need MNSPD wiring clarification

[laszlo]

I am looking at ordering my first Midnight MNSPD-300 -- it is now available from cosolar.com (follow "solar parts" link).

I was was wondering if someone could clarify Fig 1.2 of the MNSPD installation manual. It tells to  connect the red and black phase wires on AC IN and AC out in the Midnite mini-combiner.  But I think this drawing is not applicable to 240V, two-wire systems.

I have a 240 Volt interter (magnum ms4448 ), and so it has two AC out hot legs (L R)  How should I wire  MNSPD in this scenario?

[Robin]

I didn't go back and look at the manual, but you will need two SPD300's to protect any 120/240V inverter. One can go to the input busbars on the E-Panel and one to the output busbars. If you are not using an E-Panel, you will need to somehow connect to the inpts and outputs. The green wire always goes to ground. Another way to hook it up is to use one SPD between the input and output for leg1 and the other SPD for leg2.

[vineyfig]

Looking at the manual instructions for connecting the 300 to a 240VAC service panel/breaker box -- in Figures 1.6 and 1.7 the red and black wires are shown both connected to only one leg of the 240VAC supply. This can't be right? New member Zeke

[Robin]

Figures 1.6 and 1.7 are a bit misleading. the electrical box busbars the feed back and forth from one side to the other have been ommitted for clarity. In a 120/240 distribution panel, the breakers always alternate from legA to legB on each side. You will notice that the two breakers are located adjacent to each other. This will be both legA and B. If distribution panels were not built this way, then a 240V breaker could not be made as a 2 pole breaker joined together.
I will be more careful when making drawings in the future.

[vineyfig]

Ah so! of course. Thanks for the clarification, Robin -- Zeke

[laszlo]

I wired my SPD300 across the inverter's  L and R hots since it's supposed to clamp above 300 V RMS.  This is also how my Delta SPDs  are wired. Based on the drawing later on in the manual, that shows the SPD  wired across the two the legs of a 240V breaker in a house distribution panel, I inferred this was the intention of the engineer. The manual is not too bad, but I think a 1-line drawing in addition to the photos might be useful.

[Robin]

You can certainly wire across both legs of AC in your distribution panel. The green wire goes to ground of course. The SPD300 starts conducting at about 470VAC. The max you will see in your house is 775VAC with 100 amps being sucked up into the SPD. Lightning is very fast and you can see that type of current for brief periods of time although 100 amps would indicate a pretty severe close lightning strike. By the way, your Delta arrestors will be sitting there doing absolutely nothing until the voltage reaches 7000 volts. What is it actually protecting at this voltage? Nothing that I can think of. Most listed appliances and inverters, charge controllers etc. have been hi-potted at the factory to 1800VDC or so. Our classic has to pass 2250VDC before we can ship them. What this means is that a lightning arrestor that clamps a surge to 1000V or so will protect your stuff. The delta arrestors will not. Most products will arc over internally to the case (earth ground) at about 3000V. If that happens, they are toast. Grounding alone does not solve the problem. Lightning surges come into your house or system on both the positive and negative PV wires and hot and neutral AC wiring. Even though one of these wires is grounded, the grounded conductor will see the surge voltage due to resistance of the wire. The surge is looking to jump over to earth ground. That usually happens inside the inverter, charge controller, TV etc. Lightning is very unforgiving. We had no intention of creating our SPD's until we actually tested a Delta. We had no idea that they were just three wires stuck in sand.

[Volvo Farmer]

We had no intention of creating our SPD's until we actually tested a Delta. We had no idea that they were just three wires stuck in sand.

Wow! Uhhh. I think you just sold me a hand-full of your arrestors. Thanks for the detailed explanation.

[mike90045]

We had no intention of creating our SPD's until we actually tested a Delta. We had no idea that they were just three wires stuck in sand.

But It's calibrated sand !

[Halfcrazy]

We had no intention of creating our SPD's until we actually tested a Delta. We had no idea that they were just three wires stuck in sand.

But It's calibrated sand !

Yes and you can not find calibrated sand on just any old beach 

[ericwahl]

I noticed in the MNSPD manual, p2 chart, it says the 300V is for off grid combiner boxes, but that use is not listed for the 115V version. Is the 115 version OK for solar circuits if the voltage is under 115V at all times? Or would the limit be under 150V? Or should you always use the 300 or higher on solar circuits? Thanks.

[Halfcrazy]

The 115 is ok for offgrid pv combiners as long as you keep the voltage down they say max 150vdc but they can start to clamp around 162vdc so I would tend to use say 125 VOC as the tipping point to switch to the 300.