AC / DC isolators

[GaryM]

it's not.

well, we generally wire the panels into T1 & T3 rather than T2 & T4, but am pretty sure that's just our convention rather than serving any practical purpose.

Panels are wired into T1 & T3, the outgoing side to the inverter is T2 & N (T4).

Looking at the PDF created by the manufacturer that Julian linked to on Page 1 suggests the termination order isn't to manufacturers instructions.

They suggest:

+ in from panels to T1
+out to inverter to T2
-out to inverter to T3
-in from panels to N (T4)

 

[Gavin A]

Thought I'd check this with K&N...

[FONT=&quot]I can confirm that it is okay to connected the + and – leads from the pv string as stated in your email below.[/FONT]

so as I thought, it's fine either way round.

 

[Ramjam]

I use those isolators and I think they're great, as has been pointed out by breaking the dc circuit in two places rather than just one the arcing is halfed. DC isolators on PV systems are for maintenance purposes not general use so will see little action in reality.

But I've seen Bosch dishwashers and IBM monitors burst into flames, electiricty is dangerous and there is little point in stressing over what is beyond our control, if a reputable manufacturer sells an isolator which is rated for DC use then why lose sleep over whether or not it is a modified AC design?

My only criticism is that I run each DC cable through it's own stuffing gland to maintain the IP rating, 2 cables through 1 stuffing gland does not seal!

 

[Gavin A]

surely that 2 into 1 problem is only an issue for isolators situated externally, or possibly those with the cables running into the top of the isolator if you're worried about condensation forming on the cable and running down it.

no other household electric switches that are inside are fully water proofed as a rule other than special locations.

 

[Ramjam]

I agree, I just like to maintain the IP rating, it satisfies my OCD!

 

[SibertSolar]

Sorry, how does series linking multiple poles together reduce arcing? All it does is increase the voltage ratings, does nothing for the current rating. In fact, increasing the number of contacts in series actually increases the number of contact surfaces potentially affected by arcing. In the case of a properly designed DC disconnector this isn't an issue (when series-linking only to achieve 1000vdc ratings, by the way) as they tend to employ sliding, knife-edge contacts that self clean and result in the final contact point not being the normal (closed) contact faces. An AC isolator tends to separate in a 180degree plane so arcing has a direct impact on the actual contact surfaces....

 

[mr murdock]

Have to agree with Sibertsolar - K&N do not have a true snap action 1000V DC switch and are only fooling people into taking a AC switch

 

[LightGEN]

Sorry, how does series linking multiple poles together reduce arcing? All it does is increase the voltage ratings, does nothing for the current rating. In fact, increasing the number of contacts in series actually increases the number of contact surfaces potentially affected by arcing. In the case of a properly designed DC disconnector this isn't an issue (when series-linking only to achieve 1000vdc ratings, by the way) as they tend to employ sliding, knife-edge contacts that self clean and result in the final contact point not being the normal (closed) contact faces. An AC isolator tends to separate in a 180degree plane so arcing has a direct impact on the actual contact surfaces....

This is exactly why I thought K&N were suggesting that two poles should be operated in parallel, thus halving the current - seems I missread their instructions....however, I still feel my approach is better than two contacts in serial.

 

[Gavin A]

Sorry, how does series linking multiple poles together reduce arcing? All it does is increase the voltage ratings, does nothing for the current rating.

K&E disagree.

They give the voltage and current ratings for their isolators when doubled up, or in single breaker mode, as the single and 2 string installation options (page 13 and 14 of this guide).

KG32-T104 is rated at
dual string (single breaker per side) = 15A at 460V
single string (dual breakers per side) = 28A at 450V

the permitted voltage also increases with the dual breakers option, so essentially it's limiting factor would seem to be related to the watts per breaker.