MNSPD Wiring for 120V AC Panel

[mjp24coho]

My offgrid cabin is 100% solar, fed by my 120V Magnum inverter in my detached garage.  I have an AC panel there, as well as an AC subpanel in my cabin.  I want to install an MNSPD in both AC panels, but I'm a bit confused on how to wire them.  The wiring diagrams for AC panels I've found assume a 240V system (with the black and red leads from the MNSPD going to both sides of the same 240V breaker).  How would I wire it in a 120V panel?

[TomW]

I am probably wrong and someone may correct me but...

I would either just use one of the Surge suppressor leads to the HOT AC line or put both AC surge suppressor leads on the one HOT AC line?

Going to review the install guide for them.

Tom

[Halfcrazy]

Here is how I would do it. Presumably one of these panels has the AC neutral and ground bonded. In that panel I would put the red and black on the AC hot lead and the green to ground. In the panel without the bond as the neutral floats sort of I would wire it Red to AC hot, Black (with included white heat shrink) on the AC Neutral and green to ground

We tend to over look Neutrals and in cases where the bond is a ways away this can be problematic. Electrically it is at ground potential but during a strike or very strong surge the resistance in the wire can make it look isolated from ground.

Ryan

[TomW]

Ryan;

Much better.

Tom

[mjp24coho]

Thanks - that helps.  I'm not entirely sure if my main AC panel (in garage) or subpanel (in cabin) has neutral bonded to ground or not - how could I tell?  For additional background, I'm utilizing the Magnum 4024 pre-wired Midnite E-Panel (came pre-assembled with the Classic CC and Magnum 120V inverter) installed by the battery bank in the garage.  From the E-Panel, I'm running 10 AWG romex 25' to the 120V main AC panel in the garage (offgrid, so there is no other AC input), which then feeds 120' into the AC subpanel in the cabin.

[Halfcrazy]

Look in the panel and see if the AC neutral (White) wires are mixed in with the ground (Bare) wires. If so then that panel is bonded. If they are all neatly separated than assume that panels is isolated.

Ryan

[mjp24coho]

I'm fairly certain they are not bonded then - there are separate neutral and ground bus bars, and the bars are not connected from what I recall.  The obvious next question then - should they be bonded?  I'm still trying to get my head around neutral-to-ground bonding, including the benefits, needs, and risks if not.  Is there any neutral-to-ground bonding that occurs in the pre-wired E-Panel?

[Halfcrazy]

yes if this is an Offgrid scenario the bond could very well be made in the Epanel. You definitely want one bond for sure but not 2. Even though the wires in the electric panel are separate one of them could still be bonded. There is a green bonding screw typically shipped with all the electrical panels and the electrician could have installed it. Typically the bond is made at the same panel that has the ground rod hooked to it.

Ryan

[mjp24coho]

Do you know if the Midnite pre-wired E-Panels (with Magnum inverters and Classics pre-installed) come with neutral to ground bonding already wired?  I looked at the magnum inverter manual, and it has a neutral-to-ground bonding included within it, which can be removed if necessary.  I need to make sure I don't have two such bondings in my system.  I'll also have to double check to make sure my main AC panel doesn't have any neutral-to-ground bonding - I know it doesn't via any bond wires/jumpers between the neutral and ground bus bars, but I don't know if the ground bus bar is bonded to the panel frame (via the bonding screw) - I'll have to check.  My generator (which feeds the inverter) does not have neutral-to-ground bonding.  I understand the entire system should only have one - even though it's preferred to be at the source, it would be easiest to have it occur within the AC panel, unless there are any concerns with it not being at the source (generator or inverter).  I recognize this has turned more into a discussion about neutral-to-ground bonding, which can be a never ending discussion, but I appreciate any input out there.

[tecnodave]

To satisfy the NEC there shall be only one bond and that needs to be in the "main panel". In this case that would be the epanel  because both that generator and inverter feed it. The generator and inverter should have separate neutral and ground, "not bonded"  The "main Panel " in the garage in this case would be considered a sub panel as there are main breakers in the epanel that are the first breakers from the power source and would have separate ground and neutral busses in the "main panel" in the garage. The cabin panel would also have separate neutral and ground,(not bonded)  but with an additional ground rod connected to the ground buss. (As of NEC 2008) (separate building)  The feed from the main panel to the sub panel needs to be 3 wire (120 volt) or 4 wire (240 volt) with separate neutral and ground conductors. The ground wire from main panel to sub panel would be 6 ga up to 100 feet but 4 ga for this installation (125 feet) assuming that the conductors are encased in a conduit or raceway. The neutral and hot wires would also be one gauge up for that distance.

