Do 2-phase (split phase) lines ALWAYS need to be switched together?

[bill.birch]

SSE install their own REC 4 isolator after the service cut out / polyphase meter on split phase. Two ways are used as L1 and L2, L3 is blanked off and the neutral is a solid non switched link. They will fit a "normal" REC 4 but will not be held responsible for any damage caused to the system if the neutral breaks first or makes last - their view is that the consequencies however small of getting momentary - or worse - 460V to earth (in a 230-0-230 tncs system) is too great to risk. I had a Hager 63A type D 3way mcb to isolate the split phase supply from a wind turbine i.e. L1, L2, neutral but since that "discussion" I have taken the neutral to a common neutral bus connection inside the mcb enclosure.

 

[Knobhead]

Very interesting, but I think after 20 months our OP will have sorted it out.

 

[bill.birch]

Thank you for a positive reply ! It is my first post and in my excitement to find something that I actually had knowledge of I completely missed the date of the OP............will try harder next time :blush2:

 

[Mark42]

Ha Ha! Thank you for your (belated) interest, gentlemen. Yes, all sorted long ago: I used the correct Double Pole MCB. No problem to source, it was just that my usual supplier, TLC, did not list them.
Welcome, Bill - if you have a split phase install at home, I'm delighted to find someone else on here who might actually know what it is! Are you saying you NEVER switch neutrals?

 

[bill.birch]

Thank you for the welcome - I decided to err on the side of caution in the belief that the SSE may actually know what they are talking about in this instance - especially as this is a common upgrade in North East Scotland and they do a lot more split phase installs than I do (and they gave me a nice REC4) so for split phase systems I don't switch neutrals - so far it has been the correct decision !! What was also vaguely interesting was that I checked with Hager Technical regarding the mcb I fitted and they told me that Hager mcb neutrals do indeed break last, make first.........but how can you be sure without 100% QA/QC ? we are talking milliseconds...............

 

[Knobhead]

Sorry Bill, just lately we’ve had lots of resurrected threads and they tend to confuse things.
Split phase supplies can be a bit of a minefield, I got used to them working in quarries 40 odd years back.
There has been a resent thread about them, which is a bit weird in the way the DNO have done it.

 

[reelectrics]

tt system on a farm what advice would members give on fitting 300ma rcds on a split phase supply looking at pv install so type a rcd required.regards

 

[netblindpaul]

180 deg split phase?

 

[Knobhead]

0° centre tapped is normal. 180° will give 0V phase to phase and the neutral would have to be 2X phase CSA conductor.
It could be a Scott or LeBlank 90° connection

So what voltage does the PV system work on?

 

[reelectrics]

single phase inverters 3.6kw tl fitting two each protected by 100ma rcd type A, farm install.treating the install as two seperate installs g83 settings so 240v nom 1%vd design swa cable regards

 

[Knobhead]

If you are going to be feeding in to the network then you could run in to problems with 230V.
You would effectively be feeding in to only ½ of the transformer winding, it won’t be happy, neither will the DNO!

I have sent you a PM