Jump to content

Texas or Southern Method - SEP Cable Bundling ??


Nolan Kienitz
 Share

Recommended Posts

My subject may be a 'tad off', but I think I read somewhere that the far too common practice of bundling the branch circuits into one entrance at the top of an SEP started in Texas or at least somewhere down South.

Goes without saying that most of the time we can't see the remainder of the wiring above the panel, but when it is possible it is all bundled up the wall through the top plates and then pulled through the attic. Obviously should be de-rated.

Newer construction actually attempts to spread out the branch circuits as required from the top plate, down the wall and into multiple entrances at the top of the SEP.

When my panel was replaced last fall it had originally been done the common bundling way. My electrician was quite fussy about spreading everything out as best he could and made it right with the new panel.

Anyway ... a few images of recent HIs I've had with "bundling":

Click to Enlarge
tn_201088113720_IMG_3404.jpg

68.83 KB

Click to Enlarge
tn_20108811384_IMG_0462.jpg

78.31 KB

Click to Enlarge
tn_201088113836_IMG_0530.jpg

78.89 KB

Link to comment
Share on other sites

Several years ago, the local code authority made a big fuss out of bundling the cables that way. They insisted on 'one cable, one connector' and everyone complied for a year or two but before long the authority was taking on so much heat that they finally backed off and everyone is back to bundling them together.

As an HI, I don't bother with doing the de-rating calculations and confirming that the adjusted ampacity is still adequate for the loads present. It's too laborious.

Marc

Link to comment
Share on other sites

I don't think Texas can take "credit" for this poor practice; it seems to be fairly universal.

For many years, the NEC didn't require that each cable be secured to the cabinet. The only concerns were that openings for conductors be effectively closed, and that knob & tube conductors be protected with loom. To avoid heating by inductive reactance, it was important that all of the conductors of a knob & tube circuit enter through the same hole. That practice of running two or three loom-covered conductors through the same hole, with no clamping, may have been the practice that later was applied to NM cables.

The rule requiring each cable to be secured to the cabinet began (like so many other rules) with the 1975 edition of the NEC.

Since the concern with bundling them is the violation of 312.5©, i.e., not securing them to the panel enclosure, I don't think that any great harm is likely for a completed installation. Is someone going to try withdrawing one cable from the bundle and cause problems to the rest? How much benefit will there be to calling this defect every time you see it? I think it is one that an AHJ should call on rough inspection, because it is still possible to fix it then. For a completed installation, there isn't much to be gained.

As to the heat or derating issue, they get a pass on that for bundles less than 24 inches in length per 310.15(B)(2)(a) and also by note 4 to table 1 in Chapter 9: "Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and 310.15(B)(2)(a) adjustment factors need not apply to this condition."

Douglas Hansen

Link to comment
Share on other sites

  • 7 months later...

OK, so each cable has to be securely fastened. But here's my problem. I'm upgrading the service at my house and the only reasonable place for the new panel is surface mounted on the exterior wall outside. The house is pier and beam and most of the branch circuits need to go into the crawl space. I want to enter the crawl space through the crawl space vent directly under the new panel. There really isn't enough room to run a separate conduit for each cable. What makes the most sense is to run a single 2" or 3" conduit into the crawl space. The total length would be less than 24" so I would not have to de-rate the ampacity. I just have to figure out how to secure the cables to the panel even though they all come in one large conduit. I thought of a cable clamp on the box adapter on the inside of the panel. But I don't think such a large clamp could grip the cables. Initially I will only have 10 12-2 cables, 1 8/3 cable and 1 6/3 cable entering this conduit. I thought of cutting two semi-circular cylinders of wood and running the cables between them so the clamp pushes them against the cables and grips everything. I'm worried the inspector is going to call it poor workmanship :(. Is there any reasonable way to secure the cables to the panel when there are few of them in one large conduit?

Link to comment
Share on other sites

If you're using conduit instead of NM clamps, I wouldn't bother with trying to clamp any of them. I'd try to install multiple conduits each sized to the largest corresponding knockout on the bottom of your panel, but no larger than about 1 1/4". You'll likely have to group some of the 12/2 w/g together which I wouldn't worry about. Would that leave you with enough room to run all of your cables?

Marc

Link to comment
Share on other sites

If you're using conduit instead of NM clamps, I wouldn't bother with trying to clamp any of them....

But if I don't clamp any of them then I won't comply with 312.5©.

I do understand it's better not to bundle. I'll post a photo soon to show why separate conduits is a problem.

I'm not sure if I would have room for all cables with your suggestion. I'll have to do some calculations.

