Fusing solar panel cables

[nicknorman]

Bit surprised at a Mod making that sort of remark. May sound a good idea, until it needs to be done in a force 4/5/6 wind. Then there is the boat with 6 panels or stick down panels or even 12 panels.

 

It is a little hard to see why it would have to be done urgently.

[FadeToScarlet]

 

Bit surprised at a Mod making that sort of remark. May sound a good idea, until it needs to be done in a force 4/5/6 wind. Then there is the boat with 6 panels or stick down panels or even 12 panels.

If it's that windy, then I'd probably use sheets of plywood with mudweights on top, over the stick down panels.

 

But I can't think of any reason why I'd need to isolate solar panels that quickly. Even if I did, it's a couple of seconds work to unbolt the negative lead from the panels to the regulator.

[Chewbacka]

 

I do worry that the panels could be live and should the male connector touch earth/boat's hull ..............

Ahhhh but if you use proper solar connectors - which I do - the pins are shrouded in plastic and you can not touch the metal pins.

http://www.farnell.com/datasheets/1256179.pdf

 

However you should not pull them apart under load as you will get a big arc. So if you are using a 240vAC switch as an isolator which will have only 3 or 4mm gap when the switch is open I would be very wary of 'opening' it under load. If you do want an isolator it must be DC rated for at least the voltage you use.

[WotEver]

Like these http://www.penninecomponents.co.uk/product.asp?P_ID=1557

[Graham.m]

Ahhhh but if you use proper solar connectors - which I do - the pins are shrouded in plastic and you can not touch the metal pins.

http://www.farnell.com/datasheets/1256179.pdf

 

However you should not pull them apart under load as you will get a big arc. So if you are using a 240vAC switch as an isolator which will have only 3 or 4mm gap when the switch is open I would be very wary of 'opening' it under load. If you do want an isolator it must be DC rated for at least the voltage you use.

To many ifs If BSS required solar installations to met the regulations controlling the installation of solar PV panels. Then it would have a DC rated DP Isolator, just before the control box. Yep the Isolators exist for that value of DC etc.

[peterboat]

when i ordered my midnite classic they did have dc double pole isolaters on the site reading the info it would appear to be the rules in the states to use these. my panels are producing 200 volts at 12 volts and are at 63 amps ish so deffo would kill you. think i will put some of those warning high voltage signs on the panels big ones to cover them and keep me safe

[Graham.m]

If it's that windy, then I'd probably use sheets of plywood with mudweights on top, over the stick down panels.

 

But I can't think of any reason why I'd need to isolate solar panels that quickly. Even if I did, it's a couple of seconds work to unbolt the negative lead from the panels to the regulator.

Well I can only say I would not do it. What I think you are telling me you would unbolt and remove a cable carrying up to 150volts DC with a current of say 4/5 amp.

 

Remember the panel negative is not earthed and both need to be isolated to be safe.

[nicknorman]

To many ifs If BSS required solar installations to met the regulations controlling the installation of solar PV panels. Then it would have a DC rated DP Isolator, just before the control box. Yep the Isolators exist for that value of DC etc.

The BSS requirements are in general evidence-based. What evidence would you present that demonstrates a requirement for a panel isolator switch? As I mentioned in another thread it is always a bad idea to take regulations from one theatre and apply them to another. So for example, it would be hard to contemplate putting duvets on the panels on a building's pitched roof-mounted panels, but a perfectly reasonable concept for a narrowboat. Regulations should require safety equipment for a demonstrable reason and not just because they can, or because it is a good idea in a completely different scenario.

[FadeToScarlet]

Well I can only say I would not do it. What I think you are telling me you would unbolt and remove a cable carrying up to 150volts DC with a current of say 4/5 amp.

 

Remember the panel negative is not earthed and both need to be isolated to be safe.

In some kind of hypothetical "I must isolate the panels now, immediately" situation, yes, I would.

 

But then I've no idea what could cause that situation, I can't think of any time when I'd need to isolate the panels in a hurry.

[nicknorman]

Let's hope the need to instantly disconnect the solar doesn't occur when no-one is on the boat!

[Chewbacka]

Well I can only say I would not do it. What I think you are telling me you would unbolt and remove a cable carrying up to 150volts DC with a current of say 4/5 amp.

 

Remember the panel negative is not earthed and both need to be isolated to be safe.

To put boat systems into perspective - well mine anyway - the VOC is a max of 70vDC which is pretty similar to the voltage of an arc welder.

Those are operated with exposed electrodes and an arc.

 

A grid tie inverter as you will find on a house is very different and runs at a much higher voltage. I think 300+ is not uncommon, but I am happy to be corrected.

