Inverter to Step-up Transformer EGC or SSBJ ?

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hill900505

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Hello everyone,
I spoke with an inspector at a project site and it seems that we have different opinions on sizing the ground wire running from a 3 phase ungrounded solar inverter ( 3 phase, 3 conduits, each conduit contains (3) 600kcmil Al conductors together with one 2/0 EGC (NEC 250.122)in each conduit, inverter has 1000A OCPD). The inverter output cables run to a step up transformer and then to the grid. However, the inspector thinks this conductor needs to be considered as a SSBJ which needs to be sized differently(600kcmil *3 *12.5%). What are you guys' opinions on this issue?
 
1000 amp breaker with aluminum needs 4/0 the way I read it not 2/0

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It is 2/0 copper 4/0 aluminum in each set of conductors
cf735bdd821f9c615a09fb501b74b246.jpg


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Is this a service transformer, i.e. on the POCO side of the service point and making this a supply side connection per 705.12?

Or is this an SDS transformer on the consumer side of the service point and after a service disconnecting means?

If the latter, I agree with your inspector. If the former, please advise.
 
Smart $ said:
Is this a service transformer, i.e. on the POCO side of the service point and making this a supply side connection per 705.12?

Or is this an SDS transformer on the consumer side of the service point and after a service disconnecting means?

If the latter, I agree with your inspector. If the former, please advise.
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The one line for the job is :
13.8kV Utility distribution pole with group operated disconnect switch– underground MV cable – a 13.8kV/(480/277) transformer and a 13.8kV/400V transformer(the one in question) in parallel.
1. The 13.8kV/400V transformer (high side grounded wye, low side ungrounded wye) connects to an inverter then solar panels
2. The 13.8kV/(480/277) (wye-wye both grounded) transformer connects to (a) 480-120V/240V load center (small transformer on top section of the enclosure, a main breaker and some branch circuit breakers all in the same enclosure). (b) a separate 100A breaker enclosure, then PVC to a grounding transformer.
With this many SDS, it is quite challenging to ground this system right.:slaphead:
 
hill900505 said:
The one line for the job is :
13.8kV Utility distribution pole with group operated disconnect switch– underground MV cable – a 13.8kV/(480/277) transformer and a 13.8kV/400V transformer(the one in question) in parallel.
1. The 13.8kV/400V transformer (high side grounded wye, low side ungrounded wye) connects to an inverter then solar panels
2. The 13.8kV/(480/277) (wye-wye both grounded) transformer connects to (a) 480-120V/240V load center (small transformer on top section of the enclosure, a main breaker and some branch circuit breakers all in the same enclosure). (b) a separate 100A breaker enclosure, then PVC to a grounding transformer.
With this many SDS, it is quite challenging to ground this system right.:slaphead:
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Even ungrounded systems are required to have a grounding system and bond noncurrent-carrying metal parts. They are also required to have a ground detection. With other grounded systems on the premises, the grounding systems should be coupled IMO but as SDS's, the NEC does not require such unless part of the same building or structure. So with that said, I still agree with your inspector... and add that there needs to be ground detection installed somewhere if the secondary is truly ungrounded. Whoever engineered this project should know that. I do not know the circumstances why they decided to go ungrounded, but as I see it, the secondary should be grounded, if not solidly, at least go with high impedance grounding, especially if there will be no one to monitor ground detection on a frequent basis.


PS: the other system, especially the grounding transformer part, sounds weird. Can you post the one line (please verify non-proprietary status and/or censor the qualifying data before posting).
 
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If the inverter doesn't have a transformer in it - and it probably doesn't if the DC is ungrounded - then the solar system is not an SDS. In case that is the confusion.
 
jaggedben said:
If the inverter doesn't have a transformer in it - and it probably doesn't if the DC is ungrounded - then the solar system is not an SDS. In case that is the confusion.
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jaggedben said:
Another point is that 690.47 ought to be the governing code for the inverter's grounding connections.
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690.47 is about the grounding electrode system. The OP's case is about sizing the grounding conductor between the transformer and the inverter.

At the very least, it should be sized per 250.122... but how does one size based on OCPD when there is none. Some, perhaps many, but the AHJ's perspective is what matters here—will call this conductor a supply-side bonding jumper (SSBJ) under 250.30 because the transformer secondary, not the PV system, is an SDS. An SSBJ gets sized per 250.102.
 
Smart $ said:
690.47 is about the grounding electrode system. The OP's case is about sizing the grounding conductor between the transformer and the inverter.
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Okay I hear what you're saying (although 690.47(C) (2011 or 2014 NEC) could still have something to say about that conductor).

