High impedance on working RCD circuit???

[BuddySpark]

Hi there,

I'm a new electrician with ELECSA & C&G 2391 to my name & i've now been left very confused, hence the post!

After adding a spur to a ring main i was doing a IR test on 250v bcus i couldn't be sure i had plugged everything out & i kept getting hardly any resistance. So i checked the continuity between L-N, L-E, N-E when cables disconnected from CU.......& i keep getting readings of no more than 30 ohms??? There seems to be no impedance between L-E or N-E???

This circuit is working fine on an RCD aswell & i don't see how this can be?

There could b a chance that things are still connected & maybe FCU's(house alarm) but how can there be continuity with live conductors & earth on a working circuit?

Enlighten me plz! lol

Sparko

 

[Des 56]

Well if you were to leave for example an extension lead plugged in and that extension lead had surge protection build in, then the reading would be extreemly low using an insulation resistance tester
No or little current flow through that surge protection would mean the rcd seeing no imbalance and operating correctly
A falut inspired reading live earth or neutral earth would either trip instantly or when an adequate load was applied to the circuit

 

[BuddySpark]

Hey Des,
thanx for the reply & i guess your right because the client did have an extension lead plugged in which i had no access to because it was behind a fitted wardrobe.

I will conduct more investigations & ask ELECSA what they reccomend i do, maybe note down 'limitations' on cert.

Thanx again!

sparko

 

[danielrobinson]

Hi also look out for boiler spurs, immersions, cooker switchs with neon lights ect all will give you similair readings. Try bridging between live and neutral then test those two to earth as discribed in onsite guide.
Daniel

 

[Mac]

Hey Des,
thanx for the reply & i guess your right because the client did have an extension lead plugged in which i had no access to because it was behind a fitted wardrobe.

I will conduct more investigations & ask ELECSA what they reccomend i do, maybe note down 'limitations' on cert.

Thanx again!

sparko

If you note limitations on a cert,have you actually completed a full test

 

[BuddySpark]

Hey guys, it turns out that i don't have to insulation res test the entire circuit i added a spur on, but only the addition radial that i've just installed on the circuit.

Still i have to Zs & RCD the circuit(which can't have such misleading results i hope! lol) so i'm happy about that. Limitations was just something i thought they might suggest if test can't b carried out fully because of accessibility.

Cheers

S