Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
Tapping main service. From my calcs nothing wring with conductor/sizing sets here correct?
Sizing Conductors
- Thread starter Alwayslearningelec
- Start date
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Your 2000A SWBD and smaller 125A breakers rated at 200kAIC?
Be sure your tap is 10' or less and include a field evaluation from UL for the Listing since you are modifying the SWBD.
Be sure your tap is 10' or less and include a field evaluation from UL for the Listing since you are modifying the SWBD.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
I'm confused, where is the tap? I'm assuming that the top portion labeled "outside" is PV and is feeding the service? A service tap wouldn't go to the load side of the 2000 amp disconnect.
Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
So that is not considered a tap? Why?
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
The run from the tap/PV switch to the outdoor switchboard is 220' which according to my VD calcs and having to keep it 3% or below the conductors may be undersized.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
If you're using 2000 amps that number is likely much higher than the actually current level.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Since this is PV, amd making some reasonable assumptions, an actual current of 1400 is under 2%
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
I know little about PV so what is the reasonable assumption here? Would you estimate that each 125 amp OCPD is only loaded to a certain %? Is that a typical design margin? His other thread shows 21-125 amp OCPD's in this 2000 amp switchboard.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Just that the conductors and
OCPD would be sized on 125% of the inverter output currents, and assuming 1600 would be too small.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
So the 2000 amp OCPD would be sized with a 125% factor?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Yeah. The max inverter output current will be an actual number that could be maintained for hours, particularly with todays high DC:AC ratios, so it is a continuous load (in practice but also 690 specifically require it).
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
So for the sake of a VD calculation if he used 80% of the 2000 amps that would be the maximum current if the system is designed correctly?
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Not necessarily. The maximum AC design current is the total published Imax for the inverters. That is the number you would use to calculate the maximum AC Vd.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Yes, if the 2000A OCPD is not 100% rated.
In the other thread, the full picture of the 2000A switchboard is shown, and it has 21 125A breakers. So if the 2000A OCPDs are 100% rated, the design current could be as high as 2000A.
Cheers, Wayne
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Use the summed maximum inverter output current to calculate Vd.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Isn't this something the solar designer has to do, rather than the estimator for the contractor?
Obviously if the voltage at the service plus the Vd calculated based on the maximum inverter output current exceeds the upper end of the inverter voltage window, and the DC/AC ratio is high enough that those conditions will plausibly occur, that's likely a problem.
But otherwise, it might be fine for the Vd calculated using the maximum inverter output current to be say 6%. For such a large array, surely the designer is modeling the array/inverter performance over the course of a year, and will have some idea of how often those conditions will occur. So I would think it would be a matter of looking at the total expected annual production using the minimum size conductors, and then checking what production increase you'd get from upsizing the conductors, and then deciding if that is worth the cost of the upsized conductors.
Cheers, Wayne
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Well, yes. A Vd calculation is part of the design process, and I use the inverter Imax to upsize the conductors if necessary so that if there is a maximum Vd the customer is willing to accept, the inverter output current cannot cause Vd to exceed it. If an estimator wants to downsize the conductors to save money, and the customer is willing to accept the Vd the estimator thinks is likely, and the change does not result in conductors that are smaller than the minimum that the design process otherwise determines, and if am not liable if the Vd losses exceed what the customer wants, then OK.
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- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
I wouldn't be surprised if there is a note buried in the spec that states the contractor is required to ensure that the voltage drop in the final product is within the written requirement.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Yes, that happens, although I would fervently hope that it would not be "buried".
