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Author Topic: Combiner and DC Isolator + Lightning/surge protector  (Read 4997 times)
Westie
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« Reply #15 on: April 30, 2017, 12:35:04 PM »

I completely agree with the surge protection but I don't see why over-current MCB's are of any use?

MCB's  normally to protect against excess current, however string the current can never exceed the Imax of any one panel in a single string anyway?  (typically 10A)

Also, say you had a short circuit somewhere on an array, how would an MCB protect it?  The S/C current will only flow around the panels in the loop contained within the shorted section?

The only way you could hope to protect against a string short would be to have an over-current device between each panel, even then what rating would you use , Imax?  But you want Imax !

When you think about it, the safety of micro-inverter arrays are way superior.







« Last Edit: April 30, 2017, 12:45:08 PM by Westie » Logged

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Tiff
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« Reply #16 on: April 30, 2017, 02:23:34 PM »

What Westie said. If anything, more chance of causing a fire than preventing one.

http://bpva.org.uk/media/38266/new-guide-to-installlation-of-pv-systems-mcs_20130530161524.pdf

PV modules are current-limiting devices, which require a non-standard approach when designing fault protection systems, as fuses are not likely to operate under short-circuit conditions.
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eabadger
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« Reply #17 on: April 30, 2017, 03:17:05 PM »

the mcb on arrays are a way of isolating not protecting.
the 150a mcb on inverters are both isolating and protection on batteries in case of inverter s/c

steve
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Westie
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« Reply #18 on: April 30, 2017, 03:30:09 PM »

the mcb on arrays are a way of isolating not protecting.
the 150a mcb on inverters are both isolating and protection on batteries in case of inverter s/c

steve

Actually if you have a system with DC coupled batteries then you definitely need MCB's to protect against current backfeeding from the batts into a short on the string.
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jonesy
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« Reply #19 on: April 30, 2017, 03:40:15 PM »

fingers crossed after fitting SPD to telephone and data cable not had anymore static issues or lost equipment, so maybe just luck or they may work?
steve
Do you mean static?  ie high voltages generated by friction.
SPD stop very little and need regular replacement.  They are one-shot devices. The ones in my phone socket went sometime this year and we've had no lightning, so maybe just a surge somewhere. I only noticed as I saw a massive increase in the broadband error rate and a reduction in speed down to 20M  Grin
I had a satellite box go a bit fut (blown transistor) following a lightning storm in the neighbourhood, but I can't be sure it was the storm.  The dish is about 20m from the house, so I'd guessed it was a difference in ground potential during the strike.  The transistor only affected channels on vertical polarisation and the channels I mostly watch are on horizontal, so it could just have been one of those things.
Panels are not lightning magnets.  Are they any more likely to be hit than any other part of the house eg TV aerial?  
The Hager breakers taking DC are good, but IIRC it's something like 45s for a B curve to trip at rated current. The MCB protects the cable. I've a Merlin Gerin dual conversion UPS which has type B MG breakers on DC, but the spec sheets don't show it last time I checked.

You can directly connect panels to batteries. The only reason I stopped was too high a voltage once the batteries were fully charged. Batteries should be protected just above the maximum demand, or cable size, whichever is smallest.
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terosity
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« Reply #20 on: April 30, 2017, 06:03:46 PM »

Hi all thanks for the replies.

Im looking for a way to safely turn off any string if required and all if needed hence why the mcb's.

So you are saying SPD are a waste of money ?

What is the safe way to disconnect a string if needed.

Thanks
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Westie
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« Reply #21 on: April 30, 2017, 06:57:19 PM »

Hi all thanks for the replies.

Im looking for a way to safely turn off any string if required and all if needed hence why the mcb's.

So you are saying SPD are a waste of money ?

What is the safe way to disconnect a string if needed.

Thanks

Every solar inverter I've looked at has built in surge protection on the string inputs. But personally I would fit external devices as well. It's easier to replace those rather than the ones built into the inverter in the event you do get unlucky.

BTW if your panels are up on a roof and can't be touched from anywhere (eg. by leaning out of a window)then it's better not to earth the supporting frames, always remember to isolate the arrays if your working on the roof off a ladder / scaffold.  Also be aware that a static charge can build up on the array frames. Personally I always flash them down to earth before I touch them. The last thing you want is a static jolt when perched on the top rung.   sh*tfan

For isolation I would use a straight forward DC isolator they're around 20 each, bring each string back to it's own isolator, do your combiner wiring on the inverter side of the DC isolators. 



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camillitech
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« Reply #22 on: April 30, 2017, 08:42:33 PM »



Every solar inverter I've looked at has built in surge protection on the string inputs.

But he does not have a solar inverter Westie, this is in the 'off grid' section and he's using a solar controller. However, as pointed out by Roger and Steve, methinks it's a waste of time anyway.
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Westie
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« Reply #23 on: April 30, 2017, 10:06:59 PM »



Every solar inverter I've looked at has built in surge protection on the string inputs.

