Surge Protector Wiring - AC Side Epanel

nobadays

I am assisting a friend installing a solar power system on an off-grid cabin.  The equipment,  Outback 150/80, Magnum 4024pae, Magnum MMP epanel with inverter bypass,  and associated boxes, breakers, batteries and Surge Protectors were purchased from a local Amish supplier. 

My question as the subject states is wiring the AC surge protector/s.  My friend was supplied with 3 surge protectors, 1 DC and 2 AC.  The DC is installed and working, no question there.  However I have reservations about installing the AC surge protectors.  FIRST, his backup power source is a Honda generator that produces only 120vac.  So 120vac going into the inverter, 220vac coming out.

I am clear per the instructions that the surge protector should be wired red or black to input and red or black to the output. My confusion is, do we need, or even should we even use 2 surge protectors?  If only one is needed then I think I understand, one wire to the generator input (on H1), one wire to the inverter output- I assume either H1 or H2.... I would wire to H1 for consistency. 

If I were to use both then should 1 wire - red or black from each surge protector be wired into H1 on the generator input then the other 2 wires to each of the inverter outputs, H1/H2?

My feeling is that only 1 surge protector is needed.... am I correct? 

Thank you for the help!

BB.

The AC main panel, I assume is 120/240 VAC split phase North American power... You connect the SPD to both L1 and L2, and the green wire to earth ground (possibly to the green wire ground bus then to a ground rod/metal water pipe, etc. (per code).

Your SPD should have at least to SPD internally. One from L1 to ground, and a second from L2 to ground... And possibly from L1 to L2. To prevent any type of surge current to make it out to your devices.

The Genset--If it is 120 VAC, you would connect a 3 ware SPD between L1 and Neutral and Earth Ground. For the genset, usually the Neutral is floating so connecting Neutral to Ground SPD is not a bad idea. And reduces the chance of any L1+N surges from hitting your main panel.

In a normal North American home, the Neutral is bonded to the green wire earth ground bus in the main panel.

From what I have seen--Most smaller gensets (say ~3,500 Watts and smaller) have "floating" AC output (Neutral wire is not grounded to genset frame). For larger gensets, the Neutral is (typically) grounded to the genset frame (and the genset frame is supposed to be earth grounded).And normally, we "single point" ground reference the Neutral+Ground only in the main panel. (larger gensets may need to lift the N+G bond inside the genset to prevent multiple N+G bonding--But that depend on your other equipment and cabin power system configuration).

Things get more complicated for boats and RVs which can have multiple power sources (inverter, shore power, genset, etc.). And sometimes a relay is needed to lift/connect neutral+ground when needed.

SPDs are typically installed at the "wall" of the building where you bring power (and other things like Telephone, Cable, solar panels, Sat TV, or even AC power that goes to a remote shop/shed--Which not many people seem to do, etc.) inside the home.

For something like a genset can save money (and have a great level of protection) by simply only plugging in the genset when power is needed/no lightning is predicted.

Surge suppressors are there to reduce the chances of lightning surges into your home (or propagating on longer wire runs--Such as your AC distribution wiring). One can argue, if your genset connects directly to your main panel (with SPDs) and then AC is distributed--The one SPD in the main panel is enough and a genst SPD (at the wall inlet box for generator) is not really needed--Just like utility power is "SPD" protected at the utility panel too.

If you connect the generator directly to the input of AC2 for an AC inverter (inverter has transfer switch, AC battery charging, etc.)--Then you should not skip the SPD for the genset/wall entry as the Main Panel SPDs will not protect the AC1/2 inputs from genset or utility surges--SPD in main panel only protects the Inverter AC output.

You may also want to review what SPDs were purchased... The typical Electrical Supply model may be the "Delta brand" type spark gap. Those are very poor SPDs. The Midnite SPDs (for example) are much better for the job. And can save you a lot of money in equipment repairs/replacements if you have a near by strike (direct strikes, all bets are off--Just reducing the chances of fire and injury is the best you can wish for).

https://www.solar-electric.com/search/?q=midnite+mnspd

This video (yes, from Midnite) is very interesting when they go and put a spark gap type SPD under stress test at a lab.

http://www.midnitesolar.com/video/videoPlay.php?video_ID=9&videoCat_ID=8

~5,500-7,200 Volt surge suppression for their 240 VAC spark gap unit (failure) approximately 5m 30s into the video (after Midnite unit testing with MOVs).

-Bill (my understanding) B.

