Consumer unit upgrade & requirement for RCD-free circuit

[Adam Funk]

Thanks.

[Adam Funk]

There might be a couple of CFLs still in use, but mostly LEDs now.

Thanks.

[Adam Funk]

Thanks.

ISTR reading here previously that DC power supplies (computer equipment and chargers) have effects that can cause nuisance trips even without a dangerous fault?

Thanks. (I think the 18-way that someone else posted should suffice!)

[John Rumm]

Switched mode PSUs generally can cause high leakage because of the filtering they need on their mains inputs to prevent them injecting noise back into the mains.

[Adam Funk]

That's it. How many of those does it typically take to trip an RCD?

[John Rumm]

Depends on the filtering used, but I have seen a worst case suggestion it could be up to 3mA of leakage per device. (and to add injury to insult, A RCD could trip at a point as low as 66% of its trip threshold).

In reality they usually leak less than that! (I must have many tens of SMPSUs running on a single circuit with no trip problems)

Note also that much electronic kit using a SMPSU these days is double isolated anyway, and so has no earth connection.

[ARW]

51% trip is a pass.

[Steve Walker]

In our house we have 4 (occasionally 5) PCs, a server, two laptop PSUs,

3 satellite boxes and numerous phone chargers and other PSUs. The (whole house) RCD nuisance tripped quite frequently - causing us to lose 3 lots of fridge and freezer contents due to trips while we were away or while we were asleep. A switch to RCBOs has eliminated that problem and we haven't had a single nuisance trip since.

[SH]

+1

I went from 2 RCDs to 16 RCBOs and not had a single nuisance trip on any circuit since it was done 9 years ago

[ARW]

Bill Wright did the same with one of his CU's on my advice. ISTR the outside power one. Either no trips or a genuine trip that only took out one circuit since he swapped it.

I swapped two very large and full dual RCD CUs at a house before Covid. They had constant trips. The sort of place with a hot tub, gym equipment, lots of outside power/lights etc

I fitted a 16 way TP DB with a single phase conversion kit.

Some circuits, such at the other DBs and garage doors, were fed from MCBs not RCBOs.

It took me 9 hours just to swap it.

No nuisance trips since I did it. I have no idea how much he was billed. (I also swapped the other DBs to RBCOs and did a full test).

[Adam Funk]

Is that really leakage to earth, or other effects that fool the RCD into tripping?

That should fix the problem!

[Adam Funk]

Sounds good, thanks.

[Adam Funk]

That sounds like a long time for a straight swap --- were there complications?

[The Natural Philosopher]

Er no

It doesnt.

The filter components on an SMPSU are upstream of the 'double isolation'

[ARW]

The house maid distracted me for an hour;-) If I could be so lucky:-(

Fitting the new trunking and separating the 40 circuits up in a good position into the new trunking to allow them to fit the new DB without having to extend the cables took quite a bit of time.

So did labelling up the new board. The stickers that come with DBs have no label pack like a CU. So I had to do it all on a Brother printer.

Plus a couple of SWAs to gland off that originally were just stuffed into the old plastic CUs with no glands on them.

[John Rumm]

And?

[Adam Funk]

_Confessions of an Electrician_

What's the difference between a DB and CU? Just the size, or number of phases? (I thought "consumer unit" was just ordinary British language for "distribution board".)

[Robin]

The regs define them but in short a CU is just a special type of DB that has double-pole isolation and MCBs/RCDs/etc tested to work together for a domestic supply.

[Adam Funk]

That makes sense, thanks.