiring pulling!