Discuss 10mA rcd tripping on Zs test in the Electrical Forum area at ElectriciansForums.net

polo1

Electrician's Arms
Messages
1,310
Location
Glasgow
As above, taking a Zs measurement on a circuit covered by a 10mA rcd. Tripping the rcd on a no trip, three lead test using a Megger 1721. Is there a change in the settings I’ve forgotten about to allow a Zs to be taken. Oh, testing at a socket rather than source.
TIA
 

Sintra

The Innkeeper
Staff member
Admin
Messages
11,968
Location
Belfast/London
Link out line and cpc at the end of the circuit and test using no trip setting at the device.
 

Ian1981

Forum Mentor
Messages
2,975
Location
North east
If your going to the trouble of linking the line and cpc at the end of the circuit then you may as well measure the R1+R2 and add it to the Ze/zs/zdb or am I missing something ?
 
OP
polo1

polo1

Electrician's Arms
Messages
1,310
Location
Glasgow
For some reason I thought there was an option to reduce the test current on the Megger, but it appears there isn’t.
So Ze +(R1+R2) it is.
Thanks guys.
PS can’t remember the last time I had to test with a 10mA rcd in place!
 

Sintra

The Innkeeper
Staff member
Admin
Messages
11,968
Location
Belfast/London
If your going to the trouble of linking the line and cpc at the end of the circuit then you may as well measure the R1+R2 and add it to the Ze/zs/zdb or am I missing something ?
If you have the line and cpc linked for R1+R2 then for the sake of a few extra seconds just test the Zs at the device instead of calculating.
 

Sintra

The Innkeeper
Staff member
Admin
Messages
11,968
Location
Belfast/London
Is that an approved test method?
Never seen that method before, not in gn3 anyway.
Not sure about GN3 but it is in the book "Practical Guide to Inspection, Testing and Certification of Electrical Installations" It was common practice before the introduction of no trip settings on meters.
 

Loki

Trainee Access
Messages
462
Location
Devon
For some reason I thought there was an option to reduce the test current on the Megger, but it appears there isn’t.
So Ze +(R1+R2) it is.
Thanks guys.
PS can’t remember the last time I had to test with a 10mA rcd in place!
I know you can change the mA, see 5:40 onwards. 10mA is the minimum setting.




Edit: I've just looked through the megger manual & there's no mention of changing the trip current
 
Last edited:

PEG

Respected Member
Messages
4,874
Location
Manchester
Yep,you would need about 5mA ....not sure that would warrant a good enough test...i think rubbing me wooly jumper,produces more :)
 

SparkySy

Regular EF Member
Messages
127
Location
Northamptonshire
I tend to favour the link out and test at high current method, just because it's what I've done for years, and it gives me a more accurate measurement than the low current test most of the time, also it amazes me sometimes how much an rcd will influence the result if testing both way. BG rcds seem to be the worst for raising the Zs readings!
 

Electrician Talk

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
Top