Hi Guy's,

I have some questions about Fusing, MCB's and AC/DC Disconnects

I've browsed the internet and learned a lot about these topics but also some things confuse me. Here come my questions

First about sizing a Fuse or MCB. I've seen the explanation many times as follows:

Take the Isc of your PV Module For example two strings of 6 PV Modules in Parallel.

For the combiner box we connect the two minus wires of the two strings to the minus busbarr

The two plus wires are connected to the plus of a circuit breaker.

The size of the circuit breaker is calculated as follows:

Isc 8,7A x 2 (because 2 parallel) x 1,56 (I also did run into sides where they claim it's not 1,56 but 1,25) = the MINIMUM breaker size In this case 8,7 x 2 x 1,56 = 27,14 A

They say alway minimum breaker size, so 63 A would be ok also?

I don't understand this. The breaker is installed to protect the wire right?

So if for some reason the current becomes higher than 27,14 A then the MCB will trip and prevent the wiring from burning right?

If this is the case how can they say minimum? Higher will be wrong then. If for some reason the current becomes 50 and it will burn up the wiring but the MCB of 63 A still will not trip so it's not pprotecting anything? Where do I go wrong?

Other question is if you use MCB's do you still have to use AC and DC disconnects. Some say the MCB can function as a disconnect as well and some say that's wrong?

And when would you decide to use Fuse and when MCB?

Thanks a lot

Regards

I have some questions about Fusing, MCB's and AC/DC Disconnects

I've browsed the internet and learned a lot about these topics but also some things confuse me. Here come my questions

First about sizing a Fuse or MCB. I've seen the explanation many times as follows:

Take the Isc of your PV Module For example two strings of 6 PV Modules in Parallel.

For the combiner box we connect the two minus wires of the two strings to the minus busbarr

The two plus wires are connected to the plus of a circuit breaker.

The size of the circuit breaker is calculated as follows:

Isc 8,7A x 2 (because 2 parallel) x 1,56 (I also did run into sides where they claim it's not 1,56 but 1,25) = the MINIMUM breaker size In this case 8,7 x 2 x 1,56 = 27,14 A

They say alway minimum breaker size, so 63 A would be ok also?

I don't understand this. The breaker is installed to protect the wire right?

So if for some reason the current becomes higher than 27,14 A then the MCB will trip and prevent the wiring from burning right?

If this is the case how can they say minimum? Higher will be wrong then. If for some reason the current becomes 50 and it will burn up the wiring but the MCB of 63 A still will not trip so it's not pprotecting anything? Where do I go wrong?

Other question is if you use MCB's do you still have to use AC and DC disconnects. Some say the MCB can function as a disconnect as well and some say that's wrong?

And when would you decide to use Fuse and when MCB?

Thanks a lot

Regards

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