PS:

Midnite SPD product page. And links to video/webinars:

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=23&productCatName=Surge Protection Devices
http://www.midnitesolar.com/videoDisplay.php

nobadays

BB... thank you for your in depth reply. The SPDs are indeed Midnite Solar. 

Here is an excerpt from the instructions: 
 3.  Install  green  wire  to  the  GROUND  bus  bar.  In  AC  circuits  it  is  not  uncommon  to  connect  the  green  wire  to  AC neutral,  install  the  white  sleeving  over  the  green  wire  when  connecting  to  AC  neutral.  Make  sure  the  green  wire takes the  shortest  path  to  earth  ground!!
4.  Connect  phase  conductors.  The  phase  wires  are  black  and  red  in  color.  The  orientation  is  not  critical  to  the operation.  (AC)  With  the  POWER  OFF,  connect  one  wire  to  AC  HOT  IN  (line) and  other  wire  to  AC HOT  OUT  (load)  as shown  in  fig.  1.2  (DC)  connect  the  red  wire  to  PV  +  and  the  black  wire  to  PV  -   or  battery  minus.  PV  combiners  get installed  as  shown  in  figure  1.1 

Their wiring diagram unfortunately does not cover 120vac input/220vac output BUT.... does indicate the input from either grid or generator.   The diagram clearly shows 2 SPDs with red wires to AC inputs L1 & L2, black wires to AC outputs L1 & L2, greens to ground.  No where do I see mentioned or diagramed to wire to the generator HOT in and nuetral as you are suggesting.  If this is correct, great, I'm just not seeing it in their directions.

I must admit I got a bit lost in your reply but, it seems you are suggesting to wire the second SPD to the 2 hots on the output side of the inverter.... correct?  This would be the same as wiring to the 2 inputs in the load center, yes?

According to their diagram/schematic it appears I should wire, say the RED wire to L1 (H1 on the epanel) of the generator input, and the BLACK wire to the L1 inverter output.  I wish I could post their diagram but I can't copy it.

I really don't want to injure these $100 SPDs!

BB.

NBD,

You have a L1+N AC generator output and AC inverter input; and a L1+L2+N/G 120/240 VAC output from the inverter.

If you had a "simple" DC in and AC out inverter--Then the output of the inverter is "isolated" by a transformer (for TSW/PSW types, NOT MSW types). So it is "easy" to figure out--DC SPD on the input side (near battery bank, wherever in DC side). And the AC SPD on the AC output (main breaker panel, etc.)...

As always, looking at the manual (should be yours?):

file:///home/chronos/u-692c286a534ff9598de6b1795503c61d5d4c0005/MyFiles/Downloads/64-0032%20C%20(Owners%20Manual,%20MS-PAE%20Series).pdf

2.3.4 AC Input and Output Wiring Connections The MS-PAE Series inverter/charger has a six-connection AC terminal block and two AC ground terminals that are used to connect the inverter’s AC input/output wiring. To access the AC terminal block and the ground terminals, remove the two Phillips screws that hold the AC access cover plate to the left side of the inverter (see Figure 1-3, Item 15).

Each connection on the AC terminal block is rated for 221°F (105°C) and can accept a #18 to #4 AWG (0.82 to 21.1 mm2) CU solid/stranded wire. Each connection uses a set screw with slot-head, and the recommended tightening torque is 16 in lbf (1.8 Nm).

Each AC ground terminal can accept one #14 to #6 AWG (2.1 to 13.3 mm2) stranded wire. Recommended tightening torque is 45 in lbf (5.1 Nm).

Info: The two neutral terminals are common to each other and can be used in any combination or order. In a residential application, it is often easier to connect only one AC neutral wire to the inverter and make the other neutral connections at a central point, such as in the AC electrical panel.

2.5 Installing Lightning Arrestors Unfortunately, in Renewable Energy (RE) systems where components are wired to outdoor electrical systems, there is a greater chance of damage to these components from lightning strikes. Lightning does not have to strike directly to cause damage, it can be far away and still induce power surges or spikes in the wires of the RE system. Since the RE wires are connected to the conductors coming into the house the inverters, charge controllers, batteries, and other components in the house or power shed are easily susceptible to damage.

