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Joined: Jan 2009
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This seems to be a murky area between engineers, AHJ's, contractors and utilities and I am curious to anyones input.

Does a Supply side connection of a PV system , as allowed on 690.64, and its associated PV AC Disconnect count toward the 6 disconnect rule?

The scenario that I am curious about is a typical Northern NJ Multi- Tenant building where PSEG has 6 CT cabinets (metered) feeding (6) 400-600A disconnects that then feed meter banks for individual tenants. Typically one of these metered services is the House service (common area lighting, site lighting, etc) and the one that the PV array would be feeding. The supply side connection is made after the meter and before the main.

Any experiences?

Joined: Apr 2003
Posts: 362
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I say it counts for the simple reason, that if you such 6 switches off the power then should be off to all loads.



Ob


Choose your customers, don't let them choose you.
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Ok, now what about when the PV array is tapped on the supply side of the main disconnect, shutting the main disconnect would de-energize all downstream loads from both sources (utility & PV)?

Joined: Apr 2003
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Yes again. No need to back feed the POCO lines. Think of a generator. Or servicing the meter base or overhead drop.


Choose your customers, don't let them choose you.
Joined: Dec 2002
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I see your point. The DC from the solar array enters an inverter after a disconnect. The inverter is "Grid tied" and can not generate power once main power to the building is removed. Does the solar array disconnect count as one of the 6?

The answer is, it depends. If the solar DC power never enters the buillding, I would say no. But, To inform the fire department of possible hazards required 230.2(E). If the DC enters the building, well, under 230.2 "Different Characteristics" applies and allows the additional disconnects with Identification. Disclaimer: Local jurisdictions may have rules for this, so as always talk to your local AHJ.

Shane

Joined: Jun 2004
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The trick inverter boxes absolutely will not permit power to flow in the event of grid disconnection no matter how it happens.

Next, due to the saturation effects in PV solid state physics they are NOT to be considered an 'infinite bus.' It's the infinite bus character of line power that dictates the performance of OCPD. ( Breakers & fuses )

Having said that, for anything this new, get an opinion from the local AHJ and Poco. Why take a chance they've got an alternate insistence?


Tesla
Joined: Jan 2009
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I agree to always check with the AHJ & POCO, in this case we are trying to come up with a design standard for a client constructing arrays on buildings all over the state. SO we are trying to come up with a default position on the issue, that could then be altered on a case by case basis.


Joined: Feb 2002
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Since we are on PV systems, what about the feeder that runs from a service panel to the PV sub panel. You have a panel on the PV side where a couple of 2 pole 20 amp and 30 amp breakers are, then it runs to the service panel. At this point the current is flowing toward the service panel. On the service side, you tap the main service conductors.

Now if the PV system is shut down for any reason, the current will still be on the feeder from service panel to PV sub panel.

Shouldn't there be some sort of disconnecting means and some sort of over current protection on that feeder as it leaves the service panel?

You have unprotected wires running from the service panel to the PV system, is that safe?

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I agree harold, I have noticed (to the annoyance of many design engineers) that more savvy inspectors are applying the 10' tap rule for instances such as you just described.


Joined: Jun 2004
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Harold...

My understanding is that should the grid go down so too does the inverter.

So there is no energy on the feeder.

The DC current going to the inverter backs up and saturates -- and stops flowing.

The electronics inside the trick inverter can tell when the grid is out.

This is a specific design feature demanded by our Pocos out here to get the tax credits and the utility ( by state provision ) rebates.

As for the feeder going the other way -- like night time -- ours are sized such as to qualify easily under the 25-foot tap rule. Still they are always placed as close as possible to the Service for reasons of economy.

So it's a total non-problem where I sit.

The one thing I've noted is that the PV boys want cheap labor -- that is new to the electrical trade -- so the result is that many, many installs are raceway ugly. Too much Sealtite where a clean EMT run would do nicely.



Tesla
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