There are no changes from this on the NEC 2011 or NEC 2014 but all jurisdictions do not use the same code set.

I agree with Ryan's approach to wiring the SPD's although I have not checked the NEC on this case, I have done SPD's on 240 volt utility feed panels where black goes to L1 and red to L2 through a dedicated breaker and green to ground buss. And do check if there is a green bonding screw on the neutral buss on the sub panel, if there is, remove it as this would be a violation of the NEC.


td

[mjp24coho]

Thanks for the clarification on the code. I'll wire it so that the e-panel has the only neutral-to-ground bond. I assume that can be done by either (1) installing a jumper cable (6 or 4 awg) between AC neutral and AC ground in the epanel, or (2) ensuring the AC ground bus in the epanel has the ground screw bonding it to the epanel frame (which would bond it to the AC neutral)?  Would either of those work?

I'll make sure there is no ground screw in the ground bus bars in either the main AC panel or AC sub panel. I'll also remove the neutral-ground bond in the magnum inverter.

[vtmaps]

The ground wire from main panel to sub panel would be 6 ga up to 100 feet but 4 ga for this installation (125 feet) assuming that the conductors are encased in a conduit or raceway.

A very well written explanation, technodave.   
Under what conditions is it permissible to NOT have the conductors in conduit?   Is it permissible to use a bare ground wire in the trench?  Is there a certain distance where no ground conductor is required (local grounds at each end)?

--vtMaps

[Halfcrazy]

If the magnum was wired by us it should have the bond. Verify that it has not been removed though.

Ryan

[tecnodave]

vtmaps,

Using direct burial cable (UF) it would be permissible to not run in conduit but then you may have problems with gophers , also the provision in the code that ground wire be 6 ga if protected in conduit and 4 ga if exposed, so the wire (UF) would be sheathed in conduit extending down into the ground 18 inches, then be not encased in conduit for the rest of the run. Running wire overhead would be acceptable also but the wire would need to be sunlight resistant. (TW)  My understanding is that under NEC 2008 and newer that any separate building requires a separate ground rod, but this is not hard and fast , a detached garage from a house within 15 feet with a 30 amp service does not require a separate ground but a second dwelling would require one, even if that were a guest cottage with a 30 amp service. A buried ground conductor between the buildings with buried ground road is acceptable if you use direct burial connectors on the ground rods and the ground wire cannot be spliced, it must run from first panel thru ground clamps on the ground rods to the second panel. I did a very difficult two building power installation with two meter mains in which the inspector required this installation because I could not drive ground Rod at the buildings due to concrete 3 feet down so my ground rods were 6 feet from each building with a one piece ground bonding wire. In this case being down 24 inches (240 volt required down 24 inches) the wire was "protected" so was 6 ga. In this case the neutrals and hots were in conduit and the ground was alongside the conduit.


mjp24coho,

Yes install a 6 ga jumper between the neutral and ground buss in the epanel, I am not sure if the ground buss is connected to the box of the epanel, but it must be. The ground rod would connect to the ground buss in the epanel.  The ground buss must be bonded to all metal in the system.

Notes on the NEC: the last line is "quote". When in dought refer to the AHJ. (authority having jurisdiction) , bottom line is that your local building inspector has the last word

Explanation of wire designators:

T= Thermoplastic insulation
H= Hot (75 degrees Celsius)
HH= Hot Hot (90 degrees Celsius)
No H = 60 degrees Celsius
N= Not Weatherproof
W= weatherproof

So THHN is Thermoplastic, 90 degrees, not weather proof
TW is thermoplastic, 60 degrees, weather proof.    Etc.

[mjp24coho]

There's a separate ground rod for the cabin and one for the detached garage. If there is no ground wire running between the cabin and the detached garage (I'll need to check if there is), would I need to do a separate nuetral-to-ground bond in the cabin also?

For the neutral-to-ground bond in the epanel - would I accomplish that via a green bonding screw in the ground bus bar (bonding to the epanel frame) AND a jumper wire between the neutral bus bar and ground bus bar, or just one of those two methods?

Thanks again for everyone's plain-speak help in de-mystifying neutral-to-ground bonding for me.