Which way do you do it?H

[uksparks]

Hi,

When changing a board for someone, what method do you use to obtain R1 + R2?

When I do it, I cross connect at the CU and measure at each point, and on a radial link between and measure at each point.

Does anyone just calculate it on a ring by doing this:

(r1 + r2) /4 = R1 + R2

Just seems to take me a ages doing a board change and wondered if I'm missing a trick here?

 

[Stuuk1]

Get a copy of GN3 and do exactly as it says and you will know you are doing it correctly..

 

[Meggerman]

yes, (r1+r2)/4 = an expected value of R1 + R2 at sockets. I do that calc, then at the end when doing my Zs readings do Zs-Ze to get a calculated R1+R2 and it should be thereabouts (unless spurs). A lot of DB change EIC's I see have nothing in the R1+R2 box!

 

[uksparks]

Like I said I do the three step process and cross connect etc to check for polarity etc, just wondered who calculates it on a board change opposed to going round each and every point measuring it?

 

[uksparks]

yes, (r1+r2)/4 = an expected value of R1 + R2 at sockets. I do that calc, then at the end when doing my Zs readings do Zs-Ze to get a calculated R1+R2 and it should be thereabouts (unless spurs). A lot of DB change EIC's I see have nothing in the R1+R2 box!

Thats bad leaving boxes empty! Zs-ze shouldn't be relied upon due to parralel paths etc, but I guess it will give you a rough idea. Presumably then you don't go round each socket or light fitting then?

 

[Meggerman]

I don't cross connect on a db swap. Like I stated I take Zs reading, then Zs-Ze that is my R1+R2.

- - - Updated - - -

I take Zs at every point.

 

[uksparks]

But surely you are not relying on that to be correct due to parrallel paths?

 

[uksparks]

Surely though you would better off just adding the calculated R1 + R2 to Ze to get your Zs?

Calculated being as above.

 

[Meggerman]

Im not doing initial verification of all the circuits, Im changing a consumer unit. I just interested in correct OC protection, satisfactory insulation resistance and satisfactory disconnection times.

 

[Meggerman]

Surely though you would better off just adding the calculated R1 + R2 to Ze to get your Zs?

Calculated being as above.

I thought you were trying to save yourself some time. Why would I want to calculate it then measure it again as Zs?

 

[uksparks]

True, I think I just have a nasty habit of going over the top, I suppose it doesn't hurt, just a waste of time!

 

[Meggerman]

True, I think I just have a nasty habit of going over the top, I suppose it doesn't hurt, just a waste of time!

Well I cant knock someone for being thorough

 

[uksparks]

Very true, I suppose it's just something I have always done to satisfy what I'm doing being relatively new to the trade I prefere to be thorough, maybe time for a change, I'll get things done quicker then.

I picked up another rewire today which was good, 4 bed house, 1930's, nice job, the bloke works for WPD so I'll get him to stick an isolator in and a new shiny service head etc, I'm sure he can wangle that for free.

 

[Meggerman]

Very true, I suppose it's just something I have always done to satisfy what I'm doing being relatively new to the trade I prefere to be thorough, maybe time for a change, I'll get things done quicker then.

I picked up another rewire today which was good, 4 bed house, 1930's, nice job, the bloke works for WPD so I'll get him to stick an isolator in and a new shiny service head etc, I'm sure he can wangle that for free.

Nice one, Obviously go the whole hog on testing that install being a new job an all.

 

[uksparks]

Yes indeed, I'm not going to be starting it until start of April anyway, but it appears to e all agreed, just need to go and measure up etc.