Hi all.

I have this PV combiner box and just want to double check the correct way of wiring.

Is it:

Panels>Breaker>Fuses>Inverter

or

Panels>Fuses>Breaker>Inverter

My gut tells me its Panels>Breaker>Fuses>Inverter because if you want to replace the fuses, you disconnect the panel power feed via the breaker and then you can change the fuses.

TIA

 

1 hour ago, sjp100 said:

Panels>Fuses>Breaker>Inverter

Is the correct way.

14 hours ago, sjp100 said:

Hi all.

I have this PV combiner box and just want to double check the correct way of wiring.

Is it:

Panels>Breaker>Fuses>Inverter

or

Panels>Fuses>Breaker>Inverter

My gut tells me its Panels>Breaker>Fuses>Inverter because if you want to replace the fuses, you disconnect the panel power feed via the breaker and then you can change the fuses.

TIA

 

Is your in and out both at the bottom? If so your spd is wrong. 

Panels>fuses+spd>breaker>inverter. 

Spd must be direct on you incoming cable

1 hour ago, Chris_S said:

Spd must be direct on you incoming cable

Nope, that’s incorrect. The incoming cables go directly to the fuses and nothing else. The SPD is parallel on the fuses exit. 

Out of interest, if the breakers are downstream of fuses as suggested above, how would one remove or change a PV fuse during a sunny day (bearing in mind house loads and incoming DC current/voltage from the strings)? 

13 minutes ago, PowerUser said:

Nope, that’s incorrect. The incoming cables go directly to the fuses and nothing else. The SPD is parallel on the fuses exit. 

All the ones I have seen the spd is parallel on fuse inputs. 

If your fuse blows you still want spd protection. 

5 minutes ago, Kalahari Cruiser said:

Out of interest, if the breakers are downstream of fuses as suggested above, how would one remove or change a PV fuse during a sunny day (bearing in mind house loads and incoming DC current/voltage from the strings)? 

When you disconnect the load there is a much lower chance of DC jumping gaps. The fuse holders are also designed for the input to be at the top so less chance of fingers touching a live fuse. 

Interesting, so after the breaker (load being removed), it's quite safe to wriggle out the PV fuse(s) if needed, and replace it again, on a sunny day. I haven't, but was just curious, as above seemed counter-intuitive to me. Thanks! 

17 minutes ago, Kalahari Cruiser said:

Interesting, so after the breaker (load being removed), it's quite safe to wriggle out the PV fuse(s) if needed, and replace it again, on a sunny day. I haven't, but was just curious, as above seemed counter-intuitive to me. Thanks! 

Yes once the load is disconnected(Breaker off) you can open the fuse holder. The fuse sits in the holder door so it breaks the bottom and top connection from the cable as you open it. 

31 minutes ago, Chris_S said:

All the ones I have seen the spd is parallel on fuse inputs. 

If your fuse blows you still want spd protection. 

If the fuse blows, there is no need for SPD. No current will flow. 

34 minutes ago, Chris_S said:

All the ones I have seen the spd is parallel on fuse inputs. 

If your fuse blows you still want spd protection.

Negative. There MUST be an overcurrent protection device before the SPD.  The SPDs job is to crowbar the lines and trip the overcurrent protection.  The SPD cannot dissipate enough power to provide any real protection on its own.

59 minutes ago, Chris_S said:

If your fuse blows you still want spd protection

Thats not so important. Remember that when your SPD arrests, it can affect a short circuit in doing so. Now if you have a source that can supply lots of energy , then the spd short will  allow lots of current to flow, which you need to limit with a fuse. 

Certain types of arresting devices, including a gasfilled arrestor has the nasty habit to have a very small holding current in order to reset again. Which in practise means large currents may flow long after a short duration  surge started it all. 

46 minutes ago, JustinSchoeman said:

Negative. There MUST be an overcurrent protection device before the SPD.  The SPDs job is to crowbar the lines and trip the overcurrent protection.  The SPD cannot dissipate enough power to provide any real protection on its own.

Yeah I'm second guessing how I did mine now. I'm possibly confusing my AC protection with the DC. Anyway I better go make sure. 

