Emergency shutdown of solar panels

[farmerfred86]

Our emergency shutdown procedure shows us to switch off the AC first and then DC...

Is this correct? Wouldn't you shut down the incoming solar DC current before isolating the AC?

 

[Exfarmer]

I do not believe it will make any difference at all. shutting off the AC will switch off the inverters , shutting all power off anyway

 

[akaPABLO01]

Our emergency shutdown procedure shows us to switch off the AC first and then DC...

Is this correct? Wouldn't you shut down the incoming solar DC current before isolating the AC?

Emergancy shutdown focuses on disconnecting the array from grid. If you power off the dc there is still current held in the inverter and they need 5 minutes to discharge. Disconnecting the the ac shuts the inverter down immediately. Disconnecting the dc still provides power down the ac.

Shutting down the dc before ac in Emergancy that is on the dc side entering the inverter may cause internal string box arc.

As a rule, always shutdown ac first, when powering up engage dc so the inverter can gain charge before engaging ac

Non Emergancy shutdown is not important but still shut down ac first haha

 

[farmerfred86]

Thanks,

The problem I'm having is that one of the MC4 connectors on the roof is either disconnected or water is getting into the connector through the rubber seal.
As the whole system is earthed to the building it is tripping out the main fuse.
On a sunny day the connector dries out but in damp weather it's a problem.

If I disconnect a string at a time I should be able to narrow down which panels are at fault but I didn't want to touch anything without knowing how to shut down safely first.

I hear it's something of an issue... Solar panels earthing to the building and blowing the fuse?

 

[akaPABLO01]

Thanks,

The problem I'm having is that one of the MC4 connectors on the roof is either disconnected or water is getting into the connector through the rubber seal.
As the whole system is earthed to the building it is tripping out the main fuse.
On a sunny day the connector dries out but in damp weather it's a problem.

If I disconnect a string at a time I should be able to narrow down which panels are at fault but I didn't want to touch anything without knowing how to shut down safely first.

I hear it's something of an issue... Solar panels earthing to the building and blowing the fuse?

No, first time I've come across tripping mains.

What size array do you have, what bonding is there (are the inverters earthed, does the array earth go straight to mains, why is your array earthed?)

 

[farmerfred86]

sorry when I say earthed I mean that the negative of the DC is earthed to the building (like on a car or vehicle) and so only a single wire is needed from each panel. This is fine when everything is well insulated but means that any damp or break in a wire can mean it shorts out by touching the fram of the building.

 

[akaPABLO01]

sorry when I say earthed I mean that the negative of the DC is earthed to the building (like on a car or vehicle) and so only a single wire is needed from each panel. This is fine when everything is well insulated but means that any damp or break in a wire can mean it shorts out by touching the fram of the building.

I'm concerned.

Can you post some pictures

Beneath the inverter showing cables
The string "attached" to the roof/rails?
Your string map, how the array is wired on the roof illustration that should be in your handover pack

This, how you describe, is not correct if I'm understanding correctly

 

[Exfarmer]

Certainly sounds a new one to me!

 

[farmerfred86]

I can see the pos and neg going into the inverter so it's not quite as I thought but our electrician is certain that there is a large leak to earth somewhere causing the mains to trip.
It has to be one of the mc4 connectors on the roof somewhere...

 

[akaPABLO01]

Ok, thought you had some 3rd world wiring.

Definitely an mc4 connection. You should change them all. I find changing 1 string leads to further work in the future and changing them all is your best solution. Hire a cherry and follow your string map. You may also have extensions on the dc, I say may. Your installer should know.

Also check the panels as you go along for water ingress. The silver conductor strips at the bottom will have a rust if this is the case.

 

[farmerfred86]

Thanks,

Presumably the only way to check each panel is to unscrew from the rail and lift each one? Sadly our installer is long gone!

 

[akaPABLO01]

Thanks,

Presumably the only way to check each panel is to unscrew from the rail and lift each one? Sadly our installer is long gone!

