Speaker Wire / Low Voltage Lighting

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Karl H said:
BTW there are 90 tracks wired in this manner.
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I will make some assumptions.

90 tracks does not sound like a dwelling and if its commercial there are likely suspended ceilings, I also assume the wiring is concealed. 250 watts is beyond the ability of a class 2 power source.

That being the case;

411.4(A)(1) will require a Chapter 3 wiring method. (Pipe and wire, NM or MC cables etc.)

334.12(A)(2) prohibits using NM assuming commercial and a dropped ceiling

So this leaves you with pipe and wire or MC, running 4 AWG MC will get kind of expensive. :grin:

If it where me, I would look into moving the transformers right next to the loads, in that way you could run 12/2 MC line voltage to each transformer without having severe voltage drop problems. Then your secondaries would be very short and 10 AWG would be fine.

If you have the time take a look at the instructions that come with a low volt lighting transformer, I think you will be very surprised at the required wire sizes due to voltage drop. When your only dealing with 12 volts to start with voltage drop is a real issue that results in greatly reduced light output.


Physics exposes Ignorance!:grin:
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It sure can. :)
 
Bob stop it with your knowledge! The issue isn't voltage drop it's speaker wire. What don't you understand? :confused: :roll:

Here's the reality of the situation. It does not matter one bit what type of "speaker wire" this is. It is NOT legal for the install.

I don't get whay the op is so hung up on the ampacity of speaker wire. :confused: it's SPEAKER wire.
 
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Alfa has cable very simular to what is described as part of the fixture - I wonder if the dope who installed it didn't get his/her hands on some significant lengths of it to use as premise wiring????
 
Many otherwise good electricians get confused over low voltage. They seem to forget that amps went up by 10 when voltage went down. OP knows it was wrong wire, he simply is trying to figure out what it was. With no label it could be speaker wire. Seen some speaker wire that while looks heavy actually is #22 and not fit to wire anything.
 
Jim W in Tampa said:
Seen some speaker wire that while looks heavy actually is #22 and not fit to wire anything.
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My mom, who believes that every low price is a good deal, spent $5 on a set of jumper cables whose conductors had about a half-inch OD, but with what looked like #12 stranded wire.

They would actually work if you could leave the running vehicle attached to the dead one for about 30 minutes, but even that's hard to do when the cables are only about six feet long.

Moms. Gotta love 'em! :)
 
iMuse97 said:
Here's some info on speaker wire that suggests that not all of it is just ordinary wire:

"Although some expensive wires can have low resistance, several have a high capacitance of 100 to 300 picofarads (pf) per foot. These can introduce a significant amount of capacitive load, particularly for longer lengths. For a 50 foot length, this adds up to 5000 to 15,000 pf, which is the same as .005 to .015 microfarads (mfd)."
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Any engineering guys please correct me if I'm wrong.

Capacitance has very, very, very little effect on the total load of a lighting circuit. 100 or 300 picofarads per foot in parallel between the conductors through a dielectric will produce a very small current at 60Hz as compared with the lighting load itself. The capacitive reactance of cables isn't an issue here.

1 ? 2∏fC

or

One over two times pi times frequency times capacitance = huge amount of reactance in ohms.

The real question here is: What is speaker wire?

I believe speaker wire is anything you choose to call speaker wire. There's no type letter for it, there nothing in the code for it, it's just a label on a box or in your head.
 
Here's more info. There are 90 tracks, 70@250w-20@100w. The wiring is
in a commercial building. Where the tracks are, the ceiling is Hard-Lid
(Drywall). This ceiling has metal access doors in the ceiling, so NM is out
of the question. The lengths of the runs of speaker wire are from 3'
to an estimated MAX of 40' from multiple 600w and 300w transformers located all around the ceiling. This doesn't look like Hack work, (except
the choice of conductors). The install is very neat and they fused every
secondary conductor with a disconnect and a 25 amp fuse.

The failures have been melted track power feeds. As the power feeds
are made of plastic with a bronze buss that is inserted into the plastic
track. Other failures have been burned wires in the disconnects at the lugs,
and at the lugs of the transformers. I also found melted and burnt
conductors at various areas in the ceiling, some 3' from were they terminated
in the power feed. In some places the conductors were burnt before the
power feed but not in the power feed itself.

IMO this is insulation failure, a insulation was used that isn't rated for the
current imposed on it. I do not think VD caused the failure. I may be wrong
but I thought VD was current-limiting.

Here's my best guess. Alfa Lighting has a cable that they sell
that looks very similar to speaker wire. I talked to them and it is
UL listed and is marked. This wire in the ceiling is not marked anywhere.

I wonder if the "Electrician" received this wire and thought "This isn't
nothing but high priced speaker wire!!" "I'm going to save money,go
to Radio Shack and get a cheaper speaker wire, my boss will be so
proud!!!" Just my guess.:)

The Power feeds will be replaced with one that will accept MC.
Eight transformers will have to be relocated.