[Graham.m]

In some kind of hypothetical "I must isolate the panels now, immediately" situation, yes, I would.

 

But then I've no idea what could cause that situation, I can't think of any time when I'd need to isolate the panels in a hurry.

That is the problem you can't think of the when, the when is the unknown. I can't think of the when for the panels I have just over my shoulder on the ground. I can give you a why, possible fire in the control box. If you keep supplying the box with power difficult to put the fire out and dangerous.

 

Shalom have a good night

[Keith M]

In some kind of hypothetical "I must isolate the panels now, immediately" situation, yes, I would.

 

But then I've no idea what could cause that situation, I can't think of any time when I'd need to isolate the panels in a hurry.

I have see two case where the solar regulator was starting to fail

Causing the insulation on the input cable from the panels to melt

No isolator installed

 

Keith

[Graham.m]

To put boat systems into perspective - well mine anyway - the VOC is a max of 70vDC which is pretty similar to the voltage of an arc welder.

Those are operated with exposed electrodes and an arc.

 

A grid tie inverter as you will find on a house is very different and runs at a much higher voltage. I think 300+ is not uncommon, but I am happy to be corrected.

Really does not matter what the voltage is once you go over 60 the power is there to damage and cause fire. Shalom

[Graham.m]

I have see two case where the solar regulator was starting to fail

Causing the insulation on the input cable from the panels to melt

No isolator installed

 

Keith

Thanks Keith, I know of one that melted the control box

[nicknorman]

I have see two case where the solar regulator was starting to fail

Causing the insulation on the input cable from the panels to melt

No isolator installed

 

Keith

Surely this is the concerning part. A solar system is "always on" during the day and as such is left unattended for long periods eg when the owner is at work. Having a manually operated switch is of course of no use unless there is someone there to operate it.

[Nickhlx]

Yes - our domestic system inverters are rated at up to 500 V DC input from the string..

 

and I wouldn't hesitate (worry at all) about unplugging something carrying 150V DC, although I wouldn't stick my fingers in the arc, but if you were wanting to disconnect something quickly, a bit of a flash is probably the least thing you will be worrying about !

[Keith M]

Surely this is the concerning part. A solar system is "always on" during the day and as such is left unattended for long periods eg when the owner is at work. Having a manually operated switch is of course of no use unless there is someone there to operate it.

 

I am not aware of an automatic system

A fuse needs roughly a 100% over load for less than a 1 second operation

So some faults can cause a fire without the fuse operating

As was the case with one of the regulators

 

Keith

[Graham.m]

Yes - our domestic system inverters are rated at up to 500 V DC input from the string..

 

and I wouldn't hesitate (worry at all) about unplugging something carrying 150V DC, although I wouldn't stick my fingers in the arc, but if you were wanting to disconnect something quickly, a bit of a flash is probably the least thing you will be worrying about !

Sorry I would not attempt to remove a DC cable at those sorts of voltages and currents I want to be alive tomorrow.

I am not aware of an automatic system

A fuse needs roughly a 100% over load for less than a 1 second operation

So some faults can cause a fire without the fuse operating

As was the case with one of the regulators

 

Keith

 

I think the panels are current sources so always deliver Max current, think it is the voltage that varies. Thus what size fuse or DC breaker. Edited December 15, 2015 by Graham.m

[nicknorman]

I am not aware of an automatic system

A fuse needs roughly a 100% over load for less than a 1 second operation

So some faults can cause a fire without the fuse operating

As was the case with one of the regulators

 

Keith

 

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.

[WotEver]

I have see two case where the solar regulator was starting to fail

What was subsequently determined to be the cause of the failure?

 

Tony

[Graham.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.

 

I suspect that as it was the input cables that were affected and not the battery cables the problems were at the front end of the box.

 

My guess would be that as there was not a major fire the boxes were just replaced and no forensics done as the costs of that are quite high and frequently inconclusive. This is not the airline industry where people like the CAA etc have pots of money to throw at the problem and employ labs etc to investigate.

[matty40s]

 

I suspect that as it was the input cables that were affected and not the battery cables the problems were at the front end of the box.

 

My guess would be that as there was not a major fire the boxes were just replaced and no forensics done as the costs of that are quite high and frequently inconclusive. This is not the airline industry where people like the CAA etc have pots of money to throw at the problem and employ labs etc to investigate.

But you don't know, you aren't Keith M and are just making things up again.

[Graham.m]

But you don't know, you aren't Keith M and are just making things up again.

 

Oh dear Oh dear perhaps the wrong side of the bed syndrome

 

Oh I do have knowledge of the one I was involved with and many years of experience of what tends to happen.

Edited December 15, 2015 by Graham.m

[nicknorman]

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.