Separating high and low voltage in the same box

Location
Minnesota
Occupation
ee
Keep in mind both ends of this communications cable terminate within a high voltage wiring compartment.

Telsa used to have a requirement in their instructions that "Class 1 wiring methods must be used for all class 2 circuits," but they have removed this. Any code compliant install of the Modbus wiring may be used. However, from a practical perspective, reclassifying as a Class 1 circuit makes the installation possible as the intention is to use a single knockout in the PowerWall with some type of conduit (even if only to get a nearby panel), so this is what must be done ala 725.130(A) and to make the install compliant with Tesla's knockout instructions. (And their installers just wont do it any other way.)

Current instructions state:

Page 19 "Run the 4-conductor communication cable, the AC power conductors an ECG from the backup Gateway through the conduit or cable gland and pull them into the Powerwall wiring compartment."

"On the Backup Gateway side of the 4-conductor communication cable, cut the cable shield. The shield should be terminated at the PowerWall chassis Earth terminal only.

Prior versions used to permit use of any category 5/6 twister pair cable (24-16 awg, distance determined shielding and gauge), but now they stipulate a higher gauge for the 12V pair and provide a suitable cable with the product to their installers. The current requirements are in Appendix B. 16-18 AWG meets the requirement of both twisted pairs that are used. So for practical purposes 600 V insulation makes installation possible with the PowerWall since they are suppose to use a single KO (see below regarding reclassifying as Class 1). Conduit is best to allow for future design changes. Previously you could use 23-24 AWG for this wire, so Cat 5/6 with a 600 V insulation used to be what they installed. Note that in current specs, maximum cable length for 16 awg is 150 ft and 18 awg is 90 ft for this ModBUS connection (total length through all daisy-chaned PowerWalls if multiple).

The wiring between the Neurio "meter" that essentially goes in the Backup Gateway or CSED/main panel to provide information about net power usage and hence determine if the PowerWall should charge or drain when possible, is generally connected by wireless now, so no need to worry about wiring requirements for it at this time. Appendix C has some example placements but this should affect this type of early provisioning decision making. If solar is far from this area, a second "meter" can be ordered and will connect wirelessly also. So just forget about this component for the time being.

So getting back the Article 725 regarding reclassifying the ModBUS connect as Class 1. Some relevant bits:

"725.130 Wiring Methods and Materials on Load Side of the Class 2 or Class 3 Power Source. Class 2 and Class 3 circuits on the load side of the power source shall be permitted to be installed using wiring methods and materials in accordance with either 725. I30(A) or (B).
(A) Class 1 Wiring Methods and Materials. Installation shall be in accordance with 725.46.
Exception No.1: The ampacity adjustment factors given in 3JO.15(B)(3)(a) shall not apply.
Exception No.2: Class 2 and Class 3 circuits shall be permitted to be and installed as Class 1 circuits if the Class 2 and Class 3 markings required in 725.124 are eliminated and the entire circuit is installed using the wiring methods and materials in accordance with Part II, Class 1 circuits."

So these class 2 conductors can be installed using class 1 methods (and as I mentioned, this used to be required by Tesla but is no longer however is still the only straightforward way to be complaint), and if so, you need 600 V insulation to reclassify as Class 1. Relevant code portions below:

"725.48 Conductors of Different Circuits in the Same Cable, Cable Tray, Enclosure, or Raceway. Class 1 circuits shall be permitted to be installed with other circuits as specified in 725.48(A) and (B).
(A) Two or More Class 1 Circuits. Class 1 circuits shall be permitted to occupy the same cable, cable tray, enclosure, or raceway without regard to whether the individual circuits are alternating current or direct current, provided all conductors are insulated for the maximum voltage of any conductor in the cable, cable tray, enclosure, or raceway.

"725.49 Class 1 Circuit Conductors.
(A) Sizes and Use. Conductors of sizes 18 AWG and 16 AWG shall be permitted to be used, provided they supply loads that do not exceed the ampacities given in 402.5 and are installed in a raceway, an approved enclosure, or a listed cable."

