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John (and other Wrenches),
I read with great interest this post about Sunny Island breaker size. We are about to install a large semi-off grid system for a wealthy and eccentric customer. The system has 17kW of PV, and four SI5048 inverter/chargers, along with an Outback Radian serving as an inverter only to some separate protected circuits. The system has utility backup power available as well as a backup 30kW generator, but for a complicated reason the system can't be set to feed back into the grid; the SIs' sell function will be disabled. The four SIs are set up as a pair on each 120V phase, as SMA allows. After consultation with SMA tech support, I have designed each SI to be on a 125A dc breaker. This is done to keep the total protected ampacity of the dc battery cabling and bussing to 850 amps (125 A x 4 = 500 A, plus 175 A x 2 for the Radian, all passing through a common 1,000 A shunt to allow accurate SOC metering). It's hard enough to address battery cabling and shunting with 850 amps; with 175 A dc breakers the total would be 1,050 amps, and with 250 A dc breakers the total would be 1,350 amps. Given that the loads supplied are residential, primarily electronic and resistive, and thus few if any large surges, and given that the inverters on each phase are paralleled, how much should I worry about the 125a dc breaker size? Are there SI programming settings that I should know about to better protect against nuisance tripping? Thank you, Allan
Allan Sindelar
On 2/4/2013 1:29 PM, John Berdner wrote:al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc. 3209 Richards Lane (note new address) Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com Ryan: Not sure what is in the manual now but...The lugs in the SI 5048U are dual 2/0.We had to use parallel AWG #1 because we kind of painted ourselves into a corner. The breaker in the SI ended up being 250 Amps, the conduit fitting was only 1.5" and the wire bending space was too small for a 3/0. The only way to get enough Ampacity in a 1.5" conduit and that wire bending space was to go with dual #1's. The 250 Amp breaker was used just to get enough current for the very short duration surges without tripping the breaker (12kW per SI). If not for this a 200 A breaker would have been fine. Note that the actual full power ampacity required for normal operation is 5kW @ 40 Vdc = 125 Amps continuous. It is the high surge loads that require more current. I run mine with a single 2/0 and we have never even come close to hitting full power. Worst case current is typically while charging not when inverting and I set the current limit so that I do not exceed ampacity of 2/0. In my experience it takes >= 14kW generator to drive a pair of SI's to full power while charging Best Regards, John Berdner General Manager, North America SolarEdge Technologies, Inc. 3347 Gateway Boulevard, Fremont CA 94538 USA (*Please note of our new address.) T: 510.498.3200, X 747 M: 530.277.4894 |
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