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Are two-pole breakers required on single-phase 230 V loads when connected to a 3-phase supply with IT earthing system (with distributed neutral) in Germany?

Where in the standards is this requirement specified? What fault would be isolated by a two-pole breaker that wouldn't be isolated by a single-pole breaker?

I'm looking at https://www.se.com/ww/en/download/document/ECT178/ and it says:

Multi-pole breaking, including the neutral conductor when distributed.The reasons for this are:
--breaking only of the faulty phase conductor of a feeder means that three-phase machines are supplied by the two other phases
--breaking of the neutral exposes to phase-to-phase voltage, single-phase loads normally supplied by phase to neutral voltage

The 3-phase load has no neutral, and is protected by a 3-pole breaker, so the first point above is covered

The single-phase loads wouldn't have a breaker on neutral, only on the live phase, so the second point above...doesn't make sense to me.

I'm also about to purchase IEC 60364, but I'm not hopeful that I'll see a cut-and-dry answer in there.

Thanks.

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  • \$\begingroup\$ This question is much better suited for the DIY Stack IMO. \$\endgroup\$
    – brhans
    Commented Mar 23, 2022 at 19:15
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    \$\begingroup\$ If you have multiple unbalanced single-phase loads on your 3-phase supply, and you lose neutral, you could potentially see the full phase-to-phase voltage appear at some of your single-phase loads (depending on how unbalanced they are). \$\endgroup\$
    – brhans
    Commented Mar 23, 2022 at 19:21
  • \$\begingroup\$ Thanks, It's an industrial application, not home DIY. Looking at other posts here, and other posts there, I would have thought that this was the right place. I'm happy to take advice wherever it comes from though? Anyone else have thoughts in this regard? \$\endgroup\$
    – Mike Jones
    Commented Mar 23, 2022 at 19:21
  • \$\begingroup\$ Yeah even though it's industrial I think the member population over there deals with this kind of thing more often, particularly when looking at it from a "code rules" perspective, but I wouldn't say it's off-topic here. \$\endgroup\$
    – brhans
    Commented Mar 23, 2022 at 19:23
  • \$\begingroup\$ "If you have multiple unbalanced single-phase loads on your 3-phase supply, and you lose neutral, you could potentially see the full phase-to-phase voltage appear at some of your single-phase loads (depending on how unbalanced they are)." - OK, I understand, but I'm not proposing to put a single-pole breaker on neutral. The single-pole breaker would be on whatever phase feeds that branch. \$\endgroup\$
    – Mike Jones
    Commented Mar 23, 2022 at 19:24

1 Answer 1

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EN 60364-4-43:2010 section 431.2.2 contains the answer:

It clearly specifies that on IT earthing system, with distributed neutral, two pole breakers are required for single phase loads.

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