"(B) Insulation. Insulation on conductors shall be rated for the system voltage and not less than 600 volts. Conductors larger than 16 AWG shall comply with Article 310. Conductors in sizes 18 AWG and 16 AWG shall be Type FFH-2, KF-2, KFF-2, PAF, PAFF, PF, PFF, PGF, PGFF, PTF, PTFF, RFH-2, RFHH-2, RFHH-3, SF-2, SFF-2, TF, TFF, TFFN, TFN, ZF, or ZFF. Conductors with other types and thicknesses of insulation shall be permitted if listed for Class 1 circuit use."

"725.30 Class 1, Class 2, and Class 3 Circuit Identification. Class 1, Class 2, and Class 3 circuits shall be identified at terminal and junction locations in a manner that prevents unintentional interference with other circuits during testing and servicing." Hence, label the cable durably at every JB and panel between the Gateway and PowerWall. The terminals are manufacturer labeled.

"725.41 Class 1 Circuit Classifications and Power Source Requirements. Class 1 circuits shall be classified as either Class 1 power-limited circuits where they comply with the power limitations of 725.41 (A) or as Class 1 remote-control and signaling circuits where they are used for remote-control or signaling purposes and comply with the power limitations of 725.41 (B)." The latter.

"725.48 Conductors of Different Circuits in the Same Cable, Cable Tray, Enclosure, or Raceway. Class 1 circuits shall be permitted to be installed with other circuits as specified in 725.48(A) and (B).
...
(1) In a Cable, Enclosure, or Raceway. Class circuits and power-supply circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated."

"725.130 Wiring Methods and Materials on Load Side of the Class 2 or Class 3 Power Source. Class 2 and Class 3 circuits on the load side of the power source shall be permitted to be installed using wiring methods and materials in accordance with either 725. I30(A) or (B).
(A) Class 1 Wiring Methods and Materials. Installation shall be in accordance with 725.46.
Exception No.1: The ampacity adjustment factors given in 3JO.15(B)(3)(a) shall not apply.
Exception No.2: Class 2 and Class 3 circuits shall be permitted to be and installed as Class 1 circuits if the Class 2 and Class 3 markings required in 725.124 are eliminated and the entire circuit is installed using the wirining methods and materials in accordance with Part II, Class 1 circuits.
Informational Note: Class 2 and Class 3 circuits reclassified and installed as Class I circuits are no longer Class 2 or Class 3 circuits, regardless of the continued connection to a Class 2 or Class 3 power source."

This avoids the need to separate the comms conductors from the power ones that would otherwise be required by 725.136(D)(1) by 1/4", and a barrier in conduit or raceway.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
I think you are tring to overthink this, what are you using to cycle the fan? A dry contact off a 120 volt time clock? A simple RIB relay that already has the partition built into it. 120 volts thru the time clock to power the relay, which would give contact closure to activate the fan.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Could not find the one I ususally use, but this one will work too. Low voltage wire is connected outside the box.
 

jap

Senior Member
I started working for a new builder and they are claiming that the building inspector is requiring that they make the gas furnace be able to turn on the exhaust fan in the utility room a couple times a day for whole house ventilation. This is fine with me but the HVAC crew is running a 18-2 conductor to a junction box directly under the switch that controls the exhaust fan. They are claiming that as long as I junction the 18-2 into a 14-2 NM-B before it goes into my switch box then I don't have to separate the high and low voltage in the box. I have never heard of this. Can anyone confirm that this is true?
I may be wrong ,but, to me, I think you may be misunderstanding the HVAC guys, and the 18-2 cable from the Furnace should not be in the 120v switch box at all.

Sounds like the are giving you a 24v control circuit from the furnace to signal when the exhaust fan needs to comes on.

This does not connect to your standard 120v switch that now controls the exhaust fan.

