solar max mt 10

[jonnyboy1]

Hi all,

I've got a problem with a 20kw system in Hertfordshire. System is split into 4 strings over 2 10kw inverters.

1 inverter is showing DC insulation fault, I have had a look at the manual which says - the insulation resistance of the Pv generator against earth is too low. It then goes to to say check the Pv generator but that's all.

I have tested the strings with the dc insulation resistance coming back fine (seaward 150).

Has anybody had any of the same type of issues regarding this type of fault or am I missing something here?

 

[SolarCity]

Have you tried testing when it is has been raining?

What test exactly did you carry out?

 

[jonnyboy1]

Hi solar city

I have the seaward tester which test the voltage current and insulation resistance all in the one go. Both inverters had the same fault, one kicked in after the shut down procedure while the other one had a fault on one string but the other string was within volts range for start up, but still showing the fault DC insulation fault.
The inverter or array is not earthed apart from AC earth.

I was only at the job 10mims the other day as it is booked in for Wednesday this week coming.
I was seeing if any has had this fault before.

 

[SpitfireW'sale]

DC Insulation fault means DC Assymetry. If the difference between the DC+ to GND and DC- to GND is more than 100V, this messages comes up on the display. sometimes it happens early in the morning due to humidity. First of all, you have to do insulation resistance test per cable and find out if any cable is damaged and then to be replaced.

Could you also swap the strings and check if the system comes up with the same error msg?

Having checked cables and no fault found, the inverter has possibly an internal software fault and needs to be replaced with a new one.

The SolarMax hotline is always happy to help with problems 02089732556

 

[Gavin A]

when you're doing the insulation resistance test what are you testing to?

if it's a metal roof then chances are there's a direct path to earth not via the MET, particularly if it's wet, so you want to also be testing the IR from the DC circuit to the metal roof itself, ideally in the rain. And / or just pull out the made MC4 connectors at the end of the affected strings and check for water ingress / tightness of the seals, as this is the most likely cause if there is an issue in the wet.

 

[jonnyboy1]

Will extend the strings and check for internal fault, good idea! I have called solar max last year, very good service.

It was first thing In the morning i was there, the panels had been removed last week one string is down, this explains the fault code.

Gavin just testing the insulation resistance of the cable + - of each string. It's a slate roof.

Problem solved I think cheers