D/C isolators? | on ElectriciansForums

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W

wozzit99

Hi

Is it mandatory to have a seperate d/c isolator per string or can you rely on the ess isolator built into SMA inverters? I have seen several installations where d/c isolators are used on the same inverter where just the ess switch is used on others.

Wozzit
 
If you don't put a DC isolator in next to the inverter then it's not safe to test the array. You need to switch off the DC isolator, connect your test leads then switch it on to test Voc. More importantly you need to switch it off to short out the two ends and clamp on your DC Amp meter. If you relied upon the inverter's DC disconnect then you'd have sparks during this test.
 
Cheers Ramjam, just wondering why some other firms don't us the d/c isolators. There is a test box about can't think of the name of it where you plug in the d/c and do your testing there.

Wozzit
 
Have this conversation regularly with an ex-colleague and neither of us reach a conclusion. I am now coming round to thinking that the isolator built in to the inverter is sufficient. However, this is providing that you have some sort of test box for string testing (either an off-the-shelf unit or a custom made jobby cobbled together from a DC isolator, some spare MC4 connectors and a loop of cable on the output side for Isc testing)

I still fit separate DC isolators though - 1 per string. Just seems a better job that way!
 
I have read 712.537.2.1.5 a few times and think it can be interpreted both ways, Personally, I suspect the isolator in the inverter is sufficient from a safety point of view once commissioned, but the point is well made that an external dc isolator is useful for testing. I also suspect some assessors will not have a flexible mindset.

Regards
Bruce
 
I have read 712.537.2.1.5 a few times and think it can be interpreted both ways, Personally, I suspect the isolator in the inverter is sufficient from a safety point of view once commissioned, but the point is well made that an external dc isolator is useful for testing. I also suspect some assessors will not have a flexible mindset.

Regards
Bruce
also the ESS switch has no way of being locked off which I think is a requirement had our Mcs annual today and I asked what he thought and he preferred the separate isolator approach and said its a grey area
 
DC isolator ÂŁ24 from segen and it's a better job.

I've cut the ends off my test leads and fitted some sunclix to measure Voc then I can connect to the cables as they're ready to go into the SMA inverter. Then 4 inches back up the lead I crimped on some MC3 connectors which I can use on the sharp panels. Both connectors are touch safe by definition so I don't have to stick probes into live plugs, easy!
 
It is a grey area but I look at it like this.

The DC's coming in off the panels are plugged straight into the inverter. We label systems with manufactured off the shelf labels stating "do not disconnect under load" (or similar) By only using the ESS it isn't possible to unplug the inverter with out being on load. OK the inverter may be isolated but the DC's are still at voltage. So is this none compliant? Not sure.

We always fit DC isolators regardless of the inverter. Why? I would rather be criticised for going over the top than not being compliant and after all we are looking a very small cost item so why not fit it.

Consider what would happen IF a manufactures service agent was to visit the installation on a warranty call for example. I bet some of us have witnessed the unrelenting ignorance of a boiler service agent shouting "this isn't wired right!" Well the same will happen here if a DC isolator is missing (even if not needed) and guess who YOUR customer will be ringing saying this isn't wired right. Trust me They WILL side with the service guy.

Just my thought.
 
It is a grey area but I look at it like this.

The DC's coming in off the panels are plugged straight into the inverter. We label systems with manufactured off the shelf labels stating "do not disconnect under load" (or similar) By only using the ESS it isn't possible to unplug the inverter with out being on load. OK the inverter may be isolated but the DC's are still at voltage. So is this none compliant? Not sure.

We always fit DC isolators regardless of the inverter. Why? I would rather be criticised for going over the top than not being compliant and after all we are looking a very small cost item so why not fit it.

Consider what would happen IF a manufactures service agent was to visit the installation on a warranty call for example. I bet some of us have witnessed the unrelenting ignorance of a boiler service agent shouting "this isn't wired right!" Well the same will happen here if a DC isolator is missing (even if not needed) and guess who YOUR customer will be ringing saying this isn't wired right. Trust me They WILL side with the service guy.

Just my thought.

I think Mark has it right but I guess it can be considered a bit of a "grey" area by some. As far as I am aware, under MCS guidelines a seprate means of isolating the DC supply back from the PV array is required. Inverters fitted with DC switches tend to have been developed for the European marketplace where a separate DC disconnector is often not required.

In any case, what are the forum's opinions on "true" DC disconnectors, as oppose to modified AC switches being used to break DC voltage/current?......
 

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