RCD trips in power outs

[stunlawless]

Afternoon all,

Got a friend (honest !) who has a problem...

He lives in Surrey, a bit in the sticks. Overhead supply, TT, VOELCB and a CU wth a single 30mA RCD. Unsure of age, but all visible cables are PVC.

I have seen it, but haven't had any kit or done any delving, so no test or inspection results.

Trouble is, everytime there's a powercut, the RCD trips, but not the VOELCB. The same thing happens if you use the VOLELCB to isolate the installation.

He's had one elctrician in who pronounced that "there's nothing wrong, that's just the way it is", and is reluctant to pour more money away.

Plan on going down again in June, with test kit this time. Any ideas where to start looking (after, in effect, doing a PIR) ?

Thanks, David

 

[ricicle]

For a start I would be getting rid of the VOELCB totally.

Out of interest has a new earthing conductor been installed rather than relying on the connection through the VOELCB ?

Do any of the neighbours suffer the same ?

 

[ban-all-sheds]

Can you get active RCDs to go into CUs?

 

[stunlawless]

There is a rod, connected to the MET near the VOELCB.

Could the "electrician" have been right, and it's a cxonsequence of the VOELCB, but failed to explain it ? My mate didn't say that he'd been quoted to remove it.

I can't see a need to retain it - the RCD will suffice as a main sw.

Don't know about the neighbours - will get him to check. Now he knows what a VOELCB looks like, I will ask him to see if his neighbours still have one.

Thanks, david

 

[stunlawless]

BAN,

I'm a little confused....I thought an active RCD would open on power failure, and was also know as a non latching ?

Surely what's needed here is a passive, latching device ?

Here's a SO one:

http://www.tlc-direct.co.uk/Products/SMTGV204.html

Haven't found one suitable for a CU yet. In any case, what do the panel think about the suitability of a single passive RCD protecting the entire installation (including SO used for portable outdoor kit), rather than just for specific ccts like freezers ?

Thanks, David

 

[ban-all-sheds]

I'm a little confused....I thought an active RCD would open on power failure, and was also know as a non latching ?

But that's the behaviour you're describing.

I wondered if rail mount active RCDs were available, because if so it might be worth checking if one had been installed here.

Surely what's needed here is a passive, latching device ?

Yup.

Haven't found one suitable for a CU yet.

I've only ever seen them in sockets and spurs, but I guess if a manufacturer wanted to make a rail mount one he could. I could see the merit in having one in a workshop CU, for example, so maybe they exist?

In any case, what do the panel think about the suitability of a single passive RCD protecting the entire installation (including SO used for portable outdoor kit), rather than just for specific ccts like freezers ?

I think you'd really struggle to show that that complied with the Wiring Regulations....

 

[stunlawless]

Hallo BAN,

I thought you were advocating fitting an active RCD, now I see that you're referring to the one currently fitted. Alle ist klar, as the teutons say.

Does this mean that rail mount RCD's are usually active ?

My instincts agree with your sentiment about about a complete install being protected by a passive RCD, but I haven't had time yet to search the BRB to work out exactly which reg numbers are called into play. I'm sure, with your encylopedic knowledge, you could do this quicker than me...

Thanks David

 

[Spark123]

Does it do it if you turn off the individual MCBs before opening the VOELCB?

 

[RF Lighting]

Plan of action would be run a full set of tests on the installation.

Also ramp test the present RCD.

Check that the RCD is not an active type, but I would have thought it is unlikely.

Remove the VOELCB completely.

Check the tightness of all connections in and around the CU.

A loose connection to the cutout, meter or CU can somtimes do strange stuff to RCDs

 

[stunlawless]

Thanks everybody,

Looks like we're all agreed that the VOELCB must go.

But the passive/active RCD issue is unclear to me:

Passive = no trip on powerfail
Active = opens on powerfail

I've checked MI from Hager, MK & Wylex and found no mention of active or passive for rail mount types. A/P only comes up in connection with RCD accessories.

So, is a "normal" RCD passive or active ?

If my mate has an active one, then the behaviour is normal, and can only be rectified by fitting passive devices (RCBO for freeze, lights & boiler cct, rather than the whole install ?)

If it's a passive device, then there is an imbalance between L & N suffiicent to trip the RCD during powerfail. Possibly related to VOELCB, but I & T might find something.

Are there any markings on the unit indicating active or passive ?

Thanks, David

 

[bernardgreen]

mis read the original so deleted erroneous observation

 

[ban-all-sheds]

So, is a "normal" RCD passive or active ?

Passive. Never seen an active one, I just wondered, if they exist, if that's what the problem is.

If my mate has an active one, then the behaviour is normal, and can only be rectified by fitting passive devices (RCBO for freeze, lights & boiler cct, rather than the whole install ?)

If it's active (v. unlikely) doing that wouldn't help because the device would still trip if there's a power cut.

 

[333rocky333]

could it be the Rcd is tripping when the power comes back on, rather than when it goes off, possibly due to whatever loads are connected.

 

[ebee]

Just a note about front end RCDs.

No they do not comply.

However, in real life, there are many installations that do have a front end RCD (usually fitted as a Main switch on a consumer unit) . Not very many years ago it was a pretty normal practice. RCDs became "In Vogue" and you either had one front end or non at all - Hobson's choice. Later we had split load, then Dual (so called 17th Edition board).

In consequence many installations have one RCD covering the whole installation and the problem trips are very few and far between, never tripped in 20 years of service is quite common until that faulty kettle causes a trip. Indeed, until that point, an owner does not have a clue what an RCD is.

Of course the potential problem is something we engineer out these days but in real life it is not as big a problem as some might think it is or as it could be.

No doubt there will be a few exceptions

 

[stunlawless]

MK just confirmed that all their RCD's are passive. Waiting for Hager & electrium to respond, but I expect the same answer.

So, something in the install is causing it to trip. Rocky, good point; I assumed it was as power was cut, but will check whether it goes on power restore.

Odds on it being related to the VOELCB anyone ?

Thanks for all the thought and stimulation, David