HPWC signal cable

[Cosmacelf]

When daisy chaining multiple HPWCs together to share a common breaker, you also connect the HPWCs with a signal cable. The HPWC manual specifies the cable must "Be at least 18 AWG, 2 conductor, shielded, twisted-pair wire.". It then goes on to say max. distance is 50'.

This strikes me as slightly nuts. My understanding is that Tesla is using RS485 signaling between the HPWCs. 18 gauge wire is ridiculously large for RS485 signaling. While there is no cable spec for RS485, you normally would use ordinary 24 gauge twisted pair cable (as found in a Cat 5 ethernet cable) and it would work over hundreds and even thousands of feet.

It is hard, if not impossible, to even find 18 gauge shielded twisted pair cable (18 gauge shielded is easy to find, it is used for audio, but it generally isn't twisted pair, and the twisted pair part is what is important for noise rejection).

What do you guys think? I personally would use a high quality cat 6 shielded, or unshielded cable for connecting HPWCs and I would bet it would work over much longer distances than 50'.

 

[araxara]

Im using this RS485 cable from eBay: 60ft feet RS485 Signal Transmission Cable for Control CCTV PTZ Security camera 722512229693 | eBay . It's twisted and shielded, although I have not actually grounded the shielding to anything. I don't really know the gauge of this wire, but according to my wire stripper it's 20 gauge.

I had previously used 2' of CAT5 cable between 2 HPWCs and it was inconsistent and would sporadically fail. Of course, one HPWC wound up failing completely and was replaced under warranty (possibly due to lighting). I added a surge suppressing circuit breaker to the panel and switched to the above RS485 cable.

I now have 3 HPWCs connected with this cable. One cable run is about 2' the other is 35'. it's been working great so far. It's also more flexible than the CAT5 cable since it's not solid.

Each of the HPWCs is actually going to a 100A circuit breaker. It was primarily wired this way due to historical reason when I had the old version of the HPWCs.

I should also add, since this cable is stranded it was a bit of a hassle to insert it into the screw down posts. I was going to tin the ends, but wound up using it as is.

 

[Frisco-Dad]

I just went to Home Depot and bought 18/2 "speaker wire" and that works fine. I bought the one that you can buy by the foot. The actual wire run is about 25 feet.

 

[brkaus]

Note the spec says if sharing the conduit with the power line it should match the insulation rating of the high voltage wire - 600v.

Belden Cable: 3088A 18/1P PVC/NYL FS PVC Industrial Cable | ProWireandCable.com

 

[TechVP]

Similar wire, with lower bend radius, also meeting the 600V requirement:
Belden Cable: Belden 1120A 18/1PR Bare Copper PVCN/PVC Shielded Industrial Cable | ProWireandCable.com

Both are not inexpensive, vs. your bulk cable price at a box store.
Also note: what gets you the 600V rating is the outer jacket's diameter. Its very large. The cable diameter is .48" which you should use for any in conduit calculations -- ie running parallel to the THHN in the same conduit.
Outer Jacket Material Nom. Wall Thickness (in.) PVC - Polyvinyl Chloride .048
I can post a picture of the 1120A cable if anyone is interested.
For signal wiring, personal opinion, I think .48" is a beast. But that is the requirement to be in the same conduit.

-TechVP

 

[Cosmacelf]

Of all the things to worry about, having 600V signal wire isn’t something I’d spend time on. What’s the failure scenario? A short circuit AND a simultaneous breaker malfunction causing, what, THHN wire jacket to melt and conduct 240v onto the shielded, grounded signal wires, which would evaporate in a puff as the current got fed to ground. So what?

 

[TechVP]

Of all the things to worry about, having 600V signal wire isn’t something I’d spend time on. What’s the failure scenario? A short circuit AND a simultaneous breaker malfunction causing, what, THHN wire jacket to melt and conduct 240v onto the shielded, grounded signal wires, which would evaporate in a puff as the current got fed to ground. So what?

Our logic for in conduit was purely for aesthetics.
A paying insurance company adjuster could find negligence here. $100k vehicle and a garage, likely attached to a > $300K+ structure. Code sometimes seems silly, but I did pay the money and my install is by the book. When I sell our home I will sleep at night when new buyers do full home inspections.

Seriously though, nothing wrong with running the signal wire in separate conduit and avoid this particular restriction. Which is way easier and could be done in a trivial hour or so. For the time and money, that’s the way to go.
-TechVP