RCDs in Series

[Channel Hopper]

I'm trying to retain some outdoor lighting in a private estate, its not recently installed and I've replaced much of the junctions and floodlights. Once in a while however something trips the RCD in the consumer unit which also takes out the kitchen ring main (and with it the fridge).

I'm tempted to add an external IP66 socket with its own RCD but need to know if it a lower rating or faster time that will make it trip before the one indoors.

Thanks in advance.

 

[jeallen01]

Here are some ideas that might trigger your brain to help track down the basic problem:

Firstly, what is the spec (and preferably the exact model) of the existing RCD (so that the trip characteristics can be identified)?

Secondly (& possibly regardless of the first question) do any of the newly fitted units have switched mode PSUs?

Asking that because (as you already know) the input rectifiers on those have large high voltage reservoir caps - and if those have discharged over time because the device has not been recently used/triggered then the PSU inrush current can be very high indeed. If the latter is not very well controlled (i.e. lack of NTC thermistor etc) then some types of RCD also have over-current protection facilities could trip ?

OTOH, one or more of the new devices might have input over-voltage protection in the form of Gas Discharge Tubes (GDT) or Metal Oxide Varistors (MOV) which are tripping due to incoming line voltage spikes - causing a momentory major Line/Neutral current imbalance and thus tripping the RCD?? NB: GDT's etc., can also result in high "standing" earth/ground leakage currents, which might then only require another brief source of extra leakage current to drive an RCD to the trip level.

What could cause that sort of spike? Local lightning strikes (might not even hit the supply cables!) could induce them, or maybe a large motor (e.g. for a lift, or the entry gates) that is only started very occasionally, because it has been known for that sort of equipment to cause quite major radiated &/or conducted EMI if situated very close to sensitive equipment in office blocks etc.

As for fitting that additional RCD & socket, see the First Question to start with!

 

[Channel Hopper]

No recent changes to any of the internal appliances, I suspect the issue does lie in the grounds where a wayward spider or morning dew impacts on the overall supply requirement.

I will probably move the garden circuit onto a ring main that is not as populated, there is an outdoor IP66 socket nearby for this purpose, the original question was over the possibility changing this to a built in RCD type will offer little advantage, with the exception of the fridge remaining operational.

 

[Channel Hopper]

All RCDs in the consumer unit and the external sockets appear to be 30mA trip current.

 

[Terryl]

Not up on your electrical terminology...Whats an RCD??

 

[anto@]

RCD type A
usually reduces unwanted shots
if the switch opens for unknown reasons

usually when there are air conditioners or heat pumps or refrigerators with inverter motors
Type A RCDs are recommended

provided that some dispersion in the plan provokes these sudden shocks

 

[anto@]

to know the current leakage this device is needed

 

[Fisty McB]

Not up on your electrical terminology...Whats an RCD??

Residual Current Device - a British/Irish term for what is called a GFCI in North America, though how they're applied in both areas appear to be somewhat different. If ElectroBOOM! has taught me anything, GFCIs in North America tend to be restricted to use at sockets/receptacles in "wet" zones like bathrooms & kitchens (though I'd assume that this would be ultimately down to local electrical codes) with a reset button/LED light, while over here the RCDs are located in the distribution cabinet - but for very old electrical setups such RCDs can be incorporated into a socket like the North American example I mentioned.

Residual-current device - Wikipedia

en.wikipedia.org