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Posted By Topic: Re-terminating porcelain fuses

Nov 23 2019 22:15

I have a couple questions regarding porcelain /ceramic fuses.

The other day I had to shift a porcelain fuse to fit a 4 way enclosure on the board (bossman prefers enclosure with RCD and space for future breaker or two)

The fuse was protecting the HW cct, when I relocated it I changed the base and installed a plugin breaker for good measure since I would've had to reterminate the porcelain base.

1) Would it have been legal if I had terminated the cct into the shifted porcelain base? (I assume not) And if not what reg does that relate to?

And another [silly] question I have relates to porcelain fuses and RCDs:

If a board is pretty well full and I need to RCD protect a CCT, I usually mount a 2way enclosure with RCD and protect plug in breakers (if the cct is protected by ceramic fuse I'll always replace base and install plug in breaker)

I feel like the advantage of doing that is with a two way enclosure you could mount two RCBOs or one RCD and protect 3 plug in bases.

2) My question relating to that scenario is would it theoretically be legal to protect ceramic fuses with RCD? I wouldn't ever do that but it is an interesting question in my view.

Cheers for reading and potentially answering


Nov 24 2019 09:01

Yes it's permitted to re-locate an existing SERF on an existing circuit. ESR 113 covers this.
The thing you can't do with a SERF is use it to protect new wiring, including both new subcircuits and extensions of existing subcircuits.

Yes it's OK to add RCD protection to existing SERFs.

WRT your preferred method of using a 2-way enclosure for the RCD, and then replacing the existing SERFs with plug-in mcbs.
Suggest you consider using a 6-way enclosure, ans use rail-mount mcbs instead of plug-in.
Better technically (no risk of the mcbs being swapped to the wrong base); and cheaper.

Nov 24 2019 21:53

@AlecK Cheers for the answers mate that's good to know

If there is enough physical space I'll mount a 6way, I just mount a 2way with RCD if that's all I can fit on the board :D