Raceway

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ggunn said:
I have seen that, but what is the purpose of the partition? Is it to provide extra insulation between the wires or is it just so they won't get mixed up and you can tell one source from the other when you open the gutter??
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According to Bill Brooks, the purpose of the partition is suppose to solve is to prevent faults between AC and DC sides of the system.
 
electrofelon said:
Seems silly. Why would that be an issue? We have boxes with different circuits and systems together all the time.
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Seems that way to me as well. Why would a fault between AC and DC conductors be worse than a phase to phase fault at 480/277V? But it's not ours to reason why, only to fail the inspection or comply.
 
ggunn said:
Seems that way to me as well. Why would a fault between AC and DC conductors be worse than a phase to phase fault at 480/277V? But it's not ours to reason why, only to fail the inspection or comply.
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One explanation is that faults between phases on a circuit on the AC side will trip the breaker or fuse, which will stop current from flowing that would exacerbate the issue of the fault. While faults across the AC and DC are less likely to do this. Particularly when the DC conductors come from a source that cannot be shut off, other than when the sun goes down.
 
I believe the code specifies that the PV panels need to have a shut off switch and also the current codes need to have rapid shut down for fire protection within 30 seconds of an emergency shut off switch activation for each panel so there is a per panel shut down system already required in the code. For example each panel I have has a Tigo rapid shut down module in line with it which each panel plugs into and it needs to be constantly communicating with a central brain to remain producing power. If the inverter gets shut off or if the there is a short in the system or if the emergency power off switch is engaged the panels will not produce power.
 
SolCon said:
I believe the code specifies that the PV panels need to have a shut off switch and also the current codes need to have rapid shut down for fire protection within 30 seconds of an emergency shut off switch activation for each panel so there is a per panel shut down system already required in the code. For example each panel I have has a Tigo rapid shut down module in line with it which each panel plugs into and it needs to be constantly communicating with a central brain to remain producing power. If the inverter gets shut off or if the there is a short in the system or if the emergency power off switch is engaged the panels will not produce power.
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Not all systems are necessarily on/in buildings, and therefore rapid shutdown may not necessarily apply. As an example, if this is for a line-up of string inverters on a ground-mounted system, there is no need to deploy rapid shutdown on a ground-mounted array. The DC conductors would all be "uncontrolled", and would always be voltage-energized until the sun sets.
 
That makes a lot of sense for ground mounted systems, but in the case of a building mounted system where there is already a rapid shut down system required that should be noted in the code maybe a future code will have this provision for partitions.
 
Worst case -- say one PV DC conductor faults to ground and the other to an AC hot conductor -- then every line-to-neutral load on the AC system sees the PV DC voltage, and there's no protective device other than the circuit breakers which are not rated for that.

Rapid shutdown is for the saftey of fire fighters working on roofs and has zilch to do with this.
 
electrofelon said:
Seems silly. Why would that be an issue? We have boxes with different circuits and systems together all the time.
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True. I suppose the counterpoint is that those systems are typically all powered from the same basic AC source. PV source circuits may exceed the ratings of all the components on the premises and isn't easily shut down. But I agree it seems somewhat arbitrary.
 
ggunn said:
I have seen that, but what is the purpose of the partition? Is it to provide extra insulation between the wires or is it just so they won't get mixed up and you can tell one source from the other when you open the gutter??
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This is kind of a weird addition to 690. NEC 300.3(C)(1) allows AC and DC conductors to occupy the same space, 690.31(B) takes that away. I think it was just part of the general PV Panic where the people on the CMP have always operated under the assumption that PV DC is inherently more dangerous than any other DC covered in chapters 1-4 and therefore needs to be isolated and protected differently. Probably due to the inability to turn off the PV modules to isolate the DC conductors. If it were simply an identification issue then it seems to me that they could call for bundling and identification in a shared raceway.
 
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