R1+R2 question

[Welsh_sparky_21]

Seen some guys when doing EICRs just doing live tests and subtracting the Ze off of the Zs to get their R1+R2 reading. Is this is a bad way of doing it? I know you’re supposed to do tests in the order of dead tests first etc but wondering if this is going to give you readings that are way off or what

 

[Julie.]

Seen some guys when doing EICRs just doing live tests and subtracting the Ze off of the Zs to get their R1+R2 reading. Is this is a bad way of doing it? I know you’re supposed to do tests in the order of dead tests first etc but wondering if this is going to give you readings that are way off or what

Yes, it's a pretty poor way of doing it.

With an eicr, the system is live, and has been so for some time, so the sequence of tests isn't important.

It is more about the inspector gaining an indication of the condition of the installation, rather than doing things in a specific way prior to initial energisation.

Measuring the Zs rather than r1+r2 is around the best way though, however it should be identified that that is what has been done rather than back-filling values.

The exception is on rfc, where you need to confirm the complete connection around the ring.

In saying that, you would sanity check the values, even if a Zs was within the mcb maximum, if it's too high given a size/length of circuit, it's still a fault.

 

[Rockingit]

Agree with Julie, it's a poor technique and should be regarded as a back-stop rather than a start. You also need to remember that a Zs value at an outlet can also exist because of parallel earth paths via bonding etc so may not necessarily guarantee either a reflection of the true R1+2 or even that R2 correctly exists back to the consumer unit.

 

[Rockingit]

Sometimes one of the reasons people do this is out of laziness in a CU where it's all a muddle and mess, trying to identify the conductors etc - you can always pop a socket or switch off a wall in seconds and do it from there instead.

 

[telectrix]

personally, i do ZS. if it'sa RFC then i'd do r1.r2,rN (dead) and divide by 4 to see if the R1+R2 tallied with the Zs.

 

[i=p/u]

Wonderlead and the brain

 

[Deleted account]

I sometimes don5 do R1+R2 if Zs is acceptable. But do not calculate backwards as this in inaccurate due to parallel paths to earth.

 

[timhoward]

Question is always what is best use of (sometimes limited) time to achieve the most, and this obviously varies tremendously.
I had rare luxury of previous test results for one last week. One Zs stood out as being much higher than the previous result on a RFC so I spent time looking into that in more depth. On that occasion it was at the expense of doing R1+R2 on the lighting circuits (had done Zs on them).
I had another one where everything had metal face plates so on that one spent more time with wander lead checking every single one.
I'm sure we all adapt to the situation and sometimes that is deciding what not to do.

 

[Julie.]

Question is always what is best use of (sometimes limited) time to achieve the most, and this obviously varies tremendously.
I had rare luxury of previous test results for one last week. One Zs stood out as being much higher than the previous result on a RFC so I spent time looking into that in more depth. On that occasion it was at the expense of doing R1+R2 on the lighting circuits (had done Zs on them).
I had another one where everything had metal face plates so on that one spent more time with wander lead checking every single one.
I'm sure we all adapt to the situation and sometimes that is deciding what not to do.

Agree, with an EICR you are trying to gain an idea of the condition of the installation, so you end up being very flexible with what you look at and test, doing whatever is best to get the right information.

If you're just following a fixed set of steps, you're not really looking at it properly.

- unless it's a fly-by, then you are allowed to ignore everything in a set sequence.

 

[cliffed]

Agree on the EICR ,it’s just laziness not doing the R1 + R2 on a new installation it’s so easy to do?

 

[telectrix]

the whole point of dead testing (R1+R2 etc.) is the ensure that the (new) installation is safe to be energised. with an EICR, the ibstallation is already energised and performing as it should. therefore, i'd not perform all the dead testing as you wolud in a new install, unless the Zs and IR readings were suspect.

 

[Mike Johnson]

Wonderlead and the brain

Sounds like a new thriller staring................

 

[i=p/u]

Telectrix and lucien Nunes on tour in Romania electrical jungle

 

[Mike Johnson]

But which one will be Wayne Johnson.