New Enphase Field Wireables

[wwhitney]

The newer IQ series from ENPHASE uses a 2-wire trunk cable with no neutral and no ground.

Maybe this is a stupid question, but how do the inverters operate with no ground reference? And if you wanted to island such a system using an ESS (battery), you'd be relying on the ESS inverter to handle all the unbalanced load?

Cheers, Wayne

 

[Carultch]

Maybe this is a stupid question, but how do the inverters operate with no ground reference? And if you wanted to island such a system using an ESS (battery), you'd be relying on the ESS inverter to handle all the unbalanced load?

Cheers, Wayne

The inverters are grounded to the module frames and racks (if metal) through the mounting fastener. The modules and metal racks already have to be grounded, if not already done so by the nature of the racking system. Outputs are connected phase-to-phase in a 208 system, so if there is any imbalance, it wouldn't be on the neutral anyway. One possibility is that the inverters reference the mounting tab's electric potential as a negligible current ground reference.

The input circuit is ungrounded on both polarities, and the output circuit is ultimately grounded at the center wye point of the service. It is possible that the inverter operates without ground referencing altogether.

 

[Carultch]

This is very interesting. Enphase seemingly acknowledges 3rd party cables.

What does TC-ER mean as opposed to TC?

BTW - what I do know is that the Enphase cable is flat, black, 2 conductors.

Would you deem 12-2 TC-ER suitable for PV applications?

ER stands for Exposed Run. It meets a UL testing for crush and impact resistance. TC is tray cable, TC-ER is tray cable rated for outdoor use.

 

[ggunn]

Maybe this is a stupid question, but how do the inverters operate with no ground reference?

L1 and L2 from the service are already referenced to ground; the inverter just matches what it sees.

 

[jaggedben]

... And if you wanted to island such a system using an ESS (battery), you'd be relying on the ESS inverter to handle all the unbalanced load?

Yes, basically.
This would be true of any solar inverter, pretty much, and has nothing much to do with microinverter trunk cable design.

 

[wwhitney]

This would be true of any solar inverter, pretty much, and has nothing much to do with microinverter trunk cable design.

OK, so now I guess my question is with the Engage 4-conductor cable for a 120/240V system, what is the microinverter (e.g. M215) using the neutral conductor for? If I tried to island such a system with a 240V only ESS inverter, would the microinverters sync to that, and if so would any unbalance in the 120V cause a problem?

Thanks, Wayne

 

[shortcircuit2]

I'll buy a length of 12-2 TC-ER cable and compare on the roof to an actual Enphase Cable.

Costs half. and they'll cut it.

(I remember the older, round, 4-conductor Enphase trunk cable markings matched perfectly with a certain TC-ER cable.)

It will be interesting to see if you can find TC-ER without the EGC...

Where is TC-ER cable permitted for PV?

The new 336.6 requires associated fittings to be listed.

 

[Zee]

It will be interesting to see if you can find TC-ER without the EGC...

Where is TC-ER cable permitted for PV?

The new 336.6 requires associated fittings to be listed.

I have found 2 conductor TC ER without the EGC online.

I have no idea where TC ER is permitted for PV.
PV Noob has said it is.

If the Enphase field wireable sheet specifies the requirements of a cable and I find those requirements in a TC ER then in theory it would be listed for use, or no?


In any case I suspect my search will be fruitless for an alternative. Enphase specifies that the cable contain 19 strand conductors.
I just cut a piece off some 12 - 3 TC ER cable and it is only 7 strands.

 

[Zee]

Btw, Enphase cable is marked type DG.

 

[ggunn]

I have found 2 conductor TC ER without the EGC online.

I have no idea where TC ER is permitted for PV.
PV Noob has said it is.

If the Enphase field wireable sheet specifies the requirements of a cable and I find those requirements in a TC ER then in theory it would be listed for use, or no?


In any case I suspect my search will be fruitless for an alternative. Enphase specifies that the cable contain 19 strand conductors.
I just cut a piece off some 12 - 3 TC ER cable and it is only 7 strands.

Why would Enphase care how many strands the wire has?

 

[Zee]

Why would Enphase care how many strands the wire has?

Funny you should ask I was just going to ask about that myself .....anyone else here want to chime in?

The Enphase connectors are crimped with a standard MC connector crimper. Since I have always used 7 strand PV wire for these MC connectors I'm going to call 7 strand conductors okay. Unless someone here says everything's going to blow up.

 

[jaggedben]

OK, so now I guess my question is with the Engage 4-conductor cable for a 120/240V system, what is the microinverter (e.g. M215) using the neutral conductor for? If I tried to island such a system with a 240V only ESS inverter, would the microinverters sync to that, and if so would any unbalance in the 120V cause a problem?

Thanks, Wayne

This is why SolarEdge has an autotransformer as part of the StorEdge system. I suspect there's one inside Tesla's Powerwall, too. Not that I really understand transformer physics, but that's what provides the neutral in the islanded system.

 

[wwhitney]

This is why SolarEdge has an autotransformer as part of the StorEdge system. I suspect there's one inside Tesla's Powerwall, too. Not that I really understand transformer physics, but that's what provides the neutral in the islanded system.

You didn't answer my questions directly, but the implication is that the answers are (a) the M215 inverters don't use the neutral conductor and (b) yes, with M215 inverters and a 240V only battery inverter, an islanded system can't handle any 120V loads. Is that your understanding? (b) is consistent with (a), but why does the Engage cable have a neutral if the M215 inverters don't use it?

