DB Box requirements located between PV and Battery

General Discussions
1

Hi guys

Whats the current requirement for the DB box located between the panels/array and the battery/s…

Switches, trips, fuses, both pos and neg lines.

G

2

PV Combiner Box between Panels and MPPT and a fuse for cable between MPPT and Battery/Inverter. I only have a fuse on the Red from Panels.
EG: 2 strings to a single MPPT

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3

Is there a Sans requirement for both a circuit breaker and fuse, or is an isolater in conjunction with a fuse a better idea instead of the circuit breaker.
Apologies, this is for, between panels and inverter

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4

The requirements are many and varied.

SANS effectively requires a ‘switch-disconnector’ (a device capable of breaking the circuit under load and providing safe isolation of the disconnected source), and an overcurrent protection device (fuse or circuit breaker).

Most circuit breakers are rated for isolation and can safely perform both roles.

You can see what various devices are rated for by looking at the symbols printed on them:

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If you only have a single string coming in, then a single isolation rated circuit breaker can meet all the SANS requirements. (But note, this must be DC rated, although it can be polarised.)

If you have multiple strings coming in, then each source (string) needs overcurrent protection (i.e. a fuse or DC circuit breaker - but if you use a circuit breaker here, it must NOT be polarised).

SANS specifies that the overcurrent protection rating must be lower than the maximum safe current of the wires.

Solar panel manufactures may specify a maximum fuse current, in which case the overcurrent protection should be the minimum of the SANS or panel requirement.

If one panel wire is grounded (which NEVER happens), then only the non-grounded wire needs to be protected/isolated. Otherwise both must be.

Most inverter/MPPT manufacturers will specify that a surge protector is required (and specify the class of surge protector). If the device has such a requirement, then such a surge protector must be included. If the device does not have such a requirement, it is still a jolly good idea to add one anyway!

So, depending on actual installation, the requirement varies from one suitably rated single pole circuit breaker to two fuses per panel + surge protector + 2 pole isolation rated circuit breaker…

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