Fusing solar panel cables

[peterboat]

in a previous thread products from china i think a said i had had a solar controller catch fire i never found out what happened it was replaced and never fitted that wasnt down to loose cables it was just a failure they do happen but again we wont know if fuses to the panels would solve anything. i will look at the midnight web site and see what they show for the federal regs that panels have to be installed to

[peterboat]

had a look at their web site it would seem they have combiners in the panel to controller lines these turn off the panels in the event of a problem fast shutdown is what its called . i would think these shut off the panels before disconnecting the controller from the batteries have a look nick you will make more sense of it than me

[Graham.m]

Anyway, seems likely to me that the wires were overheating due to a bad connection at the controller's terminal block (but yes I am guessing). No fusing or switchery is going to protect against that, just routine maintenance such as checking connections are tight and not getting hot.

 

That is your opinion without seeing the boxes or inside. In the box I know about I would not agree

[WotEver]

 

That is your opinion without seeing the boxes or inside. In the box I know about I would not agree

And how exactly would a fuse in the panel feed have helped?

[Keith M]

Do you know if the energy for the fire came from the panels, or somehow back up from the batteries? Obviously whilst a battery is capable of producing a large fault current and thus a fuse is appropriate, a solar panel is not capable of producing anything above its rated output and thus a fuse between controller and panel is pointless.

 

After the regulator had been removered

I did take a look at the PCB

The only damage was on the input side of the regulator

Trying to answer your question I am assuming the damage was caused by the current from the panels

An Identical regulator was used as a replacement

But within the instruction of the new regulator it did suggest fusing both the positive and negative input cables from the panels at 125% of the panel output current

 

Keith

Edited December 15, 2015 by Keith M

[Keith M]

Anyway, seems likely to me that the wires were overheating due to a bad connection at the controller's terminal block (but yes I am guessing). No fusing or switchery is going to protect against that, just routine maintenance such as checking connections are tight and not getting hot.

 

Not sure how to do multi-quotes

 

I could find no fault with the termination of the input cables

Both cables had ferrules fitted and the terminations screws were tight.

 

Keith

[DHutch]

Not sure how to do multi-quotes

 

You can do it automatically with the full version using the buttons at the bottom right of each post.

 

Else you can also do it by copying and pasting them together into one reply, or with slight risk, post two replies in quick succession, which will auto-merge as long as nobody posts in between them.

 

 

Daniel

[WotEver]

... within the instruction of the new regulator it did suggest fusing both the positive and negative input cables from the panels at 125% of the panel output current

 

Keith

I truly cannot see the point. I can't think of any scenario under which they would blow.

 

Tony

[nicknorman]

I truly cannot see the point. I can't think of any scenario under which they would blow.

Tony

I agree, however it is interesting that the combiner box mentioned earlier had fuses. Perhaps we are missing something, but I don't know what. Lightning is obviously an issue with panels especially on houses but even then, a fuse is not the thing to protect against lightning.

 

Edit: just checked a few panels' spec, it seems that short circuit current is typically about 10% greater than max power current, so any fusing to protect against short circuit would be tricky, and why bother if the current only goes up 10%?

Edited December 16, 2015 by nicknorman

[WotEver]

Especially as the instructions suggested 125% value for the fuses. I wonder what, if anything, we're missing.

[Graham.m]

Especially as the instructions suggested 125% value for the fuses. I wonder what, if anything, we're missing.

 

Think you are missing that voltages and currents at the levels solar PV produces (60V+ & 4A) are capable of causing injury and fire. Thus protection is needed for down line equipment and people.

 

But then I have been saying it for days

[John V]

If you need to disconnect quickly in an emergency situation then the best answer would be a pair of insulated parrot beak cutters, just don't touch the ends.

[George94]

 

Think you are missing that voltages and currents at the levels solar PV produces (60V+ & 4A) are capable of causing injury and fire. Thus protection is needed for down line equipment and people.

 

But then I have been saying it for days

 

How does the fuse protect people down the line? What are you protecting people from? Electricity? You have to allow the electricity to flow, otherwise there is no point in having the panels.

 

I don't think you have thought this through.

 

People are protected by having sheathed cables and no access to anything live.

[Graham.m]

 

How does the fuse protect people down the line? What are you protecting people from? Electricity? You have to allow the electricity to flow, otherwise there is no point in having the panels.

 

I don't think you have thought this through.

 

People are protected by having sheathed cables and no access to anything live.

 

Sorry this is in a fault situation, as to accessing live stuff on a boat all that is needed is a screwdriver nothing more simple

Edited December 16, 2015 by Graham.m

[George94]

 

Sorry this is in a fault situation, as to accessing live stuff on a boat all that is needed is a screwdriver nothing more simple

 

I have no idea what you mean. What possible fault can require a fuse?

