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Last Post by Transparent 2 years ago
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Transparent
 Transparent
(@transparent)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 2634
03/10/2023 4:32 pm  

@allyfish - what's the function of the two black rotary isolators at the top?

Have you had that DC MCB installed yet?


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 AllyFish
(@allyfish)
Noble Member Contributor
Joined: 3 years ago
Posts: 506
Topic starter 03/10/2023 9:59 pm  
  • @transparent black isolators are DC solar PV isolators, two strings, one 4 panel, one 5 panel. I await the DC MCB from L R Renewables by Mail and a date when they will install….


   
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Transparent
 Transparent
(@transparent)
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Posts: 2634
04/10/2023 9:33 am  

That's interesting @allyfish.

I'm puzzled how a 'knife switch' mechanism can be used effectively with high-voltage DC.
When the circuit is broken by rotating the disc, I would expect the resulting arc to damage the edge of the blade.

Any chance of a close-up photo so we can see the manufacturer and model number of those rotary switches?

 

For others who are following this, and would like a bit more technical insight...

A typical solar array of rooftop panels in series will be supplying the string inverter with a voltage between 150-500v, with a current of less than 20A.

There are DC-rated MCB-style trips which can be used to handle these voltages.
They have a series of plates arranged as a ladder-network which dissipate the arc.

MCB1

Such a DC trip uses a pair of magnets either side of the contacts to pull the arc into the ladder when the contacts open.

That's why a DC trip is marked with + and - symbols which tell you which way around it must be connected.
There is no 'standard' for this.
You have to look at each unit to check the polarity.

I do have a rotary isolator on the input to the inverters to comply with the safety guidance, but it is preceded by a DC-trip and a pair of fuses.
The trip is opened first, before I turn the isolator.

DCbreakersIsolator

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 AllyFish
(@allyfish)
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Posts: 506
Topic starter 04/10/2023 10:03 am  

@transparent they are Craig and Derricott EPV252 25A 2 pole rotary isolators. Designed for DC voltage and Solar PV isolation, 25A @ 800V. https://craigandderricott.co.uk/product/photovoltaic-pv-enclosed-switchgear/

 



   
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Transparent
 Transparent
(@transparent)
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Posts: 2634
04/10/2023 11:25 am  

That's neat.
And good to see that Messrs Craig and Derricott is a UK company, based in Walsall. 😎 


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