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Omitting 30ma RCD Protection for single S/O in a domestic property

Former Community Member over 4 years ago

I installed a dedicated circuit for a hifi system for a customer last year. The customer requested a 6mm2 radial from a 16A MCB housed in its own independent consumer unit into a single, un-switched socket outlet. No problem, bit unusual but no worries.I wired it using a 3c 6mm2 armoured cable as I half anticipated the forthcoming...

The hifi equipment is causing the rcd to trip when started up. I haven't been over to have a look but I am assuming that the startup current for the many power supplies (he has told me there are ten!) coupled with electronic earth leakage is causing a CPC current that is sufficient to trip the RCD (perhaps only 16ma but enough). The earthing is high integrity having a 6mm2 cpc + armour and the Zs is sufficiently low enough that the 16A MCB can be used for fault protection. So, if this wasn't domestic I'd ditch the RCD (or replace with a 100ma) assuming that my assumptions to this point are correct.

The customer has now decided he doesn't want RCD anyway for 'reasons' but I'm still wary of removing it in a domestic situation, not because I believe the installation would become less-safe but just because it contravenes regulations.

Assuming there's no fault on the equipment and it is just a case of startup/inrush current and earth leakage, what approach would you take? Remove the RCD and write it up as a deviation from 7671 with a signed disclaimer/waiver from the customer? Install a 100ma RCD? Do nothing and walk away? Something else?

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0 Former Community Member over 4 years ago

Chris Pearson:

I am still puzzled by the requirement for one socket.

One socket, one circuit, one CU. All a bit odd, but HiFi buffs have some funny ideas. What really amuses me is that by the time one can afford to spend £tens of thousands, most of us cannot hear the high frequencies which have cost so much. ?

Most certainly! Although there are advantages to power conditioning where amplifiers are concerned, the perceivable difference by human ears approaches zero when we are talking about this particular installation. Now, an independent ground connection, isolation transformer with voltage stabilisation/regulation and a system of capacitors to smooth the waveform MIGHT make a difference but unlikely to hear it.

It's what makes people happy I suppose. You could buy a Ferrari which does 0-60 in 2 seconds and a top speed of 200mph but you still have to drive it on the terrible British road network and get stuck behind people like me driving a van. Pointless, but makes people happy.

Kelly Marie:

No one yet has said if it really is earth leakage is it not likely to be just the collective high inrush currents of all those PSUs causing a trip and if it is then wouldn't switching to a type D RCBO be the answer. Also if the customer is listening to let's say vinal then why would he need the CD player or Tuner switched on? That really makes no sense. I know of some hi fi buffs who by oxygen free gold plated leads for everything to try to improve the sound waste of money if you ask me. Oh watch out grumpy Kellys out again!

Customer reports it's the RCD (61008) tripping, not the MCB but I haven't been to verify it myself and you could well be right and the answer would be replace the MCB with a B20 or C16 maybe.

I agree that the trip is linked to inrush current but if it is tripping the RCD it could be the overload which is being leaked to earth. For example, if the unit has a startup current of 6-10x usual use and typically leaks ~1ma to earth then we are talking ~6-10ma earth leakage at startup. So 3-5 power supplies of similar construction would leak ~30ma to earth on startup causing a trip.

Of course you are right, the simple solution is to only turn on what you need. Or just leave everything on all the time. Which is probably what I will tell the customer on Monday (although worth testing the equipment to check it's within specification).
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0 Former Community Member over 4 years ago

Chris Pearson:

I am still puzzled by the requirement for one socket.

One socket, one circuit, one CU. All a bit odd, but HiFi buffs have some funny ideas. What really amuses me is that by the time one can afford to spend £tens of thousands, most of us cannot hear the high frequencies which have cost so much. ?

Most certainly! Although there are advantages to power conditioning where amplifiers are concerned, the perceivable difference by human ears approaches zero when we are talking about this particular installation. Now, an independent ground connection, isolation transformer with voltage stabilisation/regulation and a system of capacitors to smooth the waveform MIGHT make a difference but unlikely to hear it.

It's what makes people happy I suppose. You could buy a Ferrari which does 0-60 in 2 seconds and a top speed of 200mph but you still have to drive it on the terrible British road network and get stuck behind people like me driving a van. Pointless, but makes people happy.

Kelly Marie:

No one yet has said if it really is earth leakage is it not likely to be just the collective high inrush currents of all those PSUs causing a trip and if it is then wouldn't switching to a type D RCBO be the answer. Also if the customer is listening to let's say vinal then why would he need the CD player or Tuner switched on? That really makes no sense. I know of some hi fi buffs who by oxygen free gold plated leads for everything to try to improve the sound waste of money if you ask me. Oh watch out grumpy Kellys out again!

Customer reports it's the RCD (61008) tripping, not the MCB but I haven't been to verify it myself and you could well be right and the answer would be replace the MCB with a B20 or C16 maybe.

I agree that the trip is linked to inrush current but if it is tripping the RCD it could be the overload which is being leaked to earth. For example, if the unit has a startup current of 6-10x usual use and typically leaks ~1ma to earth then we are talking ~6-10ma earth leakage at startup. So 3-5 power supplies of similar construction would leak ~30ma to earth on startup causing a trip.

Of course you are right, the simple solution is to only turn on what you need. Or just leave everything on all the time. Which is probably what I will tell the customer on Monday (although worth testing the equipment to check it's within specification).
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Omitting 30ma RCD Protection for single S/O in a domestic property

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