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Hi All

Quick questions on test results

With Continuity tests i know R1 + R2 results depends on the length of run & size of cable..

When testing it cant be more than a certain figure depending on cable size and breaker size.

How would i know the maximum readings should be? Im guessing on site guide but couldn't find it?

If this is correct do we know a page??

Cheers in advance

Luke
 

widdler

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Mentor
Arms
Your maximum permitted R1&R2 would theoretically be the maximum permitted Zs of the circuit, minus the external earth fault loop impedance.

So, R1&R2 = Zs - Ze.

However these give you a worst case scenario approach which will not be accurate.

Alternatively, you can obtain the design information to establish the circuit length, then you could more accuraely calculate the expected measured R1&R2 values.
 

widdler

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Mentor
Arms
So are you looking for calculating Zs or R1&R2?

Your question now appears to make no sense.
 
Hi All

Quick questions on test results

With Continuity tests i know R1 + R2 results depends on the length of run & size of cable..

When testing it cant be more than a certain figure depending on cable size and breaker size.

How would i know the maximum readings should be? Im guessing on site guide but couldn't find it?

If this is correct do we know a page??

Cheers in advance

Luke
Student? If yes Then please state this when asking questions. we do not do students homework on this forum !
Advice if genuine however is free, and if we have given advice do feel free to hit the THANKS button
 

telectrix

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Mentor
Arms
Esteemed
OK, Luke, we are looking to have an EFLI low enough to trip the circuit's MCB/fuse within the BS7671 specified time. ( generally 0.4 secs. for circuits up to 32A.)
this EFLI ( max, ) is found in tables in the bgb, with temperature corrected figures in osg. ( the theory behind this is basically ohms law. the lower the impedance, the larger the fault current. the larger the current, the quicker the MCB/fuse will break ). this figure is Zs. which is composed of Ze + (R1+R2). Zeis obtained either by enquiry or measurement, then when you take that from Zs, you get a max. value for your R1+R2.
 
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