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Old 10-15-16, 06:30 AM   #20
stevehull
Steve Hull
 
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
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Here is another advantage of Enphase . . . .

A customer had an Enphase 6 kW system (I installed) where the Envoy (power and energy recording box) was acting abnormally. This box gets house wired digital signals from each roof mounted Enphase microinverter, converts them and sends info via Wifi or USB cable to the standard home internet router box. Then the Enphase Enlighten internet site allows you to see system total power, daily energy, each microinverter parameter (voltage, current, power, temperature, etc, etc). Very nice for geeky people like me.

Anyway, instead of the nice smooth parabolic power output that you should get over the day, there was nothing and then large square wave jumps in power output. Then all would be OK. The daily power output was appropriate, but the output curve was screwy.

I checked all my electrical connectors in roof junction boxes, at the circuit breaker and nothing was wrong. 120 V on L1, 120 V on L2, all OK. This is stuff I know - what was going on?

Called Enphase . . . They are able to look at FAR more data that I can see on their site. They have the means to see data, and where there is a fault, to capture all kinds of information (voltage, current, frequency, phase angle, etc) down to the msec on each microinverter. Turns out there was a transient L1 L2 imbalance. Normally L1 should be ~ 120 V and L2 ~120 V for a total for ~ 240 V across L1 and L2.

For a brief moment (a hundred msec, sometimes much longer, but always transient), these potentials became ~ 80V on L1 and 160 V on L2. The microinverters will accept some imbalance (5 V or so), but not this big. Note that the total potential is still 240 V - so the inverters are still sending out power. But the inverter was not sending it out to the internet in real time.

Both the Enphase tech and I immediately recognized this as a bad neutral. If the neutral is flaky or floating, then the ground is uncertain and you get odd split voltages on L1 and L2. The worst of this is that it was INTERMITTENT and incredibly short lived!

Enphase sent me the data by e-mail and I called the electrical utility company to come out and check the homeowners voltages - especially the neutral. They arrived and there was no imbalance at that moment.

The head lineman insisted that it was the customer's fault and a "capacitor was bad" on some 240 V appliance. He and a helper spent the afternoon looking and found nothing. Meanwhile I am looking at the electrical box behind their meter. This box has a wire "security" tag so that only utility people have access to that panel. This is a place that I cannot check.

Nothing in house - no issue with any 240 V appliance - and still no imbalance seen.

At this point, we are talking about having a voltage recorder put on the system and THAT is paid for by customer ($100 per day!!). The lineman also kept blaming the PV system and me (as I was installer) as the cause.

After they found nothing, and as a compromise, I suggested they look in "their" panel, the one the meter is mounted on to check those connections. "No, it can't be there" was the response. I persisted and said it would only take a couple more minutes.

Reluctantly, the panel was opened and each of the three lugs, L1, L2 and neutral were tightened (with insulated tools and rubber gloves on lineman). L1 was tight, L2 was a bit loose (took 1/2 turn to tighten), but the neutral was completely loose (3 full turns to tighten).

The utility repair person and helper were incredibly embarrassed, but I thanked them in front of customer and told them they did a GREAT job (never, ever piss off a utility person).

Now we had to wait to see if the problem came back. No it didn't and hasn't for months now. But here is the kicker . . . .

Turns out the customer had been having "odd problems" at times with appliances. Some lights would suddenly brighten, others would dim and some kitchen appliances would not work - then two minutes later they would work. Eeee gads! This had been going on for years (long before my PV install) and they just got "used to it" as it would go away. The imbalance was on a lot of the 120 V lines and it was lucky that nothing burned out.

Scary . . .

I called Enphase back and thanked them. They said they "see it all the time".

Bottom line - make sure your neutrals on your big junction boxes coming in from the utility are tight to the lug . . . .


Steve
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Last edited by stevehull; 10-15-16 at 06:53 AM.. Reason: clarity
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