[DHutch]

I have no idea what you mean. What possible fault can require a fuse?

I have to admit, while my natural reaction is the 'of cause there should be a fuse' to too am struggling to see what does to protect, given the panels have no way of producing an over-current event including during dead-short conditions.

 

I can see the logic in an isolator, and even using a fuse as an easy way of implementing isolation by a removable link, but I can also see arguments that an isolator is of somewhat limited use on the sorts or installation we have and the nature of the installations often being totally unmanned.

 

Daniel

[nicknorman]

I have to admit, while my natural reaction is the 'of cause there should be a fuse' to too am struggling to see what does to protect, given the panels have no way of producing an over-current event including during dead-short conditions.

Well it's either that we're missing something big-time, or that the companies recommending fusing are just doing it because it sounds like a good idea, but haven't actually thought it through. Wouldn't be the first time! (Former as well as latter!)

[WotEver]

I have to admit, while my natural reaction is the 'of cause there should be a fuse' to too am struggling to see what does to protect, given the panels have no way of producing an over-current event including during dead-short conditions.

It can't, Dan.

 

Once again the same person is spouting rubbish about a topic which he doesn't understand. That's why he used phrases like "protect people down the line" instead of explaining HOW he thinks the fuses would offer that protection. A fuse rated at 15% above the absolute maximum possible current will do nothing more than get a little warm.

[Chewbacka]

I agree, however it is interesting that the combiner box mentioned earlier had fuses. Perhaps we are missing something, but I don't know what. .............

Combiner boxes are used on solar installations of many Kw.

In these it is normal to have a number of strings of panels - So for example you could have a dozen panels in series, which is one string and then have 2 or 3 strings in parallel. So each string can output 110% of rated current under ideal conditions and short circuit.

The cable for a string is sized to suit the current.

If a string were to develop a fault in say it's output box it would both take it's own short circuit current, but also it would short out the other parallel connected strings.

This would result in n times the short circuit current going through cables and into the fault, where n is the number of strings.

In this example that would be 3 strings, so 330% hence the need for a fuse. ADDED a fuse for both cables for each string. So in this example 6 fuses.

 

Not a concern on my boat.

Edited December 16, 2015 by Chewbacka

[nicknorman]

Combiner boxes are used on solar installations of many Kw.

In these it is normal to have a number of strings of panels - So for example you could have a dozen panels in series, which is one string and then have 2 or 3 strings in parallel. So each string can output 110% of rated current under ideal conditions and short circuit.

The cable for a string is sized to suit the current.

If a string were to develop a fault in say it's output box it would both take it's own short circuit current, but also it would short out the other parallel connected strings.

This would result in n times the short circuit current going through cables and into the fault, where n is the number of strings.

In this example that would be 3 strings, so 330% hence the need for a fuse.

 

Not a concern on my boat.

Oh I see, that makes sense, thanks. So it's really for current flowing back into the box from other panels. But as you say not really applicable to most narrowboats. Edited December 16, 2015 by nicknorman

[DHutch]

Oh I see, that makes sense, thanks. So it's really for current flowing back into the box from other panels. But as you say not really applicable to most narrowboat.

Makes sense.

[John V]

As has been already said, the requirement for a fuse on a boat based system does seem nonsensical. AIUI a solar cell can be viewed as a current producing device with a fixed voltage (AFAIK) less than .05V from very low solar levels to very high solar levels. So for a given level of radiation it has to be seen as a constant current generator. A fuse or breaker capable of differentiating between maximum output under normal load and short circuit current would be prohibitively expensive.

[WotEver]

Combiner boxes are used on solar installations of many Kw....<snip> In this example that would be 3 strings, so 330% hence the need for a fuse. ADDED a fuse for both cables for each string. So in this example 6 fuses.

Now THAT makes perfect sense. The fuses are actually protecting against over-current in a situation where they could actually encounter it.

 

Edited for grandma

Edited December 16, 2015 by WotEver

[DHutch]

It's not a boat, but as I'm at my parents for a few days, this is a photo of their PV installation.

 

The array consists of 18 2ftx4ft rigid pannels on the garage roof, although I don't know the on paper specs.

 

Inverter in the attic, with isolators both sides, input voltage from the pannels appears to be just over 300volts:

 

AC consumer unit, with an isolator between the cable from the inverter and the meter, and then an RCD+MCB between the meter and consumer unit:

 

One instalation doesnt write the rulebook but in this instance while there appears to be isolators everywhere, there is no over current protection on the panel side of the installation.

 

 

Daniel

[WotEver]

That installation mirrors that at our house. Isolators everywhere but the only 'fusing' anywhere is the MCB in the consumer unit.