Consumer unit change testing

[Risteard]

I don't recall stating which boxes I fill in, I just agreed that Zs-Ze=R1+R2.

It doesn't really. It can verify cpc continuity in an already energised installation which is fair enough. But some people are advocating noting down a reverse engineered value under the dead continuity test boxes which is frankly a nonsense.

 

[HandySparks]

It still doesn't explain why you feel the need to fill in a box for something which you are stating that you have not tested and have also stated that you do not need to test. If that is your position then do not fill the box for it in! To do so is both misleading and pointless.

Totally agree. My certs usually have loads of unfilled boxes. If I didn't check or measure something, it doesn't go in the box. And if I measure something once it only gets written down once. So, for RCD times, the values go on a line for the RCD and not on the lines for every circuit it protects.

 

[Risteard]

So, for RCD times, the values go on a line for the RCD and not on the lines for every circuit it protects.

Personally for an RCCB I list the times next to each protected circuit rather than list the RCCB separately on a line of its own. But so long as what you have is clear then I don't have a problem with it being done that way.

 

[westward10]

It doesn't really. It can verify cpc continuity in an already energised installation which is fair enough. But some people are advocating noting down a reverse engineered value under the dead continuity test boxes which is frankly a nonsense.

It isn't necessarily nonsense, where there are no parallel paths the reading is probably quite accurate. This isn't much different to people calculating Zs which I have seen recommended on this forum where a live reading should be obtained. For example dead testing R1+R2 then adding on Ze.

 

[Risteard]

It isn't necessarily nonsense, where there are no parallel paths the reading is probably quite accurate. This isn't much different to people calculating Zs which I have seen recommended on this forum where a live reading should be obtained. For example dead testing R1+R2 then adding on Ze.

A calculated Zs will err on the side of safety. To reverse engineer the R1+R2 will err on the side of danger. It also serves no purpose when you are verifying cpc continuity on an already energised installation with live (Zs) testing. Filling in a box simply because it exists on the form has no merit when you are excluding dead continuity tests. If you are excluding it then exclude it!

 

[Andy78]

It isn't necessarily nonsense, where there are no parallel paths the reading is probably quite accurate. This isn't much different to people calculating Zs which I have seen recommended on this forum where a live reading should be obtained. For example dead testing R1+R2 then adding on Ze.

It is entirely different to calculating Zs.
Calculating Zs from (R1+R2)+Ze gives a value based on two measured readings, so it is not really calculated, merely an addition of measured values. It also gives a worst case scenario, a maximum figure for Zs for that circuit without any connected parallel paths to earth that, if compliant, can only mean that a live (connected) Zs will be less and therefore also comply with disconnection times. That is the reason this value is permitted to be entered as a value on a schedule of test results to BS7671

Calculating R1+R2 from Zs by subtracting Ze accounts for no connected paths and therefore will not be accurate. As Risteard says, this is an valid enough method of verifying continuity of protective conductors on an already energised circuit, but not a valid way of obtaining a reliable value of R1+R2.

 

[davesparks]

I may be wrong, (I am new to this). but i thought you could use 250v as long as the results comply with 500v

No, 250V is below the peak voltage it will normally be exposed to so is a useless test as far as proving the integrity of the insulation.

 

[davesparks]

Joking im not. Zs-Ze does equal R1+R2, its a very popular method of testing and not to mention quicker.

That is not a method of testing, it is a method of calculating an estimated value.

It is not a viable method of attaining a value for the continuity of the CPC, for initial verification it is a requirement that the R1+R2 or R2 be measured prior to making a circuit live,

 

[E.E.I]

What about when live testing through RCD's, this gives a higher value on your zs reading. This would effect the calculated R1+R2

 

[davesparks]

What about when live testing through RCD's, this gives a higher value on your zs reading. This would effect the calculated R1+R2

Just don't live test through the RCD, use a more suitable test method