Ground neutral bond

[Oldphile]

I read today that ground neutral bond should be at the first point of disconnect. Is this true? I had a Sol-Ark 15K installed with an external AC disconnect. I doubt my installer moved the ground neutral bond from my main service panel to the disconnect. Why would this be important?

 

[FilterGuy]

I read today that ground neutral bond should be at the first point of disconnect.

That is true, but it seems that in retrofits where a new disconnect is put in, most people don't change it....and I have not heard of inspectors complaining. If the new disconnect is close to the point where the bond exists, I don't think anyone will complain and I would not worry about it.

I think they want the bond near the service entrance in order to make it unlikely it will get disconnected during a system modification. By having the NG bond, the Grounding Electrode Conductors, and the main disconnect all in the same place at the service entrance it is easy to check and not likely to be accidently disconnected. As an example, if the NG bond was in a downstream breaker panel it would work but 1) the inspector would not know where to find it and 2) if that panel got decommissioned, they could inadvertantly lose the bond.

 

[fafrd]

That is true, but it seems that in retrofits where a new disconnect is put in, most people don't change it....and I have not heard of inspectors complaining. If the new disconnect is close to the point where the bond exists, I don't think anyone will complain and I would not worry about it.

I think they want the bond near the service entrance in order to make it unlikely it will get disconnected during a system modification. By having the NG bond, the Grounding Electrode Conductors, and the main disconnect all in the same place at the service entrance it is easy to check and not likely to be accidently disconnected. As an example, if the NG bond was in a downstream breaker panel it would work but 1) the inspector would not know where to find it and 2) if that panel got decommissioned, they could inadvertantly lose the bond.

I have a follow-on question to this:

My understanding is that if adding a dual HF off-grid inverter, the neutral-ground bond used for the main grid service can also be used to provide neutral to the inverter (both to AC input and AC output) but my question regards where that neutral connection should be drawn from:

The easy thing to do is to draw neutral from the MSP (along with L1 and L2).

The N-G bond is in a main breaker box which is connected to the MSP via ~6” of 2” conduit and I could probably bond a second smaller neutral wire to the same primary grounding lug if a ‘star’ configuration for the on-grid and off-grid neutral would be preferable (there are already two ground wires in the primary grounding lug - one from a grounding rod and a second from copper water main piping at entrance to the house).

So would a star configuration at the primary Neutral Ground Bond be preferable and if so, is it worth worrying about if te alternative is taking neutral from the MSP after a ~6” foot run of 2” conduit from primary Neutral Ground Bond to the Neutral Busbar in the MSP?

 

[FilterGuy]

I have a follow-on question to this:

My understanding is that if adding a dual HF off-grid inverter, the neutral-ground bond used for the main grid service can also be used to provide neutral to the inverter (both to AC input and AC output) but my question regards where that neutral connection should be drawn from:

The easy thing to do is to draw neutral from the MSP (along with L1 and L2).

The N-G bond is in a main breaker box which is connected to the MSP via ~6” of 2” conduit and I could probably bond a second smaller neutral wire to the same primary grounding lug if a ‘star’ configuration for the on-grid and off-grid neutral would be preferable (there are already two ground wires in the primary grounding lug - one from a grounding rod and a second from copper water main piping at entrance to the house).

So would a star configuration at the primary Neutral Ground Bond be preferable and if so, is it worth worrying about if te alternative is taking neutral from the MSP after a ~6” foot run of 2” conduit from primary Neutral Ground Bond to the Neutral Busbar in the MSP?

I am not following. Can we get a drawing?

 

[Oldphile]

The electrician said something about a ground issue when he was last here. Hopefully I'll remember to ask him tomorrow.

Meter--Fused Disconnect--Sol-Ark--------25'------------MSP (where I assume neutral-ground bond is now). There's no critical loads panel.

Would this warrant moving the neutral-ground bond?

 

[FilterGuy]

I assume MSP is Main Service Panel.

No. Moving the bond would not make any significant difference electrically. However, some inspectors might balk at the NG bond being 25' from the first means of disconnect.

 

[raurre]

You normally want it as close as possible to the meter to have the shortest amount of parallel paths it can return to the transformer on.

 

[garetwo]

When a short to ground occurs, the hope is to mitigate the path back to the transformer going back through a neutral wire, which could then be through components/devices/other loads. So, a utility bonded neutral on a 120/240 3-wire split phase would typically be at the first disconnect, then 4 wires would leave from there and all future neutral bars would be isolated from ground. I am just an electrician, very new to solar, so I find bonding the neutral derived from an inverter that is tied to the grid very interesting! I look forward to finding the definitive answer, if there is one.