What fuse do I need ?

[publin]

Hi Again !

If I have 4 panels wired in series connecting to an 80Amp MTTP controller what fuse etc would I need between the panels and the controller.

Also what type / size fuse would go between the controller and the battery bank ( 12V )

Panel spec:

Maximum Power	190 Watts
Voltage at Max Power (Vmp)	36.5 Volts DC
Current at Max Power (Imp)	5.20 Amps
Open Circuit Voltage (Voc)	43.8 Volts DC
Short Circuit Current (Isc)	5.83 Amps
Module Efficiency	14.90%
Dimensions	62.2" x 31.8" x 1.38"

Many many thanks for all the input
Dave C.

[sensij]

For a single series string, no fuses are required on the PV circuit.

If the controller is rated to produce 80 A continuously, OCPD between it and the battery must be at least 80 * 1.25 = 100 A. With that size protection, 1/0 conductors are probably right, in some cases, you might be able to go smaller.

Since your panels are not going to produce the full 80 A for which the controller is rated, you could justify going smaller, but it wouldn't be code compliant, and you'd have to replace it if you ever add more panel power.

[Amy@altE]

4 of those panels wired in series? What charge controller are you using? 43.8Voc x 4 = 175.2V, without factoring in cold weather. Many charge controllers can only handle up to 150V. Unless it's a 200V charge controller, like the Midnite Classic 200, I'd break it into 2 strings of 2.

[publin]

Nicely spotted "Solar Queen"

The Controller is an Outback 80amp MPPT. with a MAX of 150VDC

They'll now be wired in series / parrallel.

Thanks
Dave

[sensij]

Good news is that with just two PV strings, still no PV fuse required. If you go to three strings, then you'd need to protect each of them.

[Amy@altE]

This ain't my first rodeo
I suggest a Midnite MNPV3 with two 10A breakers in it. (5.83AIsc x 1.56). Makes transitioning to conduit for the run back to the DC load center a breeze.

[Amy@altE]

NEC 690.9(A) does require over current protection for battery based PV systems, even if there is only 1 string. Grid tie systems don't need it for 1 or 2 strings.

[Sunking]

NEC 690.9(A) does require over current protection for battery based PV systems, even if there is only 1 string. Grid tie systems don't need it for 1 or 2 strings.

Incorrect answer. Fuse between the controller and battery protect the panel wiring. Go ask your question on Mike Holt as that is where the professionals are. No DIY allowed.

[sensij]

I don't think it is that black and white. The exception to 690.9(A) in 2011 NEC states:

Exception: An overcurrent device shall not be required for PV modules or PV source circuit conductors sized in accor-dance with 690.8(B) where one of the following applies:
(a) There are no external sources such as parallel-connected source circuits, batteries, or backfeed from inverters.
(b) The short-circuit currents from all sources do not exceed the ampacity of the conductors or the maximum over-current protective device size specified on the PV module nameplate..

Informational Note: Possible backfeed of current from any source of supply, including a supply through an inverter into the photovoltaic output circuit and photovoltaic source circuits, is a consideration in determining whether adequate overcurrent protection from all sources is provided for conductors and modules.

For MPPT controllers, at least of the quality discussed here, there are blocking diodes and other reverse current protection to prevent backfeed, no? The informational note gives the freedom (and responsibility) to consider whether backfeed is possible. Grid-tie inverters clearly meet the standard required for backfeed prevention, since systems are routinely approved without PV source OCPD when there are one or two strings. Is there anything out there that says an MPPT controller would not meet that same standard?

By including "batteries" in the list of external power sources, it looks like the code just considering the case where panels are hooked directly to the batteries without any other protection in place. I could also imagine an ebay PWM controller, with no backfeed protection, could have two PV strings in parallel. The fuse on the output side would be sized for the combined current, but that is too big to protect the individual strings from the battery in the event of a fault.

[inetdog]

By including "batteries" in the list of external power sources, it looks like the code just considering the case where panels are hooked directly to the batteries without any other protection in place. I could also imagine an ebay PWM controller, with no backfeed protection, could have two PV strings in parallel. The fuse on the output side would be sized for the combined current, but that is too big to protect the individual strings from the battery in the event of a fault.

Actually, it is also considering the case of having a CC which then fails.
As SK pointed out it is not the presence of the CC which removes the need for a fuse on the PV side, it is the presence of a fuse between the CC and the batteries. An internal DC output breaker in the CC might not count either.

[sensij]

Actually, it is also considering the case of having a CC which then fails.
As SK pointed out it is not the presence of the CC which removes the need for a fuse on the PV side, it is the presence of a fuse between the CC and the batteries. An internal DC output breaker in the CC might not count either.

But a grid-tie inverter could "fail" too, yet no PV fuse is required even if the inverter output circuit fuse is too big to protect the PV source circuit. How is a good mppt CC any different?

[Sunking]

But a grid-tie inverter could "fail" too, yet no PV fuse is required even if the inverter output circuit fuse is too big to protect the PV source circuit. How is a good mppt CC any different?

Yes sir you are correct and an AC line fault is more dangerous than a battery fault. There is no difference between a MPPT Controller input and Inverter input. With the controller and fuse you have 3 protection modes. The fuse between battery and controller, the controller built in breaker/fuse, and the nature of the design of the controller.

New code cycle will remove the wording in the next code cycle along with major changes to the using the EGC as a grounding conductor. Most cities who have adapted 2014 have amended out the very stupid ground requirements. John slipped it in there to reduce installation cost. It is one of those cases where special commercial interest out voted sound engineering fundementals. The backlash from cities amending it out finally broke the camels back. One of the problems with NEC is manufactures and special interest have too many voting members.