Lighting Circuit Zs

[rigby]

I must be confused about some wording,

Light circuit R1+R2 is 1.84 Ze measured = 0.28

So if I do Ze +(R1+R2) I get 2.06

Maximum Zs allowed is 6.14

actual measured Zs is 0.88

This measured Zs is much lower than the max value, I know higher is not good but lower Zs leads to any problems ??

 

[dwardy]

make sure you batteries are not low and that you have good connection with your test leads. could also be parrallel paths make earth loop lower

 

[rigby]

Low batteries!! yes I do have low batteries, I wonder if this is the reason. I shoulds change batteries and see. Thanks dwardy

 

[Deleted member 9648]

I must be confused about some wording,

Light circuit R1+R2 is 1.84 Ze measured = 0.28

So if I do Ze +(R1+R2) I get 2.06

Maximum Zs allowed is 6.14

actual measured Zs is 0.88

This measured Zs is much lower than the max value, I know higher is not good but lower Zs leads to any problems ??[/QUOTE]



You cant expect your Zs to be bang on the maximum every time....it's a maximum for a reason. If a lower than maximum Zs would be a problem we would have to measure Ze before installing any cables,work out the reistance required to reach the maximum and install a length of cable of exactly that resistance....dont happen does it?

 

[rigby]

Thank you wirepuller, this clarifies the concept clearly.

 

[Farmelectrics]

Measured is always better than a calculated reading

 

[GaryM]

Measured is always better than a calculated reading

I agree in a way but if calculated is within spec then no need to measure as you're working on live equipment when it isn't necessary just to gain another still compliant figure. You've already measured Ze so know there's an earth path and you've proved the CPC is continuous.
You're also wasting time by effectively doing the same test again......

You may consider this a little over the top but that in itself would contravene the EAWR section 14(a):

Work on or near live conductors

14. No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless–
(a)it is unreasonable in all the circumstances for it to be dead; and
(b)it is reasonable in all the circumstances for him to be at work on or near it while it is live; and
(c)suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.

 

[Marnik]

I agree in a way but if calculated is within spec then no need to measure as you're working on live equipment when it isn't necessary just to gain another still compliant figure. You've already measured Ze so know there's an earth path and you've proved the CPC is continuous.
You're also wasting time by effectively doing the same test again......

Defo not a waste of time! Ok so you did your R1+R2 test , which you disconnected at the CU, measuring your Zs is the only way to prove you remade the connections properly and also to establish wether or not there is a possible loose connection in the circuit.
Do it Properly

 

[dwardy]

just because you get an earth loop value doesnt mean your cpc is continous. you should ALWAYS do a R1+R2 test

 

[ezzzekiel]

Regulations state calculated is an accepted method, and R1R2 tests should be carried out so if you wish to use a calculation or go on and do a live zs either is acceptable - cant see the problem