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Author Topic: THHN  (Read 2455 times)

Ivan Beaver

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Re: THHN
« Reply #20 on: December 07, 2016, 01:08:27 pm »

Here's crosstalk across a roughly 25' run of parallel, untwisted, tight bundled #10 THHN. In the neighborhood of -30dB, it is audble in the high end.

This cable run, 36 amp channels for a 3 channel mains system, exits the rack bundled, and runs together across a tray for about 20 ft before breaking into individual runs of EMT per hang (L,R,C) .

Blue trace is one box driven in the R hang, on ax, in the nearfield. In the purple trace the mic hasn't moved, but L side is now driven.


Maybe I am missing something, but I am not sure that proves crosstalk.

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Hayden J. Nebus

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Re: THHN
« Reply #21 on: December 07, 2016, 02:07:27 pm »

Maybe I am missing something, but I am not sure that proves crosstalk.

The blue trace is a normal electroacoustic transfer function. In the purple trace, there was one change to measurement conditions: input signal was removed from the amplifier connected to the loudspeaker under test, and applied to another amp.

So an amplifier which is not circuited to the loudspeaker creates acoustic output at the loudspeaker.
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Hal Bissinger/COMSYSTEC

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Re: THHN
« Reply #22 on: December 08, 2016, 12:33:41 pm »

The blue trace is a normal electroacoustic transfer function. In the purple trace, there was one change to measurement conditions: input signal was removed from the amplifier connected to the loudspeaker under test, and applied to another amp.

So an amplifier which is not circuited to the loudspeaker creates acoustic output at the loudspeaker.

To do an accurate test- did you replace the driven speaker (L) with a dummy load so as to eliminate any possibility of the mic picking up sound from the driven speaker?

-Hal
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Hayden J. Nebus

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Re: THHN
« Reply #23 on: December 08, 2016, 01:26:07 pm »

To do an accurate test- did you replace the driven speaker (L) with a dummy load so as to eliminate any possibility of the mic picking up sound from the driven speaker?

-Hal

Yes IIRC the test was repeated with the driven speaker both in and out of circuit.  Geometry and windowing were also on our side.

On site RMS voltage measurements with a quality DMM on the speaker conductors themselves corroborate this @ ~ -30dB crosstalk, and was replicated at the shop with a similar length bundle of multiple THHN pairs, resistive  load banks and an HP analyzer. Twisting the pairs at the shop bought a crosstalk reduction upwards of 10dB .  I suspect you could repeat this experiment and see similar results.

Judging by the HPF-iness of the coherence mask, I suspect the mechanism in this case is capacitive in nature.
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Hal Bissinger/COMSYSTEC

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Re: THHN
« Reply #24 on: December 09, 2016, 10:22:23 am »

Yes IIRC the test was repeated with the driven speaker both in and out of circuit.  Geometry and windowing were also on our side.

On site RMS voltage measurements with a quality DMM on the speaker conductors themselves corroborate this @ ~ -30dB crosstalk, and was replicated at the shop with a similar length bundle of multiple THHN pairs, resistive  load banks and an HP analyzer. Twisting the pairs at the shop bought a crosstalk reduction upwards of 10dB .  I suspect you could repeat this experiment and see similar results.

Judging by the HPF-iness of the coherence mask, I suspect the mechanism in this case is capacitive in nature.

Yes it would be. It would be interesting to measure the capacitance between two parallel runs then substitute the equivalent capacitor in series with a speaker to see if you get similar results.

-Hal
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Hayden J. Nebus

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Re: THHN
« Reply #25 on: December 09, 2016, 04:37:14 pm »

Yes it would be. It would be interesting to measure the capacitance between two parallel runs then substitute the equivalent capacitor in series with a speaker to see if you get similar results.

-Hal

I'd be interested to see if something like XHHW, which is available for near the price of THHN but has a jacket with different dialectric properties, would have measurably better performance than the THHN.

Belden 8477 #12 UTP is around $1.50 a ft. #12 THHN comes in around $.60/ft for a pair, XHHW is maybe 0.10 more per ft depending on where/how you buy it.



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Hal Bissinger/COMSYSTEC

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Re: THHN
« Reply #26 on: December 10, 2016, 12:16:18 pm »

I have no experience with XHHW, it's a new product in the 14, 12 and 10ga sizes and only comes in stranded. Stranding is not a problem here but electricians like solid because you can wrap it around a screw. So I don't think XHHW is going to be widely stocked when THHN is available. But if you can get your hands on like 50' as a sample give it a try.

I suspect with parallel runs of Belden 8477 the crosstalk problem would be further minimized because of the twisting and the additional spacing due to the outer jacket.

-Hal
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Jean-Pierre Coetzee

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Re: THHN
« Reply #27 on: January 14, 2017, 03:51:17 am »

I have no experience with XHHW, it's a new product in the 14, 12 and 10ga sizes and only comes in stranded. Stranding is not a problem here but electricians like solid because you can wrap it around a screw. So I don't think XHHW is going to be widely stocked when THHN is available. But if you can get your hands on like 50' as a sample give it a try.

I suspect with parallel runs of Belden 8477 the crosstalk problem would be further minimized because of the twisting and the additional spacing due to the outer jacket.

-Hal

I don't think skin effect has too much bearing on speaker cable runs but I can't see that an electrical inspector would prefer solid to stranded on electrical runs considering the added harmonics present in electrical systems these days. Electrical code here in South Africa calls for stranded at the very least on the neutral but if I remember right on all cables, would need to confirm with electrician though.
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Hal Bissinger/COMSYSTEC

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Re: THHN
« Reply #28 on: January 14, 2017, 03:22:45 pm »

I don't think skin effect has too much bearing on speaker cable runs but I can't see that an electrical inspector would prefer solid to stranded on electrical runs considering the added harmonics present in electrical systems these days. Electrical code here in South Africa calls for stranded at the very least on the neutral but if I remember right on all cables, would need to confirm with electrician though.

Here in the US if there are harmonics we upsize the neutral. That was common years ago with offices full of computers for instance. But it would be unusual these days to see such inefficient power supplies. All wire can be had in either solid or stranded with the exception of #6AWG and above. That can only be had in stranded. Only reason being who would want to bend solid?

-Hal
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Adam Kane

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Re: THHN
« Reply #29 on: January 17, 2017, 10:20:32 am »

Here in the US if there are harmonics we upsize the neutral. That was common years ago with offices full of computers for instance. But it would be unusual these days to see such inefficient power supplies. All wire can be had in either solid or stranded with the exception of #6AWG and above. That can only be had in stranded. Only reason being who would want to bend solid?

-Hal

You can still get solid bare ground wire in 6awg and 4awg. Horrible to work with.

Friend of mine was selling a house and the home inspector called out grounding issues with rods/piping etc. I told him what to buy and I came to fix everything. I show up and there's a coil of #4 solid by the panel. Had to use linesman pliers and every bit of muscle I had to bend it into lugs in the panel and into ground clamps. He paid me in pizza though...so I guess it was kinda worth it...?
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