But he does not have a solar inverter Westie, this is in the 'off grid' section and he's using a solar controller. However, as pointed out by Roger and Steve, methinks it's a waste of time anyway.

OMG... Sorry guys. I've accidentally strayed into an area I know nothing about, all my comments, as Camillitech pointed out, relate to Grid Tied Solar inverter - Sorry terosity I'm sure the off grid guys will sort you out!
 surrender



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camillitech
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« Reply #24 on: April 30, 2017, 10:44:33 PM »



Every solar inverter I've looked at has built in surge protection on the string inputs.

But he does not have a solar inverter Westie, this is in the 'off grid' section and he's using a solar controller. However, as pointed out by Roger and Steve, methinks it's a waste of time anyway.

OMG... Sorry guys. I've accidentally strayed into an area I know nothing about, all my comments, as Camillitech pointed out, relate to Grid Tied Solar inverter - Sorry terosity I'm sure the off grid guys will sort you out!
 surrender





Methinks you still need 'lucky underpants' even with a solar inverter Westie  fingers crossed! Far better than surge protectors  ralph

Cheers, Paul
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« Reply #25 on: May 01, 2017, 03:13:19 AM »

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bautsche
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« Reply #26 on: May 01, 2017, 09:34:04 AM »

I've only skim-read the post, so if I'm missing the point, feel free to flame me... ;-)

If you're direct attached (i.e. DC and high amperage), go for something like this:
https://inverterdrive.com/OrderCode/20988/

It's a fuse box and if you pull the handle it disconnects.

If you've got an inverter, something like this will do:
http://uk.rs-online.com/web/p/non-fused-switch-disconnectors/3813578/

HTH
Eric

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eabadger
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« Reply #27 on: May 01, 2017, 11:11:35 AM »

do the spd's work? not on lightning strike that i am sure, but static build up in air? i dont know, i know i lost items before i fitted them, but i also disconnect the telephone line now, which is also now isolated from the solar technology by wifi, so kind of too many changes to confirm.
But, in the scheme of things they are peanuts so i would fit no matter what.
biggest issue when my mppt died was i had a standard pwm controller, but i had to reconfigure all the panels to get it working.

after all for most of us it is all a big experiment.

steve
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Westie
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« Reply #28 on: May 01, 2017, 04:08:37 PM »

do the spd's work? not on lightning strike that i am sure, but static build up in air? i dont know, i know i lost items before i fitted them, but i also disconnect the telephone line now, which is also now isolated from the solar technology by wifi, so kind of too many changes to confirm.
But, in the scheme of things they are peanuts so i would fit no matter what.
biggest issue when my mppt died was i had a standard pwm controller, but i had to reconfigure all the panels to get it working.

after all for most of us it is all a big experiment.

steve

Yep, they definitely work.  The cheapo ones just use voltage dependent resistors (VDRs), there's usually one or more connected per conductor to earth, they're okay for attenuating low energy surges, the best 'arrestors' have VDR's and avalanche diodes. Serious energy triggers the avalanche diode with virtually shorts the conductor to earth.  When you get a surge of high enough energy to trigger the diode it's normally destroys it, I've had them literally blow apart, but the fact it shunted all that energy to earth usually saves the device that's being protected.

It the surge protector doesn't have a fat connection to earth don't bother buying it, the best one's have VDR's, Avalanche diodes, and a 4 or 6mm separate earth cable to dump the energy down.  I use APC and Furse arrestors to protect comms lines (PSTN, ISDN, Ethernet etc.)  I'm afraid Pauls lucky underpants are chocolate fireguards where I live, I'm about a half mile away from a 750ft (disused) TV mast and it's an absolute lightning magnet, which is good as it's all the lightning ever strikes. Sadly, tho all our overhead  telephone lines run along a road that runs along side the mast, within about 100Mtrs. When the mast is struck megaamp currents are conducted down it to earth, a huge electromagnetic pulse induces high voltages into the phone lines which then looks for ways out, before I started fitting arrestors I regularly replaced master sockets/ phones/faxes and routers, now I just replace arrestors.

These arrestors ain't cheap ... They're around 100 a pop for a PSTN line. Mine have blown twice in the last 3 yrs, I now buy the VDR's and avalanche diodes to repair them myself, that's if the PCB hasn't vapourised sh*tfan.

http://new.abb.com/low-voltage/products/earthing-lightning-protection/furse

http://www.apc.com/shop/au/en/products/APC-ProtectNet-standalone-surge-protector-for-10-100-1000-Base-T-Ethernet-lines/P-PNET1GB






« Last Edit: May 01, 2017, 04:24:03 PM by Westie » Logged

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Scruff
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« Reply #29 on: May 02, 2017, 12:00:59 AM »

but i had to reconfigure all the panels to get it working.

How did the real world outputs compare? Same manufacturer or different?
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