Cheers, Wayne

 

[jaggedben]

You didn't answer my questions directly, but the implication is that the answers are (a) the M215 inverters don't use the neutral conductor and (b) yes, with M215 inverters and a 240V only battery inverter, an islanded system can't handle any 120V loads. Is that your understanding? (b) is consistent with (a), but why does the Engage cable have a neutral if the M215 inverters don't use it?

Cheers, Wayne

Okay, so speaking of M215s and all other Enphase inverters prior to the IQ series, yes, my understanding is that the neutral is used only for voltage sensing and never current output. My understanding was that the neutral was necessary to measure phase angle to determine if the inverter is looking for 240 or 208 V. However this has obviously been gotten around, somehow, with the IQ series.

If you pair M and S series Enphase inverters with a 240V only battery inverter in an islanded system with no provision (e.g. autotransformer) for a balanced neutral, then I presume the Enphase inverters would not turn on for lack of proper voltage to said neutral. And yes, that system would not handle 120V loads. I don't know what the effect would be with the IQ series.

Again, to my knowledge, there aren't any 240V solar inverters that would support 120V loads in an islanded system. That is, the 120V reference has to come from something else.

 

[wwhitney]

Thanks much! Wayne

 

[Whalepod]

I work for a non profit solar installer, and our region uses Enphase equipment almost exclusively for our residential projects for a whole bunch of reasons, some of which may not translate perfectly into the for profit world... so your mileage may vary.

I really like the Q Cable in the right scenario. In general we do lots of small systems (most of our jobs are 1 branch). We have mostly been using it where we have 2 arrays on the same branch that aren't located in the same roof plane, and eliminating the Junction Box on the array located farthest away from the roof penetration. I like the fact we are almost center feeding the second array, I like the fact I get to eliminate a junction box, wire nuts, crimps, and pulling a second mod during inspections in AHJ's that want to look in J Boxes, I also like the fact that my crews get a chance to practice with MC4 crimps which they don't see every day. In general it does seem slightly faster to install field wirables vs a J box in my experience, but it's not huge.

It also makes installing systems that are just slightly over 1 branch a little less irritating... I'm building a single roof plane 17 mod job tomorrow. With M250's we may have seriously considered not installing a MaxBranchLength+1 design and just dropping a module because the juice for one extra mod may not be worth the squeeze of upsizing conduit, pulling the extra conductors and barely fitting 6 wire nuts into one SnapNRack Junction box. With field wirables I can take this same 17 mod design and break it up into a branch of 8 and a branch of 9 and land both into the same junction box really easily and not burn extra drops. In fact, with IQ and Field Wirables the only reason I still carry 3/4" EMT hardware is for service on existing systems, training, and the real off chance that we need to install a 3 branch job.

There are a couple other small advantages we've found which may not be applicable in the For Profit world:

We work with a large volunteer base and job training organizations, because we don't have to land EMT into a second J box it makes our conduit runs just a little easier for our crews, who may be teaching folks who have never been on a roof before how to bend pipe in a little less precise application. Also in general, the fewer wire nuts and bare copper crimps we can run is generally a better situation with less opportunity for error.

Our experience may not translate perfectly into the For Profit world, those are just my observations! I wont use them every job, but I'll keep them on my van in case I find a good use for them.

 

[pv_n00b]

It will be interesting to see if you can find TC-ER without the EGC...

Where is TC-ER cable permitted for PV?

The new 336.6 requires associated fittings to be listed.

In the 2014 NEC this was added to 690.31:

(D) Multiconductor Cable. Multiconductor cable Type
TC-ER or Type USE-2 shall be permitted in outdoor locations
in PV inverter output circuits where used with utility-interactive
inverters mounted in locations that are not
readily accessible. The cable shall be secured at intervals
not exceeding 1.8 m (6 ft). Equipment grounding for the
utilization equipment shall be provided by an equipment
grounding conductor within the cable.

In 2017 that was changed to:
Multiconductor Cable. Jacketed multiconductor cable
assemblies listed and identified for the application shall be
permitted in outdoor locations. The cable shall be secured at
intervals not exceeding 1.8 m (6 ft).

So the 2014 NEC specifically allows TC-ER limited use and 2017 if it is identified for the application. There is also article 336 which puts a lot of limits on TC use. Before 2014 690 did not specifically address multi-conductor cable and I don't know if anyone was trying to use TC.

There was a problem with people wanting to use non-TC in trays in the PV array and 690.31(C)(2) was added in 2014 to allow the use of PV Wire in cable trays.

What's the driver for wanting to use TC anyway? Just cost or are their other advantages?

 

[shortcircuit2]

In the 2014 NEC this was added to 690.31:

(D) Multiconductor Cable. Multiconductor cable Type
TC-ER or Type USE-2 shall be permitted in outdoor locations
in PV inverter output circuits where used with utility-interactive
inverters mounted in locations that are not
readily accessible. The cable shall be secured at intervals
not exceeding 1.8 m (6 ft). Equipment grounding for the
utilization equipment shall be provided by an equipment
grounding conductor within the cable.

The EGC requirement in the TC-ER cable would rule out the 2-wire cable your searching for...

2014 NEC

 

[shortcircuit2]

I do not see how to use TC-ER cable as you are thinking because 336.12(2) generally requires TC to be in a raceway or cable tray.

Just buy the Q-cable because it is listed and identified for the application.

 

[GoldDigger]

I do not see how to use TC-ER cable as you are thinking because 336.12(2) generally requires TC to be in a raceway or cable tray.

Which is why TC-ER is a distinct wire type intended to be used without a raceway for a limited distance from where it exits the cable tray. TC-ER can be used anywhere that TC is allowed, plus some additional locations.