This 24v signal from the furnace (if that's what it is) more thank likely needs to pull in a coil on a contactor to control the exaust fan.

The 120v switch you have in place now becomes an over ride if you want to bypass the contacor, or it will supply the 120v power to the line side of the contactor, or, will be between on the load side of the contactor to the exhaust fan depending on how it is wired.

JAP>
 

jap

Senior Member
Now , if the 18-2 cable the HVAC guys pulled to the switch location is nothing more than a switch loop from a relay they already have in place to control the exhaust fan, then that's a different story.

It's hard to tell without knowing exactly what purpose that 18-2 cable has.

Is it a signal out of the furnace to control an external contactor ? or, is it a switch loop out and back to the unit to a relay already provided to control the exhaust fan?

JAP>
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
... they are claiming that the building inspector is requiring that they make the gas furnace be able to turn on the exhaust fan in the utility room a couple times a day for whole house ventilation.
I assume that when the furnace is running the fan must be on. The inspector want's the fan to also run independently a couple of times a day. It also looks like there is either a low voltage contact closure or 24VAC (when on) provided by the furnace to operate a remote relay that controls the fan line voltage.

Without knowing whether the relay is made specifically for this purpose it's not possible to advise if thermostat wire can occupy same enclosure. HVAC relays from Honeywell (RA89A) or Argo for instance, fitted with a timer are made for this and would certainly be suitable.

Unfortunately HVAC guys have little knowledge of the NEC and proper electrical practices and tend to cobble up things from whatever their supply house has on the shelf.

So really, there is no way to answer your question until you can provide a picture of what they did.

-Hal
 
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jap

Senior Member
I assume that when the furnace is running the fan must be on. The inspector want's the fan to also run independently a couple of times a day. It also looks like there is either a low voltage contact closure or 24VAC (when on) provided by the furnace to operate a remote relay that controls the fan line voltage.

Without knowing whether the relay is made specifically for this purpose it's not possible to advise if thermostat wire can occupy same enclosure. HVAC relays from Honeywell (RA89A) or Argo for instance, fitted with a timer are made for this and would certainly be suitable.

Unfortunately HVAC guys have little knowledge of the NEC and proper electrical practices and tend to cobble up things from whatever their supply house has on the shelf.

So really, there is no way to answer your question until you can provide a picture of what they did.

-Hal
I totally agree.

JAP>
 

kwired

Electron manager
Location
NE Nebraska
I'm not seeing where 600V is being applied anywhere.
Me neither, I am seeing 24V and 120 V circuits involved. That said when one is a class 2 control circuit, you do have some limitations on what it can be run with and even if allowed in same enclosure still typically needs some separation within that enclosure.

What OP needs is a "RIB" (relay in a box) or similar device with 24 volt control signal coming from furnace and the relay contacts switch the exhaust fan power circuit. Can still be parallel with a wall switch if you want to override it or even a double throw switch so you can have hand/auto or hand/ off/auto.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Me neither, I am seeing 24V and 120 V circuits involved. That said when one is a class 2 control circuit, you do have some limitations on what it can be run with and even if allowed in same enclosure still typically needs some separation within that enclosure.

What OP needs is a "RIB" (relay in a box) or similar device with 24 volt control signal coming from furnace and the relay contacts switch the exhaust fan power circuit. Can still be parallel with a wall switch if you want to override it or even a double throw switch so you can have hand/auto or hand/ off/auto.
See post #23,24 LOL!
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
The RIB will be OK if you stick the LV coil leads back out of the box through a KO with a bushing then wire nut them to the 18/2 24VAC control from the furnace.

-Hal
 

caribconsult

Senior Member
Location
Añasco, Puerto Rico
Occupation
Retired computer consultant
What is the Neurio WiFi? The cellphone (Samsung S5) I use to enter the Powerwall GUI detects this open wifi net as "Neurio-81178." Is is part of the TEG wifi that exists in the gate for installer/customer entry to the GUI? Anyone know what this is?
 
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