At the very least, it should be sized per 250.122... but how does one size based on OCPD when there is none. Some, perhaps many, but the AHJ's perspective is what matters here—will call this conductor a supply-side bonding jumper (SSBJ) under 250.30 because the transformer secondary, not the PV system, is an SDS. An SSBJ gets sized per 250.102.
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The OP did mention a 1000A OCPD. It's unclear if the inspector wants the SSBJ to extend beyond that or not. I'd agree it's an SSBJ up to the point where that's normally required, i.e. from transformer to first disconnecting means, to my understanding. There's gotta be a disconnecting means in there somewhere.
 
jaggedben said:
...
The OP did mention a 1000A OCPD. It's unclear if the inspector wants the SSBJ to extend beyond that or not. I'd agree it's an SSBJ up to the point where that's normally required, i.e. from transformer to first disconnecting means, to my understanding. ...
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OP mentions a 1000A ocpd, but none mentioned in f/u post and that's what I was going on in my last post. With a disconnecting means in there, an ssbj is definitely required, and it is sized per 250.102.

jaggedben said:
There's gotta be a disconnecting means in there somewhere.
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Not necessarily. See 690.9(F) Exception
 
Smart $ said:
Yes, a disconnecting means is required... but where does it say it has to be between the inverter and transformer.
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The inverter is energized from both sides so it needs an AC and DC disconnect 'grouped' at the inverter. Maybe not if there's an AC disco inside the inverter, that's more likely on a 1MW inverter.

I suppose if the transformer is also grouped together then maybe it's okay.
 
jaggedben said:
The inverter is energized from both sides so it needs an AC and DC disconnect 'grouped' at the inverter. Maybe not if there's an AC disco inside the inverter, that's more likely on a 1MW inverter.

I suppose if the transformer is also grouped together then maybe it's okay.
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Article 690 Part II is all about the PV System Disconnecting Means. I do not see where disconnecting means for both the AC and DC sides must be grouped.
 
Smart $ said:
Article 690 Part III is all about the PV System Disconnecting Means. I do not see where disconnecting means for both the AC and DC sides must be grouped.
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I should have checked the changes in the 2017 NEC. Here is the quote from 2014:

690.15 Disconnection of Photovoltaic Equipment.
Means shall be provided to disconnect equipment, such as
inverters, batteries, and charge controllers, from all
ungrounded conductors of all sources. If the equipment is
energized from more than one source, the disconnecting
means shall be grouped and identified.
Click to expand...
 
jaggedben said:
I should have checked the changes in the 2017 NEC. Here is the quote from 2014:
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I've never taken the grouping required therein as applying to both AC and DC disconnecting means.

As to 2017, the grouping requirement is dust in the wind...
690.15 Disconnection of Photovoltaic Equipment. Isolating
devices shall be provided to isolate PV modules, ac PV modules,
fuses, dc-to-dc converters inverters, and charge controllers from
all conductors that are not solidly grounded. An equipment disconnecting
means or a PV system disconnecting means shall be
permitted in place of an isolating device. Where the maximum
circuit current is greater than 30 amperes for the output circuit
of a dc combiner or the input circuit of a charge controller or
inverter, an equipment disconnecting means shall be provided
for isolation. Where a charge controller or inverter has multiple
input circuits, a single equipment disconnecting means shall be
permitted to isolate the equipment from the input circuits.

Informational Note: The purpose of these isolating devices are​
for the safe and convenient replacement or service of specific​
PV system equipment without exposure to energized conductors.​

(A) Location. Isolating devices or equipment disconnecting
means shall be installed in circuits connected to equipment at a
location within the equipment, or within sight and within 3 m
(10 ft) of the equipment. An equipment disconnecting means
shall be permitted to be remote from the equipment where the
equipment disconnecting means can be remotely operated from
within 3 m (10 ft) of the equipment.

(B) Interrupting Rating. An equipment disconnecting means
shall have an interrupting rating sufficient for the maximum
short-circuit current and voltage that is available at the terminals
of the equipment. An isolating device shall not be required to
have an interrupting rating.

(C) Isolating Device. An isolating device shall not be required
to simultaneously disconnect all current-carrying conductors
of a circuit. The isolating device shall be one of the following:
(1) A connector meeting the requirements of 690.33 and listed​
and identified for use with specific equipment​
(2) A finger safe fuse holder​
(3) An isolating switch that requires a tool to open​
(4) An isolating device listed for the intended application​
An isolating device shall be rated to open the maximum
circuit current under load or be marked “Do Not Disconnect
Under Load” or “Not for Current Interrupting.”

(D) Equipment Disconnecting Means. An equipment disconnecting
means shall simultaneously disconnect all currentcarrying
conductors that are not solidly grounded of the circuit to
which it is connected. An equipment disconnecting means shall
be externally operable without exposing the operator to contact
with energized parts, shall indicate whether in the open (off) or
closed (on) position, and shall be lockable in accordance with
110.25. An equipment disconnecting means shall be one of the
following devices:
(1) A manually operable switch or circuit breaker​
(2) A connector meeting the requirements of 690.33(E)(1)​
(3) A load break fused pull out switch​
(4) A remote-controlled circuit breaker that is operable locally​
and opens automatically when control power is interrupted​
For equipment disconnecting means, other than those complying
with 690.33, where the line and load terminals can be
energized in the open position, the device shall be marked in
accordance with the warning in 690.13(B).
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