Just now, Jaco de Jongh said:

In my case you will be sending 220VAc to 12 panels in series, that is 18volts for each panel. The SB1240 diode in @The Terrible Triplett picture above can handle 30Volt and its forwarding current is rated at 280Amps. Look at the direction of the Diodes, it will be a Dead Short. 

If you feel your panels can handle that, when can we do the test, But please can I be there, I want to make the video.  

Yes it will cause a dead short. Yes the panels will be damaged. But I doubt if the fuse will blow before the diodes blow. The SB1240 diode can withstand 280A for 10ms. But it will probably not draw that much current as the V rating is only 40V

As example. I built a 16x 30V/5A relay board, with 16x 250ma fuses, one for each battery. Due to a fault, the load of the batteries on the relays took the relays out before the fuses could blow. It was actually nice to watch the fuses glow slight red, and now blowing quick enough. This is was fast blow fuses.  

What I am saying, is don't just depend on a fuse to blow, if other faults can occur due to poor component or installation choices....

56 minutes ago, Jaco de Jongh said:

The 220V and PV wires should not run in the same trunking

Thanks Jaco for mentioning this. In my installation the AC and DC wires run in the same trunking. To change this would be a huge project. When you say "should" does this mean that it is not a legal requirement but only a guidline?  

8 minutes ago, Fuenkli said:

When you say "should" does this mean that it is not a legal requirement but only a guidline?  

I am not aware of regulations about this in SA yet, but I know that in Aus it is regulation already. I think for now its a good guideline and even in the normal electrical field we have been running AC and DC in separate wire ways since I can remember. 

 

8 minutes ago, Fuenkli said:

To change this would be a huge project.

I know this all to well, I am currently redoing my complete installation and included double tier Metal trunking to split DC from AC as I realized the danger a while back. Also had interference from the AC on my comms cables.  

5 hours ago, The Terrible Triplett said:

Guys, fuse are not a nice to have, money making racket.

Put fuses on the blerrie wires, positive and negative, as Chris pointed out and move on. 

If you don't and need a CoC for the panels, you ain't getting one.

It must be done. "Finish and klaar".

I quickly checked SANS SANS 60364-7-712  ( This is totally out of my field Im here to learn)

And on page 29:

 

712.430.3.103 Requirement for string overcurrent protection

String overcurrent protection shall be used if:

((Ns –1) × ISC_MAX ) > IMOD_MAX_OCPR

where:

Ns is the total number of parallel connected strings protected by the nearest overcurrent

protective device.

When circuit-breakers with overcurrent protection elements are used, they may also provide

the disconnecting means required in 712.536.2.101 to 712.536.2.103.

 

Which basically says that if you have a single string ie Ns = 1 then 1-1 = 0 > Imod_MAX_OCPR you dont not require overcurrent protection.

 

Now my poor brain can relax as up to now having fuses on a single array made no sense to me

 

***** PERSONALLY I WILL ALWAYS ADVOCATE INSTALLATING FUSES EVEN ON A SINGLE ARRAY******

 

but strickly speaking I cannot see why a COC can not be issued if you dont have fuses on a single array.

 

 - This is why I love the internet other peoples questions forced me to do a bit a digging and learning a bit along the way -

 

 

4 minutes ago, Jaws said:

***** PERSONALLY I WILL ALWAYS ADVOCATE INSTALLATING FUSES EVEN ON A SINGLE ARRAY******

Ditto. 

Most of the users here have rather large volts / amps coming in. 

A fuse is also there to protect the wire against someone like me.

So to simplify it down to bare bones, regs or no regs, everyone should have fuses installed.

Makes it simpler all round see. :-)

 

4 minutes ago, The Terrible Triplett said:

Ditto. 

Most of the users here have rather large volts / amps coming in. 

A fuse is also there to protect the wire against someone like me.

So to simplify it down to bare bones, regs or no regs, everyone should have fuses installed.

Makes it simpler all round see. :-)

 

 

Further down in the SANS the  highlighted bits just confirms everything we have been saying, nice to know with logical reason one can reach the same conclusions as the nice people compiling the IEC standards

 

712.433.1.101.3 PV sub-array overload protection

The rated current or current setting (In) of overload protective devices for PV sub-arrays shall

be determined with the following formulae:

In > 1,25 × ISC S-ARRAY and

In ≤ 2,4 × ISC S-ARRAY.

The 1,25 multiplier used here instead of the 1,5 multiplier used for strings is to allow designer

flexibility. A multiplier of 1,25 should not be used in areas where heightened irradiance occurs

frequently as this would be likely to cause nuisance overload protective device operation.

NOTE In case of specific constraints such as side by side mounting of equipment used simultaneously at nominal

current and/or high ambient temperature, the choice of current rating of the protective device could be impacted.

712.433.1.101.4 PV array overload protection

PV array cable overload protection is only required for PV installations connected to batteries

or where other sources of current may feed into the PV array under fault conditions. The rated

current (In) of PV array overload protective devices shall be rated as follows:

In > 1,25 × ISC S-ARRAY and

In ≤ 2,4 × ISC ARRAY

The PV array overload protective devices are commonly installed between the battery or

batteries and the charge controller as close as possible to the battery or batteries. If these

devices are appropriately rated, they provide protection to both the charge controller and the

PV array cable, and consequently no further PV array cable overload protection between the

PV array and the charge controller is necessary.The 1,25 multiplier used here instead of the

1,5 multiplier used for strings is to allow designer flexibility. A multiplier of 1,25 should not be

used in areas where heightened irradiance occurs frequently as this would be likely to cause

nuisance overload operation.

17 hours ago, Jaws said:

712.433.1.101.4 PV array overload protection

PV array cable overload protection is only required for PV installations connected to batteries

or where other sources of current may feed into the PV array under fault conditions. The rated

current (In) of PV array overload protective devices shall be rated as follows:

In > 1,25 × ISC S-ARRAY and

In ≤ 2,4 × ISC ARRAY

Thanks @Jaws