The proper wiring method wasn't my issue. My issue how do you
select a conductor if you don't know the load. When you know the load,
how do you select a conductor if you don't know it's rating.:mad:

This guy didn't consider this at all.
 
I never did find the insulation rating of any size of speaker wire.
I guess I'm going to do some tests in my "Electric Shop of Horrors."
(My garage):grin:
 
Karl H said:
IMO this is insulation failure, a insulation was used that isn't rated for the current imposed on it.
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Is it 10 AWG copper?

Then 20 amps was not 'to much current' for any insulation type.

But regardless it was not a code compliant wiring method.

I do not think VD caused the failure.
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I never said that it was the cause of the failure, no one did I was simply stating a fact.

It appears that you have been hired to make it right and IMO part of making it right would be correcting the VD issues when you select your new conductors.

I have no idea why you are so hung up on the original wire:-? ........ it was the wrong stuff replace it and move on. :)
 
Karl H said:
The proper wiring method wasn't my issue. My issue how do you
select a conductor if you don't know the load. When you know the load,
how do you select a conductor if you don't know it's rating.:mad:
Click to expand...

Who's the manufacturer of the transformers and track? Tech Lighting, maybe?

300 and 400 watt transformers don't sound like class 2 or 3, so if you can't get something from the manufacturer I'd say you'd have to go to chapter 3 of the NEC.

For the original cables see 310.11. They shouldn't have been installed on that basis alone.
 
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iwire said:
Is it 10 AWG copper?

Then 20 amps was not 'to much current' for any insulation type.

But regardless it was not a code compliant wiring method.



I never said that it was the cause of the failure, no one did I was simply stating a fact.

It appears that you have been hired to make it right and IMO part of making it right would be correcting the VD issues when you select your new conductors.

I have no idea why you are so hung up on the original wire:-? ........ it was the wrong stuff replace it and move on. :)
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It is #10 and it appears to be tinned copper. How do you know that 20 amps
isn't "to much current" when the insulation isn't known? Two #12 THHN
conductors can safely carry 30 amps in EMT @90C. But, can two #12
conductors covered in rubber cement safely carry 30 amps in EMT too?:)

Regarding VD, within the first 10 minutes of seeing this job I knew I had to
relocate the transformers for VD. That's why I'm relocating eight of them.

I'm not "Hung-Up" on the speaker wire. I just have never seen anything
like this. It just sparked my curiosity as to what this insulation could safely carry. Didn't you bury your nose in the NEC cause "something" sparked your
curiosity? That's why I did. Why didn't you just listen to what your boss told
you instead of looking it up for yourself? :)
 
ike5547 said:
Who's the manufacturer of the transformers and track? Tech Lighting, maybe?

300 and 400 watt transformers don't sound like class 2 or 3, so if you can't get something from the manufacturer I'd say you'd have to go to chapter 3 of the NEC.

For the original cables see 310.11. They shouldn't have been installed on that basis alone.
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I don't know the Manufacture of the transformers. The track is Alfa Lighting.

310.11 was how I knew this was unlisted cable. I figured since we are
20 min from Mexico the cable could have been purchased there.
 
Karl H said:
I don't know the Manufacture of the transformers. The track is Alfa Lighting.

310.11 was how I knew this was unlisted cable. I figured since we are
20 min from Mexico the cable could have been purchased there.
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Unlisted products from a foreign country? Hmm. Seems a likely possibility. Even cheaper than radioshack prices.

And to Bob, I'm not humg up on that speaker wire either, but I sure wonder what kind of insulation could deteriorate that much.
On a slightly related tangent, I once pulled some hardware-store-bulk lamp cord out of a conduit that fed most of the lights and outlets in a basement. Probably sixteen gauge. The lady wanted us to fix a couple recepts., and said, "Here, you'll need this work light, because for some reason the lights don't work down there, either."
 
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IMHO, although the cable was clearly non-compliant, voltage drop WAS the most important factor here, the installer didn't do his calculations.

300W @ 12V @ 40 ft (80 for VD calc) requires larger conductors than #10.

V = IR = 300W / 12V x R = 25A x .001(ohms/ft for #10) x 80 ft
=2V =16.6 % VD

Even #8 conductors would give you a barely (some would say not) acceptable 10 %

25A x .0006 x 80 ft. = 1.2 V

I think overheating due to VD, along with noncompliant insulation caused
the situation. However, I have seen Chapt. 3 installations (type mc cable) with similar mis-sizing start to melt and peel back the insulation on the conductors. It is my opinion that overheating due to voltage drop causes excessive expansion and contraction, loosening the terminations, causing more heating, etc.
 
Whoops ! My VD calculations are for DC-- (have been helping a friend wire
a boat on weekends !)
 
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