# Cable Bundle OD

#### mityeltu

##### Senior Member
I am in the middle of a problem caused By Fukushima. We have a bunch of 4" conduits that are unsealed leading to out ERCW building. These conduits have various cables in them. Our current plan is to use Roxtec seals to eliminate (as much as possible) the flooding of the building. Here's my problem. Some of my conduits have up to 23 cables of differing diameters. The Roxtec seals are good for certain diameters or for bundles if the bundles have an OD of certain diameter.

I need a verifiable method (what I mean is documentable - I will have to show where I got my equations) for calculating the OD of a bundle of cables. I have looked everywhere I know to look. Can one of you smart people help me out?

#### don_resqcapt19

##### Moderator
Staff member
I have no idea how to do that, but I think I would be looking at something like this for that application.

#### mityeltu

##### Senior Member
We are installing BOTH... Yes, Both. We tested the FST at our lab and found it to leak and fail under our design basis flood conditions. The Roxtec seals are superior, but still allow leakage through bundled cables and minimally though the plugs. It is not my idea to install both, but I was overruled. Anyway. I need to be able to tell the field which Roxtec module to use and to do that I need to know what my OD for this bundle of cables is. I also have to be able to demonstrate this with referenced material in our design change package.

Any ideas?

There's bound to be some kind of book out there that has this in it. I just don't know where to look.

#### don_resqcapt19

##### Moderator
Staff member
I guess you could draw the cables to scale in a cad program, bundle them and then draw a circle around the bundle and measure it.

#### JoeStillman

##### Senior Member
I just took a CEU course in stranded conductors that offered these formulae;

?RedVector.com said:
The number of layers in a concentric stranded conductor can be estimated based on the
number strands in the conductor using the following formula,

Nlayer = {(sqrt [(12*NStr)-3] –3) / 6} +1

The overall conductor diameter is based on the number of strands in the conductor and
the diameter of those strands. The formula is,

DiaCond = DiaStr * (2 * NLayers – 1)
These assume all strands in the bundle are the same diameter though. They might serve as a rough approximation if you used the weighted average conductor diameter, then confirm with the CAD solution.

Why not measure the circumfrence and divide by ∏?

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#### Julius Right

##### Senior Member
I think you have to put the bundle in a pvc conduit [split a short length of pvc conduit in two parts and press to close it on the cables] and fill it with RTV rubber. So you'll know the diameter and all will be well sealed.