RCD Query

[Dishman]

Hopefully an easy query.

Having great problems isolating RCD tripping. Happens only occasionally, say once a week. If I put fridge and electric water heater on their own plug in RCD plug would that plug trip first (if the appliance was faulty) or would the fusebox RCD, or would they trip together?

Thanks in advance.

 

[eskimo39]

Unfortunatly not so easy. Depending on age/brand ect it becomes very difficult to find 2 RCD's where you can specify one that trips before/without the other. I come accross problems frequently when installing sub main CU boards and try to find and RCD which will trip before tripping the main CU RCD.

I believe most RCD plugs or plug adaptors are spec'd at 30mA in 40mS, what is the rating of your board RCD?

Could you do an insulation test on the appliances you believe to be faulty with a PAT tester?

Another option you could try is if you have an RCD ramp test feature on your meter, plug your meter into the circuit where the fault lies, unplug one of the suspect appliances at a time, and do a ramp test on the circuit. Plug the appliance back in and remove another, then repeat the test again. Does the RCD trip at different levels?

As a final option, is your upstairs ring on a different RCD? If so could you run an extension cable down and try one of the appliances on that? If the upstairs RCD trips that time, you have your culprit.

Hope this helps

 

[Dishman]

Hi,

Thaks for prompt reply. Main board is new 30ma trip (bought to replace older one which I thought was suspect - but as it turns out wasn't). Apt all on one floor so not able to run extention.

Just keen DIYer so don´t have instruments you mention. Electricians unable to find fault so was trying to resolve myself.

Just thought plug in RCD might have hepled isolate faulty appliance.

 

[Davey101]

Its going to be pretty tedious, but you could try writing in a diary of what you are doing when the RCD trips, i.e. what appliances are plugged in/turned on/ being used. Make sure you remember anything such as heating, oven, outside lights etc (if the whole board is on an RCD). Bear in mind it could be an appliance, or the actual wiring at fault.

Good luck, Dave.

 

[Dishman]

Have been keeping diary of times. Last time tripped was when everyone was in bed. Early hours of 26th December. fridge and freezer powered on. various items on standbye - Sky box etc. Water heater on maybe.

 

[Brian Boyd]

I recently had similar problem. The installation tested correct through everything and all appliances were disconnected. I replaced the rcd unit as this was last resort. It seems it had intermittant fault and problem was sorted. Fridge freezers and similar appliances if they develop a fault 9 times outta 10 would keep rcd off until the appliance was removed from circuit.

 

[MarcT]

Same here, it took a month a scanning the diary to work out. It was a brand new FFreezer, the compressor came on and off and only periodically had an earth fault, and it PAT'd ok as well! It's very easy to discount brand new appliances because of their age

 

[pushrod]

A problem with earth leakages is that they are cumulative so it could well be two or three appliances all contributing to the tripping of your rcd. Is there only one ring for sockets at the consumer unit in your apartment? Sometimes kitchens have their own ring or is their a cooker socket (this shoud be on a separate supply) as if you can put one of the suspect appliances on a separate supply (as eskimo above suggested) you could have more luck trying to find the culprit(s).
An earth leakage clamp meter would tell you the earth leakage of each appliance but they are a bit pricey.

 

[spider]

We had a similar problem where the RCD intermittently kept tripping, it turned out to be a loose plug in a two way adapter under the utility sink which fed the dishwasher, the simplest things are sometimes the hardest to find!