Loop test tripping rcd

[dave2]

Got asked to have a look at a property as the recent lightning strikes were tripping the RCD.

No sign of any damage and all bonding/earthing in place. It's a TT supply (101 ohms) with 30mA RCD (BS4293) protecting the entire installation.

Tested RCD on auto and all ok. Ramp test indicated trip current of 15mA and time of 16mS.

There was a socket below the cu so I thought I would do a quick loop test. RCD tripped. Tried again and still tripped. This test was done with Megger ltw425 loop tester on no trip.

Got my Multifunction and hey presto it tripped with that.

Reopened cu and disconnected all L & N loads and loop tested directly to rcd and it still tripped using each tester.

The rcd is appears to be too sensitive and I will go back tomorrow and try another .

Has anyone experienced similar?

 

[Evans Electric]

No mate , but I'm thinking the lighning strike has affected the RCD .

Perhaps similar to an MCB that has taken a major short circuit and recomendation is to replace it .

 

[steptoe]

what did it ramp at with everything disconnected?

 

[pewter]

I had the same trouble with my megger mft1730 on Wylex NHX RCBOs. I emailed megger and they told me to swap my line and earth leads around which cured the problem.

 

[dave2]

what did it ramp at with everything disconnected?

15mA

 

[steptoe]

I'd change any RCD at <20mA