Link to comment
Share on other sites

Here is a photo of the existing panel. The new panel will be in the same location to take advantage of the crawl space vent. As you can see, I've already installed a 2" PVC conduit at the bottom. I am currently in the process of re-routing all the conductors that enter the panel through the other conduits so they all enter through the bottom conduit. Once that's done, I'll replace the panel.

The new panel is much taller. So the conduit exiting the bottom of the new panel will immediately enter the conduit body. So my total conduit length with the new panel will be minimal. Much less than 2' so I won't have to de-rate ampacity.

There are a couple of reasons I don't want to install individual conduits.

I'm pretty sure I won't have room for all conductors to enter the bottom of the panel with multiple small conduits. This is a 3000 square foot house with one sub panel for upstairs. I'm planning to replace all existing branch circuits and feeders, with everything going into the crawl space first. I'll probably end up needing two 2" conduits or maybe even 3"

Even if I do have room, I'll probably have to bend the conduits. But I want to use PVC instead of EMT since PVC won't corrode. Also, I don't think I will have enough height to do the bends. Also I am no good at bending EMT.

I have a surge protector (see photo) that's going to take up space at the bottom.

Click to Enlarge
tn_201146102730_panel%20001.jpg

48.13 KB

Link to comment
Share on other sites

But if I don't clamp any of them then I won't comply with 312.5©.

It's up to the AHJ, if there's one involved, but I don't think any AHJ would make a fuss over clamping some cables that are leaving a panelboard in conduit instead of an NM connector.

Marc

Link to comment
Share on other sites

There are a couple of reasons I don't want to install individual conduits.

I'm pretty sure I won't have room for all conductors to enter the bottom of the panel with multiple small conduits. This is a 3000 square foot house with one sub panel for upstairs. I'm planning to replace all existing branch circuits and feeders, with everything going into the crawl space first. I'll probably end up needing two 2" conduits or maybe even 3"

Even if I do have room, I'll probably have to bend the conduits. But I want to use PVC instead of EMT since PVC won't corrode. Also, I don't think I will have enough height to do the bends. Also I am no good at bending EMT.

I have a surge protector (see photo) that's going to take up space at the bottom.

Put the surge device on the side of the panel if you can. Use LB's instead of 90's. I'm betting that you would indeed have sufficient room for all of your cables, with some grouping of the 12/2's. It doesn't look difficult.

Install a piece of strut just above the vent opening and another piece just inside the crawlspace to secure the conduits. Use hubs on any panel opening that's above the bottom of the busbars. Helps keep the rain out.

Marc

Link to comment
Share on other sites

Hi,

I see exterior-mounted panels about once in a coon's age; it's been so long since the last one that I can't even remember how the conductors that left that panel went into the house. How do they normally run those for exterior-mounted panels?

ONE TEAM - ONE FIGHT!!!

Mike

Link to comment
Share on other sites

Hi,

I see exterior-mounted panels about once in a coon's age; it's been so long since the last one that I can't even remember how the conductors that left that panel went into the house. How do they normally run those for exterior-mounted panels?

ONE TEAM - ONE FIGHT!!!

Mike

Likewise, I've never seen a split panel before.

Cables from NEMA 3 panels here in Louisiana usually find their way into the house via conduits that open into the cornice space, the attic via a gable wall, the crawlspace or a combination of these. They are also sometimes dumped into the exterior wall cavity behind the panel via a bushing or short nipple.

Marc

Link to comment
Share on other sites

OK, so each cable has to be securely fastened. But here's my problem. I'm upgrading the service at my house and the only reasonable place for the new panel is surface mounted on the exterior wall outside. The house is pier and beam and most of the branch circuits need to go into the crawl space. I want to enter the crawl space through the crawl space vent directly under the new panel. There really isn't enough room to run a separate conduit for each cable. What makes the most sense is to run a single 2" or 3" conduit into the crawl space. The total length would be less than 24" so I would not have to de-rate the ampacity. I just have to figure out how to secure the cables to the panel even though they all come in one large conduit. I thought of a cable clamp on the box adapter on the inside of the panel. But I don't think such a large clamp could grip the cables. Initially I will only have 10 12-2 cables, 1 8/3 cable and 1 6/3 cable entering this conduit. I thought of cutting two semi-circular cylinders of wood and running the cables between them so the clamp pushes them against the cables and grips everything. I'm worried the inspector is going to call it poor workmanship :(. Is there any reasonable way to secure the cables to the panel when there are few of them in one large conduit?

When you go to get your permit, make an appointment to meet with whoever will be your inspector. Show him your pics and ask his advice.

- Jim Katen, Oregon

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...