This is how I'm planning to do mine

My installer told me that the connectors on the SPD's are tougher than the others, so my panels are connected to the SPD's and then bridged from there to the fuses and onwards to the breaker. It makes sense to me since the SPD is probably more geared to handle high voltage situations. Also, no current flows through the SPD under normal circumstances so they can happily sit in parallel with the fuses and breaker combo. The only discussion is hence whether the fuses must be before the breaker or after. Even this seems moot to me since if either of these 2 pops/trips the connection is broken and no current can flow. Turning off the breaker allows you to safely swap out the fuses, so there's no reason to not have the fuses first in the protection line. Besides, fuses will probably blow quicker than breakers will trip?

3 minutes ago, p_i said:

My installer told me that the connectors on the SPD's are tougher than the others, so my panels are connected to the SPD's and then bridged from there to the fuses and onwards to the breaker. It makes sense to me since the SPD is probably more geared to handle high voltage situations. Also, no current flows through the SPD under normal circumstances so they can happily sit in parallel with the fuses and breaker combo. The only discussion is hence whether the fuses must be before the breaker or after. Even this seems moot to me since if either of these 2 pops/trips the connection is broken and no current can flow. Turning off the breaker allows you to safely swap out the fuses, so there's no reason to not have the fuses first in the protection line. Besides, fuses will probably blow quicker than breakers will trip?

I would say that the SPD should always be connected on the inverter side to protect the inverter against surges regardless if the breaker is on/off and fuses are in/out

1 minute ago, bloues said:

I would say that the SPD should always be connected on the inverter side to protect the inverter against surges regardless if the breaker is on/off and fuses are in/out

Any potential DC surges will come from the panels so rather have them closer to the panels. Likewise you have them as close to the surge source (Eskom) on the AC side.

At normal operating voltages, the SPDs are in a high-impedance state and do not affect the system. When a transient voltage occurs on the circuit, the SPD moves into a state of conduction (or low impedance) and diverts the surge current back to its source or ground. This limits or clamps the voltage to a safer level. After the transient is diverted, the SPD automatically resets back to its high-impedance state. But what happens if the SPD does not divert back to high-impedance state within large energy sources as @BritishRacingGreen stated, you need a short curcuit interrupter known as a fuse. Remember a Fuse is used for protection against short circuit, it is not used for protection against overload. MCB is used for both protection against  short circuit and overload. Therefore only MCB will operate during overload. How it should be wired in dc curcuits MCB, FUSE, SPD and for ac curcuits Eskom, MCB, SPD.

Edit mistake: DC curcuits MCB, FUSE, SPD.

 

Edited August 16, 20233 yr by TaliaB

39 minutes ago, TaliaB said:

How it should be wired in dc curcuits FUSE, SPD, MCB and for ac curcuits Eskom, MCB, SPD.

Why is the SPD before the MCB for DC but after the MCB for AC? Or is it actually in parallel with the MCB on the DC side? Would you please point us to wiring diagrams?

16 minutes ago, p_i said:

Why is the SPD before the MCB for DC but after the MCB for AC? Or is it actually in parallel with the MCB on the DC side? Would you please point us to wiring diagrams?

Sorry my mistake i have corrected in my post under edit. DC- MCB, FUSE, SPD

27 minutes ago, TaliaB said:

Sorry my mistake i have corrected in my post under edit. DC- MCB, FUSE, SPD

Interesting design.  Since fuse response time is substantially faster than breakers, the first thing that happens on a surge is the fuse blows and removes the SPDs from the circuit...

1 minute ago, JustinSchoeman said:

Interesting design.  Since fuse response time is substantially faster than breakers, the first thing that happens on a surge is the fuse blows and removes the SPDs from the circuit...

Yes, and the connection between the MCB on left and the load MCB's on right are still intact. I don't understand it either...

8 hours ago, TaliaB said:

Sorry my mistake i have corrected in my post under edit. DC- MCB, FUSE, SPD

How can the fuse only be used for the spd? If you have a surge and the SPD takes out the fuse and not the breakers the panels are still connected to the load. Surely that's how panel fires start. 

Edited August 17, 20233 yr by Chris_S
Spelling

In an ideal situation I would have the fuses as close to the panels as possible incase there is a PV cable short on the long runs to the inverter. Then have just an spd and breaker near the inverter. 

1 hour ago, Chris_S said:

In an ideal situation I would have the fuses as close to the panels as possible incase there is a PV cable short on the long runs to the inverter. Then have just an spd and breaker near the inverter. 

We will discuss this topic futher as soon as i get a chance just very busy this morning.