Zs at wall heaters (off peak)

[Pippyboy1916]

Just back from a job where (done many time before) i had to force on, off peak wall heaters , to do Zs's. the wall heater are on 2 different boards, these wall heater only come on during the nite, i link over to the first board and test (no probs) when i link the other board across it get readings of 50 ohms on all of the heaters also i take a R2 which is a good reading and a Ze on the board with is good as well, there is a contactor switch with a coil feed from the timer, how can i get good reading on one board and not the other? also when i limk over to dodgey board all the heaters come on, even though im doing one at a time? just to see if it's the boad, i aslo extened each heater circuit to the other board and the reading are fine? i have a sore head!! lol if it's para paths surley i would have got them on the first board?

 

[robdav99]

sometimes the time clocks/meter that control the off peak board have an over ride switch. That would be the easiest thing to check.

If not then I wouldn't be bothered linking the boards out. I would just measure the R1+R2 of the circuit and then add on the Ze and that will give you the ZS.

 

[jjjinx]

you can take the Ze from the main board and call it the origin then add the R1+R2 as rob said

 

[Pippyboy1916]

yeah i thought of that but at the time with the readings, the head gets sore! lol your answers lead me onto another question, i work up in scotland, we have organisation called "select" and when you do "there" inspection and testing, also city and guilds, they state you only take a R2 reading on a radial circuit. So if i did do a R1+R2 and get a good reading and add it to the Ze, what would i put down on the cert? remember my high reading at the switch and if someone checked my work and checked at the switch?

thanks for your replys tho

 

[jjjinx]

well if your forced only to record R2 then you would have to do that with a wander lead, I think you might be able to calculate it from R1+R2, R2 being 1.67 times greater than R1 provided your using T+E up to 2.5mm2 (don't quote me on that).

If you do the wander lead dont forget to null the wander lead out.

If your unsure contact "Select" and ask them what they'd prefer but I'd say Ze at the main switch of the live board & R1+R2 from the dead board =Zs. you only need to take Ze from the origin.

Hope that helps.

 

[Sparky Ninja]

I think you might be able to calculate it from R1+R2, R2 being 1.67 times greater than R1 provided your using T+E up to 2.5mm2 (don't quote me on that).

You would need the value of R1 for this, and not R1+R2, and you wouldn't be able to determin which part of the R1+R2 value would be from R1.
You 'could' arguably, measure R1+Rn on the circuit then half the figure.. to result with R1. Then multiply that by 1.67 for R2

but I'd say Ze at the main switch of the live board & R1+R2 from the dead board =Zs. you only need to take Ze from the origin

Origin of the supply, just incase the main switch of the live board is far downstream, i.e. a block of flats or something.

 

[jjjinx]

I don't know whether I'd go the R1+Rn route as your not measuring the conductor your going to write on the form, but saying that it would be a good indication of the R1 value if you measured the R1+R2 value calulated (1.67) it & backed it up with the R1+Rn but its a lota waffle for a situation that will probably never occur.

And better to get a Ze reading at one board than not at all, I don't no any sparky whos guna wait till the night rate kicks in lol.. also you can get away with calling the Ze reading from a futher board Zdb, all you have to do is explain in the remarks why you have that reading.


simples!

 

[empress]

If you were to upgrade storage heater circuts from say an old wylex rewirable to a current board on 17th anyone know the correct procedure for doin the RCD tests since like mentioned above no ones gonna wait till midnight.
elfyn

 

[Sparky Ninja]

I don't know whether I'd go the R1+Rn route as your not measuring the conductor your going to write on the form

No, you are doing it to obtain a value for R1, so you can calculate R2 as I said. We measure r1+rn when testing ring mains and don't record the results.

also you can get away with calling the Ze reading from a futher board Zdb, all you have to do is explain in the remarks why you have that reading.

correct

 

[Sintra]

If you were to upgrade storage heater circuts from say an old wylex rewirable to a current board on 17th anyone know the correct procedure for doin the RCD tests since like mentioned above no ones gonna wait till midnight.
elfyn

What i would normally do is power the RCD temporarily and test with no load connected.

 

[Pippyboy1916]

yeah, i use the wonder lead method, like i said before surley i have to justify Zs? "select" say if i get a Zs reading then i should'nt bother about a R2, here's another question should i fill out a new front sheet for every board i test and take a PFC+Ze on every board? Origin at the incomers to the first board? there seems to be a few different procedures.

 

[jjjinx]

sintra would you like to give your comments on getting R2 value? this is theoretical, if you couldn't do it by a wander lead and I'm talking radials not rings cos getting R2 from a ring is simple.

 

[Sintra]

sintra would you like to give your comments on getting R2 value? this is theoretical, if you couldn't do it by a wander lead and I'm talking radials not rings cos getting R2 from a ring is simple.

Ok here goes.

I would find my R1 + Rn and divide that by 2 to get my R1
Then find my R1 + R2
From that take away your previous value of R1
That should leave you with a R2.

 

[jjjinx]

thats fair enough but what if the Rn has a higher impedence than the R1 your getting an incorrect value possibly from a bad connection or sumit, but if your measuring R1+R2 then at least your measuring with the right conductors?

I no R1+Rn is easier maths but your value doesn't include the actual conductor then your just writing down what you think it should be not it is.

R1+Rn you can reasonably record the value of R1 by halfing the value but only by measuring R1+R2 /2.67 * 1.67 can you justify that reading being true. or am I talking rubbish lol?

pippy, I think the proceedure is the same down here as up there but forms differ slightly from place to place, R1+R2 here for me on m/works forms is a tick just to say there's continuity rather than a value, but on a EIC its the value.

Continuity at every d/b
Zs at every d/b
Ze on every sheet but measured only at the origin of the supply i.e. the closest of the boards to the incoming supply.

 

[Pippyboy1916]

[quotethats fair enough but what if the Rn has a higher impedence than the R1 your getting an incorrect value possibly from a bad connection or sumit, but if your measuring R1+R2 then at least your measuring with the right conductors?

I no R1+Rn is easier maths but your value doesn't include the actual conductor then your just writing down what you think it should be not it is.

R1+Rn you can reasonably record the value of R1 by halfing the value but only by measuring R1+R2 /2.67 * 1.67 can you justify that reading being true. or am I talking rubbish lol?

pippy, I think the proceedure is the same down here as up there but forms differ slightly from place to place, R1+R2 here for me on m/works forms is a tick just to say there's continuity rather than a value, but on a EIC its the value.

Continuity at every d/b
Zs at every d/b
Ze on every sheet but measured only at the origin of the supply i.e. the closest of the boards to the incoming supply. ][/quote]

sound, we have a value for R1+R2 also value for R2 on the certs we use, im just back from an EM LT course today and spoke to the the guy running the "inpection course" again he's no even bother about Rn/crossing the tails/Zs values, if you cant get it make sure it has a good earth i'm sure the C**** really dont care!

cheers