Be careful tightening LV6548 AC connectors!! A cautionary tale of woe...

[sethile]

Many of you helpful folks will remember my installation plans from this thread:

AC side MPP LV6548 connections, critical load panel, wiring

This is an off grid installation using a single MPP LV6548. I'm working on a critical loads panel, and trying to plan the AC wiring while waiting for my LV6548. Two pressing questions I'm trying to research have me confused. In case it is relevant here is a (link to previous thread) discussing...

diysolarforum.com

I should be posting an exciting conclusion on that thread, instead, when I was literally two wire connections away from completing my instillation I broke the AC output neutral wire connector on the LV6548! RATS!!!

@Will Prowse mentioned in one of his early videos on this unit that the hardest part was cramming 6 gauge SOOW into the AC connectors. Man was he right!! Turns out it's also remarkably easy to break one!! It may be my fault, but while I was not using a torque screw driver, I would be very surprised if I applied more torque than is called for in the manual (1.4~ 1.6Nm). They also recommend 4 gauge wire. Anyone tried that? Maybe solid copper, but no way you'd get 4 gauge stranded copper in these connectors!! It maybe I had the wire in there wonky, which stressed the metal tab in the connector unevenly.

I removed the damaged connector, and I'm hoping to get a replacement from Watts247, but have not heard back yet. I REALLY hope they have some in stock, or I can get one with expedited shipping direct from MPP.



I floated an idea in my E-mail to Ian about modifying this and using it temporarily by surgically removing (with a dermal tool) the wire clamp terminals while preserving the threaded metal plates, plastic base and separations. If that was successful, I'd then reinstall it using lug terminated wires with the existing screws and the leads from the unit sandwiched in as they were originally.

I realize it's a long shot I won't destroy what's left of the connector in the process of modifying it, but I'll be posting from an institution if I have to wait for the next boatload of units and/or parts from MPP

BTW, I had previously installed a temporary extension cord to the AC output with 10ga wire and had been using that while testing for the last couple of weeks, and to provide backup power while I had the grid turned off to populate the critical loads panel. It all worked great! But now I'm dead in the water until I get this connector sorted out.. Bummer!

Meanwhile, be careful friends!!!!!

 

[sethile]

OK, cool! I called Ian at Watts247. I had apparently not received an E-mail he had sent in reply last night. He had an easy temporary work around for me, which involved moving the the unit's AC output neutral over to the ground position on the terminal block and connecting to it there, while not connecting the AC output ground for now. The grounds for the AC input and output are both bonded to the chassis.

And Ian is sending me a new terminal block, but it was a little unclear to me if it was an exact match. Sounds like I might have a little re-engineering to do. So I'll eventually have that output ground connected. I'm not measuring any current on the neutrals anywhere. And all the metal cases are grounded back to the main panel.

@FilterGuy, I'd be interested in your opinion about the potential for this temporary solution introducing a ground loop, or a potential for one. If it does, and you think it is warranted, I can likely rig a separate connection to the chassis for the AC output ground wire.

Not a completely happy ending yet, but everything is connected and working!

Turns out I'm definitely not the only one breaking these terminals. Be careful with those folks!

 

[FilterGuy]

but everything is connected and working!

Verry interesting...... and kinda scarry that Ian would suggest this.


Do you have a diagram of your install?

This is my understanding of the LV6548



If my model is correct (and I am pretty sure it is), the Neutral and Ground are only bonded when in battery/invert mode.

When in battery mode (Invert mode), the neutral is getting hooked up through the bonding relay. There will be an objectionable current on the ground, but at least it is contained to the guts of the inverter.

When in pass-through mode, the ground is getting connected to neutral all the way back at the main breaker box. This puts an objectionable current on the Equipment Grounding Conductor between the inverter and the main breaker box. This will appear to work but it is unsafe and considered a big no-no. If you have it hooked up this way, be very careful while working on it. An innocent-looking ground wire could have a full 120V on it.

 

[sethile]

Verry interesting...... and kinda scarry that Ian would suggest this.

It's possible I misunderstood him. He sounds Australian (talks fast), and I don't hear all that well these days. He may have included connecting the output AC to the chassis for the ground (just not using the connector). That was at least mentioned as an option.

Do you have a diagram of your install?

Not that includes the workings of the LV6548, but this is how I have things wired currently

And for the record, I'm always extremely careful while working around live equipment. I will almost always turn off power to do anything, and then check to make sure...

Thanks for checking this out!
Scott

 

[FilterGuy]

It's possible I misunderstood him. He sounds Australian (talks fast), and I don't hear all that well these days. He may have included connecting the output AC to the chassis for the ground (just not using the connector). That was at least mentioned as an option.


Not that includes the workings of the LV6548, but this is how I have things wired currentlyView attachment 89422

And for the record, I'm always extremely careful while working around live equipment. I will almost always turn off power to do anything, and then check to make sure...

Thanks for checking this out!
Scott

That looks like a good setup. I notice there is no Equipment Grounding Conductor from the LV6548 out to the transfer switch. This is good.
The grounding from the LV6548 AC in will properly ground the LV6548 and there won't be any loops.

Unless I am totally wrong about the LV6548 internals, if you put the neutral from the transfer switch to the output ground of the lV6548, everything will work, but there will be a dangerous objectionable current as described in my previous post.

 

[sethile]

That looks like a good setup. I notice there is no Equipment Grounding Conductor from the LV6548 out to the transfer switch. This is good.
The grounding from the LV6548 AC in will properly ground the LV6548 and there won't be any loops.

Unless I am totally wrong about the LV6548 internals, if you put the neutral from the transfer switch to the output ground of the lV6548, everything will work, but there will be a dangerous objectionable current as described in my previous post.

Fantastic! That's a relief, and what it looked like to my rather muddled brain. Thanks very much for checking this out for me!