Testing with a CU change

[Bradley6969]

Working with a spark, now when we change a CU no new circuits just old for new, We do all end to ends on rings, IR tests and Zs making sure all the new protective devices that disconnection times are met, would you do R1+R2?

If we do a CU change and add new circuits we do R1+R2 on the new circuits what do you guys do?

 

[Welchyboy1]

no i dont really think its required for existing circuits i just do zs testing and calculate r1r2

Maybe for lighting if my meter sometimes trips 6a mcbs on zs

Obviously test rings for continuity

For a new install i would dead test r1r2 first

 

[Dustydazzler]

Existing board changes just Zs

Brand new installs I do R1+R2 tests

 

[richy3333]

Full works, but global IR or as per GN3.

 

[Andy78]

I do R1+R2 and record it.

 

[Ian1981]

no i dont really think its required for existing circuits i just do zs testing and calculate r1r2

Maybe for lighting if my meter sometimes trips 6a mcbs on zs

Obviously test rings for continuity

For a new install i would dead test r1r2 first

How do you calculate your R1+R2 as that should only be done by measurement only other than at the design stage?

 

[Ian1981]

Working with a spark, now when we change a CU no new circuits just old for new, We do all end to ends on rings, IR tests and Zs making sure all the new protective devices that disconnection times are met, would you do R1+R2?

If we do a CU change and add new circuits we do R1+R2 on the new circuits what do you guys do?

R1+R2 is for initial verification so if they are new circuits then this must be done, existing then not necessarily required tho not precluded.
Existing then I just make sure all exposed conductive parts are connected to earth with the R2 method and then just measure the Zs but it’s whatever makes you happy

 

[Pete999]

How do you calculate your R1+R2 as that should only be done by measurement only other than at the design stage?

Measure Z E and ZS and take it from there ZE = ZS +(R1+R2) Transpose the formulae Bob's yer Uncle simples as Sergei would say.

 

[SparkyAndGeorge]

Dont forget the insulation resistance test dont want to get caught out by a nasty N-E fault

 

[Andy78]

Measure Z E and ZS and take it from there ZE = ZS +(R1+R2) Transpose the formulae Bob's yer Uncle simples as Sergei would say.

I was always taught this was incorrect and not permitted due to connected potential parallel paths when taking a live Zs reading giving a falsely low reading. R1+R2 measured dead and in isolation of other parts of the installation then worked with Ze into Zs always gives a highest and worst case value so can be trusted, but not the other way round.

 

[Ian1981]

Measure Z E and ZS and take it from there ZE = ZS +(R1+R2) Transpose the formulae Bob's yer Uncle simples as Sergei would say.

That is an incorrect method as parallel paths are present

 

[ipf]

Measure Z E and ZS and take it from there ZE = ZS +(R1+R2) Transpose the formulae Bob's yer Uncle simples as Sergei would say.

For a board change, I agree with you, Pete.....but with rcd involvement, how can it be guaranteed you have a true Zs reading.
The extent of testing should be agreed with the client, really, and allowed for accordingly.

 

[Toneyz]

Ze does not = Zs +(R1+R2)

 

[Pete999]

Ze does not = Zs +(R1+R2)

go on then

 

[Baddegg]

I thought zs=Ze+ (R1+R2)...but Ze does not = Zs-(R1+R2) or something like that possibly maybe......I’m feeling really uncomfortable with the new look.....the only other time I’ve felt like this was when they spruced up my local! Took me ages to get over that....

 

[Pete999]

Ze does not = Zs +(R1+R2)

#
Sorry the wrong way around ZS = ZE (R1+R2) must leave the red alone sorry Ant you are right my apologies.














9

 

[Toneyz]

#
Sorry the wrong way around ZS = ZE (R1+R2) must leave the red alone sorry Ant you are right my apologies.

I didn't reply as I thought I would be telling you to suck eggs and you'll realise when you had another look.












9

 

[Toneyz]

I think I replied on Pete's post can't get used to new forum

 

[Toneyz]

I thought zs=Ze+ (R1+R2)...but Ze does not = Zs-(R1+R2) or something like that possibly maybe......I’m feeling really uncomfortable with the new look.....the only other time I’ve felt like this was when they spruced up my local! Took me ages to get over that....

You can not do R1 +R2 = Zs -Ze as for the parallel paths

 

[Pete999]

I think I replied on Pete's post can't get used to new forum

You can not do R1 +R2 = Zs -Ze as for the parallel paths

Gets easier the more you use it