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I recently purchased a Siemens MM0202B1200 200-Amp meter / disconnect combo panel. I would like to connect a Square D HEPD80 Type 1 SPD inside the disconnect panel.

The SPD has 4 wires: 2 black, 1 white, 1 green. From looking at the disconnect panel, I can see that I can use ring terminals on the 2 black wires and then connect them to the locking nuts on the 200A breaker's two hot lugs.

EDIT: Rookie mistake pointed out by Harper below: I somehow overlooked the two additional lugs on the load side of the 200A breaker (duh, how else are you going to connect to the main panel?). I should not connect the SPD's 2 black wires with ring terminals, but rather to the load side of the breaker with Polaris connectors.

Since the disconnect panel does not have a neutral or ground bus bar, I am unclear on how to properly connect the ground and neutral wires. In addition to the photos from the Amazon link (above), I have attached an image of the panel's wiring below.

From this image you can see lugs labeled N1 through N4 which I think are the ground and neutral lugs. On the service disconnect side there are two N3 lugs and two N4 lugs. I believe N3 is for the home's load center neutral line and the N4 is for the ground. The N3 lugs are rated for a minimum #4 wire and the N4 lugs are rated for a minimum #14 wire.

The SPD has #12 wires, meaning that I can connect the SPD's ground to the N4 lug (rated for #14 wire), but since the N3 lug requires at least #4 wire, I cannot connect the SPD's #12 neutral.

What is the proper way to connect the SPD's #12 neutral wire to the panel's N3 lug which requires a minimum of #4 wire?

Meter/Disconnect Panel

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  • What size is the equipment grounding conductor in the outgoing feeder? Aug 5 at 23:39
  • I currently only have 100A service but am preparing to upgrade to 200A service and that is what the new meter / disconnect panel is for. So I can't say what size the EGC in the outgoing feeder is because I don't have the new feeder yet. Will you please tell me how the size of the EGC relates to the question? Then I can be sure to run the correct size. Thank you!
    – stmp945
    Aug 6 at 0:45
  • It's mostly which lug the EGC occupies that is the question -- a 4AWG or larger EGC would fit into a N3 lug, leaving both N4 lugs free for the SPD, while a 6AWG EGC would have to use a N4 lug, leaving only one N4 lug free for the SPD's use Aug 6 at 1:39
  • If I understand correctly, you are saying that I could use both N3 lugs with 4AWG for the outgoing neutral and ECG wires to the main load center panel, and that this strategy would free up the N4 lugs for the SPD's neutral and ground wires. Is that right?
    – stmp945
    Aug 6 at 2:20
  • Come to think of it, who's your electric utility? My prior analysis forgot about the grounding electrode conductor... Aug 6 at 2:51
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Can't tap hot that way

From looking at the disconnect panel, I can see that I can use ring terminals on the 2 black wires and then connect them to the locking nuts on the 200A breaker's two hot lugs.

The breaker has four hot lugs. There are no accessible lugs on the protected side of the breaker, so you're clearly looking at the ones on the "always hot, totally unfused" side (the meter side).

That's a baaaad idea. For a half dozen reasons. It'll be written up as 110.3(B) disobeying equipment instructions of both the meter-main and the SPD.


The "right" way to do this is with 3-port Polaris connectors, with a 200A pigtail to the breaker, 200A feeder to your master panel, and probably a #6 (or whatever the smallest legal wire is for the Polaris) pigtail to the SPD. Then you will need to have another splice from that wire to the SPD's leads.

However, this is still not really right -- see bottom.

Neutrals and grounds

On the neutral and ground, this equipment is certified as service equipment only - meaning neutral and ground are permanently bonded and are effectively the same thing in this panel. Neutral and ground must be carried separately to your breaker panel. Note also that EMT, IMC or RMC metal conduit are themselves valid ground paths, possibly removing the need for a ground wire there.

So for neutral-ground, this panel gives you 4 screws. You'll need 1 for neutral to your breaker panel. 1 for ground to your breaker panel (maybe). And 1-2 to attach your grounding rods. You must use the supplied bar for neutrals. But if you need more ground lugs, you can always add an accessory ground bar or just bolt a lug to the enclosure.

Another option, if a bare copper ground wire is used, is use a split-bolt to tap the ground wire inline.

SPD needs real breaker protection

None of this addresses the fact that the SPD's instructions require circuit breaker protection for the SPD. It recommends a breaker no larger than 20A but does not require it. But still, it is at the discretion of the AHJ, and I doubt they'd allow anything bigger than 50A.

Really, since you want to put equipment out in this box, you would have been better off going with a "ranch panel", which is the same thing plus a few branch circuit breaker spaces for things like this. Something like a MC0816B1200RCT or MC0816B1200RTH.

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  • Since ground and neutral are bonded in this panel, I think that means that they will NOT be bonded in the main load center, correct? In other words, what I am calling the main load center is actually considered a sub-panel since it is not the first disconnect means, and sub-panels need to have the ground and neutral separate. Since ground and neutral are bonded in this panel, does that mean I can add a ground bar and connect both the SPD's ground and neutral to it?
    – stmp945
    Aug 5 at 17:58
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    Also, regarding your comment about the SPD needing breaker protection: I thought that the difference between type 1 and type 2 SPDs is that type 1 SPDs do NOT need breaker protection, specifically so that they can be installed in places where a breaker is not available? In fact, the installation instructions for the type 1 HEPD80 specifically show separate instructions for installing it with a breaker OR for "direct bus" connection, without a breaker.
    – stmp945
    Aug 5 at 18:12
  • Yes, panel with all the breakers will need separated neutral and ground, and a 4-wire feed. You can add a ground bar here, but you can't put neutrals on it. Neutral is not ground. I read the actual UL approved instructions for this and they do allow tapped off a main breaker, but not totally unfused. Aug 5 at 18:43
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Your best bet is to use a pigtail off one of the N4 terminals, nutted to both ground and neutral on the SPD

What I would do to deal with the shortage of neutral/grounding terminals on your meter main is use a wirenut to connect both the neutral and grounding leads from the SPD to a 12AWG THHN pigtail, then connect that pigtail to a N4 terminal on the meter-main. The two hot leads, then, get connected to the feeder hots using an insulation piercing tap connector (Ilsco IPC-4/0-6 or equivalent) to make the connections -- these require less pigtailing than a standard insulated setscrew-type splicing connector, and are inexpensively available as well.

This, then, leaves the N3 terminals available for the feeder's neutral and grounding conductors, provided the feeder grounding wire is 4AWG or larger (always true if you're using SER for the feeder), and the remaining N4 terminal open for the grounding electrode conductor coming in. If your feeder is in conduit, you can either upsize the feeder grounding wire to 4AWG from the normal 6AWG, or swap the EGC to a N4 terminal and use the remaining N3 terminal for the GEC provided the latter is 4AWG or larger. Note that you can't use the N1 terminal for the GEC, best I can tell, as it's already occupied by the pigtail lead to the factory-fitted fifth jaw on this unit, even though your utility otherwise permits GEC connections in the meter base.

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