Sheesh, so I gather you don't have a string map showing the connections then. This is of a high difficulty repair then.

You are best trying to isolate the offender.

Each string circuit below the inverter is a positive and negative. Experiment buy removing one at a time and leaving the rest in.

Does your system trip every day? If so you can isolate the offending string easily. If it's every several days then you may want to run it for longer.

Switch off the ac supply, switch off the dc supply. Wait 5 minutes.

Pull a set of string out the inverter they should be pinch clipped in.

Get a sandwich bag or something to cover the pos and neg and wrap elastic band around so it doesn't contaminate. Leave string out until the system trips, test others.

When the system stops tripping you've located the faulty string.

This will give you time to start phase 2.

Draw out on a piece of paper your roof array.

When you get time get some ladders up to gutter and see which panels connect to which before you locate the string connection.

Now if your shed is high or you have say 3/4/5 rows, you may find it easier getting on a cherry and unlocking every other panel along the middle popping your head under to map out the connections.

This is very important!!!

Accidents with falls are very serious do not do this alone, make sure you have a harness and it's tied off to the cherry. You are able to walk on the outer edges of the frame of the panel especially take care and try to stand on the clips. Do not do this in high wind or rain. Tools you will need are a size 5 Allen key, a crimper. Make sure the panel is tied securely back. Make sure you have broken the dc connection with the isolator before attempting repair.

Seeking out a firm to do this will set you back a few grand.

I cannot stress the importance of safety whilst working on the roof!

 

[farmerfred86]

Thanks,

I have some of the sting paperwork but it will take me some time to understand it. Hopefully all the cables are marked on the roof so that I can locate the offender (If Ive narrowed it down first at the inverter).
Thanks for the advice about safety... this particular array (One of 3) is on a building 10m to eaves so def a genie boom and harness job. I think a fall arrester and harness would be a good purchase for many of the jobs we do tbh!

 

[akaPABLO01]

If you post the string map I'll tell you where to go.

As far as the connectors rooftop; these mc4 are also pinch connects, uncouple them and inspect both sides for rust. If no rust then snip the string length not the panel and connect the new mc4. Make sure it's tight. Once connected give both ends of the cable a tug to test if your new connection is tight.

If both the panel and string mc4 comes apart easily then change both.

However many cables are below your inverter halve the amount and pick up say 6 pairs of mc4. Make sure they understand that a pair is a "male" and "female". Change like for like. You can probably get your yard spark to pick them up from his wholesalers. Get more than you need.

Let us know if you run into any issues, good luck!

 

[Exfarmer]

While I can well believe you may have a leaking connector, I am far from convinced it would make your trip go. In fact I would go as far as to say it won't!
RCD work by detecting a difference on the live neutral wires. Any difference must be a leak to earth. Your situation is totally different.
I would guess you may well have a fault in the inverter

 

[akaPABLO01]

Will not be the inverter. That'll shut down if it's the problem. This is earthing rooftop.

Make sure your breaker is correctly sized at db.

 

[Exfarmer]

Firstly is this and RCD or an MCB which is tripping.
RCD s trip in the event of an uneven current flow in the live and neutral. This should always be the same unless there is a leakage to earth.
An MCB trips when there is a surge in the current for any reason. Low voltage can do this as motors pull more amps in a low voltage situation.
An MCB may trip when the production is too high pushing the voltage in the system up.
Another factor is that RCDs them selves leak a very small amount of current, too many in the circuit and you will get problems. It may be cured by replacement with a less sensitive model.
It will be very simple to test the DC circuit for leaks. If you isolate the inverter from the earth then you should have no issues as the DC circuit will not complete.
Be aware that doing this can be dangerous and should only be done in a controlled situation

 

[Exfarmer]

My previous post is incorrect!
Aka is right and a DC fault can cause RCD tripping.

 

[akaPABLO01]

Don't worry about it. As long as he doesn't fall off the roof, it's all good.

 

[farmerfred86]

or get electrocuted!