Dti Guide

[Worcester]

Because TL inverters are not galvanically isolated...

If you put a connected up mc4 connector underwater in a big pool of water on a flat roof (we had one....) you will then get an 'insolation failure' warning on the inverter and you'll be able to measure a voltage between either of the poles and earth (the different voltages will also tell you where it is in the string )

Because there was an LPS system on the roof the array was linked in to / bonded to it anyway, which we would still do under the new guidelines (we did one last week).

MC4's ironically don't seem to be up to IP67 rating

 

[Worcester]

wouldnt that create a short circuit
Top rail live bottom negative fault flow thru panel ??

Its short circuits that give you the jolt / kill you. And it's the panel that provides the potential anyway...

Fortunately PV panels are current limiting devices, though 1000V @ 7 Amps could kill...

 

[jason121]

Because TL inverters are not galvanically isolated...

If you put a connected up mc4 connector underwater in a big pool of water on a flat roof (we had one....) you will then get an 'insolation failure' warning on the inverter and you'll be able to measure a voltage between either of the poles and earth (the different voltages will also tell you where it is in the string )

Because there was an LPS system on the roof the array was linked in to / bonded to it anyway, which we would still do under the new guidelines (we did one last week).

MC4's ironically don't seem to be up to IP67 rating

Understand short circuits i am a sparky
But not seeing the big picture above any chance of a sketch sometime

 

[Worcester]

Imagine the panels as a load of car batteries, joined in series.
Join 12 x 12 v batteries in series.
+ 12v - + 12v - + 12v - etc..
Now stick a lead from the +ve / -ve junction between batteries 8 and 9 to earth. Measure the voltage between +ve terminal on battery 1 and earth and it will read about 96V measure between earth and -ve terminal on battery 12 and it will measure about 48V remove the lead from batteries 8 -9 to earth and both voltages will read 0V i.e. no potential difference.

 

[Gavin A]

Understand short circuits i am a sparky
But not seeing the big picture above any chance of a sketch sometime

in the scenario I gave, the circuit would be made through the installer & rail.


+ >> installer >> rail >> -
<<<<solar panels<<<<<

 

[jason121]

How do you test earth spike to make sure resistance is low enough, use a earth ground tester ?

 

[infinity]

So has anyone had an inspection and shown to be using the new decision tree? Just wondered how the inspector viewed it as i have my annual inspection coming up.

But i agree, the new one makes more sense, i assume you just test the rails when installed to ensure the resistance to MET is more than 22KOhms?

Then omit the bonding!

 

[Gavin A]

We actually test the continuity to earth instead to avoid the issues with tripping RCD's etc that you can get doing an insulation resistance test but it's effectively the same thing just in reverse.

How do you test earth spike to make sure resistance is low enough, use a earth ground tester ?

We've not had to install an earth spike yet on domestic since following the revised decision tree, but when we were doing it previously we were just doing a Zs reading and ensuring it was within the acceptable TT range. As this reading changes between wet and dry periods though, I doubt many of the ones done in winter would pass on a dry summer etc. We'd pretty much realised it was a box ticking exercise and entirely pointless by that stage anyway though.

 

[yellowvanman]

We've not had to install an earth spike yet on domestic since following the revised decision tree, but when we were doing it previously we were just doing a Zs reading and ensuring it was within the acceptable TT range. As this reading changes between wet and dry periods though, I doubt many of the ones done in winter would pass on a dry summer etc. We'd pretty much realised it was a box ticking exercise and entirely pointless by that stage anyway though.

Not seen anywhere an expected value for the earth spike, it's not your main earth so is the 'accepted' value relevant? Generally if you have omitted any RCD in the inverter circuit it wouldn't help tripping an MCB anyway, and even if you have an RCD then as long as its below 1666ohms it should trip it ok in the event of a fault to the array.

 

[SibertSolar]

Because TL inverters are not galvanically isolated...

Because there was an LPS system on the roof the array was linked in to / bonded to it anyway, which we would still do under the new guidelines (we did one last week).

MC4's ironically don't seem to be up to IP67 rating

Gordon - if you linked/bonded to an existing LPS, did you fit Type1 lightning/surge protection at the inputs to the inverter(s)?

PS: Our MC4-compatible connectors are IP67 rated when mated together ;-)

 

[Worcester]

@Sibert, yep in those cases the Inverters have surge protection installed.