RCD Advice Please

[Gobble.D.Gook]

We live in a new house (well 18 months old) and the RCD on the main consumer unit seems very sensitive. Using an iron will quite often trip it.

However, main gripe is the water feature we put in. The cable for this is laid in a plastic conduit under what is now our lawn. The join is in a proper underground joining kit (the one you pour gunk into which sets solid) and then it drwas power from a switched spur in the garage.

Last year it worked fine. This year, it trips the entire main within 1 minute of being on.

Does anyone have a sugestion on how to get around this, or why it should now be happening ? Is it possible to put another RCD on the spur which would trip prior to the house going (as its a pain when the computer goes down).

thanks.

[Andy Wade]

Steam iron? - Chances are the iron has developed a low insulation resistance to earth and is tripping the RCD. Get a new iron.

Again it's more likely to be leakage to earth somewhere in the pump installation than anything wrong with the RCD. Can you borrow a megger (insulation resistance tester) or get an electrician in to test it for you?

Not really. What you could though, at a cost, is feed the pump through a 1:1 isolating transformer, with another RCD on the secondary side. (Earth one side of the transformer secondary ahead of the RCD to create a neutral, or if the transformer has a centre tap, earth that instead.) That should certainly stop it tripping the house RCD.

Or get a UPS for your computer.

[Owain]

Good :-)

Buy a new iron.

If it's consistently a minute of being switched on, that suggests to me some mechanical seal on the water feature is failing slowly, rather than being a cable fault. But I could be wrong.

Probably not in series with the existing. If you have a split-load consumer unit (one with a main switch, and the RCD about half-way along protecting the socket circuits only, the garage could be moved to the non-RCD side and then provided with its own RCD or RCBO (combined MCB and RCD in a module)

If it's a whole-house RCD that's deprecated and should really be replaced with a proper split-load CU, so that among other things your lights don't go out unexpectedly/unneccessarily.

Changing CUs or installing new RCDs is probably covered by Part Pee of the Building Regulations.

Owain

[bigcat]

What goes off when the rcd trips? Hopefully not everything.

Put the pump on its own feed from the CU, on an rcbo. Then only the pump power goes off. Get a new pump. Get a new iron.

The only really satisfactory setup with rcds is to have each socket circuit on its own rcbo (rcbo = combined rcd and mcb). Then trips are much less likely, and only take out some loads when they occur.

NT

[Stephen Dawson]

Or fix the problem

[Doctor Evil]

What is wrong with using a shaver socket in the garage , and plug the external pump into that. That has an isolating transformer.

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[Peter Parry]

There are at least 4 possible reasons - one is the obvious one of a fault on the devices being used. However there are three other possibilities.

One is the amount of IT equipment on the circuit. Computers, many printers and other electronic devices which require an earth connection have noise filters which pass a small current to earth. With sufficient such devices or a faulty noise filter there may be sufficient leakage to pre-sensitise the RCD and cause any momentary glitch (such as the iron thermostat switching it on and off)to nuisance trip the RCD. High earth leakage items like IT equipment should not usually be on RCD circuits.

Secondly you may have a neutral to earth fault. The usual cause of this is someone putting a nail or screw through a wire while the house was being built. The fault need not be on any particular circuit but the effect is similar to above, the RCD is permanently carrying a low leakage current and switching things can trigger it. These faults can be difficult to find and cause odd effects. For example in one house I saw this in plugging a long extension lead (with nothing connected)in to a socket would trip the RCD. The extension lead had no fault at all but the inductance to earth was sufficient to trip the RCD.

Thirdly, the RCD could be too sensitive. It is not uncommon.

[Andy Wade]

An isolated shaver socket is rated at 20VA. The pump will need a little more juice than that.