The best line of defense against these high voltage surges—caused by lightning—is to ensure you have proper system grounding. Proper grounding attempts to divert lightning surges to earth, instead of going through your electrical components. However, for additional protection in lightning prone areas or where good grounding is not feasible, install lightning arrestors (also known as high voltage surge arrestors) on the DC and AC circuits of your renewable energy system. Lightning arrestors are devices that respond to voltage variations instantaneously, effectively intercepting potentially damaging spikes and surges and reducing them to acceptable power levels to protect electrical equipment. Metal Oxide Varistors (MOVs), Silicone Oxide Varistors (SOVs), and Zinc Oxide Non-linear Resistors (ZNRs) are three types of lightning/surge arrestors.

Install the lightning arrestors as close as possible to the equipment you are trying to protect. Install additional lightning protection (secondary lightning arrestor) if equipment is more than 60 feet away from where the primary lightning arrestor is connected.

Info: For more information on lightning protection in RE systems, review “Protection Against the Effects of Lightning on Standalone Photovoltaic Systems – Common Practices“ at www.iea-pvps.org.

Your inverter has an 120/240 VAC input and 120/240 VAC output. And a (hardwired?) AC Neutral connection (N1 = N2 terminals).

So, it is difficult to say if AC input is transformer isolated from AC output. But since Neutral input is connected to Neutral Output, it is probably best to treat the inverter as having both isolated output (at least on the L1/L2 power connections when running inverter only/transfer switch open; and as non-isolated when genset running and transfer switch closed) and you would want SPDs on both sides (one on the Generator AC wall box input) and one on the Inverter AC output (main panel, E-Panel, etc.).

As long as both units are the MNSPD-300-AC units, then they will be safe and effective on both your Genset (120 VAC only) and AC inverter output (120/240 VAC).

You will not damage the SPDs as long as they are rated for the correct voltage.

Connecting the SPD "green wire" to neutral--As long as the Neutral is "Neutral/Ground Bonded" somewhere in your system, then it does not matter (a lot) if you connect to Neutral or Green wire ground.

HOWEVER--You want the lightning path to be as short and direct to "earth ground rod" as possible. The longer and more twisted the path, the more chance for lighting to leave the neutral (or grounding) wire.

AND--If you connect the SPD "green wire" to your neutral--You are risking "injecting" lightning/surge current into the cabin's AC power system (L1/L2/N)--Which is what you are trying to avoid...

SO--I would connect SPDs to the Green wire ground bus bar and have a short/straight path to ground rod for the system grounding.

Using both an AC generator SPD and AC main panel SPD may be overkill in this case--But it is the safest way to proceed. They will not damage each other as Current only flows through an SPD if there is >300+ VAC surge current surge. At that point, you want them to conduct and short that surge current to ground.

-Bill

nobadays

BB.....  I wish I could say it was crystal clear but at least I can say I've learned a little, enough that I feel confident enough to go ahead and wire these 2 SPDs into place.

Thank for your time and knowledge! 

BB.

I don't have any drawing tools handy... Try Text:

Genset (floating N)=======SPD(L1/N/Ground)=|Wall box|====epanel ==== in [AC Inverter] out ====== Main panel=SPD (L1/L2/Ground)
                                                                                                                                                               [Neutral+Ground Bond]

Recommended:
Solar array============SPD(+/-/Ground)=|Wall======Solar Charge Controller

Maybe:
Battery bank==SPD(+/-/Ground)


"Ground" 6 AWG minimum Green Wire to Ground (ground rod, cold water pipe, etc.)

If you have several ground rods (i.e., Ground Rod near SPDs+Wall and a second Ground Rod near main panel--The two (or more) ground rods should be tied together with 6 AWG cable (insulated or not) to tie all ground rods together (for 120/240 VAC electrical safety).

Lots of people use SPD (rated lower DC Voltage) for use on the Battery bank, and the Solar Array (low or higher voltage depending on Voc-array).

I am not sure an SPD on the battery bank is really needed--You have a bunch of Large Batteries that will hold 12/24/48 volts between +/- cables and usually we tie - cable to ground rod... Probably much better than any SPD (big lead plates close together--giant capacitor/voltage clamp).

In theory, the SPD will "protect" devices ~20-60 feet of cable run from the SPD (i.e., if you have AC power at a pump house 120 feet away--You should put an SPD in both the main panel (home) and in the panel/box at the pump house.

An SPD is just something that "shorts out" high voltage spikes to the green wire/ground. I.e., a 300 VAC rated SPD (Midnite) will "conduct" at 380+ volt spike.

Other than a direct lightning strike, the only other way to damage a Midnite SPD would be to put a low voltage SPD on a higher than rated voltage source. The Midnite units have series fuses to prevent "too much current"/surge energy from overheating SPD/Wiring and starting a fire.

-Bill