Sittingbourne Fire the other week

[JulianC]

ps. on a domestic install i'd be surprised if it was an undersized dc

I wouldn't - local outfit got a massive rent-a-roof contract and I heard last week they are having to revisit each job to fit new DC isolators 'cos the ones they fitted were burning out. Quite easy to save a few quid on a 450v rated switch - or even just a bog standard AC isolator with a black knob (seen that before now) on the end of your 600v string if you are that way inclined.

 

[jupestar]

i just assumed there would be no market for low rated dc breakers... obviously i'm wrong.. luckily i don't spec them for our installs....

 

[Glen Powell]

It is not that there is no market for it, it is simply the fact that there is no enforcement of good practice and standards of said switches.

Some modified AC switches simply link two poles together to take the load. If there is no Rachet Sprung action on the handle then it is not a DC isolator but a modified AC switch with a black handle.

 

[SibertSolar]

Thanks for all the feedback chaps, certainly isn't clear yet as to the root cause of the issue. As most would already know, we've promoted the considered selection of true DC disconnectors over modified AC isolators for some time now and I suspect that an incorrectly rated switch is at the core of the issue in this instance....although I can't be sure yet. It's not difficult to achieve DC21B current/voltage rating on any isolator, the key is whether the switch has been designed to load-break DC and minimise (or remove completely) the impact of arcing on the contacts etc. IMO (Benedikt) and Santon DC disconnectors are specifically designed for purpose which is why we only recommend them and don't promote other (lower cost but less value) brands.

 

[mdovey]

Slightly off topic - although very relevant. What is the best type of smoke alarm to put in the loft (if you have an inverter and isolators in the loft) - optical or ionisation?

 

[pro s e]

This is my first post but I had to get this off my chest, if it was a faulty dc isolator then it's the first I've ever heard of.. Maybe an incorrectly connected dc isolator, if you are new to the game I suppose you could find a dc switch confusing. God knows how but it's certainly possible. Yes the problem with pv is that it continuously generates during daylight hours, however a house can only have up to 4kw installed, not exactly enough to power the starship enterprise's warp drive (no I am not a trekky just being sarcastic.) I have however had a shock from a 16 panels connected in series and yes it did smart somewhat.
The problem with badly installed pv is that if the dc starts to arc, whether it be at the isolator or at the roof entry it will arc continuously, there is no protection against this and the arc can best be described as looking like a welder in action, it's quite site to behold and could definitely cause a fire.
My best guess is that he simply missed the lugs when tightening the cable/s into the terminal/s of the dc isolator, a similar scanario to when meter tails are screwed into the main isolator of a CCU and miss thus melting the main switch.
The best advice I could give any fireman is just pull the head fuse or turn off the CCU, this will send the pv system into islanding mode and at least make the ac side of the pv system safe.
Or pray the house has a solar edge inverter as when the inverter loses ac power it forces all the connected panels into safe dc mode locking each panel at 1 volt.