Interesting report...
http://www.copper.org/applications/electrical/building/pdf/bundle_evaluation_report.pdf

I've been wondering about this recently.

Eric

[This message has been edited by ehill (edited 08-26-2006).]

Wow. I never knew that using a butt load of smaller holes, like do was actually a better wiring method. I always thought that I was just too cheep to buy a larger drill bit.

That's darn interesting. I have to admit, having never personally witnessed the adverse effects of bundling Romex, and having seen it ignored by almost every local "authority" in residential electrical construction, I was darn skeptical about what threat bunlding posed.

Obviously, the bundling does have a serious impact on heat generation.

However, I would have liked the study to address several things: What was the average temperature rise for a single cable carrying the same load as identical bundled cables?

And speaking from personal experience I can say that in a lot of resi. construction cables are regularly bundled for distances far in excess of 24". They may not be packed together in a hole and fire-stopped, so their is certainly more heat dissipation, but by how much? What happens when that same bundle is covered with ten inches of blow-in fiberglass?

I think I'll be a lot more cautious about how I route cables now after seeing this.

-John

I question their test method, though... To have the bundle pass through the top plate, and then back down the top plate? That's not a "real-world" situation. (Maybe I'm missing something.)

Seems like with all they went through in their test scenario, they could have simulated the "real world" a little better.

Still, the report is interesting.

Eric

You know, John, I think there's a lot of factors involved, too... I mean... South facing walls without shade in Las Vegas are going to get a lot hotter than a north facing wall in colder places of the county.

OT, a little, we sometimes balk at local code, but I think that's exactly why local codes should exist. Local needs might be complete overkill for other parts of the country.

Eric

I am not as concerned by the routing of the cables in the test but the loading is IMO unrealistic in dwelling units.


I find it extremely unlikely you would find a bundle of NMs (6) in a dwelling all loaded to 73% or any combination that averages out to 73% at the same time.

How would that happen in any modern dwelling construction?

Even the simultaneous 60% loading of six two wire circuits in a dwelling unit seems remote to me.

Used to be that inspectors here required only one cable per hole, but in the last few years they realized that this turned the framing into swiss cheese, and now allow two only. (Allowing two 12/2/2's) In the guiese of not exceeding 9 current carrying, as you would in conduit, same for stacker and other bundles. Taking a large bundle of cables, like some would above a panel into a single connector isnt allowed for these same reasons.

That said, if I go a few cities over, where bundling is ignored, you can tell the difference. You really can feel the difference in warmth in the bundles. And on occassion see a slight discoloration of romex sheathes in stuff installed around ten years ago.

Any building with base-board heat, or AC...

Both of those examples are non-continuous loads.

If you had the six circuits all supplying electric heat circuits it would be unusual for all six circuits to have each of their zones all needing heat at the same time.

I take, as I am sure you do many current readings.

It is unusual for many circuits to be at 60% load in a dwelling unit.

Proof of this is the fact you may have 500 amps worth of breakers in a 200 amp panel.

Anything is possible but we regularly assume certain loading characteristics, most of Article 220 is based on assumptions.

And besides all that.

It's the copper org bringing us the message, more copper less heat.

Who stands to benefit the most from that conclusion?

First, I agree with I-Wire as to the actual loading. When we de-rate, we do so based upon the size of the circuit breaker. This is just fine when you are applying this method to dedicated equipment- but, to assume that typical household convenience circuits are ALL completely loaded ALWAYS is simply silly. Yet, the code makes no distinction between a 20 amp circuit for a 19 amp refrigerator... and a 20 amp circuit that's feeding maybe 5 amps worth of TV and stereo!

I also think that there is a proposal for 08 that more closely defines "bundling," I've had a few disagreements over at the HI forums, where many seem to favor a definition a lot more inclusive than mine.

While I agree that you always have to consider the source of information presented, my point is that to many people bundling is a non-issue: I've never once met a residential j-man who had any qualms about zip-tying 10 or 15 home-runs traveling the entire length of an attic full of blow-in insulation. And most of my resi. experience is in southern states where attic temperatures can easily reach 110-115 degrees.

The situation presented in that report is basically a worse-case scenerio: Maximum load, maximum bundling, minimum ventilation.

I see value in that report because, regardless of their motives, they made me aware that there are circumstances (however remote) that can create a hazard. And there are probably more common circumstances were there is a mitigated hazard, but it's hazardous non-the-less.

It wouldn't be wise for me, or anyone, to know this and continue to ignore bundling issues out-of-hand.

-John

I do alot of residential work and I never pull more than 3 romex cables in any one 3/4" hole. I also use 3M stackers wherever I have more than 2 cables in any one run, like to a multiple switch location or homeruns in the bsmt.

I stopped reading after looking at fig 4. The 10AM wire temp is 194 degree F (90 degree C). This is amazing since the power has just been turned on after being off for over 12 hours. I expect the data is simply wrong.

(My engineering shows a 2.33" dia bundle is safe. Note I did not say hole. A 1-1/2"dia x 3-1/2" long hole, the size used in the test, is safe according to the code.)

Bob, Continous or not those two could easily be on for hours loaded above 60%. As well as many lighting circuits consisting of cans these days, or a circuit with computers and the many, many perifreals. Like this one.... Or ANY home during Chistmas or Thanksgiving, EVERYTHING IS ON! I preffer to wire homes to have it all on, all the time. As I know there will be a few times a year when they do.

As for the source, I don't think they would stand to benifit as much as companies like Irwin, Greenlee, or Lenex, the guys who make drill bits, or for those who cheap out on new ones, the guys who make files and grinders will profit. Like I said, I have been limited to two cables per hole for a long time, and before that only one.... You dont jump the wire size, just blast more holes and learn to plan your work better. Real easy to miss the nails with a 1/2"-5/8" drill bit, easier on the wrist too. And you become very articulate with it after a while.

Back on topic, I dont think it too silly to follow the rules for derating in bundles, or holes. Just because the code allows us to ignore it under 24", doesnt mean we should not take it into consideration on shorter lengths.

Mark we have had to follow the 'not bundling deal' for years here as well and I am not complaining.

As for the rest we will have to remain in disagreement.

I will have to assume you do not take any demand factors into service calcs.

Bob

Like I have said here before and on many other forums. Show me the real data. Show me the fires caused by "Bundling" romex in a dwelling. I am not about to say it won't or never did happen, just my personal wish is for somebody to back up the issue with "real" data, not lab testing. You get me lab testing AND hard real anecdotal data and then you have changed my thinking. By the way, any dumb homeowner can screw in a 150 watt light bulb into a socket that is rated for 60 watts. That causes romex to change color also and to lots of times start on fire. How about they start fixing real problems and not invent new ones.

Something is wrong.

I sure wish they would of plotted the attic temp. And then ran the whole test again with proper vented soffits and a ridge vent.
And then did it again with a power ventilator installed in the roof.

They created a heat box to manipulate the results, IMO....

I guess a proper test would have included a single cable firestopped in a standard sized hole.

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I have often wondered about wisdom of using foam in place insulation. I suspect 80% amperage would cause a problem.

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There are lots of academic problems that don't